ANALYSIS OF ALTERNATIVES non-confidential report
Legal name of applicant(s): LANXESS Deutschland GmbH in its legal capacity as Only Representative of LANXESS CISA (Pty) Ltd.; Atotech Deutschland GmbH; Aviall Services Inc.; BONDEX TRADING LTD in its legal capacity as Only Representative of Aktyubinsk Chromium Chemicals Plant, Kazakhstan; CROMITAL S.P.A. in its legal capacity as Only Representative of Soda Sanayii A.S.; Elementis Chromium LLP in its legal capacity as Only Representative of Elementis Chromium Inc; Enthone GmbH.
Submitted by: LANXESS Deutschland GmbH in its legal capacity as Only Representative of LANXESS CISA (Pty) Ltd.
Substance: Chromium trioxide, EC No: 215-607-8, CAS No: 1333-82-0
Use title: Functional Chrome Plating
Use number: 2
Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Disclaimer
This document shall not be construed as expressly or implicitly granting a license or any rights to use related to any content or information contained therein. In no event shall applicant be liable in this respect for any damage arising out or in connection with access, use of any content or information contained therein despite the lack of approval to do so.
ii Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
CONTENTS
1. SUMMARY ...... 1 2. INTRODUCTION ...... 11 2.1. The substance ...... 11 2.2. Uses of chromium trioxide ...... 11 2.3. Purpose and benefits of chromium trioxide ...... 11 3. FUNCTIONAL CHROME PLATING ...... 13 3.1. Metallic chrome coatings ...... 13 3.2. Surface treatment process description “functional chrome plating” ...... 17 3.2.1. Pre-treatment processes ...... 18 3.2.2. Functional chrome plating ...... 19 3.2.3. Post-treatment processes ...... 20 3.3. Key functionalities of functional chrome plating ...... 21 3.3.1. Key functionalities of chromium trioxide based surface pre-treatment ...... 21 3.3.2. Key functionalities of metallic chrome coatings ...... 22 3.3.2.1 Wear resistance ...... 23 3.3.2.2 Hardness ...... 23 3.3.2.3 Layer thickness ...... 23 3.3.2.4 Corrosion resistance ...... 24 3.3.2.5 Coefficient of friction ...... 24 3.3.2.6 Effect on surface morphology ...... 25 4. ANNUAL TONNAGE...... 27 4.1. Annual tonnage band of chromium trioxide ...... 27 5. GENERAL OVERVIEW OF THE PROCESS FOR ALTERNATIVE DEVELOPMENT AND SECTOR SPECIFIC APPROVAL PROCESS ...... 28 5.1. Aerospace ...... 28 5.1.1 Development and qualification ...... 31 5.1.1.1 Requirements development ...... 31 5.1.1.2 Technology development ...... 32 5.1.1.3 Qualification ...... 34 5.1.1.4 Certification ...... 35 5.1.1.5 Implementation / industrialisation ...... 37 5.1.1.6 Examples ...... 38 5.2. Automotive and general engineering ...... 38 5.2.1. Current production parts in automotive applications - general considerations ...... 38 5.2.2. Current production parts - requirements for alternatives to chromium trioxide ...... 39 5.2.3. Past model service parts – general considerations ...... 40 5.2.4. Past model service parts – requirements for alternative metallic chrome coating ...... 41 5.2.5. General engineering ...... 42 5.3. Steel ...... 44 5.4. Metal precision parts ...... 46 5.5. Manufacture of printing equipment ...... 47 6. IDENTIFICATION OF POSSIBLE ALTERNATIVES ...... 49 6.1 Description of efforts made to identify possible alternatives ...... 49 6.1.1 Research and development ...... 49 6.1.2 Data searches ...... 51 6.1.3 Consultations ...... 52 6.2 List of possible alternatives ...... 52 7. SUITABILITY AND AVAILABILITY OF POSSIBLE ALTERNATIVES ...... 54 7.1 ALTERNATIVE 1: Electroless plating ...... 54 7.1.1 Substance ID and physicochemical properties of relevant substances ...... 56 7.1.2 Technical feasibility ...... 56 7.1.3 Economic feasibility ...... 63 7.1.4 Reduction of overall risk due to transition to the alternative ...... 63 7.1.5 Availability ...... 64 7.1.6 Conclusion on suitability and availability for alternative electroless plating ...... 64
Use number: 2 iii Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
7.2 ALTERNATIVE 2: Nickel and nickel alloy electroplating...... 65 7.2.1 Substance ID and properties ...... 65 7.2.2 Technical feasibility ...... 66 7.2.3 Economic feasibility ...... 71 7.2.4 Reduction of overall risk due to transition to the alternative ...... 71 7.2.5 Availability ...... 72 7.2.6 Conclusion on suitability and availability for alternative nickel and nickel alloy electroplating ..... 72 7.3 ALTERNATIVE 3: Case hardening: carburizing, carbonitriding, cyaniding, nitriding, boronizing ...... 73 7.3.1 Substance ID and properties ...... 73 7.3.2 Technical feasibility ...... 74 7.3.3 Economic feasibility ...... 78 7.3.4 Reduction of overall risk due to transition to the alternative ...... 78 7.3.5 Availability ...... 78 7.3.6 Conclusion on suitability and availability for alternative case hardening ...... 78 7.4 ALTERNATIVE 4: Chemical vapour deposition (CVD)...... 78 7.4.1 Substance ID and properties ...... 78 7.4.2 Technical feasibility ...... 79 7.4.3 Economic feasibility ...... 83 7.4.4 Reduction of overall risk due to transition to the alternative ...... 84 7.4.5 Availability ...... 84 7.4.6 Conclusion on suitability and availability for alternative CVD ...... 84 7.5 ALTERNATIVE 5: Nanocrystalline cobalt phosphorus alloy coating ...... 85 7.5.1 Substance ID and properties ...... 85 7.5.2 Technical feasibility ...... 86 7.5.3 Economic feasibility ...... 90 7.5.4 Reduction of overall risk due to transition to the alternative ...... 90 7.5.5 Availability ...... 91 7.5.6 Conclusion on suitability and availability for alternative nanocrystalline cobalt phosphorus alloy coating ...... 91 7.6 ALTERNATIVE 6: High velocity thermal process ...... 91 7.6.1 Substance ID and properties ...... 91 7.6.2 Technical feasibility ...... 94 7.6.3 Economic feasibility ...... 98 7.6.4 Reduction of overall risk due to transition to the alternative ...... 99 7.6.5 Availability ...... 99 7.6.6 Conclusion on suitability and availability for alternative HVOF ...... 99 7.7 ALTERNATIVE 7: Trivalent chrome plating ...... 100 7.7.1 Substance ID and properties / Process description ...... 100 7.7.2 Technical feasibility ...... 101 7.7.3 Economic feasibility ...... 107 7.7.4 Reduction of overall risk due to transition to the alternative ...... 107 7.7.5 Availability ...... 108 7.7.6 Conclusion on suitability and availability for alternative trivalent chrome plating ...... 109 7.8 ALTERNATIVE 8: Physical vapour deposition (PVD) ...... 109 7.8.1 Substance ID and properties ...... 109 7.8.2 Technical feasibility ...... 111 7.8.3 Economic feasibility ...... 115 7.8.4 Reduction of overall risk due to transition to the alternative ...... 116 7.8.5 Availability ...... 116 7.8.6 Conclusion on suitability and availability for alternative PVD ...... 117 CATEGORY 2 ALTERNATIVES ...... 117 7.9 ALTERNATIVE 9: Plasma spraying ...... 117 7.9.1 Substance ID and properties / process description ...... 117 7.9.2 Technical feasibility ...... 119 7.9.3 Economic feasibility ...... 120 7.9.4 Reduction of overall risk due to transition to the alternative ...... 120 7.9.5 Availability ...... 121 7.9.6 Conclusion on suitability and availability for alternative plasma spraying ...... 121 7.10 ALTERNATIVE 10: General laser and weld coating technology...... 122
iv Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
7.10.1 Substance ID and properties / process description ...... 122 7.10.2 Technical feasibility ...... 122 7.10.3 Economic feasibility ...... 123 7.10.4 Reduction of overall risk due to transition to the alternative ...... 124 7.10.5 Availability ...... 124 7.10.6 Conclusion on suitability and availability for alternative general laser and weld coating technology ...... 124 7.11 ALTERNATIVE 11: Stainless steel & high speed steel (HSS) ...... 125 7.11.1 Substance ID and properties ...... 125 7.11.2 Technical feasibility ...... 125 7.11.3 Economic feasibility ...... 127 7.11.4 Reduction of overall risk due to transition to the alternative ...... 127 7.11.5 Availability ...... 127 7.11.6 Conclusion on suitability and availability for alternative stainless steel & HSS ...... 127 7.12 ALTERNATIVE 12: Thermal spray coatings ...... 128 7.12.1 Substance ID and properties / processes ...... 128 7.12.2 Technical feasibility ...... 128 7.12.3 Economic feasibility ...... 129 7.12.4 Reduction of overall risk due to transition to the alternative ...... 129 7.12.5 Availability ...... 130 7.12.6 Conclusion on suitability and availability for alternative thermal spray coatings ...... 130 PRE-TREATMENT ...... 130 7.13 Mineral acids ...... 130 7.13.1 Substance ID and properties ...... 130 7.13.2 Technical feasibility ...... 131 7.13.3 Economic feasibility ...... 133 7.13.4 Reduction of overall risk due to transition to the alternative ...... 133 7.13.5 Availability ...... 133 7.13.6 Conclusion on suitability and availability for mineral acids ...... 134 8. OVERALL CONCLUSIONS ON SUITABILITY AND AVAILABILITY OF POSSIBLE ALTERNATIVES FOR FUNCTIONAL CHROME PLATING ...... 135 9. REFERENCE LIST ...... 142 APPENDIX 1 – MASTERLIST OF ALTERNATIVES WITH CLASSIFICATION INTO CATEGORIES 1-3 AND SHORT SUMMARY OF THE REASON FOR CLASSIFICATION OF ALTERNATIVES INTO CATEGORY 3 (SELECTION PROCESS) ...... 146 APPENDIX 2 – INFORMATION ON SUBSTANCES USED IN ALTERNATIVES ...... 149 APPENDIX 2.1 - ELECTROPLATING ALTERNATIVES (MAIN PROCESS) ...... 149 APPENDIX 2.2 - PRE-TREATMENTS: MINERAL ACIDS ...... 167 APPENDIX 2.3 – SOURCES OF INFORMATION ...... 170
Use number: 2 v Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
List of Tables:
Table 1: Technical deficiencies of category 1 alternatives by sector...... 9 Table 2: Substance of this AoA...... 11 Table 3: Examples on sector specific metallic chrome coating applications...... 14 Table 4: Key functionalities of chromium trioxide based pre-treatment...... 21 Table 5: Key process functionalities of chromium trioxide based pre-treatment...... 21 Table 6: Sector specific key functionalities of metallic chrome coatings...... 22 Table 7: Technology Readiness Levels-Overview. Data source: US Department of Defense, 2009 ...... 29 Table 8: List of alternatives categorized...... 52 Table 9: Typical properties of electroless nickel-phosphorus coatings...... 56 Table 10: Comparison in process performance for nCoP and functional chrome plating (McCrea, 2003 and Gonzales, 2010). 85 Table 11: Material properties of nano Co-P alloys. Data source: McCrea, 2003 and Gonzales, 2010...... 86 Table 12: Test results field test on nCoP, which is commercially available. Data source: Neolor, 2014...... 88 Table 13: Typical materials properties of HVOF coating using WC-Co. Data source: Legg K., 2003a...... 95 Table 14: Comparison of production costs of the coating: HVOF & functional chrome plating...... 98 Table 15: Cr(III) based bath chemistry...... 100 Table 16: Material properties of typical PVD coatings. Data source: Legg K., 2003a...... 110 Table 17: Comparison of production costs of the coating: PVD & functional chrome plating ...... 116 Table 18: Material properties of plasma sprayed WC-Co coatings. Data source: Legg K., 2003a; Holeczek, 2011...... 119 Table 19: Martensitic Steels – Hardness (Yang, 2011)...... 126 Table 20: Properties and test characteristics of chromium trioxide coatings vs. HSS rolls...... 126 Table 21: Technical deficiencies of category 1 alternatives by sector...... 140
vi Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
List of Figures
Figure 1: Simplified overview of different steps that may be involved in functional chrome plating using chromium trioxide. . 1 Figure 2: Illustration of the development, qualification, certification and industrialisation process required in the aerospace sector (Data source: EASA; 2014, adapted)...... 3 Figure 3: General engineering - delivery cylinder pipe. Data source: ZVO, 2014...... 15 Figure 4: Functional chrome plated rods with metallic chrome coated layers between 20 and 75 µm. Data source: http://www.uk-finishing.org.uk/N-COAT70/electrolytic_hard_chrome.htm ...... 15 Figure 5: Printing rolls used for high output printing on to “magazine” quality paper (left) and functional chrome plated and polished parts as example for thick metallic chrome coatings up to few hundred µm thickness (right). Data source: http://www.uk-finishing.org.uk/N-COAT70/electrolytic_hard_chrome.htm ...... 16 Figure 6: Multiple examples of metal chrome coatings based on chromium trioxide for automotive applications. Data source: Enthone, 2014...... 16 Figure 7: General engineering sector - functional chrome plated hydraulic cylinder. Data source: Ovako, 2014...... 16 Figure 8: Simplified overview of different steps that may be involved in functional chrome plating using chromium trioxide. 17 Figure 9: Metallic chrome plated roughness illustration and detailed view as photomicrographs from a scanning electron microscope. Data source: Hoco-RST, 2014...... 25 Figure 10: Microscopic view of a hemispherical structure coating of a roll. Data source: Salzgitter AG, 2014...... 26 Figure 11: Example for stepless variation of structure parameters (open / closed) topography. Data source: Salzgitter AG, 2014...... 26 Figure 12: Illustration of the qualification, certification and industrialisation processes. Data source: EASA, 2014, http://echa.europa.eu/documents/10162/13552/aviation_authorisation_final_en.pdf ...... 29 Figure 13: Illustration of the technology development and qualification process. Data source: EASA, 2014, http://echa.europa.eu/documents/10162/13552/aviation_authorisation_final_en.pdf, amended...... 34 Figure 14: Car dismantled into constituent parts; Data source: Volkswagen AG, 2013 (left). Principal engine parts of a car; Data source: HubPages, undated (right)...... 39 Figure 15: Typical life-time of a car model starting in production in 2018 compared to a four years period until sunset date. . 40 Figure 16: EU passenger car fleet (share in % by age in 2010). Note: Information from 12 EU member states where information was available...... 41 Figure 17: High density of narrow and shallow cracks. Data source: Enthone 2014...... 44 Figure 18: Roll hanging above the functional chrome plating tank. Data source: HOCO-RST, 2014...... 45 Figure 19: Electroless plating. Data source: NDCEE, 1995...... 55 Figure 20: Plating of complex geometries. Data source: Sonntag, ZVO, not dated...... 58 Figure 21: Nickel and nickel alloy electroplating process design. Data source: NDCEE, 1995...... 65 Figure 22: Case hardening. Data source: NDCEE, 1995...... 73 Figure 23: Typical CVD system. Data source: Legg K., 2003a...... 79 Figure 24: Microstructure of nano CoP coatings. Data source: Legg K., 2003b...... 85 Figure 25: Cross section of a typical thermal spray coating. Data source: TURI, 2006...... 92 Figure 26: HVOF process. Data source: http://spray-molybdenum-wire.com/pic/spraying-molybdenum-wire/HVOF-spray- molybdenum-wire.jpg, as of 07.05.2014...... 92 Figure 27: HVOF thermal spraying onto a landing gear cylinder. Data source: Legg K., 2001...... 93 Figure 28: Appearance rankings for various coatings on 4340 steel after 1,000h of ASTM B117 salt spray test. Data source: Sartwell, 1999...... 94 Figure 29: Microstructure of Cr(III) chrome (77 µm) under optical microscope (left) compared to chromium trioxide chrome under scanning electron microscope (right) (50 µm). Data source: pfonline, 2013...... 102 Figure 30: Cross-section image from Cr(III) coatings in relation to layer thickness and to different spots located at the coated part. Daat source: pfonline, 2013...... 102 Figure 31: Plasma spraying process. Data source: http://www.roymech.co.uk/images/plating_1.gif, as of 05/06/14...... 118 Figure 32: Cross section of a typical thermal spray coating. Data source: TURI, 2006...... 118
Use number: 2 vii Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Abbreviations
ACE Aerospace Chrome Elimination ACEA European Automobile Manufacturer Association ACF Airbus Chromate-free Advanced Materials, Manufacturing, and Testing Information Analysis AMMTIAC Center AoA Analysis of Alternatives Approx. Approximately ASETSDefense Advanced Surface Engineering Technologies for a Sustainable Defense ASTM American Society for Testing and Materials CAS Chemical Abstracts Service Cr(III) Trivalent Chromium Cr(VI) Hexavalent Chromium CSR Chemical Safety Report CTAC Chromium Trioxide REACH Authorization Consortium CVD Chemical Vapour Deposition D-gun Detonation Gun DLC Diamond Like Carbon DoD Department of Defense EASA European Aerospace Safety Agency EC European Commission EDT Electro Discharge Textured EHS Environmental Health and Safety EN European Norm ESD Electrospark Deposition ESTCP Environmental Security Technology Certification Program EU European Union EU27 European Union, 27 Member States HCAT Hard Chrome Alternatives Team HSS High speed steel HV Vickers Hardness HVAF High Velocity Air Fuel HVOF High velocity oxy-fuel IARC International Agency for Research on Cancer ID Inside Diameter
viii Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
ISO International Organization for Standardization MRL Manufacturing Readiness Level MRO Maintenance, Repair and Operation NDCEE National Center for Energy and Environment NSST Neutral Salt Spray Test OEM Original Equipment Manufacturer PE Polyethylene PECVD Plasma Enhanced Chemical Vapour Deposition PTFE Polytetrafluoroethylene PVD Physical Vapour Deposition QPL Qualified Products List R&D Research and Development REACH Registration, Evaluation, Authorisation and Restriction of Chemicals RoHS Restriction of Hazardous Substances RPA Department for Environment, Food and Rural Affairs SDS Safety Data Sheet SEA Socio Economic Analysis SHSS Semi High Speed Steels SME Small and Medium-sized Enterprise specs Standard of Specification SST Salt Spray Test STC Supplemental Type Certificate SVHC Substance of Very High Concern TNO Netherlands Organisation for Applied Scientific Research TRL Technology Readiness Level TSM Surface Treatment Mechanics, French company UNE Spanish Standard ZVO Central Association for Surface Technology
Use number: 2 ix Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Glossary
Term Definition Parameter describes the tendency of dissimilar particles or surfaces to cling to one Adhesion another (for example adhesion of coating to substrate, adhesion of paint to coating and/or substrate). Alternative Potential alternative provided to the respective industry sector for their evaluation. Typical method for surface treatment of parts. May also be referred to as dipping or Bath immersion. None-bath methods include wiping, spraying, and pen application. Category 1 Alternative considered promising, where considerable R&D efforts have been alternative carried out within the different industry sectors. Category 2 Alternative with clear technical limitations which may only be suitable for niche alternative applications and not as a general alternative. Category 3 Alternative which has been screened out at an early stage of the Analysis of alternative Alternatives and which is not applicable for the use defined here. Parameter is defined as the ability of solid materials to resist damage by chemical Chemical resistance exposure. When brought in contact with water, chromium trioxide forms two acids and several oligomers: chromic acid, dichromic acid, and oligomers of chromic acid and Chromic acid dichromic acid. For the purpose of this document the terms chromic acid is synonymous with a mixture containing chromium trioxide and water. This is intended to be in line with ECHA Q&A #805. A coating is a covering that is applied to the surface of an object, usually referred Coating to as the substrate. The purpose of applying the coating may be decorative, functional, or both. Means applied to the metal surface to prevent or interrupt oxidation of the metal part leading to loss of material. This can be a metal conversion coating or anodizing, Corrosion protection a pre-treatment, electrolytic or electroless metal/metal alloy coatings, paint, water repellent coating, sealant, liquid, adhesive or bonding material. The corrosion protection provides corrosion resistance to the surface. Counterpart Structural zone (like assembly, component) to which a given assembly/part is fitted. Electroplating is forming a metal coating on the part by an electrochemical method Electroplating in an electrolyte containing metal ions and the part is the cathode, an appropriate anode is used and an electrical current is applied. Process changing surface morphology as well as removing material. This is a pre- treatment step of the process chain preparing the surface before subsequent plating. Etching This term has significant overlap with the term pickling. As there is no clear demarcation, the term etching is used to cover both etching and pickling as chromium trioxide pre-treatment in this document. An industrial use, meaning the electrochemical treatment of surfaces (typically metal) to deposit metallic chromium using a solution containing chromium trioxide (amongst other chemicals), to enhance wear resistance, tribological properties, anti- stick properties, corrosion resistance in combination with other important functional Functional chrome characteristics. Such secondary functional characteristics are chemical resistance, plating able to strip, unlimited in thickness, paramagnetic, deposit not toxic or allergic, micro-cracked brightness. Process characteristics are closed loop processing, high speed, flexibility in size, plating of inner surfaces, low process temperature, surface can be machined, assemblability.
x Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Term Definition Functional chrome plating may include use of chromium trioxide in pre-treatment and surface deposits unlimited in thickness but typically between 2 µm and 5,000 µm. Functional chrome coatings are widely used in many industry sectors. After having passed qualification and certification, the third step is to implement or Implementation industrialize the qualified material or process in all relevant activities and operations of production, maintenance and the supply chain. Legacy part A legacy part shall mean any part of an end product which is manufactured in accordance with a type certification applied for before the earliest sunset date (including any further supplemental or amended type certificates or a derivative) or which is designed in accordance with a specific development contract signed before the earliest sunset date, and including all production, follow-on development, derivative and modification program contracts, based on that development program. The main treatment, functional chrome plating using chromium trioxide, occurs Main treatment after the pre-treatment and before the post treatment. Metallic chrome Resulting coating layer of the functional chrome plating process. coating Passivation Process providing corrosion protection to a substrate or a coating. Is designed to both remove embedded iron/steel particles from stainless steel and Passivation of oxidise the surface chromium in the alloy to augment its natural corrosion resistant stainless steel passive oxide layer. Pickling is the removal of oxides or other compounds from a metal surface by chemical or electrochemical action. The term pickling is not used consistently Pickling within the surface finishing industry and is often referred to as the following processes: cleaning, scale removal, scale conditioning, deoxidizing, etching, and passivation of stainless steel. This term has overlap with the term Etching. Plating Electrolytic process that applies a coating of metal on a substrate. Post-treatment processes do not involve chromium trioxide and are performed after Post-treatment the main functional chrome plating process. Pre-treatment process using chromium trioxide to remove contaminants (e.g. oil, Pre-treatment grease, dust), oxides and scale. The pre-treatment process must also provide chemically active surfaces for the subsequent treatment. (See also: Etching). A series of surface treatment process steps. The individual steps are not stand-alone processes. The processes work together as a system, and care should be taken not to Process chain assess without consideration of the other steps of the process. In assessing candidate alternatives for chromium trioxide, the whole process chain has to be taken into account Original Equipment Manufacturer’s (OEM) validation and verification that all Qualification material, components, equipment or processes meet or exceed the specific performance requirements. Temperature change The ability of a coating or substrate to withstand temperature changes and high resistance / heat temperatures. resistance Tribological Tribological properties relate to friction, lubrication and wear on surfaces in relative properties motion and are important for moving machine parts. Wear resistance / The ability of a coating to resist the gradual wearing caused by abrasion and friction. abrasion resistance
Use number: 2 xi Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed.
ANALYSIS OF ALTERNATIVES
1. SUMMARY Introduction This Analysis of Alternatives (AoA) forms part of the Application for Authorisation (AfA) for the use of chromium trioxide in functional chrome plating of articles. Functional chrome plating using chromium trioxide is a surface treatment process that involves depositing a layer of metallic chromium on the surface of a metallic (e.g. steel, hardened steel, stainless steel, titanium alloys, nickel alloys, copper alloys, aluminium, and bronze) component. This metallic chrome coating provides the article with high mechanical and wear resistance, excellent anticorrosion performance (with a nickel underplate for steel) and a low coefficient of friction. The process is therefore specified for particular applications where this combination of performance characteristics is critical. Functional chrome plating using chromium trioxide is therefore used for technical applications or in parts that must perform under demanding conditions that involve high temperatures, repetitive wear and mechanical impact. Approximately 6,000 tonnes of chromium trioxide are used in functional chrome plating within the scope of this AfA per year. The use is also intended to cover the downstream use of chromic acid and dichromic acid (in-line with ECHA Q&A #805). Surface treatments modify the surface of a substrate so that it performs better under conditions of use. Different chemicals and operating conditions are specified for individual plating processes in order to effectively treat different substrates and/or confer specific performance criteria to the treated article. Functional chrome plating using chromium trioxide involves immersion of the component in each of a series of treatment baths containing chemical solutions or rinses under specific operating conditions and is normally the final step in the overall surface treatment process (see Figure 1). Chromium trioxide is a pre-requisite for the main treatment of functional chrome plating to ensure the highest quality of the product and to meet the requirements of the industry. Chromium trioxide is also used in the etching / pickling pre-treatment process to prepare the substrate. There are no post- treatment processes for functional chrome plating which involve chromium trioxide.
Figure 1: Simplified overview of different steps that may be involved in functional chrome plating using chromium trioxide.
The characteristics of chromium trioxide, a detailed description of the plating process, and the key functionality of the plated parts are discussed in Chapter 3. A number of industry sectors, including aerospace, automotive & general engineering, steel, metal precision parts and manufacture of printing equipment, as discussed below, specify the use of functional plating using chromium trioxide in order to meet the strict performance criteria necessary for regulatory compliance, public safety and customer expectations. These are described further below and in Chapter 5.
Use number: 2 1 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
This summary aims to explain why use of chromium trioxide in functional chrome plating is essential to certain industry sectors. It describes the steps and effort involved in finding and approving a replacement for chromium trioxide in these applications and evaluates potential alternatives in detail (Chapter 6 and 7).
Functional chrome plating with chromium trioxide Chromium has been used for more than 50 years to provide surface protection to critical components and products within several sectors where the products to which they are applied must operate to the highest safety standards, often in demanding environments, for extended time periods. Functional chrome plating based on chromium trioxide has unique technical functions that confer substantial advantage over potential alternatives. These include: - Wear resistance; - Hardness; - Corrosion resistance; - Low friction coefficient; - Adequate layer thickness; - Anti-stick properties; - Supports lubrication (due to micro-cracking); and - Flexibility to plate complex parts (such as the inside diameter (ID) of tubes).
The chemistry behind chromium trioxide metallic chrome coatings and functional chrome plating processes is complex. As described above, chromium plating processes typically involve numerous steps, often including a pre-treatment step as well as the main treatment process itself (see Figure 1). These steps are almost always inter-related such that they cannot be separated or individually modified without impairing the overall process or performance of the final product. Compatibility and technical performance of the overall system are primary considerations of fundamental importance during material specification. As of today, no drop in alternative for chromium trioxide in functional chrome plating, providing all the required properties to the surfaces of all articles in the scope of this application, is industrially available. Furthermore, functional chrome plating using chromium trioxide has been successively refined and improved as a result of many decades of research and experience in the sector, and reliable data is available to support its performance. While corrosion cannot be totally prevented, there is also extensive experience, amassed over decades, on the appearance and impact of corrosion to support its effective management in these systems. On the other hand, data available so far for potential alternatives does not support reliable conclusions regarding their performance as part of such complex systems, in demanding environments and real-world situations. The long-term performance of such potential alternatives can currently only be estimated. Decreased corrosion protection performance would necessitate shorter inspection intervals and more substantial maintenance. Functional chrome plating is a specialist activity requiring trained personnel and a substantial investment in facilities. In the majority of cases, plating shops act as suppliers to customers across many sectors, because it allows them to operate cost effectively and according to high standards. Nevertheless, there may be important differences between the rationales for selection of and challenges associated with replacing functional chrome plating using chromium trioxide across these sectors.
2 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
The aerospace sector Functional chrome plating with chromium trioxide is specified in the aerospace sector because it provides superior corrosion and wear resistance, requisite hardness, and a low coefficient of friction. These characteristics are essential to the safe operation and reliability (airworthiness) of aircraft and spacecraft, which operate under extreme environmental conditions. These structures are extremely complex in design, containing millions of highly specified parts, many of which cannot be easily inspected, repaired or removed. Structural components (e.g. landing gear, hydraulic actuators), engine parts, bearing and high lift systems on aircraft are particularly vulnerable to corrosion, fatigue and wear, and need to meet further key requirements. There are no technically feasible alternatives to functional chrome plating with chromium trioxide for key applications in the aerospace sector. Furthermore, even assuming a technically feasible potential alternative is identified as a result of ongoing Research and Development (R&D), extensive effort is needed beyond that point before it can be considered an alternative to chromium trioxide within the aerospace industry. Aircraft are one of the safest and securest means of transportation, despite having to perform in extreme environments for extended timeframes. This is the result of high regulatory standards and safety requirements. The implications for substance substitution in the aerospace industry are described in detail in a report prepared by ECHA and European Aerospace Safety Agency (EASA) in 2014 (http://echa.europa.eu/documents/10162/13552/aviation_authorisation_final_en.pdf), which sets out a strong case for long review periods for the aerospace sector based on the airworthiness requirements deriving from EU Regulation No 216/2008. Performance specifications defined under this regulation drives the choice of substances to be used either directly in the aircraft or during manufacturing and maintenance activities. It requires that all components, equipment, materials and processes incorporated in an aircraft must be certified, qualified and industrialised before production can commence. This system robustly ensures new technology and manufacturing processes can be considered ‘mission ready’ through a series of well-defined steps only completed with the actual application of the technology in its final form (and under mission conditions). When a substance used in a material, process, component, or equipment needs to be changed, this extensive system must be followed in order to comply with airworthiness requirements. The system for alternative development through qualification, certification, industrialization and implementation within the aviation sector is mirrored in the defence and space sectors. The detailed process involved in qualification, certification and industrialisation, and the associated timeframes, are elaborated in Chapter 5.1. Of course, these steps can only proceed once a candidate alternative is identified. Referring to experience, it can take 20 to 25 years to identify and develop a new alternative, even assuming no drawbacks during the various stages of development of these alternatives. Experience over the last 30 years already shows this massively under-estimates the replacement time for functional chrome plating using chromium trioxide. Taken together, available evidence clearly shows that no viable alternative for chromium trioxide is expected for at least the next 12 to 15 years.
Figure 2: Illustration of the development, qualification, certification and industrialisation process required in the aerospace sector (Data source: EASA; 2014, adapted).
Use number: 2 3 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
As a further consideration, while the implications of the development process in the aerospace sectors are clearly extremely demanding, specification of an alternative, once available, can be built into the detailed specification for new aircraft types (and new spacecraft). This is not the situation for existing aircraft types (e.g. Airbus 300, Boeing 747), for which aircraft may still be in production and/or operation. Production, maintenance and repair of these models must use the processes and substances already specified following the extensive approval process. Substitution of chromium trioxide based plating for these ‘legacy’ craft introduces yet another substantial challenge; re-certification of all relevant processes and materials. In practice, it can be impractical and uneconomical to introduce such changes for many such aircraft types. In this context, the scale and intensity of industry- and company- wide investment in R&D activity to identify alternatives to chrome oxide surface treatment systems is very relevant to the findings of the AoA. Serious efforts to find replacements for chrome oxide have been ongoing within the aerospace industry for over 30 years and there have been several major programs to investigate alternatives to chrome oxide in the aerospace sector over the last 20 years.
The automotive sector Chromium trioxide is used by automobile supply chains to manufacture several thousand parts of chrome-plated parts per vehicle manufacturer. Parts cover a wide range of applications, from belt locks to injector valves, in vehicle models with a production period of 7-10 years. Introducing new materials into the automotive market is a complex process, involving multiple phases and checks. Safety is the main driver for this. Metallic chrome plated parts offer superior performance in terms of corrosion resistance, hardness, layer thickness, adhesive strength, coefficient of friction and wear resistance. Potential alternatives in the automotive industry must be able to cover all of these requirements. As a drop-in replacement is not available, careful testing and evaluation of potential alternatives’ functional behaviour is needed. Current testing procedures in the automotive sector include laboratory tests, summer and winter tests, and continuous-operation tests. Thorough evaluation of possible alternatives is crucial to avoid failures in the field / daily application. As well as consequences for safety, failure could result in expensive and brand damaging product recalls. In the case of replacing functional chrome plating using chromium trioxide, all affected components must be revalidated using alternative materials. Substance substitution may cause change of function geometry, thermal durability and leads to unexpected impacts on related parts. Even though the automobile industry is highly experienced in material testing procedures, the validation and testing of alternatives will require several years due to the sheer number of parts involved. In addition, performance of potential alternatives must be tested under conditions of large scale production. Type approval is the confirmation that production samples of a design will meet specified performance standards. The specification of the product is recorded and only that specification is approved. Within the European automotive industry, two systems of type approval have been in existence for over 20 years. One is based around European Commission (EC) Directives and provides for the approval of whole vehicles, vehicle systems, and separate components. The other is based around United Nations (UN) Regulations (formerly known as UNECE Regulations) and provides for approval of vehicle systems and separate components, but not whole vehicles. Automotive EC Directives and UN Regulations require third party approval - testing, certification and production conformity assessment by an independent body. A stepwise introduction of alternative technologies in new type-approved models is foreseen by the automotive industry due to the magnitude of the change and impact on the industry. To make sure
4 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES production volumes of vehicles are not affected, sufficient capacities for the production of alternative coatings in Europe must be confidently in place. Furthermore, due to the high complexity of the supply chain in the automotive industry, tracking down chromium trioxide depending parts is a time- consuming and complicated task. Assembly of vehicles is carried out across a complex network of manufacturing plants, with an average number of 1,500-4,500 OEM suppliers, each of which have an average of 500-1,500 suppliers themselves. With regard to both the highly complex nature of supply chains in the automotive industry and the lifetime of vehicles, planning reliability is crucial. The average life cycle of an automobile model is about 22 years, comprising 3-5 years development time, 7 years of production and at least 10 years’ service life when there is a need to guarantee availability of spare parts. Realistically, changes to a vehicle model can only be made in a certain period of time, which decreases rapidly after type- approval by a certified body in the early stages of new model development. The majority of European cars are removed from the fleet after 13-15 years. About 36% of the EU passenger car fleet of 224 million vehicles – approx. 80 million cars - are older than 10 years, further underlining the need for an efficient supply of past model service parts beyond the end of serial production. Commonly, past model service parts are provided for vehicles that have been out of production for more than 20 years. A minimum of ten years availability of spare parts must be assured to comply with legislation in some member states. To make sure that possible alternatives are interchangeable with original spare parts, a complete new type-approval is necessary. Besides these service considerations, warranty obligations must be fulfilled. Practical considerations are also relevant when considering the need for function coating using chromium trioxide in service part production for post-production models. Once serial production of an automobile ends, the tooling and bill of design for the car model parts are transferred to a supplier (usually a small or medium size enterprise (SME)). Such suppliers are able to produce the desired amount of past model service parts using the original method. However, they have neither the know- how nor capacity to perform costly and highly technically demanding re-development and re- validation procedures. A complete testing of all related components may be necessary to exclude unexpected impacts and to ensure functionality and safety in the field. Additionally validation processes must be based on the original vehicle, which may not be available in many cases. The effort needed to develop and validate alternatives for a relatively small number of spare parts would result in an enormous increase in cost per item. The identification of possible alternatives and the careful validation of their functionalities is a labour/time intensive process that will certainly take several years. According to the European Automobile Manufacturer Association (ACEA), the development of suitable alternatives for functional chrome plating using chromium trioxide for current vehicle parts will require a time period of 10 years followed by industrialization of the technique and implementation in the supply chain leading to a minimum timeframe of 12 to 15 years after the sunset date.
General engineering, steel and metal precision parts Functional chrome plating using chromium trioxide are used in thousands of different complex equipment, vehicles and machines within the scope of general engineering. This includes agricultural machinery as well as trucks and forklifts. As an example, hydraulic cylinders are commonly used in a broad range of applications, such as agricultural equipment, wind mills, ships, and oil platforms. High pressure (up to 35,000 kN/m²) is generated within the cylinder, which must function in a range of challenging environments (e.g. sand, dust, moisture, salinity, extreme temperatures). Functional chrome plating with chromium trioxide is necessary to ensure critical parts such as hydraulic rods do not corrode or wear and can withstand heavy duty operations over long periods of operation. Damage to the hydraulic cylinder surface could result in oil leakages which would, in turn, significantly impair
Use number: 2 5 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES operation of the hydraulic cylinder. In some sectors, such as the food sector, leakage of oil is strictly prohibited to protect public health. Particular performance criteria are set to ensure safety as well as reliable performance. Specialist equipment manufacturers rely on prevailing technology to meet these requirements: such specialist equipment manufacturer cannot afford significant R&D initiatives. Approval processes for trucks in particular are very similar to the automotive-sector. Based on the current state of research, it will be 10 to 15 years at least before an alternative to functional chrome plating using chromium trioxide is available within the general engineering sector. Functional chrome plating using chromium trioxide is also used in critical equipment such as the rolls in steel mills where functional chrome plating provides numerous important characteristics including inter alia hardness, wear resistance, high lubricity, low coefficient of friction and a high reproducibility of the substrate roughness. Although intense research on two potential alternatives has been ongoing for over 5 years, tests are at laboratory scale. The scale up process requires significant financial investment as well as time for engineering, construction, testing and evaluation, as testing must be conducted in full size mills under normal operating conditions and realistic maximum roll forces. Significant future R&D effort over at least 7 years are expected prior to adapt the manufacturing processes accordingly which will take another 7 years. The steel sector needs a minimum of 11 to 14 years after the sunset date for a complete introduction of an alternative. Precision metal parts and filters (e.g. fine sieves) are usually manufactured via an electroforming process and can thereafter be plated using chromium trioxide. The electroforming process is characterized by excellent process control, high quality production and very high repeatability. The high resolution of the conductive patterned substrate / mould (e.g. stainless steel) allows finer geometries, tighter tolerances and superior edge definition. Testing alternatives is particularly time consuming and difficult for this sector and the variety of products is wide. For instance, campaign- wise production of sugar is limited to 3-4 months a year and test capacities are rare. It will take a minimum of 10-15 years before an alternative is available within the sector of metal precision parts. Printing equipment Functional chrome plating using chromium trioxide is applied to the printing cylinders of all rotogravure printing processes, for which the surface must be homogeneous, scratchproof, highly wear resistant, and hard. Low friction and the tribology between the cylinder surface and the ink and paper are important. Rotogravure printing is used for long printing runs with sharper, fine and clear images across many applications, such as magazines, catalogues, inserts and flyers, gift-wrap, and labels for bottles. The metallic chrome surface can be removed and re-plated to re-use the engraved surface; the metallic chrome coated surface protects the engraved surface. No other process is capable of such long runs and colour schemes. The printing cylinder production operates with time critical jobs and very short lead times. The metallic chrome coated roll may be in contact with various sensitive products, such as food packaging materials and textiles. Potential for migration from the printing rolls to the food packaging or textile must be considered, but is not a concern for chromium plated equipment. Functional chrome plating is also essential for other applications in the manufacture of printing equipment sector, such as moulds used in production of nickel printing screens and sheet guiding cylinder jackets. There are no technical alternatives available for these applications. The realistic time for complete introduction of a new coating is 10 – 12 years for the manufacture of printing equipment sector.
6 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Identification and evaluation of potential alternatives An extensive literature survey and consultation was carried out to identify and evaluate potential alternatives to chromium trioxide in functional plating. 18 potential alternatives were identified. 6 of these substances could be excluded from further consideration based on proven performance as category 3 alternatives. 12 alternatives (including processes and substances) are a focus for ongoing R&D programs and are examined in further detail in this report. 8 out of 12 alternatives have been identified as promising alternatives, where considerable R&D efforts have been carried out within the different industry sectors (category 1 alternatives) and are discussed in chapters 7.1 to 7.8. Table 1 at the end of this section summarises the main findings of the AoA for the use of chromium trioxide in functional chrome plating. Further 4 out of 12 alternatives showed clear technical limitations and may only be suitable for niche applications and not as a general alternative (category 2 alternatives, refer to chapters 7.9 to 7.12). In summary, the analysis shows there are no technically feasible alternatives to functional chrome plating with chromium trioxide for key applications. Several potential alternatives are subject to ongoing R&D, but do not currently support the necessary combination of key functionalities to be considered technically feasible alternatives. Some alternatives (e.g. electroless nickel, thick chemical vapour deposition using WC-Co, high velocity oxygen fuel (HVOF) using WCCoCr, and physical vapour deposition using WC-CH) are qualified for individual applications when less critical criteria of performance requirements are sufficient but none of these alternatives have all the key properties of functional chrome plating with chromium trioxide. Trivalent chromium has passed the laboratory research stage for the manufacture of printing equipment. No scale-up tests are available to date and larger scale testing needs to achieve stable process conditions which is difficult for the trivalent chromium process. The next stage of research is expected to take 10 to 12 years, and there is no guarantee that it will be successful. Trivalent chromium fails key requirements at laboratory scale for the other industrial sectors. Alternatives for the etching / pickling pre-treatment requiring chromium trioxide are assessed separately in chapter 7.13. A chromium trioxide free etching pre-treatment of metals (aluminium and its alloys) based on sulfo nitro ferric acid is commercially available and qualified for some applications and substrates, but not as general replacement for chromium trioxide pre-treatment. The development of a pre-treatment alternative to chromium trioxide depends on the potential alternative for functional chrome plating and is no standalone process. While an alternative for functional chrome plating is investigated, adequate custom-tailored pre-treatments are evaluated in parallel or after the potential alternatives for the main process has been qualified. Therefore, the time needed for R&D and industrial implementation of an alternative are identical for pre-treatment and main treatment which is a minimum of 10 – 15 years.
Concluding remarks A large amount of research over the last 30 years has been deployed to identify and develop viable alternatives for the use of chromium trioxide in functional chrome plating. Due to its unique functionalities and performance, it is challenging and complex to replace chromium trioxide based plating in applications that demand superior performance for wear and corrosion resistance, hardness, layer thickness and coefficient of friction to deliver the required product performance over extended periods and extreme environmental conditions. Several potential alternatives to functional chrome plating with chromium trioxide, such as trivalent chromium plating systems, electroless nickel, HVOF, CVD and PVD, are under intense investigation across industry sectors. Some are qualified for specific applications, none of them are able to meet all the performance requirements of functional chrome plating.
Use number: 2 7 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
As a result, a review period of 12 years was selected because it coincides with best case (optimistic) estimates by all the industrial sectors (aerospace, automotive and general engineering, steel, metal precision parts and manufacture of printing equipment) of the schedule required to industrialise alternatives to chromium trioxide for functional chrome plating (including pre-treatment) for key applications.
8 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Table 1: Technical deficiencies of category 1 alternatives by sector. Automotive & General Manufacture of printing Alternative Aerospace Steel industry Metal precision parts engineering equipment - hardness - corrosion resistance - corrosion resistance - layer thickness - hardness Electroless nickel - hardness - hardness - anti-adhesion 1 - wear resistance - corrosion resistance plating - layer thickness - wear resistance - hardness - coefficient of - endurance - process conditions - friction friction - hardness - wear resistance - hardness - hardness - coefficient of - hardness - anti-adhesion Nickel and nickel - coefficient of friction 2 alloy - wear resistance friction - corrosion resistance - wear resistance - wear resistance electroplating - microstructure - morphology - plating bath - hardness - microstructure - wear resistance conditions - corrosion resistance - corrosion resistance - coefficient of friction/ - rebuilding of parts - corrosion resistance - corrosion resistance lubricity - coefficient of friction - rebuilding of parts - rebuilding of parts - hardness 3 Case hardening - process temperature - anti-stick properties - hardness (depends - hardness (depends - rebuilding of parts - hardness (depends on - hardness (depends on on substrate) on substrate) substrate) substrate) - corrosion resistance - size limitations - size limitations - layer constitution - size limitations - process temperature 4 (Thin) CVD - process temperature - process temperature - suitability for the - process time - layer thickness - corrosion resistance - process time sectors’ products - process temperature - Large geometries Thick CVD - process temperature
(aerospace) - size limitation - uniformity Nanocrystalline - anti-adhesion cobalt - hardness - hardness - corrosion resistance 5 - hardness - hardness phosphorus alloy - layer thickness - adhesion (for Ni- - hardness - wear resistance coating W-Plating) - geometry - brittleness - brittleness - homogenous surface/ High velocity - process temperature 6 thermal - wear resistance - geometry - reproduction of porosity (depends on the - surface conditions processes - process temperature surface - constant thickness coating, loads, wear
Use number: 2 9 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Automotive & General Manufacture of printing Alternative Aerospace Steel industry Metal precision parts engineering equipment mechanisms and the counterparts) - corrosion resistance (depends on the coating) - hardness (depends on coating) - roughness/ - hardness microstructure - microstructure - wear resistance - hardness - microdistribution Trivalent - scale up 7 functional hard - process maturity - layer thickness - adhesive strength to - layer thickness - stable process conditions chromium - layer thickness - endurance substrate - hardness - microstructure - layer thickness - corrosion resistance - corrosion resistance - process temperature - brittleness - layer thickness - layer constitution - layer thickness - geometry - wear resistance - wear resistance - geometry 8 PVD - corrosion resistance - internal stress - geometry - longevity/ fatigue - brittleness - geometry - layer thickness - process temperature - coefficient of friction - internal stress - rebuilding of parts - rebuilding of parts (depends on process)
10 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
2. INTRODUCTION
2.1. The substance The following substance is subject to this AoA:
Table 2: Substance of this AoA.
# Substance Intrinsic property(ies)1 Latest application date2 Sunset date3
Chromium trioxide, CrO3 Carcinogenic (category 1A) 1 EC No: 215-607-8 21 March 2016 21 September 2017 Mutagenic CAS No: 1333-82-0 (category 1B)
1 Referred to in Article 57 of Regulation (EC) No. 1907/2006 ² Date referred to in Article 58(1)(c)(ii) of Regulation (EC) No. 1907/2006 3 Date referred to in Article 58(1)(c)(i) of Regulation (EC) No. 1907/2006 Chromium trioxide is categorized as a Substance of Very High Concern (SVHC) and is listed on Annex XIV of Regulation (EC) No 1907/2006. Chromium trioxide is an inorganic salt based on hexavalent chromium (Cr(VI)). Adverse effects are evaluated in detail in the chemical safety report (CSR). When brought in contact with water, chromium trioxide (EC No 215-607-8) forms two acids and several oligomers: Chromic acid (EC No 231-801-5), Dichromic acid (EC No 236-881-5), oligomers of chromic acid and dichromic acid (further referred as "Chromic acids and their oligomers"). This AoA discusses many situations where this is the case. For the purpose of this document the terms chromic acid is synonymous with a mixture containing chromium trioxide and water.
2.2. Uses of chromium trioxide The processes with chromium trioxide for functional chrome plating are: - Pre-treatment processes, such as etching, pickling, functional cleaning, deoxidising; and - Main treatment process: applying a metallic chrome coating on specific substrates and underplates to enhance wear resistance, tribological properties, anti-stick properties, and corrosion resistance in combination with other important functional characteristics.
2.3. Purpose and benefits of chromium trioxide Using chromium trioxide has multifunctional positive effects, mainly based on the characteristics of the hexavalent chromium compound. The following desirable properties of metallic chrome coatings produced from chromium trioxide have made this compound a state of the art substance for a wide range of applications for more than 50 years. - Excellent wear and abrasion properties combined with hardness; - Low coefficient of friction; - Corrosion protection; - Adequate layer thickness; - Ability to maintain lubrication due to micro-cracking; - Ability to plate complex parts and ID surfaces. Although chromium trioxide is used in functional chrome plating processes, no chromium trioxide residues are present on the functional chrome plated article. Several alternatives are being tested to substitute chromium trioxide. The challenge is to find a substitute which meets the requirements for all different types of products, and for the different uses of each specific application that at the same time is technically and economically feasible. Many
Use number: 2 11 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES alternatives are now qualified for individual applications when some of the functional chrome plating requirements are sufficient but none have all the key properties of functional chrome plating with an aqueous solution of chromium trioxide: for instance, for aeronautics applications, some are better in fretting wear, some in sliding wear, some require lubrication, some do not, some offer corrosion resistance some do not, etc.
12 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
3. FUNCTIONAL CHROME PLATING Chromium trioxide is used for a large variety of applications in the aerospace, automotive and general engineering, steel, metal precision parts, and manufacturing of printing equipment sectors as well as sectors involved in general engineering applications. Applications of these sectors and industries are illustrated in the following sections.
3.1. Metallic chrome coatings Metallic chrome coatings are usually applied in a layer with a thickness between 15 and 500 µm although the potential thickness of a metallic chrome coating is unlimited. Metallic chrome coatings generally form as a heavy layer resulting in high mechanical and wear resistance, with a high anticorrosion performance (with a nickel underplate for steel) and a low friction coefficient. They are usually used for technical applications such as industrial parts that must perform under demanding conditions comprising high temperatures, repetitive wear and impact forces. Functional chrome plating is used in a number of different industries and the metallic chrome coating is predominantly applied on steel or hardened steel as substrate. Other substrates commonly plated include stainless steel, titanium alloys, nickel alloys, copper alloys, cast iron, bronze and aluminium. Typical applications of functional chrome plating include hydraulic cylinders and rods, crankshafts, printing plates and rolls, pistons for internal combustion engines, landing gear, screens for plastic or fiberglass parts manufacture and mandrels for nickel printing screens, as well as cutting tools. The functionalities of metallic chrome coatings from chromium trioxide solutions were evaluated during the consultation phase within the CTAC Consortium and the key functionalities (functionalities of highest priority) identified. The layer thickness depends on the sector specific applications and requirements and may vary significantly between different applications. The layer thickness has a high impact on the properties of the final metallic chrome coating. Thin deposits make the coating more flexible and reduce the risk of cracks, whereas thick deposits increase wear resistance and corrosion performance. Extreme hardness of the metallic chrome coating is generally required for most functional chrome plating applications. Additionally, superior corrosion resistance (with a nickel underplate for steel) and resistance to chemicals is required, to prevent corrosion of the underlying layers and the whole plated product. This aspect in combination with high resistance to wear is useful for all types of hydraulics (treads/surface) or for example rotary driers which are exposed to corrosive chemicals. A high wear resistance is for example important with regard to jet turbine engine parts, parts exposed to mineral/inorganic material such as concrete pumps or manufacturing equipment, and those exposed to fibres such as in paper manufacturing and processing. Low friction and tribological advantages are mainly required in the aerospace industry, the manufacturing of steel, and in the use of piston rods in cars and trucks, especially for hydraulic cylinders for automotive and general engineering. In combination with wear resistance, low friction and tribological advantages are required for critical parts in landing gear and hydraulics. Furthermore, good tribological properties in combination with superior corrosion resistance and resistance to chemicals are important for shock absorbers. Given the use of tools and screens for manufacturing of sheet metal/film and plastics, or screens for manufacturing nickel sheets and cylinders, the surface is required to be anti-adhesive. These screens, plastics and rubbers are functional chrome plated to reduce wear and sticking. Further requirements with regard to plated or replated tools and machine parts are the machinability and reparability. The metallic chrome coating layer is required to be resistant to temperature which is necessary for the use of piston rings and cylinders in combustion engines in combination with good tribological
Use number: 2 13 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES properties, and also for the operation of jet turbine engine parts. Its micro-cracked structure provides excellent functionality for lubricants. Metallic chrome coatings form inert oxides and thus significantly reduce the risk of galvanic corrosion to more active counterparts. Another prerequisite is the ability to coat complex parts with functional chrome plating. Some exemplary sector specific examples of metallic chrome coating applications are provided in Table 3.
Table 3: Examples on sector specific metallic chrome coating applications.
- Undercarriage / landing gear and control components - Wheel axles or pins or rods of hydraulic actuators - Jet turbine engine parts (rotating hardware such as bearings, shafts, rotors and smaller hardware like fasteners) - High lift systems (flaps and slats) Aerospace - Hydraulic actuators - Pins and axles - Wear pads, latches and bushes - Bearing systems - Suspension splices - Moving parts of: engine driven train, transmission, steering, differential components - Shock absorbers, piston rings, power train, fuel injection parts, pistons for breaks, engine valves - Hydraulic cylinders, blanket cylinders, plate cylinders Automotive and General Engineering - Ductors, feed rolls - Delivery cylinder pipes - Saw shafts - Headrests - Belt tongues - Rollers and rolling mill bearings Steel Industry - Forging dies - Mandrels Manufacture of printing - Cylinder jackets equipment - Rotogravure plates/rolls - Sugar sieves Metal precision parts - Other filtration & separation media
Importantly, in these demanding environments corrosion occurs even in the highly developed chromium trioxide-containing coating systems used today. For the currently used coatings, extensive experience exists on the appearance and impacts of corrosion. Without a well-developed chromium trioxide-free alternative, corrosion will certainly increase, as these coatings do not offer all the crucial properties of chromium trioxide coating systems and their long-term performance can currently only be estimated. As a consequence, decreased corrosion protection performance may lead to shorter inspection intervals, which has a significant impact on the maintenance costs, e.g. for aircraft. Some of the corrosion prone areas are illustrated in the following Figure 3 to Figure 7:
14 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Figure 3: General engineering - delivery cylinder pipe. Data source: ZVO, 2014.
Figure 4: Functional chrome plated rods with metallic chrome coated layers between 20 and 75 µm. Data source: http://www.uk-finishing.org.uk/N-COAT70/electrolytic_hard_chrome.htm
Use number: 2 15 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Figure 5: Printing rolls used for high output printing on to “magazine” quality paper (left) and functional chrome plated and polished parts as example for thick metallic chrome coatings up to few hundred µm thickness (right). Data source: http://www.uk-finishing.org.uk/N-COAT70/electrolytic_hard_chrome.htm
Figure 6: Multiple examples of metal chrome coatings based on chromium trioxide for automotive applications. Data source: Enthone, 2014.
Figure 7: General engineering sector - functional chrome plated hydraulic cylinder. Data source: Ovako, 2014.
16 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
3.2. Surface treatment process description “functional chrome plating” Surface treatment of metals is a complex and stepwise process in many industry sectors. For the operation of high performance surfaces in demanding environments, the use of chromium trioxide in metallic chrome coating components is mandatory to ensure quality and safety of the final product over decades. As illustrated in Figure 8, there are various steps within the whole surface treatment process which involve the use of chromium trioxide. These are classified into the pre-treatment process (for an adequate preparation of the substrate for the subsequently applied process steps), and the respective subsequent process step (main process). There are no post-treatment processes for functional chrome plating which involve chromium trioxide.
Figure 8: Simplified overview of different steps that may be involved in functional chrome plating using chromium trioxide.
It is of greatest importance that only the combination of adequate pre-treatment and the appropriate main process step leads to a well-prepared surface providing all of the necessary key requirements for the respective applications as described in detail in chapter 3.3. Chromium trioxide is a pre- requisite for the main treatment of functional chrome plating to ensure high quality of the product and to meet the requirements of the industry. Although single process steps can be assessed individually, they cannot be seen as stand-alone processes but as part of a whole process chain. Consequently, when assessing alternatives for chromium trioxide-based surface treatments, the whole process chain and the performance of the end product must be taken into account. Indeed, although R&D on replacement technologies in surface treatments has been ongoing for decades, industry has developed and partly qualified alternate treatments for a limited number of applications only. Therefore, it is possible that for either pre- treatment or main process steps, chromium trioxide free alternatives are already on the market and industrially used. However, it is crucial to consider the following points: - In each case, the performance of the alternative materials/techniques must also - and even more importantly - be evaluated as part of the whole system. - Any change of single steps in the process chain of surface treatments, will require component and/or system level test and evaluation, (re)qualification and implementation into the supply chain. - In fact, current coating systems still typically incorporate at least one process step containing chromium trioxide. We therefore clearly state that for a thorough assessment of replacement technologies it is mandatory to include the whole process chain (including pre-treatment), taking into consideration that for all steps involved, chromium trioxide-free solutions must be developed, which in combination are technically equivalent to the current chromium trioxide containing treatments. As of today, complete chromium trioxide free process chains are industrially available for some special functional chrome
Use number: 2 17 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES plating applications only. For the majority of functional chrome plated products at least one process step, usually the main treatment, requires chromium trioxide to provide the required properties to the surfaces. The process description presented below covers the most relevant and critical process steps. Nevertheless company specific and sector specific adaptions are rather the rule than the exception. In general, all process steps are performed by immersing the product to be plated in a bath containing the process step specific aqueous solution. It is a wet-in-wet process, generally without any intermediate storage of the product at any time in the process chain, except for the final drying step. However, mandrels manufactured within the printing equipment industry may be stored after copper plating for up to 2 months before functional chrome plating. If other substances are used for the pre-treatment process than chromium trioxide, numerous rinsing steps are necessary to prevent the carry-over of solutions from the pre-treatment bath to the functional chrome plating bath, as this might lead to interferences with the respective subsequent process step and can cross contaminate the plating bath. The thickness of the metallic chrome coating varies depending on the application in the industrial sectors from thin (5-25 µm) in the manufacture of printing equipment sector to thicker layers for steel rollers and the aerospace industry (up to 100 µm). Furthermore, heavy duty parts like piston rings can reach a thickness of 500 µm or more in order to provide long term wear resistance. A detailed description of the key performance parameters and the sector specific minimum requirements of the metallic chrome coating are provided in chapter 3.3.
3.2.1. Pre-treatment processes A number of pre-treatments are necessary to prepare the surface of the substrates for the subsequent process steps. However, only one pre-treatment involves the use of chromium trioxide, which is etching / pickling. Adequate preparation of the base metal is a prerequisite: adhesion between the metallic chrome coating and the substrate depends on the force of attraction at a molecular level. Therefore, the surface of the metal – which is mostly steel, nickel alloys and copper alloys for functional chrome plating – must be absolutely free of contaminants, corrosion and other residuals until the plating process is finished. In general, there is not a clear demarcation between the processes of pickling and etching. When comparing specifications from different sources, the terminology is not always consistent from one document to another. Pickling is the removal of stains, inorganic contaminates and oxides (as rust from a metal surface by a chemical or electrochemical process). Pickling removes only the surface oxides and limited parts of the underlying substrate. For example, during a 5 minute pickling process, 0.4-0.6 µm of the substrate is removed. The removal rates vary for different substrates. Pickling removes less of the substrate material than etching. The metal parts are dipped in a bath containing the chromium trioxide-based pickling solution. The pickling is required as continuous oxidation during transport and manufacturing to generate a natural passivation layer, making the surface less reactive to the subsequent process steps. Etching is defined as a surface activation step by removal of base material, from a metal surface. Etching affects metal surfaces in a more aggressive manner than the pickling process. For example, during a 5 minutes etching step, 2-4 µm of the substrate is removed. The removal rates vary for
18 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES different substrates. Etching is performed by immersing a metal substrate in an acidic solution (bath application). The etching process creates a surface which is clean and free from defects or oxides, adequately preparing the metal surface for subsequent process steps and providing very good adhesion (RPA Report, 2005). Some small amounts of metal may be intentionally removed by etching to facilitate inspection processes (e.g. nital etch, dye penetrant inspection). As there is no clear demarcation, the term etching is used to cover both, etching and pickling as a chromium trioxide pre-treatment in the following. The vast majority of etching processes are reverse etching processes using an aqueous solution of chromium trioxide, which can be applied in the plating bath itself at the appropriate temperature, or in a separate etch bath. Using the plating bath saves time and space but has also disadvantages. Trivalent chromium and dissolved metal ions from substrates constantly build up within the plating bath. Over time these ions become detrimental, leading to formation of deposits and requiring renewal of the bath. Hence, using a separate reverse etch bath is considered to be more sustainable. Mode of action: The purpose of etching is the removal of impurities (such as metal oxides) and a certain amount of the base metal from the substrate. Chromium trioxide is necessary for controlling a moderate etch rate and to avoid over-etching. Additionally, an aqueous solution of chromium trioxide fulfils the following major purposes for the pre-treatment: An aqueous solution of chromium trioxide acts as strong oxidising agent of the base metal and an acidified solution of chromium trioxide is also used to remove oxides from the surface. In both cases, the metal substrate is dissolved and can be removed from the system as sludge. However, an aqueous solution of chromium trioxide is furthermore used to etch copper surfaces in order to remove copper burrs present after copper plating and simultaneously deoxidise the copper surface as pre-treatment.
3.2.2. Functional chrome plating The metallic chrome coating layer is applied by electroplating based on the principle of electrolysis. An optional step prior to the electroplating is a Cu or Ni-strike which is applied in some cases for certain substrates. In this pre-step, a very thin layer of a fraction of a µm of Ni or Cu is applied to improve the adherence between substrate and metallic chrome coating. Additionally, thicker deposits of electroplated nickel may be used to improve the barrier corrosion performance of the coating. Functional chrome plating is forming a coherent metal coating on the part to be plated (either the direct substrate or the substrate with already plated intermediate layers) by using the substrate as cathode and an inert anode (often platinum-coated titanium anode or tin-lead anode) and inducing an electrical current. The substrate is immersed in the electrolytic plating solution containing dissolved chromium trioxide and additives (electrolyte). During the electroplating process, the hexavalent chromium cations are reduced and build-up a metallic chrome coating layer (electrodeposition). Auxiliary electrodes or conforming anodes are placed near the substrate to ensure complete plating even on the inside or in hidden cavities of complex substrate surfaces. In the plating process, solutions of chromium trioxide, with a concentration between 80 g/l and 400 g/l are used. Catalysts such as sulphuric acid are added in concentrations of 3 to 5 g/l. Additional catalysts contain mixed sulphate and fluoride ions and pre-prepared proprietary catalysts with each less than 2% of the content of chromium trioxide. The sulphate bath is a commonly used chromium trioxide bath and has an efficiency of approx. 15%. Although fluoride or mixed catalysts baths have a higher
Use number: 2 19 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES efficiency than the sulphate bath (25%), their use is limited due to the chemical activity of fluoride ions which can attack the unplated surface. Proprietary (organic) catalysts provide higher cathodic efficiencies of up to 25% and have the advantage not to attack the steel (unplated surface) in those areas of the cathodes where the current density is too low for chromium to be deposited. Proprietary catalysts are generally not used in the aerospace sector. Perfluorinated surfactants (such as perfluorooctane sulfonic acid, perfluorooctanoic acid or Perfluorobutane sulfonic acid – perfluorinated compounds are currently evaluated by ECHA for restriction) are often added as mist suppressors to reduce aerosol formation by H2, which is formed during the process. The bath temperature usually lies between 50 and 60°C. High temperatures (70°C) and solution additives reduce the number of cracks or can even eliminate them but simultaneously make the coating softer. A catalysed plating solution containing potassium dichromate (not covered in this AoA) in addition to chromium trioxide is sometimes used for specific applications in the aerospace sector. The coating functionalities are equivalent to other functional chrome plating solutions. The primary advantage of this solution is that it contains a catalyst besides the chromates to improve plating efficiency. The plating can be applied to the desired thickness using a lower current density in a shorter time. With this specific solution, high quality thin dense metallic chrome coatings can be produced, providing similar results as with chromium trioxide under improved plating efficiency. Typically, these thin coatings provide hardness in the range of 700 to 900 HV in combination with good corrosion resistance and high abrasion resistance under controlled process conditions. During the overall functional chrome plating process chain, numerous rinsing steps are carried out to prevent the drag-out of material from one plating preparation bath to the next. Rinsing is commonly performed by immersing the parts in a bath filled with rinsing (clean) water and usually occurs in several steps (cascade technology). The most common technique is counter-current cascade rinsing, where the part is rinsed in a succession of rinsing baths that are dedicated to the preparation or plating baths. Most of the process water is handled in a closed-loop system minimizing wastewater streams by reuse of concentrated rinsing water in the process bath of the same type. Some water evaporates and must be replenished in order to keep the bath in balance. For the remaining water used during the rinsing process, intensive waste water treatment is required and a number of different steps of wastewater treatment are known. The generated wastewater streams are cleaned from chromium trioxide residues in the rinsing water by the chemical reduction to Cr(III). This is achieved under acidic conditions using reducing agents such as iron(II)sulphate. After being oxidised to trivalent iron, it serves as coagulant resulting in a precipitation with trivalent chromium in the sludge. This sludge is then disposed of. The cleaned wastewater has a chromium concentration far below the thresholds of the local wastewater regulation and can be discharged to the public wastewater system.
3.2.3. Post-treatment processes Post-treatments comprise rinsing and cleaning steps to remove potentially remaining process chemicals from the product and a final drying of the product as well as grinding, lapping, polishing or thermal treatment of the functional chrome plated substrate is performed. These post-treatments are chromium trioxide-free and are chosen depending on the base substrate as well as company specific and sector specific requirements. However, during the rinsing process minor amounts of the plating bath concentration are accumulated in the rinsing water. Process rinsing water can therefore contain minor amounts of chromium trioxide,
20 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES but this is not relevant for the cleaning process itself. As mentioned above, the generated wastewater streams are cleaned from chromium trioxide residues in the rinsing water.
3.3. Key functionalities of functional chrome plating An overview on the key functionalities of chromium trioxide in functional chrome plating is provided in the following sections, subdivided into pre-treatment processes and the main coating process. Functional chrome plating can be applied on a variety of surfaces including but not limited to steels, stainless steels, nickel based alloys, copper alloys, aluminium alloys, titanium alloys, etc. During the consultation phase, the key functionalities for functional chrome plating were identified taking the whole surface treatment processes into account. Nevertheless, the most important key functionalities of the high-quality final product are related to the chromium trioxide based electroplating step that results in a high-end wear resistance and hardness of the coating.
3.3.1. Key functionalities of chromium trioxide based surface pre-treatment The pre-treatment process prepares the surfaces for the subsequent main process step. In Table 4, selected key functionalities and relevant advantages for the pre-treatment process are listed and if quantifiable, discussed in more detail below.
Table 4: Key functionalities of chromium trioxide based pre-treatment.
Process Key Functionality
Etch rate: Aluminium: <2.5 µm/min/side, Magnesium: <1.0 - 15.2 µm/min/side, Steel: 0.25 µm/min/side, Chromium: 5 µm/min/side. Minimal intergranular Attack / End Grain Pitting (ASTM F 2111)
Etching (Pickling) Removal of residuals/oxides from the surface Corrosion resistance, adhesion of subsequent coatings treatment processes - Minimum fatigue (ASTM E466) and tensile (ASTM E8) testing Pre Removal of base metal substrate/oxides
The above presented key functionalities are achieved by key process functionalities as presented in Table 5. With its optimal behaviour chromium trioxide based pre-treatment ensures high quality products and is the decisive factor for the use of the chromium trioxide based pre-treatment solutions.
Table 5: Key process functionalities of chromium trioxide based pre-treatment.
Process Key Process Functionality
Good control of etch rate Long-time bath stability if applied in a separate etch bath Simple bath maintenance
treatment Simple analytical method for process control
Pre - Rack with treated parts also usable with subsequent process step Minimal intergranular attack
Etching (pickling) The key functionality of etching is the adequate removal of oxide and debris from a metal surface. For etching, selective removal of certain amounts of base material is required for surface activation.
Use number: 2 21 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
This process is controlled by the etch rate. The careful control of this step influences the quality of the subsequent coating layer. After the pre-treatment, the processed parts will have a reduced number of pits, be free of corrosion products, discoloration, uneven etching, increased surface roughness or other defects that would prohibit further chemical processing (visual inspection, penetrant inspection (ASTM E 1417)). The etching rate must be chosen according to the metal substrate used. Different types of steel require different etching rates. The longer and harder the etching, the greater the roughness of the surface. Under-etching or over-etching should be avoided as not to affect the key functionalities of the subsequent coating (for example: poor adhesion resulting in cracks and blistering). The etch rate is controlled by measuring the thickness before and after processing. In addition, treated surfaces should be free of intergranular attack typically in excess of 5 µm or end grain pitting greater than 25 µm deep. Fatigue and tensile testing is performed according to ASTM E466 and ASTM E8. No degradation due to processing should be observed. Further key functionalities are the long-term use of the plating baths with proper maintenance. The bath chemicals have to be refilled ensuring dosing accuracy to prevent over- or under-etching. Additionally, the racks which the parts are applied to are usually used in the overall process chain and therefore have to be compatible with the chemicals used in the subsequent process steps.
3.3.2. Key functionalities of metallic chrome coatings Selected quantifiable requirements of the key functionalities of the metallic chrome coating applied on steel with (nickel) undercoat and deposited by the chromium trioxide functional chrome plating process for the respective sectors are listed in Table 6 to give a short overview of the wide range of requirements. A more detailed description taking into account different substrates is given in the subsequent paragraphs.
Table 6: Sector specific key functionalities of metallic chrome coatings. Automotive Metal Manufacture Quantifiable key Aerospace and General Steel precision of printing functionality engineering parts equipment Not Not Not generally < 5-10 mg < 10 mg/ Wear resistance quantitatively quantitatively defined /10,000 U 10,000 U measured measured 1,000-1,400 Hardness 700-900 HV 850-1,200 HV 850-1,000 HV 1,100 HV HV Depends on 5-25 µm Layer thickness > 100 µm 20-50 µm 15µm application Not Not SST: 100–500 Depends on Corrosion resistance* SST: > 750 h quantitatively quantitatively h application measured measured Not Not generally Coefficient of friction < 0.2 < 0.1 < 0.2 quantitatively defined measured *There are different standardised SST tests available which vary between sectors, applications and substrates. An important quality criterion is given by the hours to resist certain test conditions. In addition, the results of corrosion resistance tests are evaluated using a rating scale between 10 and 1 (10 representing the best rating and no corrosion). The required minimum rating also varies between the different industrial sectors; thus comparability of sectors is limited: a rating of 10 after a 100 h SST test may be comparable to a rating of 4 after 500 h.
22 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Other key functionalities which are difficult to quantify are required from metallic chrome coatings: for example the ability to maintain lubrication or retention of inks due to micro-cracking, the prevention of galvanic corrosion of surfaces by passive chrome oxides, and the ability to plate complex parts.
3.3.2.1 Wear resistance The wear resistance of a coating for all sectors is generally tested via its sliding and abrasion resistance behaviour, although in the aerospace sector reciprocating sliding wear testing against materials used for counterparts is more common. One commonly used test method is the Taber Abrasion test according to ASTM D4060-10. During this test, a rubbing material (such as a rubber wheel impregnated with abrasive particles) is rubbed over the coated surface with a defined force and for defined cycles. The distinct test procedure is company specific, but for all companies the requirement is that the coating shall not show any visually detectable damages after Taber linear abrasion (“no scratches”). General requirements stated in ASTM D4060-10 for metallic chrome coating applications are < 50 mg/10,000 cycles. In the aerospace sector common wear resistance test methods are ASD PREN2132, electrodeposition of chromium for engineering purposes – aerospace series, pin-on-disk test, Falex block-on-ring test, gravelometer test and further tribological tests. Wear resistance requirements for the steel sector and automotive and general engineering sector are < 10 mg/10,000 U and < 5-10 mg/10,000 U respectively. The critical parameters to assess the wear resistance in the manufacture of printing equipment sector are the visible printing output quality and the service life-time of tools (e.g. a mandrel in the production of rotary screens). A functional chrome plated mandrel can normally produce up to 1,000 rotary screens before it needs to be fully reworked. In this context, wear resistance is defined in terms of hardness of the plated chromium layer: wear takes place due to deliberate surface grinding after a certain amount (20-100) of screens have been produced, in contrast to continuous wear in aerospace or automotive.
3.3.2.2 Hardness Hardness is defined as the resistance of solid matter to various kinds of permanent shape changes when a force is applied. The total hardness of the product is the combined result of the substrate hardness and coating hardness. Measuring Vickers hardness (HV) for metallic materials, ISO 6507- 1, is the most common hardness test method and applicable for many industrial sectors with minimum requirements shown in brackets, including aerospace (700-900 HV), automotive & general engineering (850-1,200 HV), steel (850-1,000 HV), metal precision parts (1,100 HV), and manufacture of printing equipment (1,000-1,400 HV). Hardness is linked to the scratch and abrasion resistance.
3.3.2.3 Layer thickness The thickness of a functional chrome plating layer varies for each application and industrial sector. Typical layer thicknesses have been identified to be >100 µm for the aerospace sector (for the repair and restoration of worn aircraft parts, layer thickness will exceed 100 µm), 20-50 µm for automotive & general engineering, 15 µm for metal precision parts and 5-25 µm for the manufacture of printing equipment. There are several non-destructive methods available to determine the layer thickness, for example
Use number: 2 23 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
- Magnetic method, ISO 2178 & ASTM D7091; - X-ray method, ISO 3497 & ASTM B 568; - Coulometric method, ISO 2177.
3.3.2.4 Corrosion resistance Corrosion describes the process of oxidation of a metallic material due to chemical reactions with its surroundings, especially under the effect of humidity and oxygen. In this context, the parameter corrosion resistance relates to the ability of a metal to withstand gradual destruction by chemical reaction with its environment. Components that inhibit corrosion can be categorized according to basic quality criteria which are inhibitive efficiency and versatility. Ideally, the component is compatible with subsequent layers and performs effectively on all major metal substrates. Furthermore it needs to guarantee product stability (chemically and thermally) and reinforce the requested coating properties. The major corrosion resistance test performed for many sectors is the Salt Spray Test (SST) according to ASTM B117 and /or ISO 9227 in Europe (Neutral Salt Spray Test, NSST/NSS). Again, minimum requirements vary largely between sectors and applications. Acetic acid salt spray or copper accelerated acetic acid salt spray in ISO 9227, and sulphur dioxide salt spray in ASTM G 85 are more aggressive test methods. The aerospace industry reported a minimum requirement of at least 750 h in neutral SST with no corrosion for functional chrome plated steel with a nickel underplate. The automotive & general engineering performance requirements range from 100 h to 500 h in neutral SST and judgement according to ISO 10289 with a rating of 10 or 9. Automotive & general engineering reported further corrosion test methods such as UNE 112017-92 (a salt spray test in artificial atmosphere for metallic coatings) with a minimum of 500 h for neutral SST and 250 h for acid SST and the Kesternich test (ISO 6988). For metal precision parts, an immersion test is also used to determine the corrosion resistance of the applied coating by measuring the concentration of dissolved metals of the coating and substrate. For example, for sugar sieves, a mixture of 2% sodium citrate / 3.5% citric-acid (pH 3.5, room temperature) is used as these substances are often used for cleaning of machines in the food industry.
3.3.2.5 Coefficient of friction Friction is the force resisting the relative motion of solid surfaces sliding against each other. The friction coefficient is low for functional chrome plated surfaces. The coefficient of friction can be determined by tribological testing. ASTM D4518 is a test method for static friction of coating surfaces and ASTM D 1894 is the standard test method for static and kinetic coefficients of friction of sheeting. The aerospace industry requires a lubricated coefficient of friction of < 0.2 analogous to the steel sector whereas the automotive sector reports a value of < 0.1. Also important in this respect are the anti-stick properties, especially for hydraulic cylinders and shock absorbers, where a smooth starting movement is important. In addition to the coefficient of friction, the steel industry set a minimum requirement for the rolling force of the layer, which is reduced by the metallic chrome coating by 5%.
24 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
3.3.2.6 Effect on surface morphology The steel industry requires that the coating does not affect the surface morphology of the substrate. The defined surface texture of the substrate, which has been created during the pre-treatment, must be kept during the plating process. In this defined surface morphology, a certain amount of oil can be retained for lubrication in order to prevent tearing of sheets, e.g. in deep forming processes in the automotive industry. The desired surface roughness varies for different applications in the range of 0.7 µm to 15 µm. Chromium trioxide provides surface roughness in the application range as required as it follows perfectly the surface during functional chrome plating (refer to Figure 9).
Figure 9: Metallic chrome plated roughness illustration and detailed view as photomicrographs from a scanning electron microscope. Data source: Hoco-RST, 2014.
The surface finish of rolls in the steel industry has major influences on the rolled products and their properties. The formability of the products as well as the appearance of the coated surface are directly connected to the surface morphology of the rolls. Moiré- and orange peel effects can be avoided using a suitable surface structure. Only chromium trioxide has the property to deposit in hemispherical structures during coating. The number, size, distribution, coverage and other structure-parameters of these hemispheres can be adjusted for each application. Using chromium trioxide is currently the only possibility to produce surfaces with structures that meet the requirements of the steel industry regarding hardness, abrasion resistance and stepless variation of structure-parameters.
Use number: 2 25 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Figure 10: Microscopic view of a hemispherical structure coating of a roll. Data source: Salzgitter AG, 2014.
Figure 11: Example for stepless variation of structure parameters (open / closed) topography. Data source: Salzgitter AG, 2014.
26 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
4. ANNUAL TONNAGE
4.1. Annual tonnage band of chromium trioxide The annual tonnage band for the use of chromium trioxide in functional chrome plating is 6,000 tonnes per year.
Use number: 2 27 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
5. GENERAL OVERVIEW OF THE PROCESS FOR ALTERNATIVE DEVELOPMENT AND SECTOR SPECIFIC APPROVAL PROCESS
5.1. Aerospace Much has already been written about the airworthiness and approvals process in the aerospace industry in the document “An elaboration of key aspects of the authorisation process in the context of aviation industry“ published in April 2014 by ECHA and EASA (http://echa.europa.eu/documents/10162/13552/aviation_authorisation_final_en.pdf). The document makes a strong case for justification of long review periods for the aerospace sector. In this section we identify key points from the ECHA EASA “elaboration” document and add additional detail and justification for long review periods with specific regard to chromates. Some of the key points identified in the “elaboration” document are: - “The aerospace industry must comply with the airworthiness requirements derived from EU Regulation No 216/2008 in Europe, and with similar airworthiness requirements in all countries where aeronautical products are sold.” - “All components, from seats and galleys to bolts, equipment, materials and processes incorporated in an aircraft fulfil specific functions and must be certified, qualified and industrialised.” In addition the new materials must be developed and evaluated prior to these three steps. - “If a substance used in a material, process, component, or equipment, needs to be changed, this extensive process [of development, qualification, certification and industrialization] has to be followed in order to be compliant with the airworthiness requirements.” - “Although the airworthiness regulations (and associated Certification Specifications) do not specify materials or substances to be used, they set performance specifications to be met (e.g. fire testing protocols, loads to be sustained, damage tolerance, corrosion control, etc.). These performance specifications will drive the choice of substances to be used either directly in the aircraft or during the manufacturing and maintenance activities.” - The development (TRL (Technology Readiness Level) 1-6) process “is an extensive internal approval process with many different steps from basic technology research up to technology demonstration in a lab environment.” - “Depending upon the difficulty of the technical requirements [qualification] can easily take 3-5 years. After initial laboratory testing, each specific application must be reviewed, which means additional testing for specific applications / parts. Airworthiness Certification begins at this same time, this certification can take from 6 months to years. Additional time is needed for production scale-up and development of a supply chain.”
Each one of these points is of significant importance for the aerospace sector with regards to chromates. Further elaboration will be made within this section. The last bullet point highlights that it can take a significant period of time to develop and implement new alternatives. It should be noted that in the case of chromates, the stated time needed for taking an alternative from the development phase through qualification, certification and implementation has been significantly underestimated. Efforts to find replacements for chromates have been ongoing within the aerospace industry for over 30 years. In this time some successful substitutions have been made, but large challenges remain. Efforts thus far to identify equivalents for substances with critical, unique properties like corrosion inhibition have proven that there are no ‘drop-in’ replacement
28 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES substances for chromium trioxide. Depending on the specific application and performance requirements many more years may be required before alternatives are identified and implemented. In this section the general process for alternative development through qualification, certification, industrialization and implementation within the aviation sector is described. This process is also followed closely by the defence and space sectors. Because of the stringent requirements for qualification and certification a formal process for technology readiness and manufacturing readiness is followed. The process for qualification, certification and industrialization as described in the ECHA EASA “elaboration” document is shown in Figure 12.
Figure 12: Illustration of the qualification, certification and industrialisation processes. Data source: EASA, 2014, http://echa.europa.eu/documents/10162/13552/aviation_authorisation_final_en.pdf This diagram is perhaps overly simplified and doesn’t indicate the significant level of research and development work required prior to qualification. As stated in the “elaboration” document “This process is an extensive internal approval process with many different steps from basic technology research up to technology demonstration in a lab environment.” The actual process followed by OEMs in the aerospace sector more closely follows the framework for Technology Readiness Levels (TRLs) and Manufacturing Readiness Levels (MRLs) originally developed by NASA. OEMs usually adapt this TRL/MRL approach resulting in individual versions which are considered proprietary and cannot be presented here. The NASA version is shown in Table 7.
Table 7: Technology Readiness Levels-Overview. Data source: US Department of Defense, 2009
TRL# Level Title Description Lowest level of technology readiness. Scientific research 1 Basic principles observed and reported begins to be translated into applied R&D. Examples might include paper studies of a technology’s basic properties. Invention begins. Once basic principles are observed, practical Technology concept and/or application applications can be invented. Applications are speculative, and 2 formulated there may be no proof or detailed analysis to support the assumptions. Examples are limited to analytic studies. Active R&D is initiated. This includes analytical studies and Analytical and experimental critical laboratory studies to physically validate the analytical 3 function and/or characteristic proof-of- predictions of separate elements of the technology. Examples concept include components that are not yet integrated or representative. Basic technological components are integrated to establish that Component and/or breadboard they will work together. This is relatively “low fidelity” 4 validation in laboratory environment compared with the eventual system. Examples include integration of “ad hoc” hardware in the laboratory. Fidelity of breadboard technology increases significantly. The basic technological components are integrated with reasonably Component and/or breadboard 5 realistic supporting elements so they can be tested in a validation in relevant environment simulated environment. Examples include “high-fidelity” laboratory integration of components.
Use number: 2 29 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
TRL# Level Title Description Representative model or prototype system, which is well beyond that of TRL 5, is tested in a relevant environment. System / subsystem model or prototype Represents a major step up in a technology’s demonstrated 6 demonstration in a relevant environment readiness. Examples include testing a prototype in a high- fidelity laboratory environment or in a simulated operational environment. Prototype near or at planned operational system. Represents a System prototype demonstration in an major step up from TRL 6 by requiring demonstration of an 7 operational environment actual system prototype in an operational environment (e.g., in an aircraft, in a vehicle, or in space). Technology has been proven to work in its final form and under expected conditions. In almost all cases, this TRL Actual system completed and qualified represents the end of true system development. Examples 8 through test and demonstration include developmental test and evaluation (DT&E) of the system in its intended weapon system to determine if it meets design specifications. Actual application of the technology in its final form and Actual system through successful under mission conditions, such as those encountered in 9 mission operations operational test and evaluation (OT&E). Examples include using the system under operational mission conditions.
In general the TRL assessments guide engineers and management in deciding when a candidate alternative (be it a material or process) is ready to advance to the next level. Early in the process, technical experts establish basic criteria and deliverables required to proceed from one level to the next. As the technology matures, additional stakeholders become involved and the criteria are refined. As specific applications are targeted as initial implementation opportunities, design and certification requirements are added to the criteria. Many more factors have to be taken into account prior to making a decision about transition of technology or replacing a material. A formal gate review process has been established by some companies to control passage between certain levels in the process. A similar set of guidelines for MRLs exist for the management of manufacturing risk and technology transition process. MRLs were designed with a numbering system similar and complementary to TRLs and are also intended to provide a measurement scale and vocabulary to discuss maturity and risk. It is common for manufacturing readiness to be paced by technology or process readiness. Manufacturing processes require stable product technology and design. Many companies combine the aspects of TRLs and MRLs in their maturity assessment criteria as issues in either the technology or manufacturing development will determine production readiness and implementation of any new technology. Referring back, now, to Figure 12: the general process steps can be loosely correlated to the steps in the TRL and MRL frameworks. Qualification begins after TRL 6 when technology readiness has been demonstrated. Certification begins around TRL 9 at the latest and may be performed in parallel with qualification. Industrialization/Implementation are not tracked on the NASA TRL scale, but some OEMs refer to this phase as TRL 10. As previously stated, what is missing from the diagram, is the necessary and significant work that is performed before reaching technology readiness at TRL 6. The following sections describe the highlights of the entire process from definition of needs before technology development begins through to implementation. The emphasis here is to provide a description of the general process while highlighting the inherent complexities. One additional point to keep in mind when reviewing the process description that follows is that there is no guarantee that the initial process to identify an alternative for a substance is successful. Failure
30 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES is possible at every stage of the TRL process. The impact of failure can be significant in terms of time.
5.1.1 Development and qualification
5.1.1.1 Requirements development A need for a design change may be triggered due to many reasons. The one of interest here is when a substance currently used for production of aerospace parts is targeted for sunset (e.g. chromates). Completely removing one substance may impact various parts and systems on an aircraft and may involve many different processes with different performance requirements. Once a substance is identified to be targeted by a regulation, a first step is to identify the materials and processes containing the specific substance. Most companies rely upon the information provided by the chemical manufacturer in the safety data sheet (SDS). This information source has many limitations when used for substance identification including: lack of reporting due to protection of proprietary data; reporting large concentration bands to protect specific formulary data; different disclosure requirements based upon country (articles exemption, thresholds, de minimis, specific substance classifications, etc.) to name a few. After identifying the materials and processes and associating these with specifications and other design references, parts are identified along with the applications and products which are potentially impacted. This is the first step in order to assess the impact for the company. This work requires contributions from numerous personnel from various departments of an aerospace company like Materials & Processes, Research & Development, Engineering, Customers Service, Procurement, Manufacturing, Certification, including affiliates in other countries and Risk Sharing Partners. Current production aircraft may have been designed 20 to 30 years ago (or more) using design methods and tools that are not easily revisited, nor were they necessarily standardized between OEMs. Checking and changing the drawings implies updating, e.g. creating the drawings under the new formats and tools, which can involve a tremendous amount of design work. Note: When a new design is needed e.g. to remove a substance, it may not be compatible with the existing one, this means that spare parts designs of the original materials/configurations may need to be preserved in order to be able to produce spare parts for the aircraft using the original (baseline) configuration. This is an additional impact to be taken into account. Once a substitution project is launched, technical specialists, from engineering and manufacturing departments, must define the requirements that the alternatives have to fulfil. Alternatives must satisfy numerous requirements. In many cases requirements are identified that introduce competing technical constraints and lead to complex test programmes. This can limit the evaluation of alternatives. For instance, for some materials, dozens of individual engineering requirements with similar quantities of industrial requirements may be defined. Categories of technical requirements may include: - Materials and processes requirements (e.g. corrosion resistance, adhesion strength), - Design requirements (e.g. compatibility of the component’s geometry complexity and with the coating application technique), - Industrial requirements (e.g. robustness and repeatability), - Environment, Health & Safety (EHS) requirements.
Use number: 2 31 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Definition of needs itself can be complex and requires significant timeframe. The complexity can be due to: - Different behaviour of the substitute compared to original product: new requirements may be defined. In this case, sufficient operational feedback to technically understand the phenomenon and reproduce it at laboratory scale is a must in order to be able to define acceptance criteria. - Requirements may come from suppliers and have an impact on the design. - Constraints from EHS regulations evolution. Once initial technical requirements are defined, potential solutions can then be identified and tested. The timeframe for initial requirements development can last up to 6 months. Note that requirements may be added and continue to be refined during the different levels of maturity.
5.1.1.2 Technology development The development process (typically TRL 4-6) is complex, and several years are often necessary before reaching development phase end (TRL 6). The following points explain why it may be long and complex: - Developing solutions usually necessitates several testing phases before meeting the numerous requirements, which often induce several loops to adjust the formulation / design. - Some tests are long lasting (e.g. some corrosion tests last 3,000h or longer). - In some cases, potential alternatives are patented, preventing multiple sources of supply, which is an obstacle to a large supply-chain deployment due to increases in legal costs and in some cases a reduction in profitability for the business. - When no 1 to 1 replacement solution is available, each alternative process must individually be considered to determine for which specific quantitative application it is suitable. This work represents a significant resources mobilization, especially in term of drawings update and implementation of alternatives which due to the multiple work streams takes longer with higher costs. Moreover, spare parts and maintenance processes redesign may result in complex management both at the OEM and the Airlines. Additionally, substances regulations are evolving throughout the long research and development phase and life cycle of aircraft, which is another challenge for OEMs. There is a risk that significant investments could be made to develop and qualify alternative solutions involving substances with low EHS impacts identified at that point in time. Solutions may be developed and finally qualified, however, in the meantime, EHS constraints on those substances increased to a point where they now meet the SVHC criteria. - When the suppliers have no “off the shelf” solutions, they must develop new ones considering a list of requirements that are often highly complex to combine (see the description of requirements in the above paragraph). - Drawings impact: The replacement of a material / process may impact the complete design of a part. Additionally, the mating part/counterpart functionality must be analysed too (materials compatibility, dimensional compatibility, stress compatibility). This may lead to redesign of the complete part plus mating parts. - Process instructions need to be developed.
The description of the development process is included in the qualification section of the ECHA EASA “elaboration” document. The text is reproduced here for continuity.
32 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
“Qualification precedes certification and is the process under which an organisation determines that a material, process, component or equipment have met or exceeded specific performance requirements as documented in a technical standard or specification. These specifications, often abbreviated as spec(s), contain explicit performance requirements, test methods, acceptance testing, and other characteristics that are based upon the results of research, development and prior product experience. The industry relies upon standards issued by government-accredited bodies, industry or military organisations, or upon company-developed proprietary Standard of Specification (specs). Most materials and process specifications include either a “Qualified Products List” (QPL) or “Materials Control” section that identifies products that have met the requirements. Application and use of these qualified products must be assessed and certification implications addressed before being used on aircraft hardware. OEMs rely upon the expertise of the chemical formulators to provide viable candidates to test against specific material and process specs.” It is important to note that many iterations of these formulas are rejected in the formulator’s laboratory and do not proceed to OEM evaluation. Formulators estimate 2 to 5 years before candidates are submitted to OEMs. “Once candidate(s) are developed, the OEM evaluates candidates by performing screening testing. If the candidate passes screening, testing is expanded to increase the likelihood that the preparation will pass qualification. If the candidate fails, which is often the case, material suppliers may choose to reformulate. It is not uncommon to iterate multiple times before a candidate passes screening. In some technically challenging areas, over 100 formulations have been tested with no success. This phase of development can take multiple years depending upon the material requirements. For those materials that pass screening, production scale-up, development of process control documents, manufacturing site qualifications, and extensive qualification testing is required to demonstrate equivalent or better performance to that which is being replaced. This phase of the process can also result in formulation or manufacturing iterations and may take several additional years. Depending on the complexity of the change and the criticality of the application (for example, fire protection or corrosion prevention have high safety implications and require development and testing against multiple, rigorous performance standards), re-certification may be required. The industry is ultimately limited by the material formulators’ willingness to expend their resources to develop alternative materials and technologies to be tested.”
The small volumes of materials sold, demanding performance requirements, and tightly controlled manufacturing processes for aviation customers provides an insufficient incentive for reformulation in some cases. When material formulators are not willing to reformulate their materials new sources need to be sought.
Use number: 2 33 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Figure 13: Illustration of the technology development and qualification process. Data source: EASA, 2014, http://echa.europa.eu/documents/10162/13552/aviation_authorisation_final_en.pdf, amended.
“This process [TRL 1-6 development] is an extensive internal approval process with many different steps from basic technology research up to technology demonstration in a lab environment. Depending upon the difficulty of the technical requirements, these initial steps can easily take 3-5 years. After initial laboratory testing, each specific application must be reviewed, which means additional testing for specific applications / parts. Airworthiness Certification begins at this same time, this certification can take from 6 months to years. Additional time is needed for production scale-up and development of a supply chain.” It should be noted that the timeframes for development and qualification stated in the “elaboration” document have been combined and may be understated in the case of chromates. Depending on the application and the complexity of material and process requirements, this process can easily take multiple years. As noted in the “elaboration” document the timeframe for development alone is typically a minimum of 3 to 5 years. Our experience with replacement of the substance addressed in this dossier is that the development takes much longer. For typically successful projects the duration is 3 to 5 years. For unsuccessful projects the development goes through repeated iterations and has taken over 30 years and still continues with limited success.
5.1.1.3 Qualification Only after a technology has demonstrated technology readiness level 6, do the OEMs begin the qualification. All material, components, equipment or processes have to meet or exceed the specific performance requirements which are defined in the Certification Specifications documented in technical standards or specifications. These are issued by military organizations, government-accredited bodies, industries or upon company-developed proprietary specifications. Products which have met all requirements are included in the documents as QPL or in the “Materials Control” section. The main reasons for qualification are: - To fulfil requirements by the Airworthiness Authorities European Aviation Safety Agency (EASA) and it is the first level of the aircraft certification pyramid.
34 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
- To ensure that only approved, reliably performing materials, parts and processes are used to produce aircraft components and systems. - To ensure that the product, the process or method is compliant with the industry regulations and aircraft manufacturer requirements to fulfil a specified function. - To provide a level of confidence and safety. - To ensure consistent quality of products and processes. - To ensure supplier control, and to guarantee production and management system robustness, throughout the supply chain. The qualification process is mandatory to demonstrate compliance with airworthiness and certification requirements: the qualification process ensures that the technical and manufacturing requirements documented in the relevant material and/or process specifications are met. The qualification process comprises several steps before materials/processes are qualified. Even if most showstoppers are identified during the development phase, process confirmation/production verification are performed during the qualification phase. In case of failure, product qualification will be cancelled and the development phase must start again from the beginning. Based upon OEM experience, the time period needed to pass the qualification process is estimated to be in the order of 8 years and can be even longer when major test failures occur. This is one of the main challenges for chromates replacement. Depending upon the materials, processes and criticality of the applications being evaluated, in-service evaluation and monitoring will be required and can extend to 15 years or more depending upon application.
5.1.1.4 Certification This next step is to certify that an aircraft and every part of it, complies with all applicable airworthiness regulations and associated Certification Specifications (specs). This step is also well described in the “elaboration” document and is reproduced here for continuity. “Certification is the process under which it is determined that an aircraft, engine, propeller or any other aircraft part or equipment comply with the safety, performance environmental (noise & emissions) and any other requirements contained in the applicable airworthiness regulations, like flammability, corrosion resistance etc. Although the airworthiness regulations (and associated Certification Specifications) do not specify materials or substances to be used, they set performance specifications to be met (e.g. fire testing protocols, loads to be sustained, damage tolerance, corrosion control, etc.). These performance specifications will drive the choice of substances to be used either directly in the aircraft or during the manufacturing and maintenance activities. Some examples of performance requirements are the following: - Resistance to deterioration (e.g. corrosion) Environmental damage (corrosion for metal, delamination for composites) and accidental damage during operation or maintenance. - Corrosive fluids - hydraulic fluids; blue water systems (toilet systems and areas); leakage of corrosive fluids/substances from cargo. - Microbiological growth in aircraft fuel tanks due to moisture/contamination in fuel cause severe corrosion. Such corrosion debris has the potential to dislodge from the fuel tanks, migrate through the fuel system, and lead to an in-flight engine shutdown. - Resistance to fire – flammability requirements fire-proof and fire-resistance. Aircraft elements are expected to withstand fire for a specified time without producing toxic fumes; this leads to using products like flame retardants, insulation blankets, heat protection elements in hot areas (e.g. around engines).
Use number: 2 35 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
The primary certification of the aircraft (or engine and propeller) is granted to the manufacturer by the Competent Aviation Authority of the “State of Design” which is typically the authority of the state where the manufacturer of the aircraft (or engine or propeller) is officially located (EASA in the case of aircraft designed and manufactured in the EU and European Free Trade Association countries). Aircraft that are exported to other countries will have to be certified (validated) also by the authority of the “State of Registry”. Manufacturers work with the certification authorities to develop a comprehensive plan to demonstrate that the aircraft meets the airworthiness requirements. This activity begins during the initial design phase and addresses the aircraft structure and all systems in normal and specific failure conditions (e.g. tire failure, failure of structural components, hydraulics, electrical or engines). The tests needed to demonstrate compliance, range from thousands of coupon tests of materials, parts and components of the airplane, up to tests that include the complete aircraft or represents the complete aircraft (system). The performance and durability of the various materials have to be confirmed while the behaviour of the parts, components and the complete airplane will have to be tested in the applicable environmental and flight conditions including various potential damage or failure conditions. For a new Type Certificate this overall compliance demonstration covers several thousands of individual test plans of which some will require several years to complete. Often, after the initial issuance of the Type Certificate, the tests that have the objective to demonstrate durability of the aircraft during its service life, will continue. All the different aspects covered by the Type Certificate together define the “approved type design” which includes, among other aspects, all the materials and processes used during manufacturing and maintenance activities. Each individual aircraft has to be produced and maintained in conformity with this approved type design. Changes to the approved type design may be driven by product improvements, improved manufacturing processes, new regulations (including those such as new authorisation requirements under REACH), customer options or the need to perform certain repairs. When new materials or design changes are introduced, the original compliance demonstration will have to be reviewed for applicability and validity, in addition to a review of potential new aspects of the new material or design change that could affect the airworthiness of the aircraft. Depending on the change, this review could be restricted to coupon or component tests, but for other changes this could involve rather extensive testing. E.g. changes in protective coatings could affect not only the corrosion resistance but could also affect the friction characteristics of moving components in actuators in the different environmental conditions, changing the dynamic behaviour of the system, which in the end affects the dynamic response of the airplane. Before the new material or design change can be introduced on the aircraft, all test and compliance demonstrations have to be successfully completed and approved by the Competent Authority. This approval results in the issuance of a Supplemental Type Certificate (STC), change approval or repair approval. It is important to note that, according to the EU Regulation No 216/2008, EASA is the design competent authority for civil aircraft only. Any other aircraft (e.g. military, fire-fighting, state and police aircraft) will have to follow similar rules of the corresponding State of Registry. To be able to maintain and operate an aircraft the responsible organisations must be approved by the competent authority and compliance is verified on a regular basis. Maintenance of an aircraft requires that the organization complies with specific procedures and materials described in the maintenance manuals which are issued by and the responsibility of the OEMs.” As noted in the “elaboration” document, in optimal cases certification can take as little as 6 months but typically will take several years. The duration really depends on the specific material and application.
36 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
5.1.1.5 Implementation / industrialisation An aircraft consists of several million parts which are provided by thousands of suppliers or manufactured internally by OEMs. Significant investment, worker training and manufacturing documentation may be required to adapt the manufacturing processes which sometimes require changes in existing facilities or the construction of new facilities. The industrial implementation is usually scheduled to follow a step wise approach to minimize the technical risks and benefit from lessons learned. This implies that the replacement is not implemented in all plants and at all suppliers simultaneously, but gradually. Each OEM may own several plants, e.g. up to 20 manufacturing sites / final assembly lines worldwide for some. Furthermore, the implementation of an alternative process may induce new development and modification in the complete process flow. The following text is reproduced from the “elaboration” document and describes the process for implementation of an alternative: “Industrialisation is an extensive step-by-step methodology followed in order to implement a qualified material or process throughout the manufacturing, supply chain and maintenance operations, leading to the final certification of the aerospace product. This includes re-negotiation with suppliers, investment in process implementation and final audit in order to qualify the processor to the qualified process. Taking into account that an aircraft is assembled from several million parts provided by several thousand suppliers, this provides an indication of the complexity for the industrialisation stage of replacement materials/processes, and the supply chain which provides these parts. Special challenges are: - Low volumes limit influence on changes to suppliers’ materials / processes - Procurement & insertion of new equipment - Scale-up & certification of new process - Incompatibility of coatings could be a risk. - Re-negotiation of long term agreements with suppliers*. - Increased complexity of repairs – Multiple different solutions for different applications as a substitute for a single, robust process. For example, currently all aluminium parts can be repaired with one chromated conversion coating. In some specific cases, the future state could require different conversion coatings for each aluminium alloy and application environment. Since different alloys are not easily distinguishable on the shop floor, ensuring that the proper repair procedures are used will be much more difficult. If alternate means of compliance approvals are requested for repair facilities or airlines, regulatory agencies are unlikely to have adequate knowledge or technical data to make informed assessments.
The operating environment, longevity of the aircraft, supply chain complexity, performance and above all airworthiness requirements are some of the considerations which can constrain the ability of the industry to make changes and adopt substitutes in the short, medium or long term.” *Changes to the design or manufacturing may require re-negotiations with suppliers which can be time-consuming, especially when long-term contracts are concerned. The supply chain is complex in the aviation industry; it includes but is not limited to chemical manufacturers, importers, distributors, formulators, component manufacturers, OEMs, Airline operators, and aftermarket repair and overhaul activities.
The timeframe for implementation and industrialisation is unknown. Simple changes may take 18 months to 5 years. Our experience with replacement of the substance addressed in this dossier is that
Use number: 2 37 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES full implementation and industrialization has yet to be accomplished. Implementation by airlines and Maintenance, Repair and Operations (MROs) further requires that an alternative is approved by the OEM and made available in the maintenance documents. When the alternative process is included in the maintenance documents, challenges described above have to be faced out by airlines and MRO to implement the alternative. Here, for operating supplies and testing time frames, another 3 years may be necessary, depending on complexity of the alternative. When a number of alternative processes have to be established simultaneously, as it is currently the case for tartaric sulphuric acid anodizing and boric sulphuric acid anodizing, more than 5 years may be necessary to fully implement the alternatives.
5.1.1.6 Examples In 2003, RoHS (Directive on Restriction of Hazardous Substances, 2002/95/EC) was adopted by the EU and took effect in July 2006. This directive triggered companies to substitute lead-based solder in electronic assemblies and all subsequent changes in the product designs and manufacturing processes: Basic research was started in the example company in 2003 with the selection and tests of alternative lead-free solder. The Research Program is still running in 2014 and the qualification and industrialization phase is ongoing: Components (IC’s, connectors, printed circuit boards etc.) had to be changed due to the higher soldering temperature that all materials have to withstand with lead-free solder and most of the manufacturing equipment had to be replaced. This fundamental replacement of lead (Pb) for aerospace and military applications with harsh environmental conditions will take more than 15 years in total to be deployed up to TRL9. Work on a replacement for chromic acid anodize began in 1982. The initial driver for this R&D effort was to reduce emissions of hexavalent chromium and comply with federal and local clean air regulations. Initial requirements were identified and four candidate solutions were evaluated. One candidate solution was selected in 1984. Qualification testing began in 1985. A process specification for boric sulfuric acid anodizing was released in 1990. In 1991 and 1992 industrialization began as several Boeing facilities began producing parts using the boric sulphuric acid anodizing process. One outside supplier also began processing parts to the Boeing specification in 1992. Evaluation of additional applications continued into the mid-1990s. In 2015, industrialization of the boric sulfuric acid anodize alternative for chromic acid anodize is still not complete. Many Boeing suppliers are shared with other OEMs and industries impeding the conversion to boric sulphuric acid anodizing from chromate acid anodizing because they must continue to support multiple customer requirements. Note that for unprimed parts a dilute chromate seal is still required to provide required corrosion resistance. Work is ongoing to develop alternatives for this application. It is also worth noting that boric acid is now being proposed for REACH Annex XIV requiring authorization. Should this happen alternatives may need to be developed for boric sulphuric acid anodizing. Other OEM solutions will need to be evaluated, qualified and certified by Boeing.
5.2. Automotive and general engineering
5.2.1. Current production parts in automotive applications - general considerations The automotive industry is a strategic industry in the European Union: 16.2 million cars, vans, trucks and buses were manufactured in 2012, employing 12.9 million people, including about 3 million high skilled jobs and having a turnover of about €840.5 billion (2011). Chromium trioxide is used by the automotive supply chains to manufacture several thousand parts of chrome-plated parts per vehicle manufacturer. Parts depending on the use of chromium trioxide are
38 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES covering a wide range of applications from belt locks to injector valves in vehicle models of a long production period of 7-10 years. Potential alternatives for chromium trioxide must be in compliance with the high demands and requirements regarding their critical performance properties within manufacturing processes and their final use. For these reasons, a simple 1:1 substitution of chromium trioxide is not possible. The identification of possible alternatives and the careful validation of their functionalities is a highly important and labour/time intensive process that will certainly take several years. According to the ACEA, the development of suitable alternatives for functional chrome plating for current vehicle parts will require a further time period of 10 years followed by industrialization of the technique and implementation in the supply chain.
5.2.2. Current production parts - requirements for alternatives to chromium trioxide Functional chrome plated parts are unique amongst others in terms of corrosion resistance, hardness, layer thickness, adhesive strength, coefficient of friction and wear resistance. Potential alternatives must be able to cover all of these requirements. A 1:1 substitution is not possible and careful testing and evaluation of an alternative´s functional behaviour is needed. Current testing procedures include: laboratory tests, summer and winter tests and continuous-operation tests. Thorough evaluation of possible alternatives is crucial to avoid failures in the field / daily application. In addition to safety aspects the consequences could otherwise be expensive and highly brand damaging product recalls. A single vehicle is constructed from 4,000 to 9,000 different main components and assemblies. The range of different kinds of components is illustrated in Figure 14.
Figure 14: Car dismantled into constituent parts; Data source: Volkswagen AG, 2013 (left). Principal engine parts of a car; Data source: HubPages, undated (right). In case one substance has to be phased out or replaced, all affected components must be revalidated using suitable alternative materials. Even though the automobile industry is highly experienced in material testing procedures, the validation and testing of alternatives would most likely not be complete by the sunset date due to the sheer number of parts involved. In particular, this is the case as potential alternatives would need to be tested in terms of their extension to large scale production and be ready for use by the sunset date in September 2017. The automotive industry deems best a stepwise introduction of alternative technologies in new type- approved models (Directives 2005/64/EC and 2009/1/EC), but this may not be feasible by sunset date.
Use number: 2 39 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
However, to ensure production volumes of vehicles are not affected, enough capacity for the production of alternative coatings in Europe must be built up. Otherwise import from non-EU suppliers would be needed to bridge the supply gap. With EU based OEM´s using 70-80% EU suppliers (and non EU based OEM´s using 20-50% EU suppliers) a change to non EU suppliers would have a huge impact on the EU economy. With more than 10 million cars being built every year, building up enough capacity in Europe to cover all relevant parts is not possible within the timeframe by the sunset date. A further point is the high complexity of supply chains in the automotive industry. The assembly of vehicles is performed in a complex network of manufacturing plants, which form a multi-tier system producing different parts, such as exterior sheets or engines. With an average number of 1,500- 4,500 OEM suppliers, which have an average of 500-1,500 suppliers themselves, tracking down chromium trioxide dependent parts is a time-consuming and complicated task. Lastly, the aforementioned multi-tier system, as well as the long-lasting nature of vehicles (up to 22 years and more) makes planning reliability crucial. Average life cycles of vehicles, are about 22 years and include 3-5 years development time, 7 years of production and at least 10 years of spare part guarantee. The opportunity to introduce changes is only possible within a certain period of time, which decreases rapidly after type-approval. Combining all these facts, the introduction of possible substitution parts has a long lead-time which cannot be met within the timeframe until sunset date (refer to Figure 15).
Figure 15: Typical life-time of a car model starting in production in 2018 compared to a four years period until sunset date. The period to introduce changes decreases rapidly after type-approval (Directives 2005/64/EC and 2009/1/EC) by a certified body. The time period until sunset date could affect any stage of the minimum 22 years life-time of different car models, even during the spare part period when changes are no longer possible.
5.2.3. Past model service parts – general considerations The EU passenger car fleet (Figure 16) consists of about 224 million vehicles. About 36 % of the overall numbers are older than 10 years (about 80 million cars).
40 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Figure 16: EU passenger car fleet (share in % by age in 2010). Note: Information from 12 EU member states where information was available. The majority of European cars are removed from the fleet after 13 - 15 years. This underlines the importance of an efficient supply of past model service parts beyond the end of serial production. Beside service consideration, warranty obligations must be fulfilled. Therefore, a minimum of ten years availability of spare parts must be guaranteed (e.g. Germany: Civil code §242). Commonly, past model service parts are provided for vehicles that have been out of production for more than 20 years.
5.2.4. Past model service parts – requirements for alternative metallic chrome coating As mentioned, the interrelation of components in vehicles is highly complex and subject to thorough testing within the development phase of vehicles. Therefore, a 1:1 substitution of metallic chrome coatings from chromium trioxide functional chrome plating is not possible. Substance substitution may cause change of functional geometry, thermal durability and lead to unexpected impacts on related parts. To ensure that possible alternatives are interchangeable with original spare parts, a completely new type-approval is necessary. This may lead to major disadvantages, which are discussed in the following. At the end of serial production, the tooling and bill of design for car model parts is transferred from a large to a smaller supplier (usually a SME). These SMEs are able to produce the desired amount of past model service parts, using the original method. The limiting factor is that in most cases they do not have the know-how and capacity to perform costly and highly technically demanding re- development and re-validation procedures. Complete testing of all related components may be necessary to exclude unexpected impacts and to ensure functionality and safety in the field. Additionally, validation processes must be based on the original vehicle, which may not be available in many cases. Another point to be mentioned is the relatively small number of spare parts being produced. Compared to the high financial input needed for validation of alternatives, a significant increase of price per item would be the consequence. The possibility of producing and stockpiling a sufficient amount of spare parts before sunset date should be discussed. However, this alternative may have some obvious drawbacks such as negative impacts on functionality due to chemical aging, waste of resources if spare parts are not needed for past model services, as well as high demand of stockpiling capacities. In conclusion, the aforementioned arguments clearly show the need of metallic chrome coatings from chromium trioxide functional chrome plating in past model service part production.
Use number: 2 41 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
5.2.5. General engineering Metallic chrome coatings for general engineering are used in many different products. Besides trucks, forklift trucks, and agricultural equipment, functional chrome plated products are used in thousands of different complex machines. They are in general produced by many different SME coating companies. From a technical perspective, these SMEs are not able to develop and introduce new coating systems because they do not have the required know how (such as requirements within all different applications) and capacities. Furthermore, developing new coatings is a time consuming and costly task. Even if SMEs from engineering or coating sectors do develop a potential alternative, the risk that this alternative fails after the scale up (to large industrial scale) exceeds the entrepreneurial risk of smaller companies. Thus, development and introduction of new coating systems must be provided by major companies from the automotive, truck and forklift truck sector, while being supported by formulators. Afterwards, SMEs may implement this new technology. Note that after an engineering company has agreed to a new coating system, another 3-5 years are necessary to introduce the needed equipment for this technology in SMEs. The key requirements for chromium trioxide based functional chrome plating in the general engineering sector are illustrated in the following paragraphs using the example of metallic chrome coated rods. Hydraulic cylinders manufactured by the general engineering sector are one example of parts which require all the beneficial properties of metallic chrome coatings. Due to their high power compared to their size, hydraulic cylinders are commonly used in a broad range of applications such as trucks, agricultural equipment, wind mills, airplanes, ships, oil platforms and many more. This power is generated by high oil pressure (up to 35,000 kN/m²) within the cylinder. The most critical parts with respect to the lifetime of hydraulic cylinders are their moving parts, such as the hydraulic rod in combination with the advanced seals. Most importantly, the hydraulic cylinder surface must not be scratched or broken to avoid oil leakages which might lead to a loss of functionality of the hydraulic cylinder. This is crucial for applications within the food sector, where leakage of oil is strictly prohibited. Hardness and adhesion properties: For applications in hydraulic cylinders, a Vickers Hardness of more than 850 HV is required. In practical applications, HV >1,000 is realized. Rods in hydraulic cylinders are wetted with a thin film of oil and are usually operated under impure conditions, in which sand and hard dust can destroy the surface of the seal. For operational environments in which heavy particles can potentially impact the underlying steel rod (such as mining or earthmoving machines), the steel rods are surface hardened, typically by means of induction hardening. Functional chrome plated coatings withstand such extreme environments and maintain their functionality due to their hardness and good adhesion properties. Wear resistance: The hard seal and scrapers within hydraulic cylinders are moving with very high speed over the surfaces. The seal as well as the surface must withstand the high strain due to movement and the high pressure for more than several hundred thousands of strokes without wearing. Therefore, in applications within hydraulic cylinders a wear resistance of less than 5- 10 mg/10,000 U is required. Corrosion resistance: For applications in hydraulic cylinders a rating of 9 after 100-500 h is necessary. Functional chrome coatings feature micro cracked surfaces with more than 1,250 cracks per cm, which improves their corrosion resistance compared to macro cracked surfaces.
42 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
The micro-cracked surfaces provide also the ability to maintain lubrication, e.g. with hydraulic oil, which further improves corrosion resistance of hydraulic cylinders. For applications within highly corrosive environments (such as seaside or seldom used cylinders), either a nickel undercoat serves as extra corrosion barrier or a stainless steel rod is used as substrate for functional chrome plating to provide the aforementioned characteristics. Corrosion resistance requirements in this context are rating 9 after more than 1,000 h in SST. Surface roughness: For applications in hydraulic cylinders, a surface roughness of Ra< 0.2 µm is required. In most practical applications, a surface roughness of around 0.1 µm is achieved with metallic chrome coatings. Several measuring methods are available to determine surface tribology. This parameter is especially important in terms of anti-stick properties and friction. Anti-stick / friction: There is a difference between the two parameters anti-stick properties and friction. Anti-stick refers to the amount of energy needed to start a cylinder moving, while friction describes the amount of energy needed to keep a cylinder moving. Both parameters are highly influenced by the wettability of the surface. Wettability is influenced by the micro cracking of the surface, surface roughness and surface oxidation. Good anti-stick properties provide a controllable and smooth start-up of the cylinder (no sudden shocks), which is particularly important in terms of safety and precision of movement. A low friction surface provides a minimal amount of energy necessary to keep the cylinder moving. Besides that, low friction is particularly important in terms of wear protection. With low friction, less heat is produced during motion, which prevents the oil from being heated and also prevents destruction of the seal. Adhesion to substrate: Good adhesion properties of the layer are especially important in terms of layer durability, stability against blistering and its flexibility without layer breaking. Non toxicity/anti magnetic properties/chemical resistance: Metallic chrome coatings are built up from metallic chrome. Therefore, they are regarded as non-toxic. Combined with their chemical resistance it is possible to apply them in the food sector. Due to their anti-magnetic nature, no magnetic parts need to be used, which helps to prevent seal destruction. Chrome plated cylinders can be produced by two different methods. Rods are cut, bent and coated with an underlayer, before the surface is finally functional chrome plated. This is usually carried out in job shops for smaller series productions or large diameter or length rods. The alternative method is applied on rods of very long length which are coated using specialized cylinder production factories. The production volume of these cylinders varies between 1 to 100,000 pieces per series. The total surface of functional chrome plated rods is more than 3 million square meters per year in Europe. Although some alternatives to functional chrome plating are currently used in niche applications, there are no technical and/or economically feasible alternatives to functional chrome plating available to date for the general engineering sector. Examples for alternatives used in niche applications are nitrated surfaces for applications with a very low oil pressure and limited rod movement and HVOF treated rods for applications with extremely high wear resistance. The approval processes within the truck and automotive sector are very similar. Hence, the time period required for approval of an innovative technology is the same for both sectors (refer to chapter 5.2.1. ). The shortest time of a complete introduction of a new coating is 10 to 15 years for the general engineering sector due to inherent high risks and the wide variety of products.
Use number: 2 43 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
5.3. Steel Similar to the automotive industry there are complex requirements for functional chrome plated products with chromium trioxide in the steel sector which is illustrated with the example of rolling mills in the following paragraphs. Functional chrome plating on rolls is commonly used for steel continous mills and temper mills combined with textured rolls, narrow strip mills, copper and zinc mills, as well as complete aluminium chains. The roll of a rolling mill must fulfil several functionalities and properties which can be obtained by depositing chromium on its surface. The metallic chrome coating layer has a micro-cracked structure and the following main characteristics: low stress, high lubricity, low coefficient of friction and a high reproducibility of the substrate roughness.
Figure 17: High density of narrow and shallow cracks. Data source: Enthone 2014. The metallic chrome coating must be hard to withstand wear and damage to rolls and to reduce the rate of removal turnover of rolls from stock into current use. Wear resistance is important to increase life-time of a roll and reduce downtime of mills accordingly. The micro-crack structure improves quality of the rolls by lubrication in the bite, cooling performance, and the flexibility to withstand deformation in rolling such as thermal crown or bending. In addition, effects of dissimilar metals and thermal coefficients of expansion are reduced. A low coefficient of friction improves lubrication, lowers the mill force and increases the wear resistance.
44 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Further important characteristics of the metallic chrome coating are corrosion prevention to increase shelf-life and its adhesive strength to the substrate to ensure that a roll stays in place under rolling conditions. Chromium trioxide can be deposited on different materials including cast iron, forged steel, high speed steel (HSS), semi-HSS, etc. The use of chromium trioxide for functional chrome plating has many advantages: - The metallic chrome coating does not affect grinding parameters, - Lower rate of stock turnover due to the metallic chrome coating and / or the longer lifetime of the roll during grinding, - The substrate morphology remains after coating, as its surface / roughness is perfectly mirrored by the metallic chrome coating, - Rolling forces are low and lubrication is improved in the rolling bite also reducing stock turnover, - Functional chrome plating does not affect total repair time of the rolls, - Quality control is improved after functional chrome plating as the metallic chrome coating acts to reveal visual marks such as feed lines, chatter marks, textruing defaults, etc.
Alternatives must have the same performance as the existing substance. Work rolls for steel and non- ferrous mills vary between 0.02 to 16 tonnes and turn arounds can be as little as 8 hours. The roll forces are extreme: up to 2,100 tons for a cold mill with a maximum strip width of 2,100 mm results in a specific roll force of 100,000 kg/cm².
Figure 18: Roll hanging above the functional chrome plating tank. Data source: HOCO-RST, 2014.
Use number: 2 45 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Most importantly, alternatives must be able to provide a comparable roll surface, adhere under rolling force, improve cleanliness of the strip, reduce the coefficient of friction, extend roll life, and be reground under normal conditions to match tight tolerances. Although intense research on two promising alternatives is ongoing for more than 5 years, all tests are at laboratory scale with no industrial scale being tested yet. Based on the difficulties during this evaluation phase including several major draw backs, significant future research and development effort is needed in the steel industry prior to testing a potential alternative on an industrial scale which then could pass all specific requirement tests. The parameters cleanliness, morphology, and grinding wear resistance affect the overall stock which must be present to insure proper manufacturing. The typical life time for a roll is about 8 hours. The longer the process takes to restore the rolls surface, the more rolls are needed in the stock. Typical costs per roll are in the range of 15,000 EUR and with the current method of functional chrome plating several thousands of rolls need to be in stock at a typical industrial facility. To re-prepare the required surface conditions on a roll after its usage approx. 0.2 mm have to be grinded. With a total thickness of 2 cm, a roll can be re-used 100 times before it must be entirely replaced. Acceptance processes take at least a few months but vary for each manufacturer. Certain functionalities are defined for each application, e.g. the surface roughness and roll texture. The customer technical support department of the manufacturer decides whether the requested specifications are met or not. All potential alternatives for the steel sector are to date in a laboratory scale. The steel industry schedules 7 years for further evaluation and testing of alternatives, especially for metallic chrome coatings for the work roll business in metal rolling mills. Further laboratory experiments and trial are required prior to move to obtain industrial experience. The scale up process requires significant financial investments as well as time for engineering, construction, testing and evaluation. Especially the big size of the rolls of up to 5 meters with a diameter of 0.6 meter make this last step extremely expensive. Furthermore, tests can only be conducted in full size mills under very heavy conditions of a cold mill in order to gain the necessary experience and test results. Smaller mills are not suitable as the maximum specific roll forces cannot be reached and simulated. A minimum of additional 7 years are expected to adapt the manufacturing processes accordingly. In general, development must be provided by major manufacturers. Besides the milling sector the following further industrial sectors are relevant for the steel industry: automotive, trucks and forklift trucks while being supported by the formulators. Smaller companies will then follow to use these inventions in their business. The approval process of the truck industry is very similar to the automotive industry and takes the same approval time. In summary, a minimum of 11-14 years are estimated for a complete introduction of an alternative for functional chrome plating in the steel sector.
5.4. Metal precision parts Functional chrome plating is used in the sector of metal precision parts after the electroforming process to add specific functionalities to the electroformed article, such as hardness, wear resistance, and corrosion resistance. Furthermore, the uniform smooth layer constitution of a metallic chrome coating allows it to adequately coat the structure of the electroformed article. This is especially
46 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES important for sugar sieves in order not to fill or change the geometry of the small holes (micro-/ millimetre size) during the plating process. Other typical products with high performance requirements include sheet-guiding cylinder jackets. The electroforming process is a separate process to functional chrome plating and does not involve chromium trioxide. Electroforming is highly specialized and used for the production of precision metal parts and filters. Electroforming is defined in ASTM B 832-93 as "the production or reproduction of articles by electrodeposition upon a mandrel or mould that is subsequently separated from the deposit." Once separated from the base form, parts fabricated by means of electroforming are usually free standing. The electroforming process is characterized by process control, high quality production and very high repeatability. The high resolution of the conductive patterned substrate (e.g. stainless steel) allows finer geometries, tighter tolerances and superior edge definition. Other metals subject to electroforming are for example nickel and copper. An electrolytic bath is used to electrochemically deposit the metallic product on a mandrel. This mandrel should be passive, in that the electroformed deposit can be released from it after it has reached the desired thickness. The mandrel can contain an electrically isolating pattern, resulting in a perforated product (holes, slots, etc.) or it can be completely electrically conductive, resulting in a replicated product of the mandrel, containing all its mirror imaged patterns. Testing alternatives has proved to be very time consuming and difficult for the metal precision industry. For example sugar sieves can be tested only during sugar campaigns, which usually take place 3-4 months per year. The life time of a sugar sieve is determined by the length of an annual sugar campaign. Very few companies are willing or able to test alternatives. One reason is limited capacities: companies do usually not have sufficient centrifuges in-house to spare a few for testing and simultaneously ensure proper work capacity during the sugar campaigns. The reporting of findings is also problematic and was insufficient in the past, which further increases research times to improve potential alternatives for the sieves. Again, the shortest time of a complete real introduction of a new coating is 10 till 15 years for the metal precision sector due to inherent high risks and the wide variety of products.
5.5. Manufacture of printing equipment Metallic chrome coatings generated using chromium trioxide are used in printing equipment to cover the printing cylinders of rotogravure printing processes: publication rotogravure, packaging rotogravure and decorative rotogravure. The surface of the printing cylinders must be homogeneous, scratchproof, highly wear resistant, hard (between 1,000 and 1,400 HV) and should be producible as quickly as possible. Low friction and advantageous tribological properties between the cylinder surface and the ink and paper are important. The surface roughness is optimized with rheological properties between 300 and 4,000 micro cracks per linear centimetre to produce a non-printing but gliding layer between cylinder and doctor blade. The chromium trioxide metallic chrome coating can be de-chromed and re-chromed (replaced by a new chromium layer) in order to re-use the engraved surface, which is especially important for very long print runs. If the protective metallic chrome coating was not present, the metal which the printing form is made of would be quickly destroyed by the doctor blade or by hard ink particles. The rotogravure printing process is used for long printing runs with sharp, fine and clear images and can be processed on a range of different materials including polyethylene terephthalate, polyvinyl chloride, polyethylene (PE) and paper. No other process is capable of such long runs from one set of
Use number: 2 47 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES printing forms and there is a larger colour range possible. Rotogravure is used for commercial printing of magazines, catalogues, inserts and flyers, postcards and greeting cards, gift-wrap, labels for bottles, flexible packaging, tobacco packaging, high quality cosmetics packaging, base papers for decorative laminates for flooring and furniture, and many more applications. The printing cylinder production operates with time critical jobs and very short lead times. Between 300 and 3,000 heavyweight cylinders are produced per month in a production plant. The metallic chrome coated roll is in contact with various products such as food packaging, labels, textiles or printed electronics. In particular, when producing packaging material for the food sector, the potential for substances to migrate from the coating of the printing rolls to food packaging must be considered. This potential migration process is also relevant in the textile sector. In this case, each printed product needs to be assessed individually, to ensure that the respective EU and national legislation e.g. regarding Ni leaching are fulfilled. Besides rotogravure printing, functional chrome plating is also essential for other applications in the manufacture of printing equipment sector. Functional chrome plated mandrels (i.e. massive cylinders used as base form) are produced and used as a mould to produce nickel printing screens. These nickel printing screens are used by customers who print textiles, labels, wallpaper, carpets, and also by engraving companies, and companies that produce banknotes, security labels and printed microelectronics. Another important application is metallic chrome coated sheet guiding cylinder jackets. The jackets, approx. 0.2 – 0.3 mm thick, have a spherical surface structure and are fitted to the cylinder of a printing press. The functional chrome plating provides the required functionalities, being ink repellent, self-cleaning and wear resistant. The latter is especially important to withstand the passing paper sheets for as long as possible. The realistic time for a complete introduction of a new coating is 10 to 12 years for the manufacturing of printing equipment sector.
48 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
6. IDENTIFICATION OF POSSIBLE ALTERNATIVES
6.1 Description of efforts made to identify possible alternatives To prepare the authorisation of chromium trioxide, the industry CTAC Consortium (Chromium Trioxide Authorisation Consortium) of 153 members was launched in 2012. The aim of CTAC was to efficiently gather and analyse all necessary information for the three pillars of the authorisation dossier (CSR, AoA, SEA).
6.1.1 Research and development As mentioned earlier in this document, much effort on alternatives for etching with chromium trioxide as well as for electroplating with chromium trioxide has been performed and is still ongoing. R&D is generally performed by specific companies by testing different plated products in feasibility studies. The unique set of functionalities of chromium trioxide are explained in detail in chapter 3.3 and make chromium trioxide an ideal and not easily replaceable substance where high requirements with regard to hardness, wear resistance, corrosion, adhesion or friction, and fatigue properties have to be fulfilled to ensure safe performance in a demanding environment. It is very difficult to find a single alternative which replaces the multi-functionality of chromium trioxide generated coatings simultaneously. Ecochrom: The project Ecochrom on the “eco-efficient and high performance hard chromium process” is an Intelligent Manufacturing System-Growth project and has the objective to study and develop an environmentally and economically acceptable process allowing thick chromium coatings which are harder and more resistant to corrosion than traditional coatings, from a new and nontoxic electrolytic solution. Ecochrom is a consortium/working group of industrial platers, fundamental and applied researchers as well as end-users in Canada, USA, Japan and Korea, and is coordinated by TSM (Surface Treatment Mechanics), the main functional chrome plating specialist in France. The results of the Ecochrom project are still confidential. The hard chrome alternatives team: The Hard Chrome Alternatives Team (HCAT), is a US-Canadian collaboration of environmental working groups of the Departments of Defence of the two nations. They pursue the objective to demonstrate and validate that the alternative High Velocity Oxygen-Fuel (HVOF) is a superior alternative to functional chrome plating. Their efforts particularly focus on the aerospace industry and on military use. Increasing time intervals between maintenance and reduced turnaround times for repair of components would lead to a more sustainable performance. However, HCAT concluded that HVOF is not a generic alternative, neither technically (temperature and geometrical limitations) nor economically (high costs). Advanced surface engineering technologies for a sustainable defense: The Advanced Surface Engineering Technologies for a Sustainable Defense (ASETSDefense) is a US Department of Defense (DoD) initiative sponsored by the department’s two environmental research programs (Strategic Environmental Research and Development Program and Environmental Security Technology Certification Program (ESTCP)). Its objective is to facilitate the implementation of more environmentally friendly technologies for surface coatings and surface treatments. This initiative wishes to provide access to background information and technical data from research, development, test, and evaluation efforts as well as the status of approvals and implementations. ASETSDefense targets defence organizations and provides information to reduce environmental safety and occupational health impacts from coatings and treatment processes that utilize e.g.
Use number: 2 49 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES chromium plating from hexavalent solutions. The database providing information on the DoD´s data on authorization and implementation of alternatives is readily accessible to the public (http://www.asetsdefense.org as of August 6, 2014). Airbus-chromate-free project: Amongst a number of initiatives in that respect, the Airbus Chromate-Free (ACF) project was launched more than 10 years ago with the aim to progressively develop new environmental friendly Cr(VI)-free alternatives to qualified products and processes used in aircraft production and maintenance. Even prior to the launch of ACF, R&D efforts included the objective to remove chromate use. The ACF project is organised into several topics for the different fields of technologies concerned by the replacement. ACF specifically addressed applications where chromates are used in production or applied to the aircraft; such as chromate acid anodizing, basic primer, and external paints. In addition, sealants, chromate conversion coatings, passivation of stainless steels, passivation of metallic coatings or alternatives to hard chromium are included in the remit of this project. In synergy with ACF, an Airbus Group chromates replacement project is also in place. Industry is not only working on one-to-one replacements for chromium trioxide applications but also reconsidering whole current coating systems. The significant investment in innovative coating technologies may lead successively to a stepwise change in the coming decades. Highly innovative technology enablers for aerospace: As an example, the Highly Innovative Technology Enablers for Aerospace project was initiated in 2012; a 17-member consortium consisting of aerospace OEMs, suppliers, paint application companies and academics with the goal to identify and evaluate suitable alternative systems. In 2014, the tested alternatives are planned to reach TRL2. After the initial phase, the project will focus on a handful of promising alternatives, where further testing will be undertaken within the next years and completion of the research project is planned for 2015. Qualification (TRL6) will take up to 5-8 years from now. Amcoat: Potential replacements of Cr(VI) have been investigated in the comprehensive “Amcoat” project in the early 2000s. The project was accomplished by an industrial group of nine companies, electroplaters and component producers from the UK, Denmark, Germany and the Netherlands and was supported by two scientific institutes (University of Nottingham and Netherlands Organisation for Applied Scientific Research (TNO)). The objectives of Amcoat were - to develop Cr(VI) free plating solutions capable of depositing amorphous metal coating, - to demonstrate that electrodeposited amorphous coatings have at least equivalent surface properties, like hardness, wear and corrosion resistance and, low friction, as metallic chrome coatings, - to demonstrate that operating an industrial amorphous plating plant result in an overall reduction of health and safety hazards for the workforce, reduction of environmental discharges and that it is technically and economically feasible. The project timescale was scheduled for more than two years. Although this project used significant combined interdisciplinary and international efforts, no alternative proved to be successful. The project failed. This example illustrates the enormous difficulties and challenges to find a suitable alternative for Cr(VI) for application within the general engineering sector.
50 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Indeed, on the basis of the aforementioned unique properties and diverse functionalities of chromium trioxide and the multiple process step coating systems, alternatives have to be identified and implemented into all process steps to be completely chromium trioxide free. Aerospace Chrome Elimination (ACE): The ACE team is comprised of material and process (M&P) engineers from U.S. aerospace companies and DoD (U.S. Department of Defense – Army, Navy, Air Force) that was formed over 25 years ago (1st meeting held in 1988) with the sole purpose to work together to identify replacements for processes used in the aerospace industry that contain or use materials that contain hexavalent chromium. The processes targeted by the ACE team are as follows: conversion coatings, anodize, anodize seals, paint primers, alkaline cleaners, titanium processing, sealants, adhesive bonding surface preparation, and chrome plating. The group meets in person once a year and has 3 virtual meetings per year. For chrome plating, the best alternative selected has been HVOF thermal spray with WC-Co or WC-Co-Cr but this is not a drop-in replacement because it is a line of sight spray process that cannot do certain complex geometries such as the inside diameter of tubes. Summary: At a first glance, the available performance data on chromium trioxide-free alternatives provided in the alternative assessment in chapter 0 indicates promising results in different tests under various conditions and operating environments. However, one has to note that most of these data is collected in laboratory testing and that the materials may have been tested individually not as part of a complete coating system or component level assembly. When selecting an alternative, the performance of the material should be evaluated as part of a whole system. In many cases, this level of evaluation will require component/system-level testing unless field-testing data exists on the exact coating system, substrate, and application (AMMTIAC: http://ammtiac.alionscience.com/). Although extensive and promising research has been conducted, no one-to-one replacement to chromium trioxide or innovative technologies, which meets all the requirements, has been discovered. The final implementation of an alternative for chromium trioxide at industrial scale will therefore take a minimum of 12-15 years.
6.1.2 Data searches For the AoA, extensive literature and test reports were provided by the technical experts of the CTAC Consortium members. Furthermore, searches for publically available documents were conducted to ensure that all potential alternate processes to chromium trioxide-containing applications were considered in the data analysis. In addition to databases for scientific literature, the following programmes were intensively consulted: Toxics Use Reduction Institute, Massachusetts, US (www.turi.org/); and The Advanced Materials, Manufacturing, and Testing Information Analysis Center (AMMTIAC: http://ammtiac.alionscience.com/). Searches for SDS for chromium trioxide-containing and chromium trioxide-free applications were conducted. Based on these data, primary scoping led to the development of a generic questionnaire containing potential alternatives to chromium trioxide based functional chrome plating. To complete the picture, additional alternate processes identified by CTAC Consortium members were included in the initial list of Alternatives, which can be found in Appendix 1.
Use number: 2 51 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
6.1.3 Consultations This questionnaire was provided to all CTAC Consortium members to get an overview on the completeness and experience with the alternatives, completeness and prioritisation of critical parameters for their specific processes and the minimum technical requirements per use. During this survey, additional alternatives have been identified and included in the aforementioned initial list. At this stage of the data analysis, some alternatives were screened out after bilateral discussions with the companies based on confirmation that they might pose a potential alternative to chromium trioxide based processes (e.g. for functional plating with decorative character) but are not applicable for the use defined here. To verify data and to obtain further detailed quantitative information, more focused technical questionnaires were sent out and discussed with the CTAC Consortium members. Moreover, site visits to selected companies were carried out which were carefully chosen to adequately represent the different uses, industry sectors, countries and the size of companies. Discussions with technical experts, followed by a final data analysis led to the formation of a list of alternatives divided into 3 categories, according to their potential to be suitable for the specific use. In summary, the categorized table of alternatives listed below is the outcome of extensive literature, in house research and consultations with technical experts in the field of surface treatment.
6.2 List of possible alternatives The most promising alternatives for chromium trioxide in functional chrome plating (Table 8) are assessed in detail in the following chapter 7, the category 3 alternatives are listed in Appendix 1. According to their relevance, the potential alternatives are classified as Category 1 (focused in the dossier, relevant R&D on these substances ongoing) or Category 2 (clear technical limitations, may only be suitable for niche applications but not as general alternative).
Table 8: List of alternatives categorized.
Category No. Alternative
1 Electroless nickel plating
2 Nickel electroplating
Case hardening: carburizing, carbonitriding, cyaniding, 3 nitriding, boronizing
4 Thin and thick chemical vapour deposition (CVD) Category 1 alternatives 5 Nanocrystalline cobalt phosphorus alloy coating
6 High velocity thermal process
7 Trivalent hard chromium
8 Physical vapour deposition
52 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Category No. Alternative
9 Plasma spraying
10 General laser and weld coating technology Category 2 alternatives 11 Stainless steel
12 Thermal spray coatings Pre-treatment 13 Mineral acids
Use number: 2 53 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
7. SUITABILITY AND AVAILABILITY OF POSSIBLE ALTERNATIVES To assess the feasibility of the alternatives, colour-coded summary tables are included in the document. The colours are as follows: - Red: not sufficient - the parameters/assessment criteria do not fulfil the requirements of the respective sector; - Green: sufficient - the parameters/assessment criteria do fulfil the requirements of the respective sector; - Yellow – the parameters/assessment criteria fulfil some requirements for some but not all applications/sectors.
The alternative assessments each comprise a non-exhaustive overview of substances used with the alternatives and alternative processes as well as the risk to human health and environment. These tables are provided in Appendix 2.
CATEGORY 1 ALTERNATIVES
The alternatives assessed in this section are considered the most promising, where considerable R&D efforts are carried out within the different industry sectors. They either show technical limitations when it comes to the demanding requirements of all the sectors, such as wear resistance, corrosion performance and/or have economical disadvantages at the current stage. However, some of these possible alternatives may already be qualified and used in certain industry sectors or for special applications / special parts but not as a general alternative of a process step in chromium trioxide functional chrome plating process chains. Note that the list of substances provided for each alternative is extensive but not conclusive.
7.1 ALTERNATIVE 1: Electroless nickel plating Electroless plating is a process in which metal ions in a dilute aqueous solution are deposited on a substrate by means of a heat induced reduction (see Figure 19) without the use of electric current. Heat induced reduction is a chemical reaction in which the substrate acts as a catalyst after being heated, causing ions to continuously deposit onto the substrate. Chemicals, such as hypophosphite, reduce metallic ions in the electroless plating solution to form a coating. Once a metal is reduced and deposited, the metal surface acts as a catalyst for further deposition in that location (NDCEE, 1995).
54 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Figure 19: Electroless nickel plating. Data source: NDCEE, 1995.
Nickel represents the most widely used base material for electroless plating. Electroless nickel deposits usually consist of nickel-phosphor (Ni-P) or nickel-boron (Ni-B) alloys. Typical bath solutions contain reducing agents, such as hypophosphite, aminoborane or borohydride and are used to deposit Ni-P or rather Ni-B alloys. The primary goal behind the alloys is to enhance existing nickel layer properties. The chemical reaction sequence is shown below for a hypophosphite bath which is commonly used to deposit Ni-P:
Another possibility to ameliorate the layer properties is to incorporate additive particles (such as silicon carbide, diamond, PTFE (Polytetrafluoroethylene), tungsten carbide) into the Ni layer to form composite coatings. By controlling the amount of both phosphorus or boron and additives, various coating properties i.e. lubricity and hardness can be influenced and modified decisively. The downside is added complexity affecting the uniform composition. The bath temperature of phosphorus based chemistry is about 90 °C whereas a boron based bath operates at lower temperatures. The latter produces coatings of higher as-deposited hardness but lower corrosion resistance due to increased crystallinity. Literature states deposition rates of 25 µm/h which decrease as the bath ages (Legg K., 2003a). During industrial testing a maximum of 10 µm/h was determined for electroless Ni-P with high phosphorus content which is about 50% slower than functional chrome plating.
Use number: 2 55 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
7.1.1 Substance ID and physicochemical properties of relevant substances A non-exhaustive overview of general information and properties of substances used in electroless plating as well as the overall risk to human health and environment caused by these substances, is provided within Appendix 2.1.1.
7.1.2 Technical feasibility General assessment: As nickel phosphorous (Ni-P) deposits are the most promising alternatives amongst the electroless nickel coatings, these were used for the assessment. The figures in the following table which was provided in the consultation illustrate the effect of different phosphorous contents on the technical properties of the Ni-P alloy layers.
Table 9: Typical properties of electroless nickel-phosphorus coatings.
Low P-content Medium P-content High P-content (1–4 %) (6–9 %) (> 11–12 %) Structure crystalline crystalline and amorphous amorphous
Hardness 700 HV 600 HV 530 HV (as deposited) Hardness 960 HV 1,000 HV 1,050 HV (heat treated) Wear resistance 11 mg/1,000 cycles 16 mg/1,000 cycles 19 mg/1,000 cycles (as-deposited) (Taber wear index) Wear resistance 9 mg/1,000 cycles 12 mg/1,000 cycles 12 mg/1,000 cycles (heat treated) (Taber wear index) Coefficient of friction not determined 0.38 0.45 Corrosion resistance (salt 24 h 96 h 1,000 h fog test)
Hardness: The hardness depends on both the phosphorous content and the heat treatment after the deposition process. In an as-deposited state low P-content alloys show values of 700 HV that decrease with higher phosphorous content (down to 530 HV for a high P-content alloy). Another possibility to improve hardness performance compared to the as-deposited state is heat treatment. However, heat treatment damages the ability of the coating to act as a barrier for corrodible materials. The deposition temperature for aluminium alloys has to be < 150°C and for high strength steels < 250°C. Above 220°C corrosion resistance is reduced because of the introduction of grain boundaries and microcracking in the nickel matrix. Heat treatment conducted at 400°C for one to 8 hours creates precipitates that give the coating its maximal hardness up to 1,050 HV. This hardness is similar to functional chrome plating, but the corrosion resistance is simultaneously reduced by a factor of 100 (Legg, K. 2003a). The substrate itself can be protected by heat treatment at lower temperatures but longer times.
56 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Wear resistance: Analogous to hardness, resistance to wear can be influenced by phosphorous content and post heat treatment. However, this effect was not reproducible in tests conducted by metal precision part manufacturers: heat treatment did not show any improvements, neither by Taber wear testing nor by field testing from screens in sugar mill centrifuges. The Taber wear index provides the rate of wear and is determined by measuring the loss in weight (in mg) per 1,000 cycles of abrasion: the lower the index, the better the wear resistance. As-deposited alloys with low P-content show better wear resistance and have lower Taber wear index values compared to medium and high P-content alloys (e.g. 11 mg/1,000 cycles with low P-content and < 19 mg/1,000 cycles with high P-content). By means of heat treatment, the wear resistance is again gradable (low P-content: heat treated: 9 mg/1,000 cycles < as-deposited 11 mg/1,000 cycles). Thus, both low P-content and heat treatment lead to better results concerning wear resistance for Ni- P alloy coatings. However, the wear resistance of a low P-content + heat treated Ni-P alloy is worse compared to chromium (as-deposited: 2 mg/1,000 cycles).
Coefficient of friction: The data concerning the coefficient of friction shows a tendency to increasing coefficients with increasing P-content, which means a degradation of the friction behaviour with increasing P-content. In composite coatings, the coefficient of friction can be increased by including additives in a similar way to metallic chrome coatings.
Corrosion resistance: The ability of electroless nickel deposits to provide protection in corrosive environmental conditions is influenced by the post-treatment of the Ni layer, and in case of phosphor alloys by the phosphorous content. Nickel can cause severe galvanic corrosion of the substrate or the counterpart if the coating is damaged. This does not occur with metallic chrome coatings, probably due to the formation of passive oxides on the surface. Low P-content Ni-P alloys are typically less resistant to corrosion than deposits with high P-content alloys. In a salt spray test, the corrosion resistance of low P-content Ni-alloys was tested to be 24 hours and for high P-content Ni-alloys 1,000 h. The corrosion resistance increases with increasing P- content. The corrosion resistance of boron-based alloys is reported to be worse than for Ni-P coatings in an as-deposited state. Concerning the influence of heat treatment, it was reported that as-deposited coatings show better corrosion resistance than heat-treated coatings or composite coatings, because the microstructure of the coating is transformed by heat treatment and/or composite coatings with particles such as diamond. The amorphous structure of Ni-P is changed into a crystalline structure by the heat treatment. Amorphous structures usually have better corrosion resistance. As a result, micro-cracks are more likely to occur in the crystalline structure which increases vulnerability to corrosion. These structural changes are responsible for a reduced corrosion resistance by a factor of 100 (compare section Hardness above).
Temperature: Heat treatment of electroless deposited nickel deposits is required to achieve better hardness and wear resistance performance due to precipitations (microstructural changes) compared to the as-deposited state. This post treatment is however an issue for the heat sensitive substrates such as high strength
Use number: 2 57 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES steels and aluminium alloys with low melting point temperatures that are widely used in the aerospace industry. As heat treatment is generally conducted at temperatures about 400°C for one up to eight hours, electroless nickel plating is unsuitable for substrates that cannot withstand this temperature. With the example of electroformed nickel sieves, the nickel becomes too soft at this temperature and is thus too weak to be used for sieves in sugar centrifuges.
Layer thickness/constitution: Since the deposition of electroless nickel is based on autocatalytic reaction and not on electric field distribution through electrodes, uniform and variable layer thickness even on complex parts geometries and edges is possible (see Figure 20).
Figure 20: Plating of complex geometries. Data source: Sonntag, ZVO, not dated.
The thickness of Ni-P layers ranges from 2.5 to 250 µm (Valero et al. 2011). Typical composite coatings achieve thicknesses between 7 and 50 µm, with most coatings in a range of 12 to 50 µm. As electroless nickel plating produces thin layers it is usually not used for rebuilding worn parts, which is one primary use for functional chrome plating. The particles’ suspension and deposition uniformity in composite coatings are difficult to control. This makes it difficult to achieve homogeneous coating properties within nickel composite coatings containing particles (such as diamond, PTFE, etc.). Layer degradation and poor performance of the layer are possible consequences of uneven particle distribution (Legg K., 2012).
Process conditions: Electroless nickel plating is, like chromium plating, a process conducted in a bath that is flexible in terms of the geometry of the parts and able to deposit a uniform coating on complex parts and small internal spaces parts. The process handling however, is more complex due to a sensitive chemical bath balance that is highly sensitive towards variations of pH, temperature, bath composition and impurities. Therefore it is more difficult to maintain stable and accurate process conditions that are necessary to ensure consistent and reliable deposition qualities. During the plating process, by-products/impurities are produced which cause e.g. tensile stress in the deposited Ni-containing layer, which can lead to spalling of the layer. Relatively small quantities of
58 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES these by-products are sufficient to require a complete bath replacement. Compared to functional chrome plating, electroless nickel deposition baths have a shorter life-time.
Process conditions are very sensitive and difficult to control. If the stability of the electrolyte changes, the deposition velocity changes as well. As a result, process control is lost and the specifications of the coating are not met. The deposition rate is low with 10 µm/h and a maximum of 25 µm/h are reported for acidic electroless baths (Daly & Barry, 2003). As a result process time is significantly longer compared to functional chrome plating. Unreliable reproducibility and different experiences with scale-up of the process leads to different opinions on its suitability both within one industry sector and between industry sectors. Whereas for example the defence departments of the aerospace companies use the electroless nickel process, the civil aerospace department of the same companies regard it as unacceptable. Based on the daily demands to ensure the airworthiness of civil aircrafts, these requirements are much more comprehensive.
Sector specific assessment: aerospace On high strength steel parts hydrogen embrittlement is a concern as hydrogen is released during the deposition process. Microcracks allow the hydrogen to escape in metallic chrome coatings, whereas electroless nickel forms a less porous layer. Therefore, some surface area needs to be left unplated for some applications to allow the escape of hydrogen during the heat treatment process step. Hardness, wear resistance and corrosion resistance are the most important key performance parameters, and respective minimum requirements have to be fulfilled in order to be an appropriate alternative for chromium trioxide-based electroplating. The minimum requirements for metallic chrome coating in the aerospace industry for hardness are between 700 and 900 HV for a like-for-like functional chrome plating replacement. As-deposited electroless nickel layers do not achieve this requirement. However, for non-heat treated electroless nickel 500 HV can be acceptable for some special applications: Specified minimum hardness for Ni- P qualification for one aerospace company range from 450 HV (without hardening) to 750 HV (with hardening, but hardening will decrease the corrosion resistance). Heat treatment with temperatures above 400°C to further enhance hardness cannot be considered as suitable possibility, because of degradations and distortion of heat sensitive materials which are widely used for aerospace applications as explained above. Hardness can be achieved in some but not all relevant applications. The corrosion resistance for electroless deposited nickel coatings in an as-deposited state were tested and evaluated by the aerospace sector. The minimum requirement for functional chrome plating in the aerospace sector concerning corrosion is given with at least 750 hr in a salt spray test. The corrosion resistance for electroless deposited nickel coatings in an as-deposited state (without hardening) were tested and evaluated as sufficient although corrosion performance of the technologies can vary. The specified salt spray resistance of electroless deposited nickel coating in an as-deposited (high phosphorous) is 336 hours. The Ni alloy with high P-content is the only coating in Table 9 that could fulfil the metallic chrome coating requirement, but at the same time hardness requirements cannot be met by this coating (as- deposited: 530 HV). For applications where corrosion resistance is necessary, unhardened Ni-P is preferred.
Use number: 2 59 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Electroless nickel layers were stated to achieve a maximal layer thickness of 100 µm. The aerospace sector requires for their application at least 100 µm for metallic chrome coatings. This means that the requirement cannot be met satisfactorily. Another main issue that was stated is the lower reliability of the electroless nickel plating process compared to chromium trioxide electroplating. Process conditions are difficult to be maintained. High sensitivity to process fluctuations affects the layer quality and adhesion which leads to a reduced reliability compared to conventional electroplated chromium trioxide derived coatings. The scope of application for electroless nickel coatings in the civil aerospace industry is reduced to specific niche applications. Acceptable hardness and corrosion resistance according to aerospace specifications cannot be obtained at the same time by electroless deposited Ni-layers. Electroless nickel plating is therefore not an appropriate alternative for chromium trioxide-based chromium plating.
Assessment overview for Electroless nickel plating (Aerospace)
Industry Corrosion resistance Hardness Layer thickness Process conditions sector Sufficient with low Sufficient with low Aerospace hardness corrosion
Sector specific assessment: automotive and general engineering Hardness, wear resistance, corrosion resistance, friction, and anti-stick are the most important key performance parameters for the automotive and general engineering sector, whose minimum requirements have to be fulfilled in order to be an appropriate alternative for chromium trioxide-based functional chrome plating. The automotive sector tested different nickel and nickel alloy coatings. As a result on hardness, nickel was stated to produce soft layers with hardness values of about 400 HV. Nickel alloys and composite coatings are able to increase hardness up to ca. 700 HV (without heat treatment) which is still softer than metallic chrome coating (ca. 1,000 HV). Therefore the deposition of nickel coatings is often combined either with heat treatment or an additional layer (currently metallic chrome coating) to obtain the required hardness. However, the performance of a single nickel layer (without post treatment) is not sufficient to fulfil the automotive requirement for hardness of 1,000-1,200 HV. The same applies to wear resistance and friction behaviour which were stated by the automotive sector to be inferior compared to metallic chrome coatings and do not fulfil the minimum requirements. An electroless deposited Ni coating was reported to be corrosion resistant in an as-deposited state because the layer was free from holes and scratches that may encourage and support corrosion. However, this resistance deteriorates due to thermal post treatment used to obtain the required hardness, and the heat treated coating is less resistant to corrosion as the as-deposited state. It was emphasized that this alternative is not a stand-alone replacement, especially not for parts that are exposed to atmospheric corrosion. In addition, the automotive sector states that electroless nickel is exclusively used in electronic applications and that electroless deposited Ni alloys and Ni composite coatings are not relevant for automotive applications.
60 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Assessment overview for Electroless nickel plating (Automotive and General engineering)
Corrosion Industry sector Hardness Wear resistance Friction resistance Automotive and Sufficient with low Sufficient with low
General engineering hardness corrosion
Sector specific assessment: steel Hardness, wear resistance, friction behaviour, layer thickness and corrosion resistance are important performance parameters for the steel sector, whose minimum requirements have to be fulfilled in order to be an appropriate alternative for chromium trioxide-based functional chrome plating. Electroless deposited Ni-P coatings achieve, depending on the phosphorous content, as maximum 700 HV in hardness in an as-deposited state. This performance is not sufficient regarding the minimal requirements of the steel sector that range between 850 and 1,000 HV. With regard to layer thickness, 100 µm are the upper achievable limit for electroless nickel coatings, which does not reach the required range of metallic chrome coatings and the minimum requirements for a suitable chromium trioxide alternative. With regard to the wear resistance of as-deposited layers in Table 9 only the Ni-P alloy with low P- content fulfils this requirement with 11 mg/10,000 U in the Taber test. Consequently the requirement concerning wear resistance is not as clearly met with electroless nickel as the Taber wear index with chromium trioxide is less than 5 mg/10,000 U (http://www.betz-chrom.de/de/bc-hartchrom.html ). The coefficient of friction is another important performance parameter. The tested alternative Ni-P coatings (Table 9) show values above 0.38. The steel sector however often requires values below 0.16 that can be achieved with chromium trioxide metallic chrome coatings. Thus, the minimum requirements on friction behaviour cannot be met by the alternative. Ni alloy with high P-content is the only coating in Table 9 that could meet the corrosion resistance requirement with a corrosion resistance up to max 1,000 h, but at the same time hardness requirements cannot be met by this coating (as-deposited: 530 HV). To date, a satisfactory performance containing electroless nickel is obtained with a combination of nickel as underlayer and a chromium trioxide derived metallic chrome top coat. It is not possible for electroless deposited Ni layers to fulfil all requirements that are necessary to represent a technically suitable stand-alone alternative to metallic chrome coatings. Consequently, electroless deposited nickel layers are not an alternative for the majority of applications where metallic chrome coatings are used.
Assessment overview for Electroless nickel plating (Steel)
Corrosion Wear Coefficient of Industry sector Hardness Layer thickness resistance resistance friction
Sufficient with Sufficient with Steel low hardness low corrosion
Sector specific assessment: metal precision parts Previous testing with Ni-P coatings regarding their potential to protect the substrate (also nickel) from corrosion in an immersion test was performed. Tests also included Ni-P alloy coating with low phosphor content (<10%) and an underlying copper layer. The tested coatings were exposed to an
Use number: 2 61 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES acidic environment (pH 3.5) at room temperature using 2 % sodium citrate / 3.5% citric acid. The protection potential of the alternative coatings was assessed by the amount of released substrate material (nickel) through cracks in the coating layer. Substrate material is released when the acidic test conditions harm the coating layer. The alternative performs well in this test if a lower or equal amount of substrate material is released compared to a metallic chrome coating (release of 4–46 mg/l substrate material (Ni)). The substrate release for the Ni-P coating was determined to be 160 mg/l and for the Ni-P coating with copper underlayer 140 mg/l. The alternative coatings did perform worse than metallic chrome coatings and lead to an increased substrate corrosion which negatively affects the endurance of the coating. For products (sugar sieves) coated with metallic chrome coatings, a life time of three months can be achieved. The life time of a sugar sieve is determined by the length of an annual sugar campaign, which is 3 months, as set forth by sugar producers. With an electroless nickel based coating the requested life-time of the metal precision parts sector cannot be met. Apart from corrosion resistance, hardness is a further critical key functionality for this sector. The minimum requirement for the alternative is given with at least 1,100 HV. As-deposited Ni-P alloy coatings achieve maximal 700 HV and heat treated Ni-P alloys ca. 1,050 HV. Neither of these two performances is sufficient and shows that electroless Ni coatings are technically not an equivalent replacement for the metallic chrome top coatings that are used to date.
Assessment overview for Electroless nickel plating (Metal precision parts)
Industry sector Hardness Corrosion resistance Endurance Metal precision
parts
Sector specific assessment: manufacture of printing equipment Within this sector screens for printing equipment are produced by electroforming. The screens are made of nickel that is first deposited onto a formative mandrel and afterwards separated from it. The removal of the finished screen assumes the anti-adhesive properties of the mandrels surface. In this context the ability to be anti-adhesive to the nickel-screen is the elimination criterion for this sector. If this criterion is not fulfilled, no further testing (e.g. for hardness) will take place. Testing was conducted with a Ni-B coating that was applied onto a mandrel. Then a nickel screen was electroformed onto the Ni-B coating, but the nickel screen could not be removed from the mandrel, not even after passivation of the Ni-B coating with KMnO4. This demonstrates that the anti- stick properties of the alternative Ni-B coating are insufficient for the use in electroforming. In addition, nickel-phosphorus coatings achieve maximum hardness values of 700 HV which is far below the functional chrome plating benchmark of 1,000-1,400 HV. Nickel is too soft to be used as a surface in rotogravure printing. For the manufacture of printing equipment sector with electroforming on a functional chrome plated mandrel as main application, the anti-adhesion of the mandrel surface is the most important performance requirement that an alternative has to provide. If anti-adhesion requirements are not fulfilled, then the alternative is not a technically suitable alternative to chromium trioxide. All processes are at laboratory scale and need further development. It will be a very long time before this technology will be mature and applicable in industrial scale use. Therefore, during the consultation companies from this industry sector evaluated electroless Ni coatings as not suitable for rotogravure printing.
62 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Assessment overview for Electroless nickel plating (Manufacture of printing equipment)
Industry sector Anti-adhesion Hardness
Manufacture of printing
equipment
7.1.3 Economic feasibility Against the background of significant technical failure of electroless nickel plating, no quantitative analysis of economic feasibility was conducted. However, the cost for electroless nickel plating depends on numerous different factors and these are presented in a qualitative to semi-quantitative way below. Generally Ni is more expensive, however the grinding post-treatment (a prerequisite for functional chrome plating), is not required. Costs depend on many factors including part size, geometry, and post treatments. Post-heat-treatment (higher energy costs) must be taken into account if increased hardness is required for selected parts for which the significantly reduced corrosion resistance is still sufficient (Legg K., 2003a). Slow deposition rates require longer process times making the process also more expensive. In contradiction to the above, a company from the steel sector stated that the costs for electricity during the main plating process is 10 times lower compared to functional chrome plating. Chromium trioxide baths require 500 € maintenance costs per year per m³ for recycling. The nickel bath maintenance costs are at least 7 times higher, since they are stable for hours only. In addition, the costs for nickel reactants are higher than for functional chrome plating. In summary, the per-part costs for electroless nickel process seem to be similar to functional chrome plating.
7.1.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (refer to Appendix 2.1.1) nickel sulphate constitutes the toxicological worst case scenario and is classified as Skin Irrit. 2, Skin Sens. 1, Resp. Sens. 1, Muta. 2, Carc. 1A, Repr. 1B, STOT RE 1, Aquatic Acute 1, Aquatic Chronic 1. As such, transition from chromium trioxide – which is a non-threshold carcinogen – to the above mentioned alternative would clearly not constitute a shift to less hazardous substances. Based on the classification, soluble nickel compounds may meet the Substances of Very High Concern (SVHC) criteria under REACH.
In addition, the size of composites such as diamond, PTFE, etc. which might be added to the process, can range from nanometres up to several microns. Depending on their size-specific properties, nanoparticles may pose additional risks to human health, especially via inhalation, which need to be adequately evaluated and addressed for material handling and working exposure. Aside from nickel, the bath chemistry can contain lead and cadmium as further hazardous substances. The legal limits related to RoHS (restriction of hazardous substances) in articles are Pb 0.1% (1,000 ppm) and Cd 0.01% (100 ppm). Electroless nickel baths have a finite bath life and last approx. 10 metal turnovers, depending on how the bath chemistry is maintained and on the materials being processed. As nickel is plated onto the
Use number: 2 63 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES part, the nickel concentrations in the bath decrease over time. Nickel sulphate is periodically added to replenish these losses. When 100 percent of the original nickel content has been replaced, this is defined as one metal turnover. After 10 metal turnovers, the bath content must be dumped and disposed of as hazardous waste. Baths must also be dumped if they get contaminated with certain metals, e.g. chromium: for a low-P bath, 3 ppm of Cr3+ creates unacceptable deposits, while 0.2 ppm of Cr6+ stops deposition completely. Given that any existing component being internally plated will have chromium plated surfaces, the risk of contamination is high (National Center for Energy and Environment, NDCEE, 1995).
7.1.5 Availability The electroless deposition of nickel is a well-defined process which has been in commercial use since the 1950s for certain products. Ni-P coating solutions are commercially more available than Ni-B and electroless nickel composite coating solutions (Legg K., 2003a). However, electroless nickel plating is suitable for some applications but they are not a like-for-like replacement for chromium trioxide functional chrome plating and failed to gain wide acceptance, especially in the aerospace industry, mostly due to the difficulty of maintaining a consistent plating. There are a number of suppliers selling commercial plating equipment and bath solutions. NDCEE states that if electroless nickel is to be used very widely, methods will need to be developed and made commercially available to continuously monitor and control the bath chemistry, temperature, and performance as well as to control the heat treatment temperature and time. The use of composites would make such control methods even more important, since one must control bath chemistry more closely to prevent deposition onto bath particulates and one must control the particulates themselves. Methods must be found to maintain the filler powders in a uniform concentration and to obtain proper entrainment in the coating. This is clearly a concern for more difficult geometries. Electroless deposition of nickel is not considered a like-for-like alternative to functional chrome plating. More than 15 years would be needed to develop a general metallic chrome coating alternative, and it is questionable whether this alternative will be part of future investigation in the described sectors.
7.1.6 Conclusion on suitability and availability for alternative electroless nickel plating To date, electroless deposited nickel is used in certain products but it cannot replace metallic chrome coatings with all their functionalities as a stand-alone alternative. Electroless nickel shows significant technical (and therefore unacceptable) deficits regarding for example, wear resistance, anti-adhesion and layer thickness. The combination of corrosion resistance, hardness and resistance to wear are crucial key functionalities for the aerospace, automotive and steel industry sectors. Whereas the minimum requirements on corrosion resistance are achieved within these sectors, the alternative is not able to fulfil the requirements concerning hardness and wear resistance. If electroless nickel coatings are heat treated, corrosion resistance is reduced. Thus, hardness and corrosion resistance requirements cannot be met at the same time. Corrosion resistance and hardness are also crucial functionalities for the sector that produces metal precision parts. Electroless nickel coatings did not pass sector specific testing with regard to these two parameters. The sector producing printing equipment tested the alternative with focus on their most important functionality, anti-adhesion. In functional testing, the electroless nickel layer applied on a tool showed no anti-adhesive properties at all, becoming inseparable from the product.
64 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
In spite of the mature plating technology, electroless nickel coating systems do not offer comparable performance to functional chrome plating, in particular, the combination of corrosion resistance, wear resistance, and hardness requirements cannot be met, and hardness in the unhardened state shows unacceptable performance compared to functional chrome plating, which makes electroless nickel plating unsuitable as a like-for-like technical alternative.
7.2 ALTERNATIVE 2: Nickel and nickel alloy electroplating
7.2.1 Substance ID and properties Nickel and nickel alloy electroplating is generally based on a similar technology as functional chrome plating, but with important differences in the anode design. Further differences are in the bath chemistry and some operating parameters such as voltage. Bath compositions are designed to either deposit a nickel coating or a nickel alloy coating. The Watts composition is a typical bath for the former coating containing nickel sulphate, nickel chloride and boric acid. Besides the Watts-type composition, nickel sulphamate is also a frequently used salt in sulphamate nickel plating. Suitable electrolytes for nickel alloy coatings can contain: nickel-boron (Ni-B), nickel-cobalt (Ni-Co), nickel- phosphorus (Ni-P), nickel-tungsten (Ni-W), nickel-tungsten boron (Ni-W-B), nickel-zinc (Ni-Zn), nickel-tin (Ni-Sn) (NDCEE, 1995).
Figure 21: Nickel and nickel alloy electroplating process design. Data source: NDCEE, 1995.
A Watts bath operates at a temperature between 25-60°C and a pH of 3.5-5.0 with a mean deposition rate of 40-90 µm/h. Raising pH to 5.5 increases deposit hardness, strength and internal tensile stress while ductility decreases. For Ni-P electroplating, NaH2PO4 is added to the Watts bath. Nickel sulphamate baths operate at similar process conditions. Magnetic and several textural properties as well as microstructure of Ni-P deposits are strongly dependent on the phosphorus content (Hu, 2000). The nickel-plating solution becomes contaminated by metals from different sources; most commonly dragged-in from previous treatments, corrosion products or work, tools, nuts, bolts, etc. which are dropped into the tank. Metallic impurities must be removed either continuously or at intervals by low current density electrolysis on a corrugated cathode.
Use number: 2 65 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Electrodeposited composite Ni-P coatings contain additives such as SiC significantly increase wear and corrosion resistance. A non-exhaustive overview of general information on properties of relevant substances used within this alternative, as well as the overall risk to human health and the environment is provided within Appendix 2.1.2.
7.2.2 Technical feasibility General assessment The major advantage of nickel and nickel alloy electroplating is that it might be a close “drop-in” replacement for current chromium trioxide process technology. There is a basic fit of the necessary equipment for bath plating and depots but the anode design, bath chemistry and operation will need to be changed. However, the performance in key functionalities is not comparable to chromium trioxide based coatings and suffers from technical limitations. Currently, nickel electroplating is often used in addition to chromium trioxide based functional chrome plating as an undercoat. Changing the operating parameters can affect the coating properties described below. If pH is increased above 5.0, temperature is decreased and the chloride content is increased, the hardness and tensile strength is increased and the ductility (elongation) is decreased. Electrolytically deposited Ni-P shows deficiencies to coat complex geometries with a highly uniform surface. Internal stress Stress in electrodeposited nickel is of tensile or compressive nature depending on the chemistry and varies largely. Nickel sulphamate stress values range between 0-55 MPa and are lower than those of additive-free Watts Nickel sulphate with 125-185 MPa (compare to a maximum of 550 MPa for very thin metallic chrome coated plates without cracks). Thin plates can contain higher stress. High deposit stress can be of concern in electroforming where the adhesion between the electrodeposit and the mandrel is deliberately kept as low as possible in order to facilitate separation. Deposit-substrate adhesion A key functionality for most applications of functional chrome plating is a high degree of adhesion between the deposit and the substrate. Atoms of the electrodeposited metal align themselves in opposition to atoms of the substrate and are held to the surface by interatomic forces. Adhesion is maximised when the atomic bond strength is greater than the tensile strength of the weaker element. Adhesive coating properties Metallic chrome coatings do have the property to be anti-adhesive. Water, grease, oil, dirt, and dust can be easily wiped off. Nickel coatings in general do not have this anti-adhesive behaviour and contaminants firmly stick to the surface. Hardness Hardness is one of the most important key functionalities. Nickel electroplates are rather soft with < 400 HV. Even significantly lower values are reported with 130-200 HV for Watts nickel and 170- 230 HV for nickel sulphamate (Di Bari, 2010).
66 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Hardness can be improved by additional heat treatment. Most nickel alloy coatings seem to require post-heat treatment to reach acceptable hardness levels. Up to 1,000 HV can be reached for electrodeposited Ni-P after heat treatment at laboratory scale (Daly & Barry, 2003). However, heat treatment damages the ability of the coating to act as a barrier for corrodible materials. Heat sensitive substrate materials (e.g. high strength steel, aluminium alloys) that are widely used in the aerospace, metal precision parts, general engineering and manufacture of printing equipment sectors require low deposition temperatures in order to avoid material degradation. The heat treatment temperature for aluminium alloys has to be < 150°C and for high strength steels < 250°C. Therefore heat treatment of these substrate materials conducted at temperatures about 340–400°C for several hours is not suitable to achieve a better hardness performance. Without heat treatment, as- deposited nickel layers do not meet the hardness criterion. Corrosion resistance Corrosion resistance is another key functionality that must be sufficiently fulfilled by a chromium trioxide alternative. A layer of nickel applied as undercoat (e.g. before functional chrome plating) raises the corrosion resistance of the coating system. However, nickel as a final layer can cause severe galvanic corrosion of the substrate (if coating is damaged). This is not the case with metallic chrome coatings probably due to formation of passive oxides on the surface. The nickel layer thickness also influences the corrosion resistance performance. An increase in corrosive service conditions requires an increase in the layer thickness (Watson, 1990). Wear resistance Wear resistance is a very critical issue for the metallic chrome coatings. It was reported during the consultation phase that wear resistance was significantly lower compared to metallic chrome coatings. The wear resistance of nickel electroplates can be increased by using nickel alloy or composite electroplates. Further R&D efforts are required to obtain more data for as-deposited and heat treated states. There is a correlation between hardness and wear resistance: in general, as hardness increases, wear resistance decreases. To date, the wear resistance properties of nickel and nickel alloy electroplatings are not sufficient to replace functional chrome plating. Sector specific assessment: aerospace Electrodeposited nickel or nickel alloy is usually used as an undercoat prior to functional chrome plating to provide sufficient corrosion protection. One important key parameter that must be fulfilled by a functional chrome plating alternative concerns hardness performance. The majority of electroplated nickel layers achieve hardness values of < 400 HV. High temperature annealing can significantly increase hardness, but simultaneously reduces corrosion resistance significantly. Post heat-treatment cannot be applied to heat sensitive structured alloys. If heat treatment is possible it is commonly used for the purposes of stress relief and evolution of hydrogen to minimise brittleness (usually at temperatures between 140-190°C with a maximum of 250°C). Electroplated nickel layers without temperature post-treatment do not reach the required hardness criteria in the aerospace sector with 450 HV (without hardening) to 750 HV (with hardening but which will decrease the corrosion resistance).
Use number: 2 67 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
With the extensive use of heat sensitive substrate materials for aeronautic applications with required hydrogen evolution temperatures < 150-250°C and stress relief with temperatures > 350°C, heat treatment is not an option to enhance hardness performance. A nickel layer is compact and does not contain micro-cracks analogous to a metallic chrome coating. This impairs post-treatment working steps on nickel and nickel alloy coatings such as sealing or lacquering. The minimum requirement of the coefficient of friction for lubricated metallic chrome coatings is < 0.2. During the consultation it was stated that electroplated Ni layers are not able to fulfil this criterion as the coefficient values are higher. Wear resistance is significantly lower compared to metallic chrome coatings and proved to be not sufficient as a replacement. Key figures for coefficient of friction and wear resistance are not yet consolidated as electrodeposited Ni is typically used for corrosion protection only or as an undercoat. With insufficient performance on hardness, friction behaviour and wear resistance, three important key functionalities are not met by an electrodeposited nickel layer. Therefore, the alternative is technically not suitable as a chromium trioxide replacement.
Assessment overview for nickel and nickel alloy electroplating (Aerospace)
Industry sector Hardness Coefficient of friction Wear resistance Microstructure
Aerospace
Sector specific assessment: automotive and general engineering Nickel is a very soft material with hardness values of about 400 HV. The hardness of electrodeposited nickel alloys and composite coatings can be raised up to ca. 1,000 HV which is still softer than metallic chrome coatings (ca. 700–1,400 HV). Therefore the deposition of nickel coatings is often combined either with heat treatment or an additional layer (currently metallic chrome coating) to obtain the required hardness. Heat post-treatment significantly decreases corrosion resistance and cannot be applied to heat sensitive structured alloys. The hardness performance of a stand-alone nickel layer (without post treatment) is not sufficient to fulfil the automotive requirement for hardness of 1,000-1,200 HV. Moreover, in the consultation wear resistance of unhardened Ni and Ni alloy coatings was reported to be insufficient and that there are no key figures available as electrodeposited nickel is currently used as undercoat only. A nickel layer is compact and does not contain micro-cracks analogous to a metallic chrome coating. This impairs post-treatment working steps on nickel and nickel alloy coatings such as sealing or lacquering. Nickel as underlayer of metallic chrome coatings is usually used to provide additional and sufficient corrosion protection in adverse conditions. Standalone electrodeposited nickel coatings are sufficiently corrosion resistant. In the consultation the automotive sector stated that electroplated nickel, without additional metallic chrome coatings, is exclusively used in electronic applications, and that electroplated Ni coatings are not relevant for automotive wear applications.
68 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Even if corrosion performance of nickel layers can be sufficient, the performance of two key functionalities, namely hardness and wear resistance, is insufficient. Therefore, the alternative is technically not suitable as a chromium trioxide replacement for this sector.
Assessment overview for nickel and nickel alloy electroplating (Automotive and General engineering)
Industry sector Hardness Wear resistance Corrosion resistance Microstructure
Automotive and
General engineering
Sector specific assessment: steel The combination of a nickel underlayer and a metallic chrome coating layer as topcoat is a typical coating for working rolls in the steel industry. A single nickel layer is no alternative, as hardness is too low compared to the minimal required 850-1,000 HV of the steel industry. The minimum requirement of the coefficient of friction is < 0.2. The coefficient of friction of a nickel layer on steel is higher than on metallic chrome coatings and does not fulfil the requirement. The surface roughness of the steel substrate is not as perfectly followed as with metallic chrome coatings and the morphology does not fulfil the requirements for the steel industry. The strip cleanliness is not sufficient. In addition, the minimum requirements for wear resistance of less than 12 mg/10,000 U are not met. With insufficient performance on hardness, friction behaviour, morphology and wear resistance, four important key functionalities are not met by an electrodeposited nickel layer. Therefore, the alternative is technically not suitable as a chromium trioxide replacement.
Assessment overview for Nickel and nickel alloy electroplating (Steel)
Industrial sector Hardness Coefficient of friction Morphology Wear resistance
Steel
Sector specific assessment: metal precision parts In order to evaluate the technical properties of an electroplated nickel alloy coating, field tests were conducted with electrolytic Ni-P layers on nickel substrates (e.g. sugar sieves). The life time of Ni-P plated sugar sieves gives an idea of the resistance to wear. The test showed that the life time of Ni-P coatings ranged from 20 to 80% compared to those plated with functional chrome plating. This means that the alternative coating does not provide sufficient wear resistance to resist life-time field testing for the minimum required period of 3 months. The minimum hardness requirement of 1,100 HV cannot be achieved by electrodeposited nickel electroplated coatings. Currently, field tests are ongoing on articles coated with an electrolytic Ni-P layer (>10% P). As the Ni-P coating needs to be hardened (annealing), this process needs to be optimized further to prevent visual defects and is therefore not yet technically feasible. During the consultation phase the layer thickness of electroplated nickel alloy layers was reported to be equal to a metallic chrome coating and fulfils the requirements.
Use number: 2 69 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
The performance regarding corrosion resistance was tested by means of an immersion test on Ni- Co-Fe, Ni-W, Ni-P (> 10% P) and metallic chrome coatings. The tested coatings were exposed to an acidic environment (pH 3.5) at room temperature using 2% sodium citrate / 3.5% citric acid.
Tested coating Nickel release additional release
Ni-Co-Fe 100 mg Ni/l 70 mg Co/l Ni-W 180-260 mg Ni/l 400-800 mg W/l Ni-P (> 10 % P) 70 mg Ni/l Metallic chrome coating 4-46 mg Ni/l
The amount of nickel released from the underlying nickel layer was determined to be 100, 180-260 and 70 mg Ni/l, compared to 4-46 mg Ni/l for metallic chrome coating. Ni-Co-Fe also released significant amounts of Co (70 mg/l), and Ni-W released significant amounts of W (400-800 mg/l). Ni-W-B was also investigated in a salt spray test and showed no corrosion of the underlying nickel layer after 53 days at 50°C with the sacrificial coating being completely gone under the extreme corrosive environment (the Ni-W-B coating is a 'sacrificial' coating which is intended to corrode faster by undergoing oxidation than the substrate underneath and thus protecting the substrate from corrosion). Therefore, and also because of the unstable plating bath, this alternative was found unsuitable for coating of metal precision parts. Field tests have shown that nickel alloy electroplated coatings are subject to several technical limitations. A nickel alloy coated sugar sieve does not resist sufficiently in difficult service conditions which reduces service life time. Even if layer thickness is found to be sufficient there are further key functionalities such as hardness and corrosion resistance that were tested with unsatisfactory results. The alternative is technically not suitable as a chromium trioxide replacement.
Assessment overview for Nickel and nickel alloy electroplating (Metal precision parts)
Corrosion Plating bath Industry sector Wear resistance Hardness Layer thickness resistance conditions
Metal precision
parts
Sector specific assessment: manufacture of printing equipment Within this sector the electroforming process is used to produce screens for printing equipment. The screens are made of nickel that is first deposited onto a formative mandrel and afterwards separated from it. To date, a metallic chrome coating is applied on the mandrels surface, to enable the removal of the produced screen. For the removal of the finished screen, the anti-adhesive properties of the mandrel surface are crucial. The majority of electroplated nickel alloys have reduced anti-adhesion properties compared to metallic chrome coatings and cannot be used as mandrel coating in nickel electroforming processes. Ni-P alloys (with < 10% P and > 10% P) were tested and have reasonable anti-stick properties; however these worsened after (essential) sanding of the mandrel. The service life of nickel plated surfaces was reported to be insufficiently short compared to metallic chrome coatings. Reduced service life time can be attributed to insufficient wear resistance.
70 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
The electroplated nickel coatings only achieve low hardness values (ca. 400-700 HV) compared to the metallic chrome coating benchmark of 1,000-1,400 HV. In the consultation, companies from this industry sector evaluated electroplated Ni coatings as too soft and therefore as not suitable for publication printing. This sector also tested a special type of nickel electroplating where SiC particles were dispersed in a Ni-Mo lattice. SiC improves surface hardness, while Mo improves corrosion and also hardness performance. A homogenous distribution and particularly a durable bonding of SiC throughout the Ni-Mo layer during plating was very hard to realize and not achievable with reasonable results. During R&D activities, the mandrel surface suffered from holes on the surface, probably caused by dropped out SiC particles. The coating showed inferior performance in hardness and wear resistance. Consequently R&D activities were ceased at this point. The minimum requirements of three important key functionalities, anti-adhesion, hardness and wear resistance, were not met by electroplated Ni coatings. Taking all the facts discussed above into account, the alternative is technically not suitable as a chromium trioxide replacement.
Assessment overview for Nickel and nickel alloy electroplating (Manufacture of printing equipment)
Industry sector Anti-adhesion Wear resistance Hardness
Manufacture of printing
equipment
7.2.3 Economic feasibility Against the background of significant technical failure of nickel electroplating, no quantitative analysis of economic feasibility was conducted. However, the cost for nickel electroplating depends on numerous different factors and these are presented in a qualitative to semi-quantitative way below. It was stated that the electricity costs during the plating process are four times lower compared to functional chrome plating. In contrast, the reactants for nickel electroplating are more expensive than the chromium reactants. Including further related costs such as investment costs for process restructuring, different anode technology, installation of new baths, etc., maintenance and chemical costs, the electrodeposition of nickel coatings, for instance Ni-P, was evaluated to be 2-8 times more expensive than functional chrome plating. The print sector also reports significantly higher total costs and emphasizes very high investment costs to be able to test the alternative on real products, as new baths and large ovens would need to be installed for rotogravure rolls, which are up to 6 m long.
7.2.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (refer to Appendix 2.1.2) nickel sulphate constitutes the toxicological worst case scenario and is classified as Skin Irrit. 2, Skin Sens. 1, Resp. Sens. 1, Muta. 2, Carc. 1A, Repr. 1B, STOT RE 1, Aquatic Acute 1, Aquatic Chronic 1. As such, transition from chromium trioxide – which is a non-threshold carcinogen – to the above mentioned alternative would clearly not constitute a shift to less hazardous substances. Based on the classification, soluble nickel compounds may meet the SVHC criteria under REACH.
Use number: 2 71 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
As some of the alternate substances used are also under observation, the replacement has to be carefully evaluated on a case by case basis. Amongst the composites used within this alternative, boric acid constitutes the toxicological worst case scenario and is classified as Repr. 1B. Furthermore, boric acid is a SVHC and was proposed for inclusion in REACH Annex XIV on September 1, 2014 due to its toxicity for reproduction. Therefore, the use of boric acid may become time limited by potentially transferring boric acid to the REACH authorization (Annex XIV). In summary, electroplates based on nickel do not constitute a shift to significantly less hazardous substances.
7.2.5 Availability Nickel electroplating is a commercially available process, similar to functional chrome plating but with different anode technology, bath composition and ingredients. Nickel electroplating is usually used as an undercoat for functional chrome plating and repair with metallic chrome coatings. Currently, there are ongoing efforts of the electroplating industry, metal parts manufacturers, and suppliers to improve the wear and corrosion resistance of the Ni-P alloy coating and make it a potential metallic chrome coating replacement. However, the testing is time intensive and several years are scheduled for further research. The aerospace sector does not consider nickel electroplating as functional chrome plating replacement. Plating of aircraft parts with chromium trioxide is often a combination of nickel strike, functional chrome plating, mechanical post-treatment and/or paint. In general, nickel electroplating is not considered a like-for-like alternative to functional chrome plating and more than 15 years would be needed to develop a general metallic chrome coating alternative.
7.2.6 Conclusion on suitability and availability for alternative nickel and nickel alloy electroplating Nickel coatings are widely used as one component in multi-layer systems with a final metallic chrome coating. In these systems, the combination of different layers provides satisfactory performance regarding the key functionalities (hardness, friction, wear, corrosion, adhesion). Systems consisting of a single nickel electroplated coating do not show satisfactory results during testing regarding the previously mentioned key functionalities. Hardness is a crucial functionality for each industry sector and electrodeposited nickel coatings do not meet the minimum requirements of any sector. Moreover, nickel coatings show insufficient anti-adhesion performance which is another key parameter for the sector that manufactures printing equipment. Although nickel electroplating is a commercially available process, it is not suitable as general alternative for functional chrome plating due to technical failure of the electrodeposited nickel coating. Nickel alloy electroplating as an alternative to functional chrome plating is at early laboratory scale. Significant time, financial and R&D efforts are necessary to evaluate the potential future replacement of chromium trioxide. Also, the chemicals used for this alternative do not constitute a significant shift towards less hazardous substances according to their classification (Ni-compounds) or are a SVHC and already proposed for inclusion on REACH Annex XIV (boric acid).
72 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
7.3 ALTERNATIVE 3: Case hardening: carburizing, carbonitriding, cyaniding, nitriding, boronizing
7.3.1 Substance ID and properties A description of case hardening as an alternative process, including the frequently used substances, follows in the next section. Process description Case hardening is a very common process that is used to harden the outer surface of metals creating a hard outer metal layer (“case”) while the deeper metallic material is unaffected, see Figure 22.
Figure 22: Case hardening. Data source: NDCEE, 1995.
The common nature of all case hardening processes is heat treatment of a metal substrate. The atmosphere contains an excess of a gaseous (or liquid) phase of the used substance, the dopant. The dopant then diffusively enters the outer layer of the metal creating the case. The process is predominantly related to steel, low carbon steel and other iron alloys. In the case of carburizing, carbon (carbon source such as carbon monoxide) is the dopant while carbo-nitriding is based on carbon and nitrogen. The dopant of cyaniding is cyanide, nitrogen for nitriding and boron for boronizing. Although dopants are commonly used, case hardening can also be conducted without dopants for certain metal alloys by heating the metal substrate (e.g. by induction) and cooling it down quickly. The case hardened area affected by the respective dopant varies depending on time and temperature of the process. The longer the treatment and the higher the temperature, the deeper the dopant is introduced to the substrate. The typical temperature of case hardening processes is between 500 to 1,000°C (TURI, 2006). The hardness of case hardened surfaces ranges between approx. 550 to 1,200 HV depending on the process, process temperature, dopants, and substrate used. Case hardening is used for gear teeth, cams, shafts, bearings, fasteners, pins, tools, screens, dies etc. and can also be used for large parts. Explosive hardening is a special hardening application. During this hardening process, explosive materials are applied directly onto the metallic surface to be hardened and are then detonated, driving the resultant forces into the metal surface. The penetration depth of the deformation can be up to 6 mm. In the following assessment explosive hardening is not further taken into account as it is limited to niche applications and is suitable for specific substrates only, for example high-manganese steel. In the consultation it was stated that it is therefore not a general alternative for functional chrome plating.
Use number: 2 73 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
A non-exhaustive overview of general information of substances used within this alternative and the risk to human health and the environment caused by this substances, is provided in Appendix 2.1.3.
7.3.2 Technical feasibility General assessment: Case hardening is used in order to increase hardness of a material surface. During case hardening, the parts are subjected to high temperatures, which can melt temperature sensitive alloys. As a consequence the process temperatures limit the substrates and applications. The deposition temperature for aluminium alloys has to be < 150°C and for high strength steels < 250°C. Thus, case hardening processes cannot be applied as they are conducted at temperatures above this value. The aluminium substrate would either be distorted or melted away. Case hardening processes result in a structural change of the substrate, leading to increased hardness of the upper 3-4 mm with "soft" metal underneath. Hardness exponentially decreases with increasing depth from the substrate surface. The change of microstructure does not lead to an additional layer or improves resistance to wear or corrosion. In the consultation the corrosion resistances of case hardened steels were reported to be even below the original corrosion resistance of the un-treated steel. Case hardening is not intended to provide corrosion protection. A nitride layer for example can rather be used as "undercoat" to provide additional hardness to the surface but it needs a corrosion resistant layer on top. An additional metallic chrome coating on parts that are exposed to wear makes it possible to increase their life-time as they can be repaired. Case hardened surfaces on the other hand are not suitable for rebuilding, as substrate is converted and no additional coating is deposited, the upper "treated" layer is not regenerative. In addition, the case hardened surfaces are characterized as less anti-adhesive, with poor friction and corrosion performance. Due to the required high temperatures, case hardening is energy intensive. Sector specific assessment: aerospace The aerospace sector stated that case hardening is only applicable on steel, specific steel alloys and materials which can withstand the process temperature. The heat treatment temperature for aluminium alloys has to be < 150°C and for high strength steels < 250°C. Therefore heat treatment of these substrate materials conducted at temperatures about 340–400°C for several hours is not suitable to achieve a better hardness performance. In the consultation it was confirmed that case hardening can be used for large parts and specific niche applications, but that it is not applicable for all parts and/or applications as a general replacement for functional chrome plating. It was also reported that case hardening is a mature process. Regarding the requirements to fatigue, they are considered to be met, although no quantitative data was provided to support this statement. Regarding the corrosion performance, none of the case-hardening processes improve the corrosion resistance. The corrosion resistance of hardened surfaces is comparable or even worse than the corrosion resistance of the base material as this alternative surface treatment does not provide a corrosion protective barrier. Case hardening is not a process intended to protect from corrosion. Case hardening as such without dopants does not improve the corrosion resistance. Several companies confirm that case hardening does not meet the requirements to corrosion resistance.
74 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Whether hardness of a case-hardened-surface is sufficient for the aerospace sector or not depends on the substrate and the case hardening process. Some companies consider the hardness requirement of case-hardened surfaces potentially to be met, other companies clearly stated that case-hardening is only applicable to a limited number of steel alloys and particularly not for structural parts (e.g. landing gears) with high requirements. These differences are reflected in the varying minimum requirements. A hardness of 400 HV can be sufficient for some parts with lower requirements. But the majority of the parts require at least 700 HV (for a like-to-like replacement). With a possible range from 550 HV to 1,200 HV for a case hardened surface, the hardness parameter can be fulfilled for some substrates and processes. The aerospace sector does not regard case hardening as replacement for functional chrome plating, as important process (temperature) and performance parameters such as corrosion resistance are not met. As the majority of airplane parts are constructed from temperature sensitive materials with processing temperatures below temperature of case hardening, this alternative is not suitable for the aerospace sector.
Assessment overview for Case hardening (Aerospace)
Endurance maturity Industry Corrosion Coefficient of Process Hardness longevity durability sector resistance friction / lubricity temperature fatigue Depends on Aerospace substrate and processes
Sector specific assessment: automotive and general engineering Case hardening is only applicable on specific steel substrates and materials which withstand the respective process temperature. The melting temperature of these substrates is in general above 1,000°C. Substrates with melting temperatures below the process temperature cannot be used in this alternative as they would either be distorted or melted away. Also, several CTAC Consortium members support that case hardening is not suitable for rebuilding parts, since no additional layer is applied. The automotive industry states that case hardening is a common process for automotive applications and that performance provided by case hardened surfaces is suitable for some specific parts. A commercially available plasma nitriding plus oxidiation process is reportedly suitable for engine, suspension, brake and transmission components for the automotive industry. Applying this process can result in production cost savings of 30-60% over functional chrome plating when used for automotive parts. Furthermore, it is stated that the part life of nitrided parts can be up to three times that of functional chrome plated parts. The general engineering sector is concerned about high friction coefficients and insufficient anti stick properties of parts coated with the above mentioned process, which do not meet the sector specific requirements. In addition, the process is currently applied on small parts only and the industrial application for large parts with a length of up to 6 m still needs to be investigated and proper functionality needs to be proven. In the consultation it was mentioned that case hardening is suitable for low pressure and non-acidic areas, however corrosion resistance does not satisfy requirements under acidic conditions.
Use number: 2 75 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Information provided by the automotive sector confirms insufficient corrosion resistance. Therefore, case hardening is not suitable for parts exposed to heavy corrosion load. In general, the automotive sector requires for metallic chrome coatings a Vickers Hardness (ISO 6507-1) of 1,000-1,200 HV (refer to Table 6). As the achievable hardness by case hardened surfaces ranges from 550 to 1,200 HV, the hardness requirement can be partly met depending on the substrate and process. Case hardening is used for specific automotive applications, where the minimum requirements can be met by case hardened substrates. However, for the majority of parts, case hardening is not a one- to-one replacement for all parts and applications in the automotive and general engineering sectors, as its use is limited to niche applications. It cannot be used where corrosion resistance, low coefficients of friction, excellent anti stick properties, and the application of an additional layer is required.
Assessment overview for Case hardening (Automotive and General engineering)
Corrosion Rebuilding of Friction Anti-stick Industry sector Hardness resistance parts coefficient properties Depends on Automotive and substrate and General engineering processes
Sector specific assessment: steel Case hardening does not improve corrosion resistance of the substrate which is a key functionality of metallic chrome coatings. According to the information provided the corrosion resistance requirements of the steel industry cannot be met by case-hardened substrates, as the corrosion resistance is comparable to the base material. In general, the steel industry requires a minimal, theoretical hardness (according to test method ISO 6507-1) of 850 HV, but the minimal, practical hardness starts with 1,000 HV. As the achievable hardness by case hardened surfaces ranges from 550 to 1,200 HV, the hardness requirement can be partly met depending on the substrate and process. Case hardening requires a long processing time of up to 4 hours per work roll and the surface cannot be restored or rebuilt. The long process time is necessary to control heat stress. Heat during the coating process introduces stress into the work rolls which can lead to roll spalling. Spalling of rolls is very dangerous as razor sharp pieces of the roll (itself up to 8 tonnes) can explode, behaving like shrapnel and therefore being potentially lethal. Case hardening does not meet the requirements for corrosion resistance, and rebuilding of the work roll surface is not feasible. Therefore it is not an alternative for coating work rolls in the steel industry.
Assessment overview for Case hardening (Steel)
Industry sector Corrosion resistance Hardness Rebuilding of parts
Depends on substrate and Steel processes
76 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Sector specific assessment: metal precision parts This sector requests a minimal Vickers Hardness of ca. 1,100 HV. As the achievable hardness by case hardened surfaces ranges from 550 to 1,200 HV, the hardness parameter can partly be met depending on the substrate and process used. For metal precision parts that are used for example as sugar sieves for food industry, corrosion resistance is important to meet the life-time of the article (e.g. 3-4 months for sugar sieves). Case hardening processes do not improve the corrosion resistance of the substrate and are not suitable for those articles. For sheet-guiding cylinder jackets maximal life-time is secured by an additional (so far metallic chrome coating) layer that can be rebuilt when worn, which is not possible using case hardening as alternative. Case hardening does not build a coating and cannot be used for repair of worn surfaces. This is why case hardening is not a replacement for functional chrome plating in this industry sector and application. Case hardening does not meet the requirements concerning layer thickness and corrosion resistance and is therefore not an alternative for the sector that produces metal precision parts.
Assessment overview for Case hardening (Metal precision parts)
Industry sector Corrosion resistance Hardness Rebuilding of parts
Metal precision Depends on substrate and
parts processes
Sector specific assessment: Manufacture of printing equipment The minimal performance requirement of the manufacture of printing equipment sector for hardness ranges between 1,000 to 1,400 HV according to ISO 6507-1. As the achievable hardness by case hardened surfaces ranges from 550 to 1,200 HV, the hardness parameter cannot be achieved for all applications. For the manufacture of printing equipment sector the number of produced units (e.g. printed sheets, screens) and the reuse of cylinders, i.e. the ability to rebuild worn parts are important issues. The life- time of a printing tool must last at least for the production of a specific number of produced units, e.g. 1,000 screens, before the complete mandrel is reworked. Mandrels have very precise specifications on a micrometre level which need to be controlled, restricting the maximum process temperature to 200°C. If temperatures are higher (e.g. 500-1,000°C) the different thermal coefficients of the materials constituting the multilayer coating lead to unacceptable surface defects. As case hardening does not provide a coating that can be repaired, this alternative is not considered to be an alternative for the manufacture of printing equipment sector.
Assessment overview for Case hardening (Manufacture of printing equipment)
Industry sector Hardness Rebuilding of parts
Manufacture of printing
equipment
Use number: 2 77 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
7.3.3 Economic feasibility Against the background of significant technical failure of case hardening, no quantitative analysis of economic feasibility was conducted. However, concerning the economic feasibility, the cost factor was reported to be three times higher for case hardening processes compared to functional chrome plating.
7.3.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 2.1.3), sodium cyanide, is classified as Acute Tox. 2, Acute Tox. 1, Eye Dam. 1, Acute Tox. 2, Aquatic Acute 1, Aquatic Chronic 1. Furthermore, carbon monoxide is classified as Press. Gas, Flam. Gas 1, Acute Tox. 3, Repr. 1A, STOT RE 1. As such, transition from chromium trioxide – which is a non-threshold carcinogen – to one of the above mentioned alternatives would constitute a shift to less hazardous substances. However, some of the used alternate substances are also under observation regarding their toxicity. Therefore, the replacement has to be carefully evaluated on a case by case basis.
7.3.5 Availability Case hardening is a well-defined process that is commercially available (TURI, 2006), but only for very specific applications. From the information provided in the consultation, mainly because of the corrosion resistance and non-repair issues, it is not expected to become a one-to-one replacement for chromium trioxide in functional chrome plating in the future. At least 15 years, would be needed to develop a general metallic chrome coating alternative, if ever.
7.3.6 Conclusion on suitability and availability for alternative case hardening Case hardening can fulfil the requirements on hardness depending on the substrate and process, but for the different sectors a combination of requirements of hardness, corrosion resistance and the possibility to rebuild parts is generally needed which cannot be achieved by case hardening. Case hardening may be suitable for specific applications (e.g. brake, suspension) in the automotive sector but can neither cover the totality of applications nor fulfil all requirements of the automotive sector. In summary, case hardening processes are not a general alternative for functional chrome plating.
7.4 ALTERNATIVE 4: Chemical vapour deposition (CVD) This section refers to the application of thin CVD if not stated otherwise. An exception is within the technical feasibility assessment for the aerospace sector in section 7.4.2, where thick CVD is assessed separately.
7.4.1 Substance ID and properties CVD as well as plasma enhanced chemical vapour deposition (PECVD) are assessed together as alternative as they basically refer to the same process but with different process conditions (TURI, 2006 and RPA, 2005):
78 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
- Thermal / low pressure CVD (sub-atmospheric pressure and high temperature) and - Plasma enhanced CVD (lower temperature with heat generated by electrical plasma).
CVD: Chemical vapour deposition is a process in which reactant gases (normally mixed with inert gases) enter a reaction chamber at room temperature and are then heated or passed over a heated substrate. The processing temperature is normally 1,000°C. A typical CVD system is shown in Figure 23. Materials, called precursors, are brought into the deposition area in the gas phase, exemplarily illustrated as precursor 1 and 2. Gases contain the desired coating materials such as metal halides, metal carbonyls, hydrides or organometallic compounds in vapour phase. Possible coating materials are e.g. titanium carbide, titanium nitride, titanium carbon nitride, silicon carbide, titanium boride, aluminium oxide. After being absorbed onto the surface of the substrate, the reactants are decomposed and react with the substrate to form the coating. By-products are then removed from the chamber. Conducting the CVD process under sub-atmospheric pressure tends to reduce unwanted gas-phase reactions and improve film uniformity across the substrate.
Figure 23: Typical CVD system. Data source: Legg K., 2003a.
PECVD: The reaction can also be initiated by plasma (ionized gas) instead of heat. The advantage of plasma enhanced CVD is that it is possible to only heat the surface region where the reaction occurs while the core of the component is maintained at a comparatively lower temperature. Due to lower processing temperature, PECVD is applicable to a broader range of materials, especially heat sensitive material. A non-exhaustive overview of general substances information used for (thin) chemical vapour deposition and the risk to human health and the environment caused by these substances, is provided within Appendix 2.1.4.
7.4.2 Technical feasibility CVD is appropriate for complex geometries (e.g. blind holes) as it deposits a uniform coating on a shape due to the gaseous reactants. The process results in a hard, acid and wear resistant coating (RPA, 2005). The deposition rate is significantly lower than in the functional chrome plating process at lower temperatures and similar at high temperatures such as 1,000°C only (compare 100 µm/h for high temperature functional chrome plating versus 3 µm/h for CVD). CVD is for example used in cutting tool industry (Legg K., 2003a) and for typically small and/or high value items with high
Use number: 2 79 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES production volumes (e.g. screens and dies). According to Davis, 1995, CVD coatings can achieve values for hardness that are > 1,500 HV and even reach values up to 3,300 HV. The CVD process usually requires the surface to be red hot for thermally driven CVD (around 1,000°C), which limits the types of substrates and alloys that can be coated. The high temperatures may lead to a distortion of component and changes in properties of the substrate. Therefore CVD is rarely used in combination with heat-sensitive materials. CVD can be used for turbine blades and hot section engine components, but is totally unsuitable for structural components (Legg K., 2003a). Using plasma or more expensive metalorganic gases reduces the process temperature to about 500°C which still exceeds the processing temperature of many alloys (e.g. high strength steel, aluminium). (Legg K., 2012). The process temperature for PECVD is typically up to 500°C but can be <300°C for specific applications. As long as their processing temperatures are above the temperature needed for the chemical vapour deposition, a variety of coating materials can be used. The coatings provided by CVD are usually only a few µm thick and the maximal achievable layer thickness is low. Consequently it is impossible to rebuild the dimensions of worn or damaged components according to the original specifications (Legg K., 2012), because repair coatings require deposition of greater quantities of material. Another significant disadvantage of this alternative is the need of a reaction chamber. Therefore, the geometry (size) of the components is a limiting factor. From a technical point of view, CVD is not suitable for large parts (e.g. work rolls of a mill process, weight: 7 tons), especially in combination with sub-atmospheric pressure. CVD can involve the use of hazardous materials such as carbon monoxide gas, hydrogen gas, hydrochloric acid and liquid chlorides (e.g. titanium chloride, vanadium chloride). It also generates waste gases that must be collected and the chamber also needs periodic cleaning; fluorinated gases (greenhouse gases) may also be used (TURI, 2006). Sector specific assessment: Aerospace – Thin & Thick CVD Thin CVD The metallic chrome coating protects the substrate from environmental impacts. An alternative coating has to be as corrosion protective as the metallic chrome coating. Tests conducted by the aerospace sector showed that CVD coatings do not perform equally to metallic chrome coatings. It was reported that many CVD coatings, such as TiN and TiC, do not protect substrates due to their porous structure and/or low thickness and are thus not an alternative. The required vacuum conditions limit the scope of parts to be coated, e.g. concerning the component size. As a CVD treated surface can achieve at least 1,500 HV in hardness test, the minimal hardness requirements of the aerospace sector are fulfilled. Although tests also revealed good results for friction characteristics, CVD did not meet the requirements for wear and shock resistance, which is due to the very low thicknesses of CVD compared to metallic chrome coatings. The aerospace sector widely uses materials such as high strength steels and aluminium alloys with low processing temperatures. The deposition temperature for aluminium alloys has to be < 150°C and for high strength steels < 250°C. Such materials cannot be used with the CVD process as the CVD temperatures are above this limit. In addition, the process requires vacuum, i.e. the size of the vacuum chamber depends on the components size. CVD processes as Diamond Like Carbon (DLC) can be used for small components such as keys and small rods in large productions. However CVD is not suitable for large parts like for example landing gears. CVD is a specialized technique that is only suitable for specific niche applications, but cannot be implemented as a general metallic chrome coating replacement.
80 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Assessment overview for thin CVD (Aerospace)
Industry Corrosion Process Layer Hardness Large geometry sector resistance temperature thickness
Aerospace
Thick CVD The aerospace sector has assessed thick CVD processes as a potential alternative which is described in the following. Substance ID and properties Thick CVD coating is applied by a chemical vapour deposition process similar to the thin CVD process. It involves a gas phase reaction in which one of the reactant gases is a source of tungsten and one a hydrocarbon (the carbon course). Depending on the exact set conditions, the processing temperature can be kept below 500°C meaning that it is more applicable to a wider range of materials such as steel, stainless steel, nickel, copper, cobalt and titanium alloys.
The coating is a binder-free, homogeneous & pore-free tungsten / tungsten carbide graduated coating applied for its sliding wear properties and barrier corrosion resistance. Different properties such as in hardness and toughness may be obtained by changing the processing conditions. Technical feasibility and sector specific assessment: aerospace Thick CVD is adaptable to a wide variety of parts, shapes, and sizes. It is not confined to line of sight and so is particularly suitable for application to complex geometries (including bores and cavities) requiring wear protection up to “high load” situations. Depending on the type of coating typical hardnesses can range from 800-1,600 HV. The coatings provided by this variant of CVD are usually in the region of 50 μm thick and the maximal achievable layer thicknesses can be in excess of 100 μm (refer to http://www.hardide.com/). Consequently it is possible to use it as a metallic chrome coating replacement without changing tolerances, although the moderately high processing temperatures mean that often material change may be needed (or the heating during processing may have to be incorporated into the material heat treatment regime). Currently, typical reaction chambers can accommodate maximum dimensions of up to 1.2 m. Currently, this process requires nickel undercoats on all substrates to be coated, either produced by electrolytic or electroless processes, using nickel salts, although there are plans to replace these with other undercoats. This coating has shown itself to be equal or superior to metallic chrome coatings in sliding wear by bench testing in configurations such as against bronze bearing materials but not against harder substrates. Testing has shown it to offer good barrier corrosion protection and for it to be able to coat complicated geometries. It has limited use in military aircraft and is currently being qualified by a major commercial aircraft manufacturer. The coating is not suitable for many aerospace materials due to the high process temperature, and requires lubrication under high load. Its main application is likely to be for complicated geometries, especially under high load, and as an environmental improvement over electroless nickel.
Although the thick CVD coating cannot be considered as a general replacement to metallic chrome coatings because of cost and the high temperature of the process, it does offer a thick coating with fairly good tribological properties suitable for materials whose mechanical properties are not affected
Use number: 2 81 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES by the high process temperature such as many stainless steels. It is particularly suitable for complicated geometries for which thermal spray coatings would be unsuitable.
Assessment overview for thick CVD (Aerospace)
Industry Corrosion Process Layer Hardness Geometry Size limitation sector resistance temperature thickness Aerospace
Sector specific assessment: automotive and general engineering Hardness is an important key functionality of a metallic chrome coating. CVD coatings can achieve hardness values of at least 1,500 HV. The minimum requirement of 1,000-1,200 HV is fulfilled. CVD processes are conducted in closed chambers under vacuum conditions. Thus, the size of the process chamber has to be adapted to the parts size. For example large size hydraulic parts of this sector have a length of up to 6 m and require a respective chamber size which is technically very difficult. A vacuum chamber large enough for such parts lead to high production and investment costs and make it not feasible. The process temperature between 500 and 1,000°C, depending if PECVD or CVD is used, is evaluated as too high and leads to structural changes and degradation in the material mainly used in this sector which is not acceptable. The process has low deposition rates and is time intensive. The produced layer does not provide adequate corrosion resistance compared to metallic chrome coatings. Furthermore, friction and anti- stick properties need to be investigated.
Assessment overview for thin CVD (Automotive and General engineering)
Process Corrosion Industry sector Hardness Size limitations temperature resistance
Automotive and
General engineering
Sector specific assessment: steel Hardness is an important key functionality of a metallic chrome coating. CVD coatings achieve hardness values starting at 1,500 HV. The minimum requirement of 850-1,000 HV is fulfilled. CVD is not considered as a suitable alternative for the steel industry as the work rolls to be coated weigh up to 7 tons, and have large dimensions of several meters in length. In addition, it was stated that stress is introduced into the material of the work roll by the process heat. This is an unfavourable effect as stress reduces the life time of the work piece. Process time is also significantly longer compared to functional chrome plating.
Assessment overview for thin CVD (Steel)
Industry Hardness Size limitations Process temperature Process time sector Steel
82 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Sector specific assessment: metal precision parts A product example of this sector is given by sugar sieves with dimensions of 1.5 m x 1.5 m and a high number of small holes in micro-/millimetre size. For these products it is important that a proper and uniform coating is applied that does not close the holes and provides minimal performance requirements. CVD processes usually take place at 800-1,000°C and thus cannot be applied on heat sensitive substrates such as electroformed nickel parts. With (PE) CVD it is not possible to coat a product with these requirements.
Assessment overview for thin CVD (Metal precision parts)
Industry sector Layer constitution Suitability for the sectors’ product
Metal precision parts
Sector specific assessment: manufacture of printing equipment Chromium plated components for rotogravure equipment can have a diameter of 150-700 mm and a length of 5.5-6 m. A vacuum chamber with 10-4 Pascal (10-6 mbar) is needed for this process and the chamber must be large enough for these parts. This is technically difficult and leads to significantly higher production and investment costs. The process temperature with 300-500°C for CrN is too high to be applied on the mandrels which makes this alternative not feasible. Typical deposition rates for PECVD are slow with approx. 3 µm/h. Thus, the process time to generate the coating would be significantly increased from less than 15 minutes for metallic chrome coatings to several hours. The quick preparation of the printing form is essential, especially for publication rotogravure, where the available time period between the editorial deadline and the delivery of a sellable printed product is very short.
Assessment overview for thin CVD (Manufacture of printing equipment)
Industry sector Size limitations Process time Process temperature
Manufacture of printing equipment
7.4.3 Economic feasibility Against the background of significant technical failure of CVD, no quantitative analysis of economic feasibility was conducted. However, the cost for CVD depends on numerous different factors and these are presented in a qualitative to semi-quantitative way below. CVD processes include relatively high costs because it is a complex technology that requires a vacuum chamber. The costs for the equipment are indicated to be $1-2 million for the coating system, with additional costs for pre- and post-treatment (Legg K., 2012). Especially for small components that require a long life-time, CVD can be a cost-effective alternative to functional chrome plating. The aerospace sector confirms that costs (including energy consumption) are higher, compared to functional chrome plating, especially if the processed volumes are low. However, a general economic assessment is not possible because the process costs depend on nature of component (batch process), energy consumption and chamber size. Costs for thick coatings may be competitive for parts with complicated geometry for which thermal spray coatings would be unsuitable.
Use number: 2 83 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
The general engineering sector reports costs that are 3 times higher for the thin CVD process. Costs are even higher for thick CVD due to longer deposition times. The steel industry also reports higher costs related to higher energy consumption that is required to heat up work rolls (substrate). The printing equipment industry stated that vacuum chambers that are large enough for the several meters long rotogravure equipment lead to high production and investment costs. The price per preparation of the cylinder surface was roughly estimated to be 16 – 80 times higher compared to functional chrome plating.
7.4.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 2.1.4), aluminium oxide, as toxicological worst case, is classified as Stot SE 3, Acute Tox. 4. As such, transition from chromium trioxide – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.4.5 Availability During the consultation phase it was stated that R&D is ongoing for thick CVD within the aerospace sector for specific applications (e.g. small parts), whereas thin CVD is not considered or further investigated due to the identified significant technical deficiencies. In general, thermal CVD and PECVD are commercially available processes. Thermal CVD is unsuitable for structural components because of its high process temperatures. PECVD is commercially available but only for limited applications and materials. For several uses there is no available technology and process. If suitable coating material is used and there are no technical limitations, the process is a viable method (Legg K., 2003a). The sector specific feedback from the consultation showed that at the current R&D stage the technical limitations have not yet been overcome. A minimum of 10 – 15 years is expected to develop a general metallic chrome coating alternative.
7.4.6 Conclusion on suitability and availability for alternative CVD The thick CVD process in the aerospace sector is currently investigated for specific applications, as it offers a thick coating with fairly good tribological properties. It is particularly suitable for complicated geometries for which thermal spray coatings would be unsuitable. However, it is only suitable for materials whose mechanical properties are not affected by the high process temperature such as many stainless steels. In addition, the size of the items to be coated is limited to a maximum of 1.2 m which restrains its application to small parts. Therefore, thick CVD cannot be considered as a general replacement to functional chrome plating. The thin CVD process cannot be considered as a general alternative to functional chrome plating, primarily due to technical failures. The process only provides very thin (few µm) coating layers that cannot be used as repair coating to rebuild worn or damaged parts back to the original specifications. Moreover, the process needs to be conducted in a vacuum chamber which limits the use of CVD for large and heavy parts. Thus, the alternative is technically not feasibly for automotive /general engineering, steel industry or manufacture of printing equipment. The sector that produces metal
84 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES precision parts mentioned insufficient layer constitution, and the aerospace industry criticise the poor corrosion resistance of CVD coatings. The process temperature (> 500°C) excludes common and widely used substrate materials such as aluminium alloys and high strength steels with processing temperatures about 150 and 250°C (Legg K., 2003a). Significantly increased process time is a criterion for exclusion for the manufacturer of printing equipment. Although CVD and PECVD are commercially available processes at high costs, the companies generally have little experience with these processes as a functional chrome plating replacement. Thin CVD processes are technically not feasible and do not represent a suitable alternative to replace functional chrome plating.
7.5 ALTERNATIVE 5: Nanocrystalline cobalt phosphorus alloy coating
7.5.1 Substance ID and properties Nanocrystalline cobalt-phosphorus alloy (nCoP) coatings are electrodeposited in an aqueous bath process that uses pulse plating technology. Pulse technology enables controlled deposition of nano grains (5-15 nm) resulting in an ultra-fine grain structure throughout the entire coating thickness from the substrate surface (Facchini et al. 2009; Legg K., 2003b). The steel industry also investigates Ni- W (nickel-tungsten) alloys with this electrodeposition method.
Figure 24: Microstructure of nano CoP coatings. Data source: Legg K., 2003b. As the process is similar to the electrodeposition of functional chrome plating and compatible with current functional chrome plating infrastructure, it is considered to be a possible drop-in replacement. During the consultation it was reported that the Co plating process is not yet a mature technology. Significant process performance parameters are summarized in Table 10.
Table 10: Comparison in process performance for nCoP and functional chrome plating (McCrea, 2003 and Gonzales, 2010).
nCoP alloy Functional chrome plating
deposition method electrodeposition electrodeposition applicable line-of-sight line-of-sight geometries non line-of-sight non line-of-sight
2- bath chemistry CoCl2 / H3PO4 CrO3 / SO4 Efficiency 85–95 % 15–35 % deposition rate 50–200 µm/h 12–40 µm/h
Use number: 2 85 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
In general Co plating solutions are in a low TRL stage. A non-exhaustive overview of general information of substances used within this alternative, and the risk to human health and the environment caused by this substances, is provided in Appendix 2.1.5
7.5.2 Technical feasibility General assessment The following table provides an overview of the performance of nano Co-P coatings. In addition, cobalt is sensitive to alkaline cleaners.
Table 11: Material properties of nano Co-P alloys. Data source: McCrea, 2003 and Gonzales, 2010.
Property nCoP alloy
hardness (as deposited) 600–700 HV
hardness (heat treated at 250 °C) 700–800 HV
hardness (heat treated at 400 °C) 1,000-1,200 HV
thickness up to 50 µm
wear resistance (Taber test) 27 mg/1,000 cycles
Hardness: As illustrated in Table 11, the hardness of as-deposited nano Co-P alloys is in the range of 600- 700 HV (Vickers Testing ISO 6507-1) and therefore inferior compared to metallic chrome coatings with 700-1,400 HV. In order to increase hardness, there are two possibilities: (a) Raising the phosphorous content for the as-deposited coating. (b) Heat treatment, also known as annealing. Annealing after electrodeposition at 300-400 °C leads to an increased hardness between 700-800 HV and 1,000-1,200 HV. However, heat treatment can easily result in changes of the substrate microstructure and lead to degradation of coating and substrate properties. Heat treatment can only be used for materials which are not heat sensitive (Facchini et al., 2009; Holeczek, 2011). Wear resistance Low achievable hardness can be an indicator for low wear resistance in service environments where the coating is extremely stressed. Abrasive (Taber) wear testing of nanocrystalline Co-P alloys confirms them to be less resistant to wear than metallic chrome coatings. The abrasion of nano Co-P alloys is 27 mg/1,000 cycles and the abrasion of metallic chrome coatings is about 2-3 mg/1,000 cycles. The resistance to wear, as one of the key requirements, is a limiting factor, because nano Co- P coatings are about 10-times less wear resistant than metallic chrome coatings.
Thickness The maximal achievable coating thickness with nano Co-P layer is about 50 µm. With metallic chrome coatings in comparison, here even 1,000 µm are possible, nano Co-P coatings perform worse than chromium, especially when thickness > 50 µm is required (repair and overhaul).
Corrosion resistance Nanocrystalline Co-P alloys show superior corrosion resistance to metallic chrome coatings, with 50 % thinner layer. Tests were conducted (according to ASTM B117) with layer thicknesses of 50 µm
86 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES for nano Co-P and 100 µm for metallic chrome coatings. The cobalt alloy performed very well and showed an approximately stable corrosion resistance during 1,000 hours of testing time, compared to metallic chrome coating with continuously decreased corrosion resistance after the same exposure time (Facchini et al., 2009).
Sector specific assessment: aerospace Hardness is a key performance parameter and coatings have to meet at least 700-900 HV for aerospace applications. Nano Co-P coatings achieve 600-700 HV as-deposited and do not fulfil the requirement. Heat treatment to increase hardness performance is not an option. Heat sensitive substrate materials (e.g. aluminium alloys, high strength steel) are widely used in the aerospace sector. The deposition temperature for aluminium alloys has to be < 150°C and for high strength steels < 250°C. Therefore heat treatment of these substrate materials at temperatures about 300–400°C for several hours is not suitable to achieve better hardness performance. The hardness requirement cannot be fulfilled by as-deposited coatings and annealing is not an option for increased hardness due to material degradation. The aerospace sector requires a minimal layer thickness of at least 100 µm in order to avoid redesign of the whole aircraft component. The Co-based alternative achieved, however, only a maximal limit of 50 µm. A thickness of 50 µm is not suitable for aeronautic applications. As stated in the general assessment, performance criteria for corrosion resistance are met for the aerospace sector. With regard to insufficient technical performance, nano Co-P coatings are not an equivalent replacement for chromium trioxide for the aerospace sector.
Assessment overview for nCoP-coating(Aerospace)
Industry sector Corrosion resistance Hardness Layer thickness
Aerospace
Sector specific assessment: automotive and general engineering Hardness is a key performance parameter for the automotive industry and performance requirements are in the range of 1,000-1,200 HV. The hardness of as-deposited nano Co-P coatings is about 600- 700 HV and can therefore not meet the mentioned specification. The deposition temperature for aluminium alloys has to be < 150°C and for high strength steels < 250°C. Therefore heat treatment of these substrate materials at temperatures about 300–400°C for several hours is not suitable to achieve better hardness performance. Automotive applications require in general layer thickness between 20 and 50 µm. Nano Co-P alloys achieve up to 50 µm and pass this performance requirement. As stated in the general assessment, performance criteria for corrosion resistance are met for the automotive and general engineering sector. However, there is insufficient data with regard to fatigue and hydrogen embrittlement testing.
Assessment overview for nano CoP-Plating coating (Automotive and General engineering)
Industry sector Corrosion resistance Hardness Layer thickness
Automotive and General
engineering
Use number: 2 87 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Sector specific assessment: steel In the consultation it was stated that field tests were conducted with a nanocrystalline cobalt- phosphorus alloy which is commercially available. For the tests it was applied on work rolls of the temper mill process for rolling steel. The temper mill process was chosen for this test because its process conditions are the most material friendly; that means the lowest load on deposit and work rolls in comparison to other rolling mill processes. The test parameter for the deposited layer is the number of coils that can be produced with one work roll before it has to be changed and repaired.
Table 12: Test results field test on nCoP, which is commercially available. Data source: Neolor, 2014.
nCoP alloy Metallic chrome coating
Number of produced 38 61 steel coils pits roughness too low
Reason for roll change
The functional chrome plated work roll produced 61 steel coils compared to 38 with the nano Co-P- coated work roll (see Table 12). The reason for roll change is shown on the pictures in Table 12. The surface is not uniform and pits are transferred from the work roll onto the produced material which is not acceptable. Nano Co-P coating fails when applied on the work roll used in temper mill process where the loads are the lowest compared to other applications in the cold rolling process for producing steel. The nano Co-P coating therefore does not represent an alternative to functional chrome plating due to its technical limitation when used on work rolls for steel production. In addition, the hardness criteria of 850-1,000 HV cannot be met by nano Co-P alloys which achieve 600-700 HV in an as-deposited state. Furthermore, heat treatment is not possible as it creates too much stress in the rolls. Besides nano Co-P, Ni-W (nickel-tungsten) alloys processed with the nanocrystalline elcetro deposition method are a possible alternative to functional chrome plating. The Ni-W deposition rate was determined to be between 0.4-1.6 µm/h in a bath chemistry consisting of NiSO4*6H2O & Na3C6H5O7 & Na2WO4*2H2O for tungsten concentrations varying between 5- 25% (Alimadadi et al., 2009). At laboratory scale similar results were obtained compared to functional chrome plating for specific OEM or dimensional repair applications Ni-W alloys using Ni 60 wt% : W 40 wt% (refer to www.sifcoasc.com/wp-content/uploads/Nickel-Tungsten-5711.pdf & www.asetsdefense.org /documents/Workshops/ASETS2012/7/Clouser%20-%20For%20Web.pdf). Investigations indicated
88 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES good corrosion and wear resistance. The Ni-W coating can be heat treated up to approx. 300°C; one test showed an increase of Vickers microhardness to 950 HV after 6 hours of heat treatment at 190°C without causing microcracks (http://www.myvirtualpaper.com/doc/nasf_aesf/pasf_may 10/2010052701/52.html#52 ). Although some key requirements could be fulfilled at laboratory scale, the steel industry reports insufficient adhesion for their applications. Further investigations are ongoing. Neither nano Co-P nor Ni-W alloys are feasible alternatives.
Assessment overview for nano Co-P coating (Steel)
Industry sector Uniformity Hardness
Steel
Assessment overview for Ni-W coating (Steel)
Industry sector Adhesion
Steel
Sector specific assessment: metal precision parts Immersion tests were conducted with 2% sodium citrate / 3.5% citric acid, pH 3.5 and room temperature on nano CoP- and metallic chrome coatings on nickel. The test results confirm that nano CoP alloys provide initially a better corrosion resistance than metallic chrome coatings with regard to the nickel release. The release of nickel with a nano CoP layer was 1 mg/l, compared to 4–46 mg/l (functional chrome plating). However, significant amounts of cobalt were released (180 mg/l) indicating that the nano CoP coating is not stable. When the layer decomposes, the coating system is not resistant to corrosion and the protective layer does not fulfil its task. In contradiction to the results presented in the general section, the corrosion resistance is not sufficient based on the test results presented by this sector. Hardness is a key functionality and the sector that produces metal precision parts requires at least 1,100 HV. As-deposited, nano CoP coatings achieve 600-700 HV and therefore do not fulfil the hardness criteria. Heat treatment to improve hardness cannot be applied on heat sensitive substrates such as electroformed nickel parts. According to Table 11, the nano CoP coating can reach up to 50 µm in layer thickness. This thickness is sufficient to cover the required 15-20 µm for this sector. Nano Co-P coatings perform insufficiently on the key functionalities hardness and corrosion resistance. Therefore, this alternative does not represent a technically equivalent replacement for chromium trioxide.
Assessment overview for nano CoP-coating (Metal precision parts)
Industry sector Corrosion resistance Hardness Layer thickness
Metal precision parts
Use number: 2 89 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Sector specific assessment: Manufacture of printing equipment Hardness is a crucial functionality of this sector and must range between 1,000-1,400 HV. A nano CoP coating achieves 600-700 HV in an as-deposited state and does not achieve the required benchmark. The heat treatment temperature for aluminium alloys has to be < 150°C and for high strength steels < 250°C. Therefore heat treatment of these substrate materials conducted at temperatures about 340–400°C for several hours is not suitable to achieve a better hardness performance. Wear resistance is also insufficient for the use in the manufacture of printing equipment and cannot withstand the inherent process conditions as ink contains hard particles, the doctor blade is hard and the paper itself is hard and abrasive. Anti-adhesion is another key performance parameter. The manufacture of printing equipment sector stated in the consultation that the anti-stick properties of nano CoP layers applied onto the mandrel are not sufficient to be used in electroforming process. Since the nickel would stick to the nano CoP layer of the mandrel and cannot be removed, the requirements cannot be fulfilled and the alternative is not suitable to replace the metallic chrome coating on the mandrel.
Assessment overview for nano CoP-coating (Manufacture of printing equipment)
Industry sector Anti-adhesion Hardness Wear resistance
Manufacture of printing
equipment
7.5.3 Economic feasibility Against the background of significant technical failure of nano Co-P alloy coating, no quantitative analysis of economic feasibility was conducted. However, in one publication it was stated that compared to functional chrome plating, the energy consumption can be reduced while throughput is increased (due to high deposition rate up to 0.2 mm/h for nano Co-P and up to 0.04 mm/h for functional chrome plating). This results in higher plating efficiency (about 90 % for nano Co-P compared to less than 35 % for functional chrome plating). The relative process costs of nano Co-P plating with 1.3 are reported to be slightly higher compared to 1.0 with functional chrome plating (McCrea 2003).
7.5.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 2.1.5), cobalt dichloride, as worst case scenario, is classified as Acute Tox. 4, Skin Sens. 1, Resp. Sens. 1, Muta. 2, Carc. 1B, Repr. 1B, Aquatic Acute 1, Aquatic Chronic 1. While this substance is currently not included in the candidate list, other cobalt compounds are on the REACH candidate list for substances of very high concern. As such, transition from chromium trioxide – which is a non-threshold carcinogen – to one of these substances would not constitute a shift to significantly less hazardous substances.
90 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
7.5.5 Availability Nano Co-P alloy coating is in early laboratory stages at low TRL. The equipment and bath chemicals are commercially available. However it is no drop-in replacement for existing functional chrome plating equipment, and not a mature technology. Based on the technical deficiencies it is questionable whether nano Co-P coatings will be part of future investigation in the described sectors. At least 15 years would be needed to develop nano Co-P as a general metallic chrome coating alternative, if ever.
7.5.6 Conclusion on suitability and availability for alternative nanocrystalline cobalt phosphorus alloy coating The nano Co-P plating was assessed by the industry sectors with regard to the latest R&D results and their key parameters.
Hardness is a very important performance parameter for the evaluation of metallic chrome coating alternatives. Nanocrystalline Co-P coatings cannot fulfil the required specifications of any industry sector. Heat treatment might be an option, but not when heat sensitive substrates (e.g. aluminium, high strength steel) are used, because heat can lead to microstructural changes and degradation of the layer quality. The alternative coating also fails in anti-stick behaviour and the requirement on uniformity of the surface. The electrodeposition of nano Co-P coatings does not produce technically equivalent and satisfying coatings compared to functional chrome plating and is therefore no suitable alternative. In the steel sector, Ni-W is also not a feasible alternative to metallic chrome coatings as major technical functionalities including adhesion are not equivalent to chromium trioxide. In summary, nano Co-P coatings are technically not feasible nor is the implementation of a Co- containing replacement technology desirable from a health perspective. Therefore, this process does not represent a suitable alternative to replace functional chrome plating.
7.6 ALTERNATIVE 6: High velocity thermal process
7.6.1 Substance ID and properties High velocity thermal processes include HVOF and the Detonation gun (D-gun) and Super D-gun processes. In the following process descriptions both HVOF and D-gun processes are described. As tribological performance depends on the coating and not on the application method, the two processes are assessed together. During the high velocity thermal spray process, coating powder is injected into a supersonic flame that accelerates the powder particles to high velocity (usually sub-sonic). The heat of the flame melts these high-speed powder particles, which hit the substrate and flatten in pancake-shaped “splats”, see Figure 25. As they overlay each other, these splats form a very coherent and low porosity coating (Legg K., 2003a).
Use number: 2 91 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Figure 25: Cross section of a typical thermal spray coating. Data source: TURI, 2006.
There are two basic forms of high velocity thermal spray processes: 1) Continuous flame HVOF: This process uses a gun with an internal combustion chamber where combustion fuels mixed with oxygen are fired continuously. Examples for combustion fuels include propylene, acetylene, propane, hydrogen and kerosene. These gases mixed with oxygen produce gas temperatures greater than 2,700°C when burned. The coating powder is injected axially into the flame where it heats and softens on its way to the substrate surface. The distance between the gun and the substrate has to be sufficient (15-30 cm) in order to heat the particles adequately before they hit the substrate (Legg K., 2003a). HVOF coatings offer the highest quality within thermal spray processes because of the high speed of the particles. High Velocity Air Fuel (HVAF) is an HVOF-related process that uses air as oxygen source, avoiding the need for compressed bottle oxygen.
Figure 26: HVOF process. Data source: http://spray-molybdenum-wire.com/pic/spraying-molybdenum-wire/HVOF- spray-molybdenum-wire.jpg, as of 07.05.2014.
2) D-gun and Super D-gun: Detonation D-gun is a proprietary process. Unlike the typical HVOF process, this process type does not operate on a continuous, steady-state basis. In the detonation guns a fuel-oxygen mixture is burned in distinct detonations (similar to a machine gun with blank cartridges). The coating powder and the hot gas are then projected onto the substrate at high velocity (Legg & Sauer, 2000). In general, high velocity thermal spray processes offer a choice of possible starting powders, gases, types of equipment, coating materials and deposition conditions and are therefore very versatile concerning their application area.
92 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Possible powder materials for high velocity processes include but are not limited to: - pure metals (Cu, Al, Zn, Ni, Mo, W, …), - alloys (NiCr, NiAl, NiMoAl, NiCrSiB, CoCrMo, Inconel, Stellite, …), - carbides (WC-Co, WC-CoCr, WC, Co-Cr, Cr3C2-NiCr, …).
Most oxides and ceramics cannot be sprayed with HVOF because their melting points are too high, but it is possible to spray most metals, alloys and some carbides. However, among possible substances used in high velocity thermal processes, tungsten carbide alloys like WC-Co, WC-CoCr and chromium carbide-nickel chromium (Cr3C2-NiCr), as well as CoCr-Mo showed promising results during R&D and/or are already applied for niche applications. Therefore the technical feasibility assessment presented in chapter 7.6.2 focuses on these substances. General information of the exemplary chosen tungsten carbide cobalt coating and the risk to human health and the environment is provided in Appendix 2.1.6. Note that the chromium in these materials is not hexavalent, but metallic. In order to prevent heat build-up in any area either the gun or the substrate are moved over the respective counterpart. Additionally these thermal processes are equipped with cooling air-jets placed around the part to be coated. Cooling systems make it possible to coat heat sensitive substrates (e.g. aluminium and high strength steel). The process generally takes place in a booth that provides an acoustic and dust enclosure to control the process noise that can reach noise levels of 130-140 dB (decibel). Figure 27 shows the coating process of a landing gear cylinder that is conducted in a booth and air cooling jets (pipes in the upper right corner) to maintain a low surface temperature.
Figure 27: HVOF thermal spraying onto a landing gear cylinder. Data source: Legg K., 2001.
Use number: 2 93 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
7.6.2 Technical feasibility General assessment Corrosion resistance The corrosion resistance of WC-Co (83 %/17 %) and a commercially available Co-Mo-Cr alloy coating deposited by HVOF on 4043 steel specimens, were tested using ASTM B117 salt spray tests. After 1,000 h of testing, the appearance was ranked according to ASTM B537. The scale ranges from 0 (complete corrosion of surface) to 10 (pristine surface). Figure 28 shows the results for the WC-Co and Co-Mo-Cr alloy coating in comparison with metallic chrome coating.
Figure 28: Appearance rankings for various coatings on 4340 steel after 1,000h of ASTM B117 salt spray test. Data source: Sartwell, 1999. In this literature study, the rating for the HVOF coatings was found to be superior compared to chromium which is contradictory to other test results produced under laboratory conditions. However, after removal of blistered areas on the HVOF coatings, this revealed a similar overall extent of corrosion as on the metallic chrome coating. Therefore the authors concluded that both HVOF coatings and chromium coatings achieved approximately equal resistance to corrosion (Sartwell, 1999). However, the industrial sectors’ experience is contradictory: HVOF using WC-Co and WC- CoCr is found to perform less well in corrosion resistance tests. Surface finish Some HVOF coatings (e.g. WC-Co) result in rough surfaces that may require, depending on the application, post treatment. This process step can be very expensive, because finish treatment of e.g. WC-Co requires costly diamond tools, whereas metallic chrome coatings can be treated with less expensive carbide tools. Geometry of coated parts HVOF as a line-of-sight process is limited in terms of coating complex shapes and inner surfaces. The problem is that a minimum gun-to-substrate distance (stand-off) is required to achieve softening and acceleration to high velocity of the powder. While the gun size could be significantly reduced, it
94 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES is the stand-off that limits the application of HVOF on narrow parts and inner surfaces with an opening diameter less than 0.3 m (Legg K., 2003a). Thickness The coating process is mostly conducted by a robot or other articulating arm equipped with the HVOF gun. The HVOF process is very fast with deposition rates of ca. 50 µm/min. The deposition of a 100 µm thick coating onto a cylinder (diameter 0.1 m, length 0.5 m) therefore generally takes less than 30 minutes. The coating can be sprayed up to 500 µm thick directly to the designated location. This is why HVOF is suitable for repair and overhaul work on worn components (Legg K., 2012). Process procedure Functional chrome plating processes are mostly automated and are well known since they have been applied for decades. HVOF coatings are a completely different technology and require workers with adequate new skills who follow with constant attention and careful control the proper process definitions in order to achieve a coating of equal quality. In addition, the process has to take place in booths due to the noise and dust formation and requires complex and cost intensive peripheral equipment as well as additional space requirements on the premises. Surface Heating A substrate surface being coated via HVOF is exposed to temperature rise due to the flame and particle temperature. This exposure to temperature can result in degradation of the substrate properties. In order to prevent overheating, cooling air has to be applied during the coating process. In spite of a cooling system, HVOF is not suitable for heat sensitive substrates because overheating cannot be completely ruled out. The performance of the HVOF process varies for the different coating materials. The following table provides test results for a coating using WC-Co:
Table 13: Typical materials properties of HVOF coating using WC-Co. Data source: Legg K., 2003a.
Property HVOF spraying Notes
hardness 1,100-1,400 HV maximum thickness up to 500 µm usually limited by cost to 500 µm (0.5 mm) equal or better to functional chrome smooth surface finish important, (grinding wear resistance plating after coating) equal or better to functional chrome depends on thickness, coating material, corrosion resistance plating grinding
Sector specific assessment: aerospace The high velocity thermal spray process HVOF is an already qualified process that is used by some aerospace companies on specific airplane parts such as on landing gear, hydraulics and flap tracks, especially with WC-Co-Cr coatings (Legg K., 2003b). HVOF coatings were tested by aerospace companies with regard to hardness, wear resistance, corrosion resistance, coefficient of friction, layer thickness and endurance. These properties are key functionalities that a metallic chrome coating provides and therefore has to be achieved by the alternative as well. Concerning wear resistance and endurance, the performance depends on load, counterpart, velocity and lubrication. In some situations the alternative is superior to metallic chrome coatings, but in general, no alternative coating using this technology is equivalent in all situations.
Use number: 2 95 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
In terms of hardness, coatings based on WC-Co have a hardness equivalent to metallic chrome coatings. Other HVOF coatings such as Mo and CoCrMo are softer (> 400HV).
The HVOF process is a line-of sight process that requires a certain gun-to-substrate distance which limits the part’s geometry (coating complex shapes, inner surfaces, small parts). The geometry influences directly and strongly the deposition velocity, which decreases with increasing complexity. These limitations indicate that HVOF is only suitable for a specific range of rather large components with simple geometry. During the consultation phase it was stated that WC- and Mo-based layers have thicknesses within a range of 100–200 µm. These values fulfil the minimum requirements for the aerospace sector that is around 100 µm. Most of the coatings do not fulfil the minimum corrosion resistance requirements although there are exceptions. For example, CoCrMo, WCCoCr and Mo layers were tested for corrosion resistance. The CoCrMo-layer achieved 750 hours in NSST which just fulfils the minimum requirements of 750 hours. The company conducting the test confirms that with CoCrMo-coatings good corrosion resistance is given to substrate with an undercoat. Coatings such as WCCoCr and Mo against alloyed steel (35NCD16) performed worse in NSST and only reached 117 hours which is insufficient compared to 860 hours for metallic chrome coatings. Mo coatings are in general considered as unsuitable for corrodible substrates. In summary, the HVOF process is successfully used for specific applications such as landing gear with WC-CoCr coatings. However, HVOF is not a like-for-like replacement for functional chrome plating. HVOF as an alternative for functional chrome plating using a combined potassium dichromate / chromium trioxide plating solution shows the same technical deficiencies as for functional chrome plating based on chromium trioxide. Functional chrome plating with potassium dichromate / chromium trioxide plating solution is a rarely used special application in the aerospace sector for the purpose of thin hard coatings with good corrosion resistance and high abrasion resistance. HVOF is not a like-for like replacement for this specific niche application.
Assessment overview for HVOF (Aerospace)
Industry Corrosion Hardness Geometry Wear resistance Layer thickness sector resistance depends on the depends on the depends on the coating, loads, Aerospace coating coating wear mechanisms and counterparts
Sector specific assessment: automotive and general engineering
Using HVOF process with carbides (e.g. WC-Co, Cr3C2-NiCr) as coating material results in very hard and wear-resistant coatings. Whilst metallic chrome coating achieves between 800 - 1,200 HV, the lower limit for HVOF coatings starts at 1,000 HV and can reach 1,500 HV. These values indicate the minimum requirements to be met concerning hardness. For the automotive sector, the brittleness of the HVOF coatings is a major problem. In the consultation it was stated that during assembly of coated components with layers thicker than 50 µm, the coating tends to show cracks and to be brittle when e.g. screws are fixed on a HVOF-coated cylinder.
96 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
It was also stated that there is a risk for the coating to be scuffed due to a decreased adhesive strength to the substrate.
The HVOF process is a line-of sight process that requires a certain gun-to-substrate distance and is limited in terms of the geometry of the parts which are coated (coating complex shapes, inner surfaces, small parts). As stated already for the aerospace sector, HVOF is only suitable for a specific range of rather large components with simple geometry. In open literature, HVOF process is described as very fast with deposition rates of ca. 50 µm/min. In contrast to that, the automotive industry stated in the consultation that HVOF processes are only suitable for low volume production and have a low deposition rate. After the coating process which is rather quick, the surface must be ground down in a post-treatment working step. The latter is very time consuming because of the extreme hardness of the HVOF coated surfaces. The total HVOF process time is longer than for functional chrome plating. Therefore it is not applicable for all metallic chrome coating uses in automotive production, such as serial production. Functional chrome plating is conducted within mild temperatures of approx. 50-60°C. The process temperature of an HVOF process however, exceeds this range and may lead to a degradation of substrate properties which excludes heat sensitive materials as possible substrates.
Assessment overview for HVOF (Automotive and General engineering)
Industry sector Brittleness Geometry Process temperature Hardness
Automotive and for carbide coatings General engineering
Sector specific assessment: steel Heat during the coating process introduces stress in the work rolls and that can lead to roll spalling. Spalling of rolls is very dangerous because razor sharp pieces of the roll can explode off the roll, behaving like shrapnel and are therefore potentially lethal. Surfaces based on HVOF tend to be brittle and cannot be reproduced as required. Furthermore, they require post coating finishing. HVOF is therefore not a technically feasible alternative to functional chrome plating with chromium trioxide.
Assessment overview for HVOF (Steel)
Industry sector Brittleness Reproduction of surface
Steel industry
Sector specific assessment: metal precision parts The process temperature is extremely high and exceeds the threshold for electroformed nickel parts which become too soft and weak. Obtaining the proper/uniform coating via spray coating of specific products (sieves with µm holes) is problematic as the coated surface is rather coarse. This alternative is not feasible for products requiring a smooth surface, such as centrifugal and filtration screens. Therefore, this alternative is not suitable for the metal precision parts sector.
Use number: 2 97 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Assessment overview for HVOF (Metal precision parts)
Industry sector Process temperature Surface conditions
Metal precision parts
Sector specific assessment: manufacture of printing equipment All surfaces based on spraying produce heterogeneous and rough surfaces. The porosity is too great for the application of printing cylinders; the pores may be larger than the diameter of a printing cell. In addition, the thickness of the coating is not constant and varies, which impairs the engraving process. In summary, coatings produced with a high velocity thermal process fail fundamental technical requirements for the application in printing equipment and are not a feasible alternative.
Assessment overview for HVOF(Manufacture of printing equipment)
Industry sector Homogenous surface / Porosity Constant thickness
Manufacture of printing
equipment
7.6.3 Economic feasibility Against the background of significant technical failure of HVOF, no quantitative analysis of economic feasibility was conducted. However, the cost for HVOF depends on numerous different factors and these are presented in a qualitative to semi-quantitative way below. The technology for high velocity processes and functional chrome plating differ fundamentally in the equipment and peripherals. The implementation of high velocity processes requires complex machines and infrastructure equipment. The installation costs for completely new plant and machine lines comprise 75,000-200,000 € for equipment, 75,000 € for the robot and 200,000 € for the room, that is in total 350,000 to 475,000 € (Legg K., 2003a). Table 14 shows the comparison of process costs for HVOF compared to functional chrome plating, with data from HVOF equipment vendors and business information from a functional chrome plating company. The total production costs for the coating are based on several items such as material, energy, waste, repair, etc. to achieve the same production output.
Table 14: Comparison of production costs of the coating: HVOF & functional chrome plating.
Percentage of total direct production cost (functional chrome plating=100%)
Functional HVOF Factor chrome plating Coating material 368 20 18.4 Labour 35 6 5.8 energy 51 39 1.3 Other costs 66 12 5.5 Depreciation 23 23 1 Production Cost total 543 100 5.4
98 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
The coating material costs are by far the biggest driver for increasing costs. In total, the costs to produce 1 m² of coated material are 5.4 times more expensive using HVOF instead of functional chrome plating. The general engineering sector states that although production costs of HVOF plating are several times higher than for functional chrome plating using chromium trioxide, HVOF may be economically feasible for specific niche applications, in which high wear resistance could cause a sufficient decrease of maintenance cost. The aerospace industry expects that the production costs for HVOF are significantly higher which is due to higher equipment costs increased by set-up costs for each part, and higher costs for post- treatment (grinding and polishing). Divergence of costs are expected to be even higher for complex parts.
7.6.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances (see Appendix 2.1.6) and products reported during the consultation were reviewed for comparison of the hazard profile. As mentioned above, various different powder materials are used for high velocity processes, for which some substances are confidential business information. As an example, the hazard profile from an often-used coating material is illustrated. According to suppliers’ SDS, the following hazard statements are given for WC-12Co: Skin Irrit. 2, Eye Irrit. 2, STOT SE 3, Carc. 2. As such, transition from chromium trioxide – which is a non-threshold carcinogen – to WC-12Co would constitute a shift to significantly less hazardous substances. However, some cobalt compounds are on the REACH candidate list for substances of very high concern so an assessment on the hazardous profile of these substances would have to be performed on a case by case basis.
7.6.5 Availability Up to the end of the last century, no full-production HVOF systems have been in operation at aircraft manufacturers, commercial aircraft maintenance activities, or DoD aircraft depots that are being used to deposit coatings on a continuous basis to components for which metallic chrome coatings have been used in the past. The only exception are some HVOF systems in operation at DoD aircraft depots that are being used for selected functional chrome plating replacement (Sartwell, 1999). In general, HVOF are fully developed commercial processes. Equipment and powders can be obtained commercially from a number of vendors. However, as per all the functional chrome plating replacements, there is less availability of aerospace qualified WCCo/WCCoCr HVOF than for functional chrome plating. In contrast to HVOF, the D-gun process is a proprietary process which means that the equipment is not commercially available. HVOF is therefore currently not considered a like-for-like alternative to functional chrome plating. To develop a general metallic chrome coating alternative, a minimum of 10 – 15 years would be needed.
7.6.6 Conclusion on suitability and availability for alternative HVOF High velocity thermal spray processes were assessed by the industry sectors with regard to the latest R&D results and their key parameters.
Use number: 2 99 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
These processes do not perform technically equivalent to chromium trioxide based products and are therefore not a general alternative. Some HVOF coatings are currently used for a limited number of specific applications. The process inherent application of the metal powder via a gun barrel (line of sight process) excludes complex geometries and internal parts from being HVOF coated. Apart from the geometrical restrictions, the alternative shows technical failure in very important sector specific performance parameters. The aerospace industry noticed failure in wear resistance and friction behaviour, whereas the automotive and general engineering sector criticized brittleness, insufficient layer thickness and excessive process temperature. Manufacturers of printing equipment report inhomogeneous and rough surfaces with a far too great porosity as well as inconstant layer thickness, which makes printing and engraving impossible. The economic assessment of this alternative showed that production costs of HVOF are at least 5 times higher compared to functional chrome plating. The HVOF process is commercially available and already qualified for specific aerospace applications. Although coatings applied by HVOF are already implemented for niche applications, HVOF is not a general like-for-like replacement for a large number of functional chrome plating applications because it cannot fulfil the properties and does not have the flexibility (complex geometries) guaranteed by metallic chrome coatings. In conclusion, these systems are technically not equivalent to chromium trioxide based products, have strong economic disadvantages and are therefore not a general alternative.
7.7 ALTERNATIVE 7: Trivalent chrome plating
7.7.1 Substance ID and properties / Process description General information The trivalent chrome (Cr(III)) plating alternative relates to an electrodeposition process for producing a metallic chrome coating from a trivalent chromium electrolyte. The chromium in the electrolyte derives from chromium trichloride. A typical trivalent chrome plating bath composition is shown in Table 15.
Table 15: Cr(III) based bath chemistry.
CrCl3.6H2O 125 g/l
KCr(SO4)2.12H2O 25 g/l
NH4NH2SO3 178 g/l
NH4Cl 80 g/l
H3BO3 30 g/l
HCOOH 30 ml/l
The Cr(III) plating process is in general based on a similar electroplating technology as the process with chromium trioxide. However, there are important differences regarding the anodes used and additional pulse-reverse equipment, such as the rectifier, which is significantly more expensive than the equipment needed for functional chrome plating from chromium trioxide. Further differences are
100 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES in the bath chemistry and some operating parameters such as pulse plating for Cr(III) instead of traditional direct current plating for chromium trioxide (TURI, 2012). The pulse changing Cr(III) process has a maximum deposition rate of about 80 µm/h for thin layers which is potentially higher than typical functional chrome plating rate of 50 µm/h. The temperature of a Cr(III) based electroplating bath is between 20 and 60°C whereas typical chromium trioxide functional chrome plating occurs between 50 and 60°C. The pH value of the Cr(III) based plating bath has to be between 2.1 and 2.3 to ensure reliable process conditions compared to the wider range of pH 1 to 3 for chromium trioxide. Examples of substrates that can be coated include e.g. iron and its alloys (such as engineering steels, carbon steels, stainless steels, aircraft steels), aluminium and its alloys, copper and its alloys, molybdenum and its alloys and nickel and its alloys. A non-exhaustive overview of general information of substances used within trivalent chromium plating, as well as the overall risk to human health and the environment is provided in Appendix 2.1.7.
7.7.2 Technical feasibility General assessment The major advantage of Cr(III) plating is that it is closest to a “drop-in” replacement – compared to all other alternatives described in this dossier – for current chromium trioxide process technology as far as process type is concerned. Although the research to generate chromium layers out of Cr(III) compounds in aqueous solutions has been ongoing for more than 40 years, it was only successful in some applications for functional chrome plating with decorative character. Results on R&D for Cr(III) metallic chrome coatings are mainly available from laboratory scale research. Almost no results are available on industrial application of Cr(III) based chrome plating applications, showing that Cr(III) as alternative for chromium trioxide is still under laboratory research. In addition to the research conducted by the industrial sectors of aerospace, automotive, general engineering, steel, metal precision parts, and manufacture of printing equipment, large plating technology suppliers are currently investing in research to try to improve the Cr(III) plating process and make it industrially available. Process conditions Cr(III) baths are more sensitive to metallic impurities and the acidity of the bath than chromium trioxide baths. Small deviations in these process conditions can strongly influence the deposition success and the layer quality (Legg K., 2003a). The process window for Cr(III) plating lies in a very narrow pH range from 2.1 to 2.3 (functional chrome plating: pH 1 to 3), which is difficult to maintain. Consequently, establishing a reliable process for Cr(III) coatings of reproducible quality (thickness, hardness, etc.) is challenging and the plating process requires careful handling, especially due to the additional issue of saturation during the electrochemical deposition. Since bath temperatures range between 20 and 60°C, the process is suitable, like chromium trioxide plating, for heat sensitive substrates such as aluminium and high strength steel alloys. The current efficiency for this process is about 35 % compared to 25 % which can be reached by functional chrome plating. However, with increasing layer thickness, the deposition decreases. The Cr(III) process takes approximately three times longer than the conventional chromium trioxide based process to achieve the desired thickness (TURI, 2012).
Use number: 2 101 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Corrosion resistance Corrosion resistance is a key functionality of metallic chrome coatings based on chromium trioxide. Therefore, any alternative must have similar corrosion resistance functionalities in order to be a suitable alternative. Currently, the Cr(III) coating will not provide corrosion resistance due to its tendency to form macro-cracks. Wear resistance Publicly available information from the ECOCHROM project stated that material loss for trivalent plated rapid steel is less than for chromium trioxide plated steel. In a Faville wear test a loss of 72 mg/h was measured for standard chromium trioxide metallic chrome coatings compared to about 30 mg/h for Cr(III) (Négré, 2002). The results were measured for a complexed and a reduced Cr(III) solution in laboratory scale. Hardness Hardness is a key functionality. In general, the maximal achievable hardness of Cr(III) coatings is between 700 and 850 HV on a 500 µm thick coating (Legg K., 2003a) compared to the range for chromium trioxide functional chrome coatings between 700 and 1,400 HV. Microstructure The metallic chromium plated from trivalent solutions has a different crystal structure compared to the metallic chromium derived from chromium trioxide solutions (pfonline, 2013). The cross-section of a 77 µm thick Cr(III) metallic chromium coating shows in comparison to a 50 µm thick chromium trioxide metallic chrome coating a similarly dense layer constitution with micro-cracks (Figure 29).
Figure 29: Microstructure of Cr(III) chrome (77 µm) under optical microscope (left) compared to chromium trioxide chrome under scanning electron microscope (right) (50 µm). Data source: pfonline, 2013. Figure 30 shows microstructures of a Cr(III) chrome layer coated on a 0.2 m long pipe, with respect to the position in the pipe (top, middle and bottom). The microstructure of the top corresponds to the left microstructure in Figure 29 and is intact. The microstructure in the middle of the pipe (Figure 30b) shows non-uniform deposits on the top of the coating, which get worse towards the end of the pipe and with increasing layer thickness. The microstructure at the bottom (Figure 30c) shows large cracks down to the substrate of the coating.
Figure 30: Cross-section image from Cr(III) coatings in relation to layer thickness and to different spots located at the coated part. Daat source: pfonline, 2013.
102 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
The Cr(III) metallic chromium coating quality depends on the applied layer thickness and is only similar to chromium trioxide based coatings when applied up to ca. 80 µm. The degradations are stated to derive from electrolyte turbulence. In the above mentioned document it was claimed that this can be solved by changes in process technique. This has to be proven, especially as macro- cracking is visible on the outside diameters of the pipe as well. The assumption made in the study that this can be solved contradict the industrial experience: the microstructure of thick Cr(III) metallic chromium coatings in the layer thickness ranges presented above have unacceptable macro-cracks which impair the layer quality and other key functionalities; as a consequence, the requirements of the chromium trioxide coating are not met. Although Cr(III) has been investigated for many years as an alternative to chromium trioxide for functional chrome plating, the process technology is still in the developing phase at lab scale and is far from being mature. Layer thickness A large range for the key parameter layer thickness of 0.1 to 500 µm is stated in the literature. (NEWMOA 2003, Legg K., 2003a). The maximum literature values of up to 500 µm are not supported by evidence and experimental details. The Cr(III) research and development has been ongoing for more than 40 years, but results are available at laboratory scale only. It proved to be extremely difficult to create layers of Cr(III) thicker than a few micrometres which fulfil the requirements defined by the OEMs. In the consultation a general maximum of 100 µm were stated for Cr(III) hard chrome. Consistent and unchanged layer thickness is a prerequisite for a fully functional coating layer. Thin Cr(III) layers (< 5 µm) tend to perform worse than chromium trioxide layers in hardness, corrosion resistance and adhesion. Some functional chrome plating applications with chromium trioxide require layer thickness > 500 µm. Even if Cr(III) layers up to 500 µm seem to be technically possible at laboratory scale, it is obvious that the coating quality decreases with increasing thickness. This is illustrated in Figure 30. A high quality, which means a dense microstructure with micro-cracks and no macro-cracks, is important to fulfil the minimum requirements on e.g. wear and corrosion resistance. It was stated during the consultation phase that process handling is difficult, which directly influences saturation during the electrodeposition and consequently the microstructure of the deposited layer. This can affect other key functionalities such as hardness, corrosion resistance and wear resistance. Concluding from all the facts presented above, the required layer thickness cannot be obtained while simultaneously maintaining the layer quality using Cr(III). Sector specific assessment: aerospace The aerospace sector is still at an early research and development stage concerning the technical readiness of the Cr(III) based plating process. Currently, the Cr(III) coating will not provide corrosion resistance due to its tendency to form macro-cracks. There are no test results available that trivalent chromium meets the minimum requirements for wear resistance in the aerospace sector. Trivalent hard chromium coatings achieve a maximal hardness of between 700 and 850 HV, which fulfils the minimum requirements of the aerospace sector between 700 and 900 HV. Hardness of 700 to 1,000 HV (similar to chromium trioxide functional chrome coatings) was achieved in a test conducted by an aerospace company – however, hardness was the only parameter tested and no information is available on the results for further key minimum requirements of chromium trioxide functionalities.
Use number: 2 103 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Aeronautic applications require a minimal layer thickness of 100 µm. Cr(III) coatings with a layer thickness of 100 µm have been achieved. However, the coating quality was not sufficient and other key requirements were not met. As stated above, a constant layer thickness with adequate dense microstructure and micro cracks on the surface but no macro cracks which meets these requirements cannot be produced to date with Cr(III). Investigations are ongoing at laboratory scale. Currently, the process exhibits low maturity for aeronautic applications. Testing of thick (100 µm) Cr(III) functional chrome plating from a number of sources by one aerospace manufacturer has shown a consistent problem – unacceptable macro-cracking irrespective of the chemistry or means of application. It is their opinion that the process is not yet mature but in view of its possibility as a close 1:1 replacement (and the potential cost saving avoiding major redesign) is worth monitoring. There is a possibility of major investment by technology suppliers which may help to improve the TRL level but more time is needed before it becomes mature. The microstructure of Cr(III) coatings shows unacceptable macro-cracks down to the substrate (Faraday, research project). This failure can significantly impair important key coating functionalities such as corrosion and wear resistance that have to be fulfilled by a chromium trioxide alternative. In general, the requirements of the aerospace sector are not fulfilled with the Cr(III) based solutions. To date, Cr(III) based electroplating is not yet implementable in the aerospace sector. All described results are related to a very early stage of R&D and have not been transferred to technical use yet. Based on the existing experience, research is very time consuming and Cr(III) is far from being a mature alternative.
Assessment overview for Cr(III) based alternative (Aerospace)
Industry Layer thickness Microstructure Process maturity Hardness sector (constant quality)
Aerospace
Sector specific assessment: automotive and general engineering In general the trivalent chromium technology offers the best chance of a possible 1:1 replacement for chromium trioxide, but the automotive sector is still at research and development stage concerning the technical readiness of the Cr(III) based metallic chrome plating alternative. To date, saturation during the electrochemical deposition turned out to be an issue. Thus, the achievable layer thickness of up to max. 30 µm with adequate microstructure (thicker layer show macro-cracks) of the coating and its surface is not sufficient for the majority of chromium trioxide plated applications within the automotive sector. The obtained hardness was 700-800 HV which does not fulfil the minimal requirements with 1,000-1,200 HV of the automotive and general engineering sector. With regard to the endurance, the Cr(III) coating showed poor performance in scratch resistance. For thicker layers the microstructure of Cr(III) coatings shows macro-cracks down to the substrate which are also unacceptable to the automotive and general engineering sector. This failure can significantly impair important key coating functionalities such as corrosion and wear resistance that must be fulfilled by a chromium trioxide alternative. Wear properties of the Cr(III) coating are thus not equal to those of a chromium trioxide metallic chrome coating. Testing on the corrosion resistance as another key functionality is in progress and has not fulfilled the acceptance criteria yet.
104 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
With regard to insufficient performance on the most important key functionalities hardness and wear resistance, Cr(III) derived coatings are technically not an equivalent replacement for chromium trioxide.
Assessment overview for Cr(III) based alternative (Automotive and General engineering)
Wear Layer thickness Industry sector Hardness Endurance Microstructure resistance (constant quality) Automotive and
General engineering
Sector specific assessment: steel industry If steel sheets need to have a specific texture, apart from the key functionalities, roughness is an additional important assessment parameter for this industry sector. The roughness of the metal sheet is a crucial, quality-related product characteristic when manufacturing metal sheets in a cold rolling mill. It directly influences the tribological forming behaviour of the sheets and is a decisive basis for further post-treatment, e.g. painting (refer to http://www.topocrom.com/index_en.php). The roughness of metallic chrome coatings from a Cr(III) plating process is not equivalent to those from a chromium trioxide plating process, resulting in different microstructure. As the microstructure impairs decisively the roughness, the required surface structure of the metal sheet cannot be generated with trivalent chromium. Currently there is no other material than a chromium trioxide metallic chrome coating which combines the features of the layer and texture. Hardness is a further key performance parameter that has to be at least 1,000 HV. Trivalent chromium coatings only achieve 700-850 HV, which does not fulfil the minimum requirement of the steel industry. Furthermore, it was stated during the consultation phase that a Cr(III) derived metallic chrome coating does not meet the requirements of the other important performance parameters such as corrosion resistance, layer thickness and adhesive strength to substrate, mainly due to microstructural failure. Therefore trivalent chromium coatings are technically not a suitable chromium trioxide replacement for the steel sector.
Assessment overview for Cr(III) based alternative (Steel)
Roughness/ Adhesive strength Layer thickness Corrosion Industry sector Hardness microstructure to substrate (constant quality) resistance
Steel
Sector specific assessment: metal precision parts For the production of metal precision parts, good results for corrosion resistance were obtained when testing trivalent chrome plating on nickel substrates. In acidic immersion test (2 % sodium citrate / 3.5 % citric acid, pH 3.5), the amount of released nickel from the underlayer (substrate) was measured for Cr(III) coatings compared to metallic chrome coatings using chromium trioxide. The trivalent chromium layer performed well with a nickel release of 25-50 mg Ni/l compared to 4-46 mg Ni/l for chromium trioxide. However, the process optimization was stopped for several reasons with insufficient microdistribution (microstructure) being an important one. Internal stress is too high leading to
Use number: 2 105 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES cracks especially at prone areas such as corners. These cracks are weak spots regarding corrosion for the underlaying substrates. The process window is narrow compared to chromium trioxide and cannot be sufficiently maintained and controlled. This affects most of the process parameters including the deposition velocity. Although the desired thickness of the layer of 15 to 20 µm can generally be achieved, the consistency of the layer thickness fails. Fluctuations both over time, and over the surface area, are very large and do not fulfil thickness variation requirements. Cr(III)-based electroplated layers also failed one of the most critical parameter: hardness. The maximum hardness of 850 HV is significantly below the required minimum threshold of 1,100 HV to withstand the abrasive work environment of the plated components. Since for the most important performance parameters minimal requirements are not fulfilled, particularly a lack of throwing power and instable process conditions, the alternative is technically not feasible as chromium trioxide replacement.
Assessment overview for Cr(III) based alternative (Metal precision parts)
Corrosion Layer thickness Industry sector Microstructure Hardness resistance (constant quality)
Metal precision part
Sector specific assessment: manufacture of printing equipment Measurements at laboratory scale showed that a thick layer up to 20 µm of trivalent chromium can be formed. The trivalent chromium layer was also tested on wear resistance, hardness, ability to grinding and anti-adhesion and performed equal compared to chromium trioxide. According to the sector, it is extremely difficult to achieve stable process conditions which are also linked with the process window of the Cr(III) bath chemistry. This process window is very narrow with ca. 5 % of the chromium trioxide based chemistry and also includes the pH value that has to be within the limits of 2.1 to 2.3, compared to the wider range of pH 1-3 with chromium trioxide. Other critical parameters are current density, temperature, flow and the concentration of formic acid, which probably need to be monitored continuously and very precisely (in-line measurement may be needed). Some experimental results indicate that the hardness criteria could potentially be met: One company stated that they are able to generate chrome layers with a hardness of ca. 1,000 HV out of Cr(III) compounds in aqueous solution under laboratory conditions. This process uses a graphite/mixed metal oxide anode, instead of a membrane. The disadvantage is that the process is very sensitive to copper impurities. The copper concentration must be Cu < 10 mg/l. In the conventional chromium trioxide based process the copper concentration must be below Cu < 10 g/l. However this process is in a laboratory stage and needs intensive further development and time before it can be applied on an industrial scale.
Experiments with the addition of B4C (boron carbide) have been carried out. The hardness can be increased to 1,150 HV. With additional thermal treatment (400°C for 1 hour), 2,000 HV could be reached. Again, investigations are at early laboratory scale and far from being a mature alternative which can be industrially applied. The manufacturers of printing equipment are concerned about the time consuming thermal treatment and the possible effects on the shape and balance of the cylinders.
106 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Another group (University of Leicester and OCAS NV Zelzate, Belgium) states that they are able to generate chromium layers with a hardness of 600 HV, and in another statement, 750 to 1,200 HV, out of Cr(III) compounds in ionic liquids (deep eutectic solvents). The disadvantage is that elemental chlorine is produced during the process. There also may be problems with the high viscosity of the solution. The conductivity of the solution seems to be low. The chemistry of the process is not known as it is kept confidential by the inventors. Investigations of all experiments mentioned above are in a very early laboratory stage. Although the research to generate chromium layers out of Cr(III) compounds in aqueous solutions is ongoing for more than 40 years, intensive further development and time is needed before these coatings can be applied on an industrial scale. The manufacturers of printing equipment are concerned, whether there are suitable doctor blades available for printable rotogravure cylinders. European Rotogravure Association has doubts that it will be possible to achieve an industrially usable alternative. To date it is technically not feasible to generate the required coating layer on the printing cylinders out of aqueous Cr(III) solutions with conventional methods.
Assessment overview for Cr(III) based alternative (Manufacture of printing equipment)
Stable Wear Layer Anti- Industry sector Hardness Scale up process resistance thickness adhesion conditions Manufacture of printing equipment
7.7.3 Economic feasibility Against the background of significant technical failure of trivalent chromium plating, no quantitative analysis of economic feasibility was conducted. However, the cost for trivalent chromium plating depends on numerous different factors and these are presented in a qualitative to semi-quantitative way below. The electrodeposition of a metallic chrome coating with Cr(III) bath chemistry has not been implemented at a commercial scale yet. Based on laboratory testing, the costs for chemicals are estimated to be approximately equivalent to chromium trioxide plating. The electricity costs are expected to be less, because the trivalent chromium process requires less current density. Accordingly less energy is needed compared to the chromium trioxide based processes. It should be noted that besides the inevitable costs of changing process and validation activity, production costs can be higher due to the need of sophisticated measuring technology in order to stabilize the more sensitive process and the need for ion exchange and filtration systems that are necessary to maintain requisite bath purity. Waste treatment and ventilation were reported to be less than those associated with chromium trioxide plating (TURI, 2006). Taking material and process costs into account, costs for Cr(III) plating might be somewhat higher but are in a similar range as for chromium trioxide functional chrome plating.
7.7.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances reported during the consultation were reviewed for comparison of hazard profile (see Appendix 2.1.7).
Use number: 2 107 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Based on the available information on the substances used within this alternative (see Appendix 2.1.7), Cr(III) chloride would be the worst case with a classification as Skin Irrit. 2, Eye Irrit. 2, Acute Tox. In general, the trivalent electroplating processes are less toxic than chromium trioxide plating due to the oxidation state of the chromium. Cr(III) solutions do not pose serious air emission issues, but still pose the problems of disposal of stripping solutions (depending on the type of stripping solution) and exposure of staff to chrome dust during grinding. In addition, there is a certain risk of Cr(VI) being generated during plating process. This is why appropriate security precaution and process management has to be adopted to prevent the formation of Cr(VI). The bath chemistry typically also comprises a high concentration of boric acid, which is a SVHC substance (toxic for reproduction) included on the candidate list and currently on the 6th recommendation for inclusion in Annex XIV. Despite these facts, the transition from chromium trioxide to trivalent chromium constitutes a shift to less hazardous substances.
7.7.5 Availability The electroplating process based on Cr(III) bath chemistry as an alternative for chromium trioxide functional chrome plating is still in the early development stage. Tests are ongoing but Cr(III) is neither technically ready nor qualified to replace chromium trioxide functional chrome plating applications. Therefore, it is not commercially available and has not gained market acceptance yet. Currently, the process exhibits low maturity for aeronautic applications. The current unacceptable macro cracking of the coating requires further research investigations. TRL for the Cr(III) based alternative remains low at this time and an aerospace company estimates the time needed for the approval and implementation process of this potential 1:1 alternative to be more than 10 years from now if all technical performance criteria can be met (which today is clearly not the case as stated above) (Faraday, research project). Based on the information from the consultation phase, for automotive applications, the time needed to develop the technology was estimated to be up to 10 years if all technical performance criteria can be met – which is not the case today after investigation over many years. The general engineering sector reports that although R&D for Cr(III) has been promoted for more than a decade the R&D development is still ongoing. The process is still in the development stage in the steel sector and the technical assessment on layer performances are exclusively based on tests at laboratory scale. To date, there is no solid information on reproducibility and performance in an industrial scale. Within the printing machine manufacturing sector one company has successfully mastered first tests at laboratory scale with Cr(III) bath chemistry although a series of further experiments needs to be conducted to verify these preliminary results. Testing at a larger research scale is expected to be conducted in the year 2015 (2m scale). If the first 2m scale-up test is successful, further scale-up experiments are required for 4m and 6m respectively. Furthermore, different diameters need to be researched. This again is a time-consuming process which needs many years. Scale-up and introduction of a new process is a complex task, during which many problems will emerge and need to be solved. The extremely narrow process window and new process control of a multitude of parameters are further key challenges. There is no guarantee that this task will be successfully accomplished. Experiments with other metals than Cr(III) did not lead to a result which is usable in industrial rotogravure practice. Based on the current information, the realistic time needed to develop the
108 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES technology for different lengths and diameters is estimated to be 10 to 12 years if all technical performance criteria can be met. In summary, significant further R&D efforts are needed in the different sectors, which will take on average another 10 – 12 years to achieve implementation of the alternative if technical performance criteria can be met, which is not the case today.
7.7.6 Conclusion on suitability and availability for alternative trivalent chrome plating The Cr(III) plating was assessed by the industry sectors with regard to the latest R&D results and their key parameters. The Cr(III) based electroplating systems do not perform as technically equivalent to chromium trioxide based products and are therefore not a general alternative at present. They offer the best chance of a 1:1 replacement which would not require drawing changes and re-qualification of parts (essential for the aerospace sector). The development efforts have shown that the Cr(III) process require more careful control than the chromium trioxide process due to higher process sensitivity towards the presence of impurities. Today the instable process conditions still lead to unreliable reproducibility and unacceptable microstructure with cracks down to the substrate. This is a major issue that impairs the most important key functionalities concerning the Cr(III) layer properties. To date there is no proof that Cr(III) performs equally compared to chromium trioxide on the most important key functionalities hardness, wear and corrosion resistance for the applications of the different industry sectors. Cr(III) based processes are not yet feasible for most industry sectors such as automotive, general engineering, steel and aerospace, wherein functional chrome plating is an essential process. Thus, further R&D is necessary to ensure process conditions and to meet the requirements of the key functionalities first in laboratory scale and then in functional field tests. Major technology suppliers to the electroplating industry also put forward efforts on researching Cr(III) as functional chrome plating alternative to investigate its eventual maturity; however certainly a further decade is required for R&D. To date, trivalent chromium plating is not an available and technical feasible alternative to replace chromium trioxide plating.
7.8 ALTERNATIVE 8: Physical vapour deposition (PVD)
7.8.1 Substance ID and properties PVD (Physical Vapour Deposition) is the general name for a variety of vacuum processes. They all start with the coating material in a solid (or rarely in a liquid) form placed in a vacuum or low pressure plasma environment. The coating material is vaporized and deposited, atom by atom, onto the surface of the substrate in order to build up a thin film. Vaporizing of the coating material may be conducted by one of the following methods: Vacuum evaporation: The coating (source) material is thermally vaporized in a vacuum and follows a “line-of-sight” trajectory to the substrate where it condenses out into a solid film. Vacuum evaporation is used for applications such as mirror coatings and barrier films on flexible packaging (TURI, 2006). Ion assisted deposition / ion plating: This is a combined method as a film is deposited on the substrate while ion plating bombards the depositing film with energetic particles. The energetic particles may be the same material as the depositing film, or it may be a different inert (argon) or reactive (nitrogen)
Use number: 2 109 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES gas. Ion beam assisted deposition describes a process in a vacuum environment where the ions originate from an ion gun (TURI, 2006). Sputtering: This process is a non-thermal vaporization where the surface atoms on the source material are physically ejected from the solid surface by the transfer of momentum from bombarding particles. Typically the particle is a gaseous ion accelerated from low pressure plasma or from an ion gun (TURI, 2006). The conditions for PVD coatings are process specific and dependent on the substrate and applied coating. In general the method is not limited by substrate, in practice however heat sensitive materials such as aluminium alloys and high strength steels are likely to be tempered because of elevated process temperatures (Legg K., 2003a). PVD coating temperatures are typically in the range between 180°C to 450°C, but processes with lower and higher temperatures are also available. The coating time depends on a number of factors, such as coating thickness, spinning time of the part in the vacuum chamber, and the geometry of the part to be coated. In general, the throughput of parts depends on the size of the vacuum chamber and the geometry of the parts. Possible PVD coatings, applied as single or multi-layer, are based e.g. on the following materials: titanium nitride (TiN), titanium-aluminium nitride (TiAlN), zirconium nitride (ZrN), chromium nitride (CrN), chromium carbide (CrC), DLC, silicon carbide (SiC), titanium carbide (TiC), and tungsten carbide (WC). DLC is a special coating and consists of combined bond types of graphite and diamond. DLC forms an amorphous diamond-like carbon layer, with hardness properties > 2,000 HV. PVD processes result in wear resistant, dense and conformal layers that are generally considered to be very smooth and therefore do not need further finishing processes. In some cases the hardness is reported to be much higher than chromium with lower coating thickness. The properties of some PVD coatings are listed in the following Table 16.
Table 16: Material properties of typical PVD coatings. Data source: Legg K., 2003a. TiN, TiAlN, ZrN, CrN, CrC, DLC, SiC, TiC (most materials are nitrides or Materials: carbides of transition metals) Property Value Note Hardness 1,200 – 2,400 HV depends on material and internal stress Max. thickness 5 µm in rare cases up to 15 µm (high internal stress) Corrosion resistance moderate limited by pinholes and consequently sensitive to pitting Wear resistance excellent better than chromium, wear life can be low, especially if layer thickness is low Stress and effect of fatigue strongly thickness- PVD coatings generally have very high compressive stress. dependent Fatigue is usually adversely affected at coating thickness above a few microns. Porosity < 1 % limited by pinholes
In addition to the mode of application, the material used in the process significantly influences the properties of the PVD coating. Therefore, the most promising materials for PVD-coatings are illustrated in the following assessment of the technical feasibility, which are WC-H, TiN and CrN based on R&D. A non-exhaustive overview of general information and the identity of relevant substances used within this alternative and the risk to human health and the environment is provided in Appendix 2.1.8.
110 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
7.8.2 Technical feasibility General assessment TiN and CrN are used as traditional PVD coatings e.g. for aerospace wear applications (as erosion coatings in some aircraft engines), for decorative surfaces, for plumbing fixtures or to create “lifetime coatings” on door hardware (Legg K., 2003a, 2012). The PVD process conditions/ PVD coatings include the following limitations (Legg K., 2003a and information from the consultation): Vacuum/Geometry: The need of a vacuum chamber limits the size and the type of parts that can be coated. PVD, a line of sight process, is not suitable for complex geometries and large parts. Deposition rate: According to information provided in the consultation, PVD processes include low deposition rates compared to functional chrome plating (typically 1-4 microns/hour for PVD coatings, the maximum has been reported to be 10 microns/hour (Lin et al., 2011)). In combination with the high costs of PVD equipment, the coating costs increase with increasing coating thickness. Temperature: The process conditions for PVD require sub-atmospheric pressure and temperatures between 150 and 600°C. Process temperature, especially the upper limit, imposes restriction to the substrate materials that can be coated. Substrates where the max. processing temperatures are below the temperature needed for PVD, such as aluminium alloys (< 150°C) and high strength steel (< 250°C), are not suitable as they would melt away or be distorted. Cleanliness: PVD coatings require an atomically clean surface because they are highly sensitive to contaminants (e.g. water, oils and paints) on the surface to be coated. In fact, inadequate or non- uniform ion bombardment leads to weak and porous coatings and is the most common cause of failure in PVD coating. Therefore, an extremely efficient cleaning and drying method is required for this process. Thickness: In most cases the ion bombardment during coating is responsible for high internal stress. This stress increases with increasing coating thickness and can lead to delamination of the coating. As a consequence, typical PVD layers are about 3–5 µm (in rare cases about 15 µm) thick. As overhaul and repair work require thicknesses of 0.08–0.25 mm, PVD coatings are generally not suitable for rebuilding worn components. Corrosion: PVD nitride coatings are reported to be essentially inert and do not corrode. However, they do not provide as much corrosion resistance as do thicker chromium coatings. Especially once the coating is scratched or damaged, the corrosion protection provided by the layer degrades compared to metallic chrome coatings. Sector specific assessment: aerospace PVD coatings are characterized by uniform layers with higher hardness compared to chromium trioxide based coatings. The hardness of PVD coatings range from 1,200-2,400 HV, depending on the coating material. This performance covers the minimum requirement of 700-900 HV. Another critical parameter is the friction behaviour. Functional chrome plated surfaces achieve a stable coefficient of friction less than 0.2. Compared to the value that is achieved by metallic chrome coating, tungsten carbide with amorphous carbon seems to achieve the requirement, whilst the coefficient of friction of titanium nitride is too high. The wear resistance is one of the most important functional parameters of a metallic chrome coating. One company states that the wear resistance of PVD coatings is not higher under high load for TiN and tungsten carbide with amorphous carbon. During the consultation concerns were raised regarding
Use number: 2 111 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES wear performance and PVD coatings to be not suitable for all aeronautic items (e.g. landing gear). However, some materials such as WC-C-H showed sufficient performance in fretting wear conditions for selected applications under low load conditions, due to the self-lubrication and low coefficient of friction. A wear rate of 6-10 mm³/nm for up to 300,000 cycles is reported against copper alloy parts. CoCrMo or Mo coatings have sufficient sliding wear properties against copper or steel counterparts. In Taber testing, the performance is better than for metallic chrome coatings (five times higher). Furthermore, a limitation for the use of PVD coatings is often given by the performance in fatigue testing. In contrast, compared to metallic chrome coatings the fatigue debit associated with PVD coatings such as tungsten carbide/carbon (WC-CH) and titanium nitride (TiN) was tested and was better for a number of substrates. A further key requirement of the aerospace industry is layer thickness. The required minimum layer thickness is about 100 µm in order to avoid redesign of the parts. The typical thickness of PVD coatings is between 3 and 5 µm. The thickness of carbide and nitride coatings is limited because internal stress occurs during application of the layer. As this stress increases with increasing coating thickness, PVD layers become brittle and tend to spall off when deposited in layers thicker than a few µm. With respect to a maximal thickness of 5 µm (PVD) compared to the required thickness of 100 µm (metallic chrome coating), PVD coatings do not fulfil the requirements concerning layer thickness. Another important performance parameter is corrosion resistance. Test results show that tungsten carbide/carbon (WC-CH) and titanium nitride (TiN) do not offer sufficient corrosion resistance due to thin coating. Even if nitride coatings are reported to be essentially inert and do not corrode, they do not provide as much corrosion resistance as thicker metallic chrome coatings, because they are thin and have an open columnar structure, especially once they are damaged. In general, PVD coatings do not achieve the corrosion requirements of the aerospace sector. According to the statement of several companies, PVD coatings are only suitable for very specific applications, where not all of the requirements for the aforementioned parameters have to be met. In general, the PVD alternative is mainly insufficient concerning fatigue, layer thickness and corrosion performance. PVD as alternative for functional chrome plating using a combined potassium dichromate / chromium trioxide plating solution shows the same technical deficiencies as for functional chrome plating based on chromium trioxide. Functional chrome plating with potassium dichromate / chromium trioxide plating solution is a rarely used special application in the aerospace sector for the purpose of thin hard coatings with good corrosion resistance and high abrasion resistance. PVD is not a like-for like replacement for this specific niche application.
Assessment overview for PVD based alternative (Aerospace)
Industry Corrosion Longevity / Layer Wear Coefficient Hardness sector resistance fatigue thickness resistance of friction Depends on Aerospace process
112 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Sector specific assessment: automotive and general engineering The minimum requirement for automotive and general engineering applications on hardness ranges between 1,000 and 1,200 HV. With a possible range from 1,200 HV to 2,400 HV for a PVD coated surface, this alternative fulfils the minimum hardness requirement. The ability to meet necessary life-time parameters of coated parts is expressed by the wear resistance. High wear resistance is achieved with CrN and TiN based PVD coatings, but only if the surface is scrupulously clean and is not contaminated by water, oil, paints or others. Apart from that, other key requirements such as corrosion resistance and the ability for repair depend on the layer thickness. The layer thickness is reported to be less than 10 µm. The low thickness does impede the corrosion resistance because thin layers can more easily be damaged down to the base material compared to a thick metallic chrome coating. Although PVD coatings are basically inert and not vulnerable to corrosion, once the layer is damaged it does not provide any further corrosion protection. The performance of PVD coating was reported by this sector to be insufficient in this respect. Applying thicker layers does not solve the problem because internal stress occurs during the coating process which increases the risk of cracks. As the internal stress as well as the risk of cracks increases with increasing coating thickness, PVD layers become brittle and tend to spall off when deposited in layers thicker than a few µm. The internal stress also is a limiting factor concerning fatigue and longevity of the coating. PVD coatings are not suitable for rebuilding which represents another key performance parameter. In comparison, functional chrome plating is often used for repair of parts. The worn area is plated to a thickness greater than required and afterwards ground to the specified dimensions. As the deposition of greater quantities of coating material cannot be achieved by PVD due to increasing internal stress in conjunction with increasing brittleness and risk of cracks, PVD is not an alternative for repair and overhaul works. The process temperatures of PVD processes are higher than those during functional chrome plating. Heat sensitive substrate materials used in products of this sector cannot be PVD coated. The vacuum chamber imposes a restriction in the substrate part’s geometries (e.g. inner coating, complex 3-D- geometries) and part size. According to the statement of several companies of the automotive sector, PVD is not suitable and feasible as a general functional chrome plating replacement that covers all of the aforementioned key functionalities.
Assessment overview for PVD based alternative (Automotive and General engineering)
Industry Wear Process Layer Corrosion Rebuilding of Hardness Geometry sector resistance temperature thickness resistance parts Automotive and General engineering
Sector specific assessment: steel The main application of metallic chrome coating in the steel sector is coating of work rolls in the milling processes. During milling the metallic chrome coating is worn out and needs to be rebuilt after the defined life time of the rolls. The life-time depends in most applications on the minimum requirements for hardness, wear resistance, layer thickness, brittleness and internal stress.
Use number: 2 113 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
The PVD process leads to very hard surface coatings with 1,200 – 2,400 HV depending on coating material. Regarding the minimal requirement of 850-1,000 HV, PVD coatings pass the hardness performance criterion. Layer thickness requirement for work rolls is rather thin with about 5 µm. Other steel applications require significantly thicker layers up to 0.2 mm. The maximal layer thickness of PVD coatings is about 5 µm and is therefore not suited for steel applications requiring coatings thicker than that. Consequently this requirement is not fulfilled by PVD coatings. Layer thickness is directly linked with internal stress. The thicker the coating, the higher the risk of internal stress. During the PVD process, internal stress can occur, especially with increasing layer thickness. Internal stress is linked to an increased risk of cracks. As a result, PVD layers become brittle and tend to spall off. Thus, PVD also fails the technical requirement for work rolls related to internal stress. The deposition of greater quantities of PVD coating material is not suitable due to increasing internal stress in conjunction with increasing brittleness and risk of cracks. Brittleness is in particular of concern because pieces of broken metallic chrome coating from the surface will disturb the strip surface. Therefore, PVD is not an alternative for repair and overhaul works. The need of a closed process chamber in combination with the vacuum conditions lead to restrictions in the geometry of the parts that can be PVD coated. Coated milling rolls with a length up to several meters and 7 tons in weight would require a vacuum chamber of this length which is technically not feasible and economically very difficult. With PVD, the combination of all the aforementioned key performance requirements cannot be achieved. As these conditions have to be fulfilled in order to be able to produce all parts currently manufactured with functional chrome plated rolls, PVD coatings are not an alternative for chromium trioxide functional chrome plating.
Assessment overview for PVD based alternative (Steel)
Industry Rebuilding of Hardness Brittleness Geometry Internal stress Layer thickness sector parts Steel
Sector specific assessment: metal precision parts Examples for metal precision parts are sugar sieves and sheet-guiding cylinder jackets that are coated with metallic chrome coatings in order to extend their life time and to make repair work possible. Hardness is an important parameter for this sector that requires at least 1,100 HV. PVD coatings fulfil this requirement. The minimum layer thickness has to be between 15 to 20 µm for sugar sieves and 8 µm for sheet- guiding cylinder jackets. With the PVD process these requirements can be met, but layers with a thickness greater than 5 µm cause increased internal stress in conjunction with increased brittleness and risk of cracks. The need of a closed process chamber in combination with the vacuum conditions leads to restrictions in the geometry of the parts that can be PVD coated. Metal precision parts with lengths up to several meters would require a vacuum chamber of this length. This is technically not feasible, due to poor
114 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES coverage in the recessed areas of the geometry which leads to insufficient corrosion protection at those weak spots. An additional corrosion resistant coating would thus need to be applied. For the sugar sieves (components with a lot of very small holes) a uniform and proper coating is very important. The coating particles must not close or narrow the holes in an inappropriate way. This requirement on the layer constitution cannot be assured by PVD coatings.
Assessment overview for PVD based alternative (Metal precision parts)
Layer Industry sector Hardness Layer thickness Brittleness Internal stress Geometry constitution Metal precision
parts
Sector specific assessment: manufacture of printing equipment The manufacture of printing equipment sector uses metallic chrome coating as outer surface coating e.g. on work tools (such as mandrels) for rotogravure printing. The use of chromium trioxide within this sector demands hardness between 1,000 and 1,400 HV. PVD coatings achieve 1,200-2,400 HV and therefore fulfil the requirement. However, wear resistance of tested PVD coatings was reported to be insufficient as they fail the sector specific requirements. The process temperature with 300-500°C for CrN is too high to be applied on the mandrels which makes this alternative not feasible. The most important disadvantage of this alternative is the need of a closed process chamber in combination with the vacuum conditions, which lead to restrictions in the geometry of the parts. The parts (e.g. cylinder rolls) that are chromium plated by this sector are 150-700 mm in diameter and 5.5-6 m in length which is not feasible in a PVD vacuum chamber.
Assessment overview for PVD based alternative (Manufacture of printing equipment)
Process Industry sector Hardness Wear resistance Geometry temperature Manufacture of printing
equipment
7.8.3 Economic feasibility Against the background of significant technical failure of PVD, no quantitative analysis of economic feasibility was conducted. However, the cost for PVD depends on numerous different factors and these are presented in a qualitative to semi-quantitative way below. The technology for PVD processes and functional chrome plating differ fundamentally in the equipment and peripherals. The implementation of PVD requires complex machines and infrastructure equipment. The installation costs for a completely new plant and machine lines are estimated to be about $1-3 million for the coating system, with additional costs for cleaning lines (Legg K., 2012). During the consultation, the investment costs for PVD processes were commented by companies to be very high whilst the implementation of the process represents a large business risk.
Use number: 2 115 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Table 17 shows the comparison of process costs for PVD compared to functional chrome plating, with data from PVD equipment vendors and business information from a functional chrome plating company (general engineering sector). The total production costs are based on a multitude of items including but not restricted to material, energy, waste, and repair. Table 17: Comparison of production costs of the coating: PVD & functional chrome plating
Percentage of total direct production Cost (chromium trioxide=100%) PVD chromium trioxide Factor Coating material 99 20 5 Labour 23 6 3.8 energy 20 39 0.5 Other costs 7 12 0.6 Depreciation 191 23 8.3 Production Cost Total 340 100 3.4
Depreciation is the biggest driver for the cost increase which is due to very high investment costs and a low deposition rate. In addition, coating material and labour costs are significantly higher. In total, the costs to produce 1 m² of coated material are 3.4 times more expensive using PVD instead of functional chrome plating. According to the aerospace sector the relative costs depend on batch requirements and the process. PVD is potentially less expensive than functional chrome plating for large batches of small components (e.g. drill bits) but is more expensive for small batches for large components. Based on the information provided by the automotive sector, the PVD process is quite complex and expensive because it requires vacuum, high temperatures, costly devices/tools, pre-treatment of the parts and skilled operators that are able to handle the machinery. Due to a low deposition rate of the coating material (a few µm per hour), PVD is only suitable for low volume production and not for automotive serial production. The metal precision parts sector reports that an additional corrosion resistant coating would need to be applied which is economically very unfavourable as the price of coated screens is estimated to be doubled. The manufacture of printing equipment sector states that the price per preparation of the cylinder surface was roughly estimated to be 16 – 80 times higher compared to functional chrome plating.
7.8.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 2.1.8), titanium nitride would be the worst case with a classification as Flam. Sol. 2, Skin Irrit. 2 and Eye Irrit. 2 As such, transition from chromium trioxide – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.8.5 Availability PVD process equipment is commercially available. Vendors for PVD coating materials (such as TiN) are found in most areas of the world. However, the process is only feasible for specific parts as stated
116 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES above and significant technical and economic issues would need to be overcome to develop this to a general functional chrome plating alternative which is expected to take at least 15 years.
7.8.6 Conclusion on suitability and availability for alternative PVD PVD was assessed by the industry sectors with regard to the latest R&D results and their key parameters. Coatings applied by PVD do not perform as technically equivalent to chromium trioxide derived products and therefore are not a general alternative. The aerospace sector criticizes failure in wear and corrosion resistance as well as the insufficient layer thickness which is needed for repair and overhaul works. For the automotive and general engineering sector failure in corrosion resistance, insufficient layer thickness and inapplicable process temperatures makes PVD a non-applicable alternative. For the applications of the steel sector, insufficient performance in brittleness, layer thickness and internal stress as well as restriction due to parts geometry are the most important performance failures. PVD coatings are technically not an alternative for functional chrome plating for the sector that produces metal precision parts because of geometrical restrictions, layer constitution and thickness. Tests conducted by the sector that produces printing equipment mentioned insufficient wear performance and geometrical restrictions as reasons why this alternative is not suitable as a functional chrome plating replacement. In conclusion, PVD coatings are considered to be a niche application for specific small/medium components (commercially available) but are not a general functional chrome plating replacing alternative. The inability to rebuild worn parts makes PVD inadequate for all parts where repair work might be needed. The PVD process differs fundamentally from functional chrome plating, which means high investment costs for the implementation. The production costs were calculated to be two times higher compared to metallic chrome coatings by the steel sector. In summary, PVD coatings are not an equivalent alternative to functional chrome plated products but are used in some niche applications, e.g. for fretting wear.
CATEGORY 2 ALTERNATIVES
7.9 ALTERNATIVE 9: Plasma spraying
7.9.1 Substance ID and properties / process description Plasma spraying is a thermal spray process and uses highly energetic plasma as a heat source. The plasma is formed by generation of high density arc current in the space between cathode and anode that is filled with gases such as hydrogen or argon, see Figure 31. The gas is ionised, heated up to 15,000°C and focused as a beam towards the workpiece. Despite of the high gas temperatures, the surface temperature of the workpieces during deposition is between 150 and 400°C.
Use number: 2 117 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Figure 31: Plasma spraying process. Data source: http://www.roymech.co.uk/images/plating_1.gif, as of 05/06/14.
The coating material in powder form is injected into the plasma beam. The heat of the plasma softens the powder particles, which hit the substrate at high speed and flatten in pancake-shaped “splats”, see Figure 31. As they overlay each other, these splats form a continuous coating, merging the boundaries of the individual splats into a coherent coating material (Legg K., 2003a). The microstructural properties of the coating are determined by the properties of the plasma stream. These depend on nozzle geometry, type of gas and electric arc settings. Thermal spray processes offer a large choice of possible starting powders, gases, types of equipment, coating materials and deposition conditions and are therefore very versatile in their application area.
Figure 32: Cross section of a typical thermal spray coating. Data source: TURI, 2006. The possible powder materials for plasma spraying are similar to HVOF (pure metals, alloys, and carbides, refer to chapter 7.6.1). Out of the list of possible substances used in plasma spraying processes, tungsten carbide (WC-Co and WC-CoCr), Mo, CoCrMo and chromium carbide-nickel chromium (Cr3C2-NiCr) showed promising results during R&D and/or are already applied for niche applications. Therefore, the technical feasibility assessment presented in the following focuses on these substances. General information of the exemplary chosen tungsten carbide cobalt coating and the risk to human health and the environment is provided in Appendix 2.1.9.
118 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
7.9.2 Technical feasibility General assessment Compared to functional chrome plating, the process of plasma spraying requires proper process definition and careful control as well as trained and skilled workers. For functional chrome plating the part is cleaned and masked, then left in the plating bath for a specific time varying largely for different applications from 20 minutes up to a day. With spray processes large items are sprayed within minutes to hours. Batches of small items can be sprayed at the same time in special fixtures. Thus plasma spraying is much faster, but requires constant attention. Thermal spray coatings can be readily sprayed up to a layer thickness of 0.5 mm and are therefore suitable for repair and overhaul work on worn components (Legg K., 2012). The quality of the coating however is quite low compared to metallic chrome coating especially regarding their porosity which provides a reduced impermeability to the layer. In combination with thin layer thickness the susceptibility to corrosion is increased. Susceptibility to corrosion can be increased even with thicker deposits on usually corrosion resistant materials due to porosity. Research is ongoing. The bond between the sprayed coating and the substrate is purely mechanical whilst metallic chrome coatings adhere to the substrate according to the laws of solid-state physics. The adhesive strength to substrate is potentially lower for the plasma sprayed coating than for the metallic chrome coating which can result in flaking off in the worst case. Because of the poorer coating quality, plasma sprayed coatings are not used in high-pressure parts. In general, plasma spraying is a line-of-sight process and parts with complex geometry. For example undercuts are very difficult to coat, if they can be coated at all. For internal coatings the opening diameter needs a minimal width of 40 mm for the plasma spray gun, but to achieve the gun-to- substrate distance (stand-off), the diameter has to be significantly larger. Another limitation is given by the need of extensive current equipment for self-sustaining the arc current for creating the plasma. The performance of the plasma spraying process varies for the different coating materials. Therefore, substances which showed promising results during R&D and/or are already applied in niche application are discussed below. As mentioned before, these substances are tungsten carbide (WC- Co and WC-CoCr), CoCrMo and chromium carbide-nickel chromium (Cr3C2-NiCr). However, example test results for a WC-Co Coating are provided within the following Table 18:
Table 18: Material properties of plasma sprayed WC-Co coatings. Data source: Legg K., 2003a; Holeczek, 2011. Property Plasma spraying Notes Hardness 1,100-1,400 HV Depends on spray conditions Thickness 500 µm (0.5 mm) Usually limited by cost Wear resistance 2-3 times compared to functional Smooth surface finish important (Taber test) chrome plating
The coating applied by plasma spraying is characterized by a layer thickness of maximal 500 µm (limited by costs) and is typically 200 µm. These values exceed the aerospace minimum requirement of 100 µm and this is why e.g. rebuilding of worn parts is possible with plasma spraying. In general, plasma sprayed coatings show equal or even better wear resistance than metallic chrome coatings. CoCrMo or Mo coatings have sufficient sliding wear properties against copper or steel counterparts, the performance is better than for functional chrome plating (five times higher).
Use number: 2 119 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Besides wear resistance, the hardness is a further important key performance parameter. In general, plasma sprayed coatings can achieve 1,100-1,400 HV, which fulfils the minimum requirement of about 700 HV for aerospace applications. However, hardness of plasma sprayed Mo and CoCrMo coatings are softer with < 400 HV which is only sufficient for selected applications with lower hardness requirements. Corrosion resistance of plasma sprayed Mo coatings to steel and stainless steel were tested to be poor with < 72 hours salt spray test. Similar poor results were revealed for CoCrMo on steel, but latter could be increased to 750 hours when applied on a NiCr underlayer. Layer thickness for thin coatings cannot be fulfilled if an undercoat is needed, as layer thickness is increased beyond the requirements. Despite the requirements which can be achieved by plasma sprayed coatings, there are also significant limitations: for example the geometry of the part. Small or complex parts with undercuts are very difficult / impossible to coat. The applied coatings are porous which can lead, in combination with insufficient coating thickness, to an increased susceptibility to corrosion because of the reduced impermeability. The process temperature is extremely high and exceeds the threshold for heat sensitive substrates such as Al-alloys, high strength steels and electroformed nickel parts which become too soft and weak. The suitability for plasma spraying must be checked for every application and part, as performance varies for each material and substrate. This process is suitable for certain niche applications only. In summary, the plasma spraying process is technically not a feasible alternative to replace chromium trioxide in general applications and uses, as the requirements of several important key functionalities are not met; for example: porosity, layer thickness and quality, process temperature, and geometry.
7.9.3 Economic feasibility Against the background of significant technical failure of plasma spraying, no quantitative analysis of economic feasibility was conducted. However, the cost for plasma spraying depends on numerous different factors and these are presented in a qualitative to semi-quantitative way below. The technology for plasma spraying and functional chrome plating differ fundamentally in the equipment and peripherals. The implementation of plasma spraying requires complex machines and infrastructure equipment. The installation costs for a completely new plant and machine lines comprise 75,000-200,000 € for equipment, 75,000 € for the robot and 200,000 € for the room. The processing costs are moderate considering 50-150 % of the costs for functional chrome plating, depending on the application (Legg K., 2003a). The aerospace industry expects that the production costs for plasma spraying are significantly higher due to higher equipment costs increased by set-up costs for each part and the higher costs for post- treatment (grinding and polishing). Divergence of costs are expected to be even higher for more complex parts.
7.9.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances (see Appendix 2.1.9) and products reported during the consultation were reviewed for comparison of the hazard profile.
120 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
As mentioned above, various different powder materials are used for high velocity processes, for which some substances are confidential business information. As an example, the hazard profile from an often-used coating material is illustrated. According to suppliers’ SDS, the following hazard statements are given for WC-12Co: Skin Irrit. 2, Eye Irrit. 2, STOT SE 3, Carc. 2. As such, transition from chromium trioxide – which is a non-threshold carcinogen – to WC-12Co would constitute a shift to significantly less hazardous substances. However, some cobalt compounds are on the REACH candidate list for substances of very high concern so an assessment on the hazardous profile of these substances would have to be performed on a case by case basis.
7.9.5 Availability In general, plasma spraying is a fully developed and already qualified commercial process with widespread industrial and aerospace uses. Equipment and powder is commercially available from a number of vendors. However, as per all the functional chrome plating replacements, there is currently less availability of aerospace qualified plasma spray processes (e.g. CoCrMo, Mo) than for metallic chrome coatings. The needed time for the approval process of plasma spraying as alternative to functional chrome plating in the aerospace sector is estimated to be about five years for specific parts. Plasma spraying is currently not considered a like-for-like alternative to functional chrome plating and to develop a general metallic chrome coating alternative, more than 15 years would be needed. Plasma spraying is a possible alternative for chromium trioxide metallic chrome coatings in the manufacturing of printing equipment. Investigations on different materials (metals/alloys) and its technical feasibility were launched. To date, research is still at an early state and there are no qualified test results available yet, therefore minimum one decade is needed for further development.
7.9.6 Conclusion on suitability and availability for alternative plasma spraying Plasma spraying was assessed as alternative to functional chrome plating with regard to the latest R&D results and the key functionalities of the aerospace industry and some information was provided in the consultation by the manufacture of printing equipment sector. For the other sectors, this alternative was not assessed. The plasma sprayed coating does not represent a technical equivalent alternative to chromium trioxide based products and is therefore not a general alternative. For specific aerospace applications, plasma spraying is a suitable alternative to functional chrome plating. However, it shows technical limitations in layer structure, layer thickness if undercoats are needed, for heat sensitive substrates, porosity and geometrical restrictions. Plasma spraying is suitable for a small range of applications in the aerospace sector, but cannot be considered as universal replacement for functional chrome plating. Investigations on different materials and its technical feasibility were launched in the manufacture of printing equipment sector but to date, research is still at an early state. Even though plasma sprayed coatings seem to have promising technical properties, e.g. hardness and layer thickness if no undercoat is needed, the suitability must be checked for every application and part with regard to the limitation posed by technical (porosity, complex geometry) and economic (high investment costs) issues.
Technical feasibility Economic feasibility Risk reduction Availability
Use number: 2 121 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
7.10 ALTERNATIVE 10: General laser and weld coating technology
7.10.1 Substance ID and properties / process description General laser and weld coating technology includes the following processes: - Laser alloying - Laser cladding - Electrospark deposition (ESD) / electrospark alloying - Explosive cladding
The processes listed above are summarized as one alternative group, since they are all based on the same technology (weld coating). Laser alloying is a process in which material is integrated within the underlying surface. It diverges only from laser cladding in some process conditions, e.g. the power and length of the laser pulse. During laser cladding, material, such as metals and alloys in form of powder, wire etc., is fused onto the substrate surfaces to form a coating (Legg K., 2003a). In a system for electrospark deposition, material from a consumable electrode is transferred via an arc to the work piece. Nearly any electrically conductive material is suitable as electrode material. Explosive cladding describes a cold process consisting of putting the materials to be bonded in close proximity and driving them together with explosives. Suitable materials include steel, wear resistant alloys, formable metals and some ceramic powders. In addition to the mode of application, the material used in the process significantly influences the properties of the general laser and weld coating. Therefore, the most promising materials for general laser and weld-coatings are illustrated in the following assessment of the technical feasibility, which are tungsten-carbide-cobalt (WC-Co) and chromium carbide-nickel (Cr3C2-15Ni). General information of the exemplary chosen tungsten carbide cobalt coating and the risk to human health and the environment is provided in Appendix 2.1.10.
7.10.2 Technical feasibility Laser alloying/laser cladding - Process temperature: Laser cladding requires high surface temperatures (> 500°C) in order to weld the materials together. This heat treat results in heat-affected zones under the coating layer, increasing serious risks of overheating, crack building and early fatigue. This effect varies from one material to another. Due to the high temperatures and the risk of overheating, laser cladding is limited to materials that can take the process temperatures and is not suitable for general use, or for small or extensive coatings (Legg K., 2003a). - Layer properties: Moreover, the weld material tends to crack during multiple coatings due to internal stress from repeated high heat and cool cycles in order to build up thicker layers. - Process handling: The process is not easy to handle because the process window between alloying and cladding is too narrow to obtain constantly reliable coating results on diverse components.
122 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Laser cladding is a line of sight process and is not suitable for extensive coatings or complex parts geometries. Especially for the overhaul and repair use, laser cladding is not a suitable general alternative to functional chrome plating. Electrospark deposition - Layer thickness The achievable layer thickness depends strongly on the coating material. With a coating material containing chromium carbide and nickel (Cr3C2-15Ni), layer thickness up to 250 µm can be obtained. In contrast, WC-Co based coatings are less-conductive and are self-limiting in thickness with a maximal layer thickness of about 25 µm (Legg K., 2003a). - Temperature: The occurring temperatures during ESD are below 1,000°C and are limited to a local surface spot that melts and leaves a heat-affected zone with a penetration depth of less than 25 µm. The heat-affected zone at the surface may lead to issues on fatigue and corrosion caused by tensile stress followed by cracks in the coating. Fatigue and cracking issues were the most critical concern for aerospace companies and the automotive sector. - Inherent process properties: The small size of the electrode allows only a small surface area to be coated and is too slow and expensive for using this alternative on large areas. Explosive cladding - Process conditions Since the method does not involve heating, dissimilar material such as aluminium and copper can be joined. However, it should be taken into account that only material and components are suitable that are able to withstand the shock of the explosion. Moreover, the layer boundaries between the different materials show a wave structure due to the dynamics of the process. This can lead to structural degradations such as sub-surface crack growth and the fatigue debit which is generally major problem of explosive cladded layers (Legg K., 2003a). - Temperature The process temperatures that occur during the cladding are below 100°C. However, the local temperature of the component that occurs during the process remains unknown. - Layer properties Explosive cladding produces thick layer coatings with thicknesses greater than 6.4 mm which makes the process suitable for rebuild and repair work. Using metal or ceramic powder, the explosion rapidly compresses and solidifies the powder into a solid layer. The porosity of the resulting coatings is unknown. In addition the coating material has to be conformable to the shape of the surface being coated. This means that complex geometries with acute angles, edges and corners are difficult to coat, and in some cases impossible. Therefore explosive cladding is only usable for simple shapes (Legg K., 2003a).
7.10.3 Economic feasibility Against the background of significant technical failure of general laser and weld coating technology, no quantitative analysis of economic feasibility was conducted. However, the cost for this technology depends on numerous different factors and these are presented in a qualitative to semi-quantitative way below.
Use number: 2 123 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
The capital costs for an ESD unit are low compared to the production costs. However, the coating of e.g. an airplane landing gear part with 1.2 m in length and 0.2 m in diameter would take 7 hours and is priced at ca. 5,000 € which is far higher than functional chrome plating (Legg K., 2003a). The automotive sector stated that for their applications the production through put for ESD is at least 10 times lower compared to functional chrome plating.
7.10.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances (see Appendix 2.1.10) and products reported during the consultation were reviewed for comparison of the hazard profile. As mentioned above, various different powder materials are used for high velocity processes, for which some substances are confidential business information. As an example, the hazard profile from an often-used coating material is illustrated. According to suppliers’ SDS, the following hazard statements are given for WC-12Co: Skin Irrit. 2, Eye Irrit. 2, STOT SE 3, Carc. 2. As such, transition from chromium trioxide – which is a non-threshold carcinogen – to WC-12Co would constitute a shift to significantly less hazardous substances. However, some cobalt compounds are on the REACH candidate list for substances of very high concern so an assessment on the hazardous profile of these substances would have to be performed on a case by case basis.
7.10.5 Availability Laser methods: Laser cladding is a commercially available process and used in production for niche applications (cladding of turbine blades) but is not available as standard equipment or as a standard workshop process. Further research is required for laser alloying (Legg K., 2003a). ESD is commercially available and is, for example, used for valves and pumps in nuclear reactors, and power turbine blades. Considering further applications, such as for aerospace, the process seems to be still in the early R&D stage (Legg K., 2003a). The process in which explosive cladding can be applied to specific aircraft parts is very new and still under development. Apart from the aerospace sector the process is in limited commercial use. This is because of remaining unknown effects of the process on both substrates and components that require further investigation (Legg K., 2003a). As all alternatives stated above are no like-for-like replacement for functional chrome plating and they are still in very early stage of R&D, a minimum of 15 years would be needed to develop a general metallic chrome coating alternative.
7.10.6 Conclusion on suitability and availability for alternative general laser and weld coating technology Laser cladding is suitable for very specific applications and components in production. The process temperatures (> 500°C) limit the range of possible substrates and cause internal layer degradation. The method is not suitable for overhaul and repair work. This alternative is considered to be an energy intensive niche technology and not suitable for aerospace and automotive applications as a replacement for functional chrome plating. ESD: is suitable for very specific applications and components in production. ESD is used especially for small areas, such as inner diameters of hydraulic actuators, lugs, pins etc. but not for large
124 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES applications such as landing gear. There are also problems regarding the reproducibility of the layers and the geometrical restrictions to the parts that are possible to be coated. Explosive cladding can be a method to obtain a very thick repair layer (> 6.4 mm), but it is only suitable for simple and specific components. It can however not be used as a general repair technology due to operator safety and liability issues and has to be evaluated and validated for those specific niche applications. It is not an alternative neither for aeronautic nor for automotive applications. In conclusion, laser and welding processes are not appropriate as replacement processes for functional chrome plating.
Technical feasibility Economic feasibility Risk reduction Availability
7.11 ALTERNATIVE 11: Stainless steel & high speed steel (HSS)
7.11.1 Substance ID and properties In metallurgy, stainless steel is an alloy with at least 11% chromium content by mass. Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion by blocking oxygen diffusion to the steel surface and blocks corrosion from spreading into the metal's internal structure. Due to the similar size of the steel and oxide ions they bond very strongly and remain attached to the surface (Qiu, 2001). Stainless steel was mentioned as an alternative to metallic chrome coatings. It could be used as cladding tube on components such as piston rods. A tube is used as a covering liner that protects the substrate surface (Yang, 2011). HSS is a loosely used term and there are no standards or definitions. HSS are multi-component alloys that contain tungsten, chromium, molybdenum, vanadium, cobalt, niobium, as well as carbon (latter with >0.6 %wt). The alloys are transformed by an appropriate heat treatment process to HSS. Varying weight percentages of the above mentioned elements are categorized as follows: - Normal steel: <= 8% - Semi-High Speed Steels (SHSS): > 8% - 12% - HSS: > 12%
7.11.2 Technical feasibility The (intrinsic) corrosion resistance of some stainless steels with lower requirements was reported to be sufficient, for example, stainless steel 15/5 PH must resist 2 hours in a specified salt spray test for the aerospace industry. Stainless steel does not provide protection against galvanic corrosion; therefore, an additional surface treatment is required to assure this functionality. Moreover, during the consultation phase it was reported, that wear resistance, coefficient of friction and hardness performance of the alternative were not sufficient. The hardness performance of stainless steel is not sufficient and often requires an additional treatment (e.g. carburizing). Table 19 shows a choice of possible stainless steels together with their hardness performance. AISI 440C reaches the highest hardness with 690 HV, which still falls below the minimal requirements of all industry sectors (850 HV).
Use number: 2 125 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Table 19: Martensitic Steels – Hardness (Yang, 2011).
Research and development activities conducted by several companies were ceased due the lack of major technical functionalities as mentioned above. In the case of the aerospace sector, the use of stainless steel is critical, since lightweight materials use is a definite requirement. The steel sector, for example, mentioned that stainless steel cannot stand the forces in the milling process. The cleanness of the strip surface could not be resolved in experiments for automotive product stands on tandem mills. Additional grinding cycle time is required which increases production costs. HSS was not yet tested on EDT materials. However, there is the risk that a white layer forms during the EDT process that would require post coating treatment to keep constant in temper mills.
Table 20: Properties and test characteristics of chromium trioxide coatings vs. HSS rolls.
Property / Test characteristic Functional chrome plating HSS rolls Plated hardness 950 HV 850 – 870 HV 1.5-2.2 mm³/1,000 cycles Good Ra retention on Std of Micro Cracks (test method: ASTM G99 packaging mills C-Steel 896 HVN) Coefficient of friction 0.85 >1.0 Bend test – good Adhesive strength to substrate Not a coating Grind test – good Reproducibility of the substrate ~0 to +-5% 0% surface roughness depending on roll roughness Corrosion resistance 750 h 2 h
HSS roll introduces new constraints to roll shops regarding crack detection, grinding productivity, and stock turnover of rolls. HSS constraints for mill users were identified for cleanness of the strip and thermal properties which lead to inadequate flatness. The printing industry states that HSS is not compatible with any application that requires surface treatment, since mandrels cannot be produced out of stainless steel. In general, this alternative requires a full redesign of the component because the process is completely different to functional chrome plating.
126 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
7.11.3 Economic feasibility Against the background of significant technical failure of stainless steel and HSS, no quantitative analysis of economic feasibility was conducted. The steel industry reports a cost increase by a factor of 2.5 for uncoated HSS rolls compared to regular forged rolls containing 5% chromium.
7.11.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of hazard profile, which is presented in the following: Stainless steel is a term that defines a diverse family of alloys, containing iron and a minimum of 10.5% of chromium or in some cases nickel (≥ 8%) and/or molybdenum. Nickel is the only substance of major importance in regard to the hazard classification of stainless steel in solid form. Although, stainless steels are generally considered non-hazardous to human health and the environment (and regularly applied in contact with drinking water, food contact materials and medical devices), stainless steels containing more than 10% nickel are (in accordance with CLP criteria), classified as STOT RE 1, with 1-10% as STOT RE 2, and with less than 1% nickel they are not classified. Furthermore, stainless steel containing more than 1% of nickel is classified as carcinogen category 2 when classified as a simple mixture. However, no carcinogenic effects resulting from exposure to stainless steels have been reported, either in epidemiological studies or in tests with animals. In addition, International Agency for research on cancer (IARC) has concluded that stainless steel implants are not classifiable as to their carcinogenicity to humans. Stainless steels containing less than 1% Ni are not classified. Since the exact composition of a possible alternative substance is not known, an assessment regarding the overall risk to human health and the environment is not possible. However, transition from chromium trioxide, which is a non-threshold carcinogen, to stainless steel would constitute a shift to a less hazardous substance.
7.11.5 Availability Stainless steel is commercially available but not as an alternative for functional chrome plating. Research and development activities conducted by several companies were ceased due to a lack of technical performance. Ultra high strength stainless steels are being researched in the aerospace sector. In general, coatings are still needed to provide the required coefficient of friction. Only in some specific cases it is possible to replace functional chrome plating on parts made of light alloy steel by using stainless steel for the part. However, this leads to new dimensioning and redesign of the part. In summary, it is unlikely that stainless steel will be a general replacement for chromium trioxide and it would take a minimum of 15 years to develop it as a general metallic chrome coating alternative, if ever.
7.11.6 Conclusion on suitability and availability for alternative stainless steel & HSS Stainless steel as alternative for functional chrome plating can only cover some niche applications. The performance of several technical functionalities like wear resistance, coefficient of friction, and hardness were not sufficient. (Semi-)HSS rolls are not able to achieve a similar range of fundamental
Use number: 2 127 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES properties and benefits compared to a micro-cracked metallic chromium surface and thus are not a feasible alternative.
Technical feasibility Economic feasibility Risk reduction Availability
7.12 ALTERNATIVE 12: Thermal spray coatings
7.12.1 Substance ID and properties / processes There are four general types of thermal spray in order of increasing coating quality which have been mentioned during the consultation phase: - Flame spraying (including wire flame spraying, powder flame spraying); - Cold Gas Spraying; - (Wire) Arc spraying; - Plasma spraying; and - HVOF.
The assessment of HVOF and Plasma Spraying can be found in chapters 7.6 and 7.9. The residual Flame, Arc and Cold Gas spraying processes are summarized here as one group of alternatives. In wire arc spraying an electric arc serves both as heat source and as the source of molten metal droplets that are transported via a gas jet to the substrate surface. Cold gas spraying: The coating particles are accelerated to high speed by an ultra-high velocity gas stream. When they hit the surface they soften and melt through a conversion of kinetic to thermal energy. To date, cold gas spraying is only suitable for depositing low melting point metals (e.g. Cu and Al) and is not feasible for serial production. Also, the process is still limited to ductile materials such as Al, stainless steel, titanium and alloys (Legg & Sauer, 2000). Flame spraying is a simple thermal spray method for lower quality alloy coatings. The coating powder is injected into a gas jet and fed through a flame. The compressed air is used to atomize the molten metal and accelerate the particles onto the substrate. In general, the coating is of poor quality (porous and low adhesion) and therefore not suitable as an alternative to functional chrome plating. Hereinafter, arc, cold gas, and flame spraying are summarised as “thermal spray processes”. Beside the mode of application, the material used in the process significantly influences the properties of the thermal spray coating. Therefore, the most promising materials for thermal spray coatings are illustrated in the following assessment of the technical feasibility, which are WC-Co, WC-Co-Cr and WC-Cr-Ni based on R&D. General information of the exemplary chosen tungsten carbide cobalt coating and the risk to human health and the environment is provided in Appendix 2.1.12.
7.12.2 Technical feasibility General assessment As a line of sight process, thermal spray processes are not suitable for complex part geometries. The gun size, constitution, and the spraying angle are limiting factors. This is a prerequisite for many
128 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES applications including the whole precision metal and manufacture of printing equipment sector and makes this alternative not technically feasible. Thermal spray processes include thermal and kinetic energy. These energies are focussed and the articles can reach temperatures > 2,500°C. Consequently substrate is heated up especially at the superficial layers. There are serious risks of overheating, crack building, and early fatigue because the substrate properties degrade when influenced by the heat. Thermal processes are limited to substrate materials that can withstand high process temperatures. With thermal spraying conducted in air, oxides will form as the molten particles are accelerated towards the substrate. The inclusion of oxides raises the porosity and brittleness of the layer and lowers the bonding strength. Hardness, as a key functionality for an alternative to metallic chrome coating, is also affected and was reported to range between 400-700 HV for the aforementioned tungsten carbides, which is below the minimum hardness requirements of all CTAC Consortium sectors (starting at 850 HV). The size of the coating particles sets a practical lower limit to the layer thickness that is approximately 25 µm. The upper limit was reported to be 20 mm. Since surface treatment is required after coating to obtain a smooth and closed surface, the sprayed coating has to be thicker, and must be resized by post treatment. The corrosion resistance of arc sprayed coatings is approximately 50% less than those of metallic chrome coatings, due to layer porosity and brittleness. The cycle time for this process is at least ten times greater than functional chrome plating. Therefore, it is only considered to be suitable for low volume production. The manufacture of printing equipment sector states that all surfaces based on thermal spraying produce non-homogeneous and rough surfaces. The porosity is far too high for application on printing cylinders, as sometimes the pores are larger than the diameter of a printing cell. In addition, the thickness of the coating is not constant, which impairs the engraving process as the new surface of the spray coating does not follow the underlying engraving. In summary, this alternative is not technically feasible as replacement to functional chrome plating.
7.12.3 Economic feasibility Against the background of significant technical failure of thermal spray coatings, no quantitative analysis of economic feasibility was conducted. The technology for thermal spraying and functional chrome plating differ fundamentally in the equipment and peripherals. The implementation of thermal spraying requires complex machines and infrastructure equipment with high installation costs for a completely new plant and machine lines.
7.12.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances (see Appendix 2.1.12) and products reported during the consultation were reviewed for comparison of the hazard profile. As mentioned above, various different powder materials are used for high velocity processes, for which some substances are confidential business information. As an example, the hazard profile from an often-used coating material is illustrated. According to suppliers’ SDS, the following hazard statements are given for WC-12Co: Skin Irrit. 2, Eye Irrit. 2, STOT SE 3, Carc. 2. As such, transition from chromium trioxide – which is a non-threshold carcinogen – to WC-12Co would constitute a
Use number: 2 129 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES shift to significantly less hazardous substances. However, some cobalt compounds are on the REACH candidate list for substances of very high concern so an assessment on the hazardous profile of these substances would have to be performed on a case by case basis.
7.12.5 Availability (Wire) arc spraying: Commercial arc guns are used for specific automotive and aerospace niche applications but are not a general alternative to functional chrome plating. Cold gas spraying: The method is in an early development stage and not commercially available. During the consultation phase, cold gas spraying was mentioned as an alternative to functional chrome plating in gravure printing which is currently at an early stage of R&D. Currently different materials are being analysed and evaluated but it is estimated that at least another decade of research and development is needed. Flame spraying: The process is commercially available but not as a general alternative to functional chrome plating. As all alternatives stated above are no like-for-like replacement for functional chrome plating and they are still in very early stage of R&D, at least 15 years would be needed to develop a general metallic chrome coating alternative, if ever.
7.12.6 Conclusion on suitability and availability for alternative thermal spray coatings In conclusion, thermal spray processes (arc-, cold gas-, flame spraying) are not technically feasible as a general alternative to functional chrome plating. The thermal spray processes result in lower quality layers compared to metallic chrome coatings due to heat degradations and oxide inclusion. Further R&D is necessary prior to this alternative potentially reaching industrial qualification.
Technical feasibility Economic feasibility Risk reduction Availability
PRE-TREATMENT After several alternatives for the main surface treatment have been assessed in the former chapters, alternatives for pre-treatment using chromium trioxide in the functional chrome plating process are discussed in the following. The purpose of the pre-treatment is the removal of surface residues. As there is no clear demarcation, the term etching is used to cover both, etching and pickling as chromium trioxide pre-treatment in the following.
7.13 Mineral acids
7.13.1 Substance ID and properties Different mineral acids are currently under evaluation as alternatives to chromium trioxide in the surface pre-treatment process. Research is currently focused on using sulphuric acid composed with other acids, such as phosphoric acid and nitric acid, or with additives, such as peroxymonosulphate salts or peroxidisulphate salts.
130 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
An overview of general information on substances used within this alternative and the risk to human health and the environment is provided in Appendix 2.2.
7.13.2 Technical feasibility General assessment Pre-treatment is necessary to prepare the surface of the substrates for the subsequent process steps. Adequate preparation of the base metal is a prerequisite: adhesion between the metallic chrome coating and the substrate depends on the force of attraction at a molecular level. The surface of the metal – which is mostly steel or hardened steel for functional chrome plating – must be absolutely free of contaminants, corrosion and other residuals until the plating process is finished. The vast majority of non-mechanical pre-treatment processes are reverse etching processes using an aqueous solution of chromium trioxide, which has the major advantage that it can be applied in the plating bath itself at the appropriate temperature (but this will decrease the life of the bath), or in a separate etch bath. The same substance is used for pre-treatment and main treatment. Therefore, no additional rinsing working step involving water is required in between. Whereas separate etch baths are typically used in automated plating facilities for mass production, etching in the plating bath is especially advantageous for large parts which are immersed in large baths. Many applications require the usage of chromium trioxide in the pre-treatment working step, especially when the etch rates need to be strictly controlled and over-etching must be avoided. For example, the steel industry requires that the coating does not affect the surface morphology of the substrate. The defined surface texture of the substrate is created during the pre-treatment and must be kept during the plating process. The desired surface roughness varies for different applications in the range of 0.7 µm to 15 µm. Pre-treatment with chromium trioxide provides surface roughness in the application range as required. Alternatives must have analogous key functionalities to chromium trioxide, most importantly excellent adhesion promotion. In addition, if another substance than chromium trioxide is used in the pre-treatment process, cross contamination with the plating bath must be prohibited. Minor contamination with sulphur or chlorides are sufficient to make the plating bath content unsuitable for functional chrome plating needs and require to dispose of and exchange the bath content. Cross contamination is especially critical for parts with complex geometry, where residues of the pre- treatment solutions may be trapped in holes, openings, excavations, inside tubes, etc. Therefore, all parts must be thoroughly cleaned in additional working steps. If chromium trioxide is the only substance used for pre-treatment in manufacturing, no such cleaning installations are necessary. Furthermore, significant amounts of water are needed for the rinsing process which need to be adequately treated and discharged accordingly. Thus, appropriate water and waste water installations become mandatory. In summary, a diversity of additional equipment need to be implemented which fundamentally changes the existing facility design and require significantly more space. In addition, the alternative pre-treatment should be compatible with all relevant substrates. If alternatives are substrate specific, a separate pre-treatment bath with appropriate installation would be required. The use of one substance for both, pre-treatment and main treatment ensures high quality and smooth process functionality. The development of a pre-treatment alternative to chromium trioxide depends on the potential alternative for functional chrome plating and is no standalone process. While an alternative for functional chrome plating is investigated, adequate custom-tailored pre-treatments are evaluated in parallel or after the potential alternatives for the main process have been qualified.
Use number: 2 131 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Alternatives Sulphuric acid based solutions are assessed as a potential alternative for chromium trioxide based etching pre-treatments on metal substrates. They are used at room temperature and the parts are not preheated. It is qualified for some applications and processes, but not as a general replacement for chromium trioxide pre-treatment. Sulfuric acid anodic etching has been used successfully for some steels but smutting can be an issue.
Nickel strike solutions (usually NiCl2 / HCl) can be used as an alternative to back etching for many stainless steels, but nickel salts present very strong health and safety issues (CMR classification). A sulfo nitro ferric acid (a mixture of sulphuric acid, nitric acid and ferric ions) based etching alternative for different metals (copper, brass, aluminium and its alloys) was stated to be under R&D. It has to be noted, that this alternative is partly qualified for aluminium substrates in line with subsequent acidic anodizing. As the performance of the subsequent functional chrome plating step is strongly linked to the pre- treatment process and to the type / chemical composition of the substrate being processed, the alternative does not currently prepare the surface equivalent to a chromium trioxide based etching process and does not meet the requirements for all applications of every sector. Therefore, additional R&D is necessary to further adjust these processes. According to information provided during the consultation, a nitric/sulphuric acid solution for etching of copper is usually used for the removal of heavy red oxides. This etching solution is more aggressive than a chromium trioxide based solution and may not be appropriate for moderate etching activities where careful control of the etch rate is mandatory. However, nitric/sulphuric acid solutions were stated to provide an adequate etch rate to copper substrates and to meet requirements for intergranular attack for specific applications. Oxides, rust etc. are adequately removed from the surface and the required roughness of the etched copper substrate is created. An etching solution of sulphuric acid with peroxymonosulphate (for example potassium peroxymonosulphate 2KHSO5·KHSO4·K2SO4) for different kinds of stainless steel was tested at ambient temperature at the laboratory scale. The etching process (removal of smut) showed rapid, suitable performance with regard to surface quality. Currently, this alternative is at a very early investigation state. A detailed visual examination is mandatory to ensure that no end grain pitting occurs on stainless steel. R&D has been performed on a mixture of sulphuric acid with sodium peroxydisulphate (for example sodium peroxydisulphate Na2S2O8 or ammonium peroxydisulphate (NH4)2S2O8) at the laboratory scale for etching of copper and provided excellent etching results. The major drawback is that the peroxydisulphate bath starts degrading after 2 weeks of use, making continuous replacement necessary to ensure adequate performance. Furthermore, large maintenance efforts disturb the process chain and result in high operational costs. Therefore, ammonium peroxydisulphate was tested (instead of (sodium) peroxydisulphate), which shows less degradation, but may affect the on-site wastewater treatment plant. The rinsing water produced during this process step needs to be collected and cannot go into the on-site wastewater treatment, due to adverse effects between the ammonium containing etching rinsing water and other process rinsing waters. These environmental and safety issues prevented testing of ammonium peroxydisulphate with sulphuric acid at larger scale. Conclusions: At the current stage, mineral acid based solutions are technically not feasible as a general alternative to chromium trioxide based etching of metals. Intensive R&D efforts are ongoing to improve their performance, as the surface is not adequately prepared for the subsequent process
132 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES step and the applied layers do not adequately adhere to the substrate. In addition, none of the evaluated alternative solutions are applicable for all the different kinds of metal substrates.
Adequate surface preparation Adhesion to the substrate Compatibility with substrates
7.13.3 Economic feasibility The economic feasibility of etching with mineral acid on metal substrates was not assessed, as the alternative is not technically feasible and already failed the requirements at early investigation stage. Switching to a chromium trioxide-free etching alternative would generally necessitate the installation of additional bath equipment for rinsing processes. The larger the parts, the larger the separate pre- treatment baths and appropriate installations. For facilities producing large parts especially with complex geometry, changes of the facility design and need for space consuming and expensive additional equipment are significant. However, based on the literature research and consultations there is no indication that the discussed alternative is not economically feasible.
7.13.4 Reduction of overall risk due to transition to the alternative As the alternatives are not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 2.2.1), nitric acid would be the worst case with a classification as Ox. Liq. 3, Skin Corr. 1A, Met. Corr. 1, Skin Irrit. 2, Eye Dam. 1, STOT SE 3. As such, transition from chromium trioxide – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.13.5 Availability To date, the pre-treatment process on steel substrates is typically conducted with chromium trioxide either in a separate bath or in the plating bath itself. Especially for large parts and large plating baths, the pre-treatment is applied in the plating bath itself. For mass production articles, the pre-treatment with chromium trioxide is commonly applied in a separate bath. For some applications and substrates, the use of sulphuric acid based solutions is qualified but not as a general replacement for the chromium trioxide pre-treatment. For example, an etching solution for aluminium and its alloys only based on sulfo nitro ferric acid is commercially available and qualified for some applications outside of the sectors analysed. As stated during the consultation, the technical feasibility for etching of metals is not yet equivalent to the current chromium trioxide based process and further R&D is necessary. The etching pre-treatment has to be adapted according to the subsequent chromium trioxide free electroplating alternative, which is also still under R&D. However, etching as a pre-treatment to adequately prepare the surface for the subsequent step is always performed in-line with the functional chrome plating step and it is not a stand-alone process.
Use number: 2 133 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
As pre-treatment and main treatment using chromium trioxide are closely related, it will take a minimum of 10 – 15 years to develop a general alternative as pre-treatment which meets all requirements - analogous to the time frame expected for functional chrome plating alternatives.
7.13.6 Conclusion on suitability and availability for mineral acids In summary, the use of chromium trioxide in pre-treatment processes is state of the art for metal substrates, especially for large parts and large plating baths. If not pre-treated in the plating itself, the parts pre-treated in a separate chromium trioxide etch bath are directly transferred to the plating bath. A chromium trioxide free etching pre-treatment of metals (aluminium and its alloys) based on sulfo nitro ferric acid is commercially available and qualified for some applications and substrates, but not as general replacement for chromium trioxide pre-treatment. The technical feasibility is not yet equivalent to the current process. Using another substance than chromium trioxide for the pre- treatment process requires significant efforts to clean the parts after the pre-treatment by means of rinsing to avoid cross contamination of the plating bath. Already minor amounts of residues from the treatment solution such as sulphates or chlorides make the bath content unsuitable. If no water supply and water treatment facilities are already in place, this constitutes in combination with required additional bath equipment, a fundamental change of the facility design and demand large additional areas. The development of a pre-treatment alternative to chromium trioxide depends on the potential alternative for functional chrome plating and is no standalone process. While an alternative for functional chrome plating is investigated, adequate custom-tailored pre-treatments are evaluated in parallel or after the potential alternatives for the main process have been qualified. Therefore, the time needed for R&D and industrial implementation of an alternative are identical for pre-treatment and main treatment, which is a minimum of 10 – 15 years.
134 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
8. OVERALL CONCLUSIONS ON SUITABILITY AND AVAILABILITY OF POSSIBLE ALTERNATIVES FOR FUNCTIONAL CHROME PLATING In this Application for Authorisation, a total of 12 different alternatives have been considered for the purpose of Functional Chrome Plating with chromium trioxide for a number of different sectors, such as aerospace, automotive & general engineering, steel, metal precision parts and manufacture of printing equipment. Pre-treatment using chromium trioxide has been assessed separately. Functional chrome plating involves depositing a layer of metallic chromium on the surface of a metallic component, for example on steel, hardened steel, nickel alloys, copper alloys, aluminium, and bronze. This metallic chrome coating provides the article with high mechanical and wear resistance, excellent anticorrosion performance and a low coefficient of friction. The process is therefore specified for particular applications where this combination of performance characteristics is critical. Functional chrome plating using chromium trioxide is therefore used for technical applications or in parts that must perform under demanding conditions that involve high temperatures, repetitive wear and mechanical impact. Functional chrome plating using chromium trioxide involves immersion of the component in each of a series of treatment baths containing chemical solutions or rinses under specific operating conditions and is normally the final step in the overall surface treatment process. Chromium trioxide is a pre- requisite for the main treatment of functional chrome plating to ensure the highest quality of the product and to meet the requirements of the industry. Chromium trioxide is also used in the pre- treatment process to the substrate, such as etching / pickling. To date, sulphuric acid based solutions are already qualified for some applications and substrates but not as a general replacement for chromium trioxide in the pre-treatment. The time needed for R&D and industrial implementation of an alternative are identical for pre-treatment and main treatment which is a minimum of 10 – 15 years. There are no post-treatment processes for functional chrome plating which involve chromium trioxide. The analysis of alternatives shows there are no technically feasible alternatives to functional chrome plating with chromium trioxide for key applications. Several potential alternatives are subject to ongoing R&D, but do not currently support the necessary combination of key functionalities to be considered technically feasible alternatives. Some alternatives (e.g. electroless nickel, thick chemical vapour deposition using WC-Co, high velocity oxygen fuel (HVOF) using WCCoCr, and physical vapour deposition using WC-C-H) are qualified for individual applications with less critical performance requirements but none has all the key properties of functional chrome plating with chromium trioxide. Trivalent chromium has passed the laboratory research stage for the manufacture of printing equipment sector. No scale-up tests are available to date and larger scale testing needs to achieve stable process conditions which is difficult for the trivalent chromium process. The next stage of research is expected to take 10 to 12 years, and there is no guarantee that it will be successful. Although trivalent chromium has been subject to several projects investigating it as a potential alternative to chromium trioxide it is still in the early development stage. Tests are ongoing but trivalent chromium is neither technically ready nor qualified to replace chromium trioxide functional chrome plating applications. Trivalent chromium fails key requirements at laboratory scale for the other industrial sectors. However, based on experience and with reference to the status of R&D programs, alternatives are not foreseen to be commercially available for key applications and pre-treatment before 12 years after sunset date.
Use number: 2 135 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Table 21 provides an overview of the technical deficiencies on all category 1 alternatives differentiated between the five industrial sectors aerospace, automotive & general engineering, steel, metal precision parts, and manufacture of printing equipment. For each sector and alternative, the parameters that failed the technical feasibility check are listed.
136 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed.
ANALYSIS OF ALTERNATIVES
Table 21: Technical deficiencies of category 1 alternatives by sector. Automotive & General Manufacture of printing Alternative Aerospace Steel industry Metal precision parts Engineering equipment - hardness - corrosion resistance - corrosion resistance - layer thickness - hardness Electroless nickel - hardness - hardness - anti-adhesion 1 - wear resistance - corrosion resistance plating - layer thickness - wear resistance - hardness - coefficient of - endurance - process conditions - friction friction - hardness - wear resistance - hardness - hardness - coefficient of - hardness - anti-adhesion Nickel and nickel - coefficient of friction 2 alloy - wear resistance friction - corrosion resistance - wear resistance - wear resistance electroplating - microstructure - morphology - plating bath - hardness - microstructure - wear resistance conditions - corrosion resistance - corrosion resistance - coefficient of friction/ - rebuilding of parts - corrosion resistance - corrosion resistance lubricity - coefficient of friction - rebuilding of parts - rebuilding of parts - hardness 3 Case hardening - process temperature - anti-stick properties - hardness (depends - hardness (depends - rebuilding of parts - hardness (depends on - hardness (depends on on substrate) on substrate) substrate) substrate) - corrosion resistance - size limitations - size limitations - layer constitution - size limitations - process temperature 4 (Thin) CVD - process temperature - process temperature - suitability for the - process time - layer thickness - corrosion resistance - process time sectors’ products - process temperature - large geometries Thick CVD - process temperature
(aerospace) - size limitation - uniformity Nanocrystalline - anti-adhesion cobalt - hardness - hardness - corrosion resistance 5 - hardness - hardness phosphorus alloy - layer thickness - adhesion (for Ni- - hardness - wear resistance coating W-Plating) - geometry - brittleness - brittleness - homogenous surface/ High velocity - process temperature 6 thermal - wear resistance - geometry - reproduction of porosity (depends on the - surface conditions processes - process temperature surface - constant thickness coating, loads, wear 140 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Automotive & General Manufacture of printing Alternative Aerospace Steel industry Metal precision parts Engineering equipment mechanisms and the counterparts) - corrosion resistance (depends on the coating) - hardness (depends on coating) - roughness/ - hardness microstructure Trivalent - microstructure - wear resistance - hardness - microdistribution - scale up 7 functional hard - process maturity - layer thickness - adhesive strength to - layer thickness - stable process chromium - layer thickness - endurance substrate - hardness conditions - microstructure - layer thickness - corrosion resistance - corrosion resistance - process temperature - brittleness - layer thickness - layer constitution - layer thickness - geometry - wear resistance - wear resistance - geometry 8 PVD - corrosion resistance - internal stress - geometry - longevity/ fatigue - brittleness - geometry - layer thickness - process temperature - coefficient of friction - internal stress - rebuilding of parts - rebuilding of parts (depends on process)
Use number: 2 141 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
9. REFERENCE LIST Daly B.P. and F.J. Barry (2003): Electrochemical nickel-phosphorus alloy formation. IoM Communications Ltd and ASM International.
Davis J (1995): Tool Materials, ASM International.
Department for Environment, Food and Rural Affairs (RPA) (2005): Environmental Risk reduction strategy and analysis of advantages and drawbacks for Hexavalent chromium.
Di Bari, George A. (2010), University of California Santa Barbara: Electrodeposition of nickel.
Facchini et al. (2009): Electrodeposition of nanocrystalline cobald alloy coatings as a hard chrome alternative, Integran Technologies.
Faraday Technology Inc. Research project.
Gonzales, P. (2010): Electroplate Alternatives to Hard Chrome: Nanocrystalline Metals and Alloys, presentation.
Hall et al. (2013): Electrodeposition of chromium from trivalent chromium using modulated electric fields, United States patent application publication.
Holleczek, H. et al (2011): Report on inclusion of chromium trioxide (CrO3) in Annex XIV, final report.
Hu, Chi-Chang (2000): Electrodeposition of Nickel-Phosphorus Deposits with a Variable Magentic Property. (https://www.electrochem.org/dl/ma/198/pdfs/0636.pdf as of 09/30/14)
Hurkmans, A., Lewis, D.B. & Munz, W.D. (2003) "Magnetron Sputtered CrNx Coatings as an Alternative to Electroplated Hard Chromium", Surface Engineering, vol. 19, no. 3. 30.
Hurkmans, T., Kubinski, J., Trinh, T., Fleischer, W. & Van der Kolk, G.J. 1999, "Perspective for Replacement of Hard Chrome by PVD".
Legg, K, Sauer, J. (2000) Use of Thermal Spray as an Aerospace Chrome Plating Alternative, final report.
Legg, K. (2001) Replacement of Hard Chrome Plating (http://www.asetsdefense.org/documents/DoDBriefings/CrPlatingAlts/Replacement%20of%20hard %20chrome%20plating,%202001.pdf).
Legg, K. (2003a): Chrome Replacements for Internals and Small Parts, final report (http://www.asetsdefense.org/documents/DoD-Reports/Cr_Plating_Alts/Cr_Rplcmnt- IDs&Sm_Parts.PDF)
Legg, K. (2003b): Chromium and Cadmium Replacement Options for Advanced Aircraft, HCAT Program Review, KSC.
Legg, K. (2012): Choosing a Hard Chrome Alternative (http://www.rowantechnology.com/wp- content/uploads/2012/06/Hard-Chrome-Plating-Alternatives.pdf)
142 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Legg, K. (2005): Alternatives to Hard chromium plating for the Aerospace Industry, conference presentation, England.
Lin et al. (2011): High rate deposition of thick CrN and Xr2N coatings using modulated pulse power (MPP) magnetron sputtering.
Mandich, N. & D. Snyder (2011): 7. Electrodeposition of chromium, in Modern Electroplating, Fifth Edition.
McCrea et al (2003): Electroformed nanocrystalline coatings: an advanced alternative to hard chromium electroplating, final report.
National Defense Center for Environmental Excellence (NDCEE) (1995): Regulatory Analysis of the Chromium Electroplating Industry and Technical Alternatives to Hexavalent Chromium Electroplating, USA, Environmental Information Analysis, final report.
Navinsek, B., Panjan, P. & Milosev, I. (1999) "PVD coatings as an environmentally clean alternative to electroplating and electroless processes", Surface and Coatings Technology, vol. 116- 119, pp. 476-487.
Négré, P. (2002): HCT Meeting, Hard Chrome Alternatives Team (presentation).
Northeast Waste Management Officials’ Association (NEWMOA) (2003): Pollution Prevention Technology Profile, Trivalent Chromium replacements for Hexavalent Chromium Plating.
Parkinson, R. (2001): Nickel plating and electroforming (Essential industries for today and the future, NiDI Technical Series N°10 088, Nickel development institute.
Qiu J.(2001) Stainless Steels and Alloys: Why They Resist Corrosion and How They Fail; Nanyang Technological University.
Santonen, T, Stockmann-Juvala, H, Zitting A. (2010) Review of toxicity of stainless steel, Finnish institute of occupational health.
Sartwell, B, Legg, K, Bodger, B. HVOF Thermal Spray coatings as an alternative to hard chromium plating on military and commercial aircraft, final report.
Sonntag, B. (not dated): Chemisch Nickel – Abscheidemechanismus und Materialeigenschaften, presentation (ZVO; WW Business Manager Electroless Nickel, Atotech Deutschland GmbH).
The Massachusetts Toxics Use Reduction Institute (2006): Five Chemicals Alternative Assessment Study.
Toxics Use Reduction Institute (TURI) (2006): Five chemicals alternative assessment study.
Toxic Use Reduction Institute (TURI) (2012): Trivalent Chromium Plating Conversion Case Study: Independent Plating, Worcester, Massachusetts.
US Department of Defense (2009): ESTCP - Cost and Performance Report (WP-0127): Replacement of Chromium Electroplating on Helicopter Dynamic Components Using HVOF Thermal Spray Technology.
Use number: 2 143 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Valero, G. (2011): 79th surface finishing Guidebook, Published as a 10th Issue by Metal Finishing Magazine, Elsevier.
Watson, S. (1990): AlecNickel electroplating solutions, NiDI technical Series N° 10 047, Nickel development institute.
Yang, Z.: Alternatives to hard chromium plating on piston rods; Zhenkun Yang, 2011 (http://kau.diva-portal.org/smash/get/diva2:452803/FULLTEXT01.pdf).
Internet sources:
1. http://www.epa.gov
2. Schulz website: http://www.schulz-metallveredelung.de/oberflaechenveredelung- metallveredelung/hartverchromen (pdf, accessed on 17.06.2014)
3. Pfonline 2013: http://www.pfonline.com/articles/functional-trivalent-chromium-electroplating- of-internal-diameters (accessed on 17.06.2014)
4. www.werkstoffoberflaeche.de
5. http://sci.esa.int/
6. Topochrom website: http://www.topocrom.com/en_sites/principle_technology.php (accessed 18.06.2014)
7. http://www.sulzer.com
8. http://epp.eurostat.ec.europa.eu
9. http://spray-molybdenum-wire.com
10. http://www.roymech.co.uk
11. http://echa.europa.eu
12. http://www.chemspider.com
13. http://www.chemicalbook.com/
14. http://pubchem.ncbi.nlm.nih.gov
15. http://www.sigmaaldrich.com/
16. www.partsfinishing.com/
17. http://www.scbt.com
18. http://www.chemblink.com/
144 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
19. http://www.epa.gov/
20. http://www.spgprints.com/graphics+printing/systems/pre-press+%28film%29/pre- press+for+rotamesh%AE?product_id=31
21. www.turi.org/
22. http://ammtiac.alionscience.com/
23. READE internet site: http://www.reade.com
24. Chemie.de internet site: http://www.chemie.de/lexikon/Titannitrid.html
25. Alfa Aesar SDS: http://www.alfa.com/content/msds/German/14510.pdf
26. Praxair Surface Technology SDS: http://www.praxairsurfacetechnologies.com/
27. Carl Roth SDS: http://www.carlroth.com
28. MAK Collection for Occupational Health and Safety: http://onlinelibrary.wiley.com
29. Merck SDS: http://www.merck-performance-materials.com
30. http://www.hardide.com/
31. http://echa.europa.eu/documents/10162/13552/aviation_authorisation_final_en.pdf
32. http://www.sifcoasc.com/wp-content/uploads/Nickel-Tungsten-5711.pdf
33. http://www.asetsdefense.org/documents/Workshops/ASETS2012/7/Clouser%20- %20For%20Web.pdf
34. http://www.myvirtualpaper.com/doc/nasf_aesf/pasf_may10/2010052701/52.html#52
Use number: 2 145 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
APPENDIX 1 – MASTERLIST OF ALTERNATIVES WITH CLASSIFICATION INTO CATEGORIES 1-3 AND SHORT SUMMARY OF THE REASON FOR CLASSIFICATION OF ALTERNATIVES INTO CATEGORY 3 (SELECTION PROCESS)
Alternative Substance/ Alternative Section Category Screened out because Process
Electroless nickel plating /nickel-tungsten, nickel-boron, nickel 7.1 diamond composite, nickel-phosphorous, 1 nickel-polytetrafluoretyhlene; Ni-SiC /NiP-PTFE
Nickel & nickel alloy electroplating /ickel-tungsten-boron, nickel-tungsten- silicon-carbide, tin-nickel, nickel-iron- 7.2 cobalt, nickel-tungsten-cobalt, nickel 1 tungsten, Fe-Ni-Cr /disperse nickel electroplating in bath containing a.o. NiSO4, MoO3 and SiC
Case hardening (carburizing, carbo nitriding, cyaniding, boronizing, nitriding) 7.3 /plasma diffusion: 1 plasma nitriding, nitrocarburizing, low pressure nitiriding /explosive hardening
CVD (thin & thick) /Chemical Vapour Deposition (CVD): 7.4 TiN, WC, ZrN 1 /Plasma enhanced Chemical Vapour Deposition Coating (PECVD)
(Nano) Co-P plating 7.5 /cobalt electrolysis 1 /(Nano) Co-P plating
High velocity thermal processes /HVOF CrC-NiCr, WC-Co, WC-Co-Cr, Co-Cr-Mo, Mo 7.6 /HVAF 1 /detonation spraying /CoCrMo commercially available product (by HVOF or plasma)
7.7 Cr(III) based processes 1
PVD /Physical Vapour Deposition (PVD) 7.8 techniques: 1 Cr, CrC, CrN, MoS2, SiC, TiAlN, TiN, WC-C:H, ZrN, Zr oxides, organic zirconates
146 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Alternative Substance/ Alternative Section Category Screened out because Process /DLC (PVD technique)
7.9 Plasma spraying 2 Weld and Laser processes weld coatings /electro spark alloying (tungsten carbids, 7.10 Co-based alloys) 2 /explosive bonding /plasma powder welding torch laser alloying and laser cladding (NiC)
7.11 Stainless steel & HSS 2
Thermal spray processes /arc Spraying /cold gas spraying 7.12 /flame spray coating 2 -wire flame spraying -powder flame spraying /molybdenum thermal sprayed coatings
Ion implantation is not working as stand-alone replacement for functional chrome plating as no additional layer is applied and the surface is not rebuilt to its original layer thickness and - Ion Implantation 3 rebuilding parts can thus not be reworked. In addition, the process has to be conducted under vacuum conditions which is not feasible for large parts.
Salt spray tests for iron phosphor coatings - Iron-phosphor coating 3 showed decomposition of the layer leading to severe substrate corrosion. Plastic coating was mentioned as alternative to copper coating with functional chrome plating in gravure printing. Early R&D coating tests showed insufficient performance for hardness. This significantly reduces the maximum amount of copies to 200,000. Furthermore, - Plastic coating 3 plastic coatings cannot be engraved with the traditional method using diamonds and existing alternative engraving methods are not compatible. Plastic coatings do not withstand shape cutting as the material is too brittle. R&D ongoing regarding alternative for - Chromium III ionic liquids 3 decorative applications but not for functional chrome plating. Cobalt-tin plating is mainly used for decorative - Cobalt-tin plating 3 applications and not for functional chrome plating.
Use number: 2 147 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Alternative Substance/ Alternative Section Category Screened out because Process Zinc is a “soft” metallic material with hardness Zinc-based materials (zinc, zinc-tin, values below 450 HV and therefore not a zinc-aluminium, zinc-nickel based metallic chrome coating alternative. Zinc-based - 3 passivation, non-electrolytic zinc coating materials show insufficient performance plating) in corrosion and wear resistance, and the coefficient of friction.
148 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
APPENDIX 2 – INFORMATION ON SUBSTANCES USED IN ALTERNATIVES
APPENDIX 2.1 - ELECTROPLATING ALTERNATIVES (MAIN PROCESS) APPENDIX 2.1.1: ALTERNATIVE 1: Electroless plating Table 1: Substance IDs and properties.
Parameter Value Physicochemical properties Value
Chemical name and Nickel sulfate (mono constituent Solid (greenish-yellow, Physical state at 20 °C and 101.3 kPa composition substance) anhydrous form) ≥ 840°C (anhydrous form EC Number 232-104-9 Melting point decomposes at 848°C) CAS Number 7786-81-4 Density 3.68 g/cm3 IUPAC name nickel(2+) sulfate Vapour pressure -
Molecular formula NiSO4 Water solubility ≥ 625 g/L Flammability - Molecular weight 154.8 g/mol Flashpoint -
Parameter Value Physicochemical properties Value
Chemical name and Sodium phosphinate Physical state at 20 °C and 101.3 kPa Solid (white) composition Substance decomposes at EC Number 231-669-9 Melting point T≥ 238°C. CAS Number 7681-53-0 Density 1.77 g/cm3 IUPAC name Sodium phosphinate Vapour pressure - 909 g/L (at 30°C, pH 5.8- Molecular formula NaPH2O2 Water solubility 5.9) Flammability Non flammable Molecular weight 85.96 g/mol Flashpoint -
Parameter Value Physicochemical properties Value
Chemical name and Sodium borhydride Physical state at 20 °C and 101.3 kPa Solid (white, granular) composition (mono constituent substance) EC Number 241-004-4 Melting point > 360°C CAS Number 16940-66-2 Density 1.080 g/cm³ (at 20°C) IUPAC name Sodium tetrahydroborote Vapour pressure < 5.4 x 10-5 Pa (at 25°C)
Molecular formula NaBH4 Water solubility -
Flammability Not highly flammable Molecular weight 37.8 g/mol Flashpoint -
Use number: 2 149 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Table 2: Hazard classification and labelling.
Hazard Class Hazard Statement Additional Substance Number of Regulatory and CLP and Category Code(s) classification and Name Notifiers status Code(s) (labelling) labelling comments
H 302 (harmful if swallowed) H 315 (Causes skin irritation) Acute Tox. 4 H 317 (may cause allergic Skin Irrit. 2 skin reaction) Skin Sens. 1 H 332 (harmful if inhaled) Skin Sens. 1; H317: C ≥ 0,01% Acute Tox. 4 H 334 (may cause allergy Nickel STOT RE 1; H372: C REACH registered. Resp. Sens. 1 or asthma symptoms or sulphate breathing difficulties) ≥ 1% Harmonised Muta. 2 Classification- Annex (CAS 7786- H 341 (suspected of Skin Irrit. 2; H315: C VI of Regulation (EC) 81-4) Carc. 1A causing genetic defects) ≥ 20% No 1272/2008 (CLP Repr. 1B (EC 232-104- H 350 I (may cause M=1 Regulation). 9) STOT RE 1 cancer by inhalation) STOT RE 1; H373: C Index Number: 028-009- Aquatic Acute H 360D (may damage the ≥ 1% 00-5 1 unborn child) STOT RE 2; H373: Aquatic H 372 (causes damage to 0,1% ≤ C < 1% Chronic 1 organs) H 400 (very toxic to aquatic life) H 410 (very toxic to aquatic life with long lasting effects)
Sodium Not classified 326 REACH registered; hypophosphite Not included in the CLP (CAS 7681- H 319 (causes serious eye Eye Irrit. 2 56 Regulation, Annex VI; 53-0) irritations Included in C&L (EC 231-669- H 315 (causes skin Skin Irrit. 2 23 inventory 9) irritation)
150 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Hazard Class Hazard Statement Additional Substance Number of Regulatory and CLP and Category Code(s) classification and Name Notifiers status Code(s) (labelling) labelling comments H 260 (In contact with water releases flammable Water react. 1 gases which may ignite spontaneously) Acute Tox. 3 H 301 (toxic if 105 Acute Tox. 3 swallowed) Skin Corr. 1B H 311 (toxic in contact with skin)
Sodium H 314 (causes severe skin REACH registered; borhydride burns and eye damage) Not included in the CLP (CAS 16940- H 260 (In contact with Regulation, Annex VI; 66-2) water releases flammable Included in C&L (EC 241-004- Water react. 1 gases which may ignite spontaneously) inventory 4) H 301 (toxic if Acute Tox. 3 swallowed) Acute Tox. 3 93 H 311 (toxic in contact Skin Corr. 1B with skin) H 314 (causes severe skin Eye Dam. 1 burns and eye damage) H 318 (causes serious eye damage)
APPENDIX 2.1.2: ALTERNATIVE 2: Nickel and nickel alloy electroplating Table 1: Substance IDs and properties for relevant substances in nickel and nickel alloy electroplating.
Parameter Value Physicochemical properties Value Chemical name and Boric acid (mono Physical state at 20°C and Solid (crystalline, odourless) composition constituent substance) 101.3 kPa No melting point detected below EC number 233-139-2 Melting point 1,000°C CAS number 10043-35-3 Density 1.49 g/cm3 IUPAC name Boric acid Vapour pressure 9.90 . 10-8 kPa (25 °C)
Molecular formula B(OH)3 Water solubility 48.40 g/L (20°C, pH = 3.6)
Non flammable Flammability Molecular weight 61.83 g/mol - Flash Point:
Chemical name and Nickel sulphate (mono Physical state at 20°C and Solid (greenish-yellow, composition constituent substance) 101.3 kPa anhydrous form) ≥ 840°C (anhydrous form EC number 232-104-9 Melting point decomposes at 848°C)
CAS number 7786-81-4 Density 3.68 g/cm3 IUPAC name nickel(2+) sulfate Vapour pressure -
Molecular formula NiSO4 Water solubility ≥ 625 g/L Flammability - Molecular weight 154.8 g/mol Flash Point -
Use number: 2 151 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Parameter Value Physicochemical properties Value
Parameter Value Physicochemical properties Value
Chemical name and Nickel dichloride (mono Physical state at 20°C and Solid composition constituent substance) 101.3 kPa EC number 231-743-0 Melting point 1,001°C CAS number 7718-54-9 Density 3.55 g/cm3 IUPAC name nickel(2+) dichloride Vapour pressure -
Molecular formula NiCl2 Water solubility - Flammability Non flammable Molecular weight 129.6 g/mol Flash Point: -
Table 2: Hazard classification and labelling.
Hazard Statement Number Additional Hazard Class and Regulatory and CLP Substance Name Code(s) of classification and Category Code(s) status (labelling) Notifiers labelling comments REACH registered; Harmonised classification- Annex VI of regulation (EC) Boric acid H360FD (May No 1272/2008 (CLP damage fertility. May Regulation); index (CAS 10043-35-3) Repr. 1B n/a - damage the unborn number: 005-007-00- (EC 233-139-2) child) 2. Included according to Annex XVI on the candidate list (SVHC substance) H 302 (harmful if swallowed) H 315 (Causes skin irritation) H 317 (may cause allergic skin reaction) Acute Tox. 4 H 332 (harmful if Skin Irrit. 2 inhaled) kin Sens. 1; H317: C Skin Sens. 1 H 334 (may cause ≥ 0,01% allergy or asthma STOT RE 1; H372: C REACH registered; Acute Tox. 4 symptoms or ≥ 1% Harmonised Nickel sulphate Resp. Sens. 1 breathing difficulties) Skin Irrit. 2; H315: C classification- Annex (CAS 7786-81-4) Muta. 2 H 341 (suspected of ≥ 20% VI of regulation (EC) (EC 232-104-9) Carc. 1A causing genetic No 1272/2008 (CLP defects) M=1 Repr. 1B Regulation); Index STOT RE 1; H373: C number: 028-009-00- STOT RE 1 H 350 I (may cause cancer by inhalation) ≥ 1% 5. Aquatic Acute 1 H 360D (may damage STOT RE 2; H373: Aquatic Chronic 1 the unborn child) 0,1% ≤ C < 1% H 372 (causes damage to organs) H 400 (very toxic to aquatic life) H 410 (very toxic to aquatic life with long lasting effects)
152 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Hazard Statement Number Additional Hazard Class and Regulatory and CLP Substance Name Code(s) of classification and Category Code(s) status (labelling) Notifiers labelling comments H 301 (toxic if swallowed) H 315 (causes skin irritation) H 317 (may cause an allergic skin reaction) H 331 (Toxic if Acute Tox. 3 inhaled) Skin Irrit. 2; H315: C Skin Irrit. 2 H 334 (may cause an ≥ 20% Skin Sens. 1 allergy or asthma Skin Sens. 1; H317: C symptoms or ≥ 0,01% Harmonised Acute Tox. 3 breathing difficulties STOT RE 2; H373: Classification- Annex Nickel dichloride Resp. Sens. 1 if inhaled) 0,1% < C < 1% VI of Regulation (EC) (CAS 7718-54-9) Muta. 2 H 334 (suspected of No 1272/2008 (CLP M=1 (EC 231-743-0) Carc. 1A causing genetic Regulation). defects) STOT RE 1; H373: C Index Number: 028- Repr. 1B ≥ 1% H 350i (may cause 011-00-6. STOT RE 1 cancer by inhalation) STOT RE 1; H372: C ≥ 1% Aquatic Acute 1 H 360D (may damage Aquatic Chronic 1 the unborn child) H 372 (causes damage of organs) H 400 (very toxic to aquatic life) H 410 (very toxic to aquatic life with long lasting effects)
APPENDIX 2.1.3: ALTERNATIVE 3: Case hardening: Carburizing, carbonitriding, cyaniding, nitriding, boronizing. Table 1: Substance IDs and physicochemical properties.
Parameter Value Physicochemical properties Value Chemical name and Sodium cyanide (mono Physical state at 20°C and Solid (white, odourless) composition constituent substance) 101.3 kPa EC number 205-599-4 Melting point 591°C (1.013 hPa) CAS number 143-33-9 Density 1.595 g/cm³ (at 20°C) IUPAC name Sodium cyanide Vapour pressure 0.10 kPa (at 800°C) Molecular formula NaCN Water solubility 390 g/L (at 20°C) Flammability - Molecular weight 49.01 g/mol Flash Point: - Parameter Value Physicochemical properties Value Chemical name and potassium cyanide (mono Physical state at 20°C and Solid (white, odourless when dry) composition constituent substance) 101.3 kPa EC number 205-792-3 Melting point 634.5°C (1.013 hPa) CAS number 151-50-8 Density 1.56 g/cm³ (at 20°C) IUPAC name Potassium cyanide Vapour pressure - Molecular formula KCN Water solubility 400 g/L (at 20°C) Molecular weight 65.12 g/mol Flammability -
Use number: 2 153 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Parameter Value Physicochemical properties Value Flash Point: - Parameter Value Physicochemical properties Value Chemical name and Carbon monoxide (mono Physical state at 20°C and Gaseous (odourless) composition constituent substance) 101.3 kPa EC number 211-128-3 Melting point -199°C CAS number 630-08-0 Density 1.18 g/cm³ IUPAC name Carbon monoxide Vapour pressure 20,664,910 hPa (at 25°C) Molecular formula CO Water solubility 21.4 ml/L (at 25°C) Flammability ≥ 10.9 % lower flammability limit in air Molecular weight 28.01 g/mol ≥ 77.6% upper explosion limit Flash Point: -
Parameter Value Physicochemical properties Value
Chemical name and Ammonia (mono Physical state at 20°C and Gaseous (colourless, odourless) composition constituent substance) 101.3 kPa EC number 231-635-3 Melting point -77.7°C CAS number 7664-41-7 Density - IUPAC name ammonia Vapour pressure 8,611 hPa (at 20°C)
Molecular formula NH3 Water solubility 482 g/L (at 25°C) Flammability ≥ 16% Lower explosion limit Molecular weight 17.03 g/mol ≥ 25% upper explosion limit Flash Point: - Parameter Value Physicochemical properties Value Chemical name and Boron (mono constituent Physical state at 20°C and Solid (odourless, black) composition substance) 101.3 kPa EC number 231-151-2 Melting point 2,075°C (1,013 hpa) CAS number 7440-42-8 Density 2.35 g/cm³ (20°C) IUPAC name boron Vapour pressure - Molecular formula B Water solubility Insoluble (< 0.1 mg/L) Flammability Non flammable Molecular weight[2] 10.81 g/mol Flash Point: -
Table 2: Hazard classification and labelling.
Additional Hazard Class Hazard Statement Number classification and Regulatory and CLP Substance Name and Category Code(s) of labelling status Code(s) Notifiers (labelling) comments H300 (Fatal if Acute Tox. 2 swallowed) Acute Tox. 1 H310 (fatal in contact REACH registered; Sodium cyanide with skin) Eye Dam. 1 Not included in the CLP (CAS 143-33-9) H318 (causes serious 94 Regulation, Annex VI; Acute Tox. 2 (EC 205-599-4) eye damage) Included in C&L Aquatic Acute 1 H330 (fatal if inhaled) inventory Aquatic Chronic 1 H400 (very toxic to aquatic life)
154 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Additional Hazard Class Hazard Statement Number classification and Regulatory and CLP Substance Name and Category Code(s) of labelling status Code(s) Notifiers (labelling) comments H410 (very toxic to aquatic life with long lasting effects)
H300 (Fatal if swallowed) Acute Tox. 2 H310 (fatal in contact with skin) Acute Tox. 1 H330 (fatal if inhaled) Acute Tox 2 58 H400 (very toxic to Aquatic Acute 1 aquatic life) Aquatic Chronic 1 H410 (very toxic to aquatic life with long lasting effects) H300 (Fatal if Potassium cyanide swallowed) (CAS 151-50-8) H310 (fatal in contact (EC 205-792-3) Acute Tox. 2 with skin) Acute Tox. 1 H315 (causes skin Skin Irrit. 2 irritation) Eye Dam. 1 H318 (causes serious Acute Tox. 1 eye damage) 47 STOT SE 1 H330 (fatal if inhaled) STOT RE 1 H370 (causes damage Aquatic Acute 1 to organs) Aquatic Chronic 1 H372 (causes damage to organs trhough prolonged or repeated exposure)
H220 (extremely flammable gas) Harmonised Press. Gas Classification- Annex H331 (toxic if Carbon monoxide Flam. Gas 1 VI of Regulation (EC) inhaled) (CAS 630-08-0) Acute Tox. 3 No 1272/2008 (CLP H360D (may damage Regulation). (EC 211-128-3) Repr. 1A the unborn child) Index Number: 006-001- STOT RE 1 H372 (causes damage 00-2 to organs)
H221 (flammable gas) Harmonised H314 (causes severe Press Gas Classification- Annex skin burns and eye Ammonia Flam. Gas 2 VI of Regulation (EC) damage) (CAS 7664-41-7) Skin Corr. 1B No 1272/2008 (CLP H331 (toxic if Regulation). (EC 231-635-3) Acute Tox. 3 inhaled) Index Number: 007-001- Aquatic Acute 1 H400 (very toxic to 00-5 aquatic life) REACH registered; Boron Not included in the CLP (CAS 7440-42-8) Not classified - 120 Regulation, Annex VI; (EC 231-151-2) Included in C&L inventory
Use number: 2 155 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
APPENDIX 2.1.4: ALTERNATIVE 4: (Thin/Thick) chemical vapour deposition Table 1: Substance IDs and physicochemical properties.
Parameter Value Physicochemical properties Value
Chemical name and Titanium carbide (mono Physical state at 20°C and 101.3 Solid (crystalline) composition constituent substance) kPa EC number 235-120-4 Melting point 3,067°C CAS number 12070-08-5 Density 4.93 g/cm3 IUPAC name Titanium carbide Vapour pressure - Molecular formula TiC Water solubility Insoluble (< 0.1 mg/L) Flammability Non flammable Molecular weight 59.88 g/mol Flash Point -
Parameter Value Physicochemical properties Value
Chemical name and Titanium nitride (mono Physical state at 20°C and 101.3 Solid (brown) composition constituent substance) kPa EC number 247-117-5 Melting point 2,930°C CAS number 25583-20-4 Density 5.22 g/cm3 IUPAC name Titanium nitride Vapour pressure - Molecular formula TiN Water solubility Insoluble in Water Flammability Non flammable Molecular weight 61.87 g/mol Flash Point -
Parameter Value Physicochemical properties Value
Chemical name and Physical state at 20°C and 101.3 Titanium carbonitride powder composition kPa EC number 603-147-4 Melting point > 350°C CAS number 12654-86-3 Density 5.08 g/ cm3 (at 25°C) IUPAC name Titanium carbonitride Vapour pressure -
Molecular formula CNTi2 (TiC/TiN) Water solubility - Flammability - Molecular weight 121.75 g/mol Flash Point -
Parameter Value Physicochemical properties Value
Chemical name and Physical state at 20°C and 101.3 Titanium silicon carbide Powder composition kPa EC number - Melting point - CAS number - Density 4.53 g/cm3 IUPAC name - Vapour pressure -
Molecular formula Ti3SiC2 Water solubility - Flammability Molecular weight - - Flash Point
Parameter Value Physicochemical properties Value
Chemical name and Titanium boride (mono Physical state at 20°C and 101.3 Solid (powder, grey) composition constituent substance) kPa EC number 234-961-4 Melting point 3,225°C CAS number 12045-63-5 Density 4.52 g/cm3 IUPAC name Titanium diboride Vapour pressure -
156 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Parameter Value Physicochemical properties Value
Molecular formula B2Ti Water solubility 0.074 mg/L (at 30°C) Flammability Non flammable Molecular weight 69.49 g/mol Flash Point: -
Parameter Value Physicochemical properties Value
Chemical name and Aluminium oxide (mono Physical state at 20°C and 101.3 Powder (colourless, composition constituent substance) kPa crystalline) EC number 215-691-6 Melting point 2,054°C CAS number 1344-28-1 Density 3.97-3.99 g/cm3 oxo(oxoalumanyloxy)aluman IUPAC name Vapour pressure 1.33 hPa (at 2158°C) e . -5 Molecular formula Al2O3 Water solubility 2.00 10 g/L (at 20°C) Flammability - Molecular weight 101.96 g/mol Flash Point: -
Parameter Value Physicochemical properties Value Chemical name and Physical state at 20°C and 101.3 Chromium nitride Powder (black) composition kPa EC number 246-016-3 Melting point 1,770°C
CAS number 24094-93-7 Density 5.90 g/cm³
IUPAC name azanylidynechromium Vapour pressure - Molecular formula CrN Water solubility Insoluble Flammability - Molecular weight 66.00 g/mol Flash Point: -
Table 2: Classification and labelling of relevant substances.
Additional Hazard Class Hazard Statement Number of classification Regulatory and CLP Substance Name and Category Code(s) Notifiers and labelling status Code(s) (labelling) comments
Titanium Carbide Not classified 18 (CAS 12070-08- Notified classification 5) (EC 235-120-4) Flam. Sol H 228 (flammable Solid) 1
Not classified 11 Titanium nitride (CAS 25583-20- H 228 (flammable Solid) Notified classification 4 ) Flam. Sol. 2 H 315 (causes skin (EC 247-117-5) Skin Irrit. 2 irritation) 10 Eye Irrit. 2 H 319 (causes serious eye irritation) Titanium carbo nitride According to suppliers’ SDS this substance is (CAS 12654-86- Not available not classified according 3) to EG Nr. 1271/2008. (EC 603-147-4)
Use number: 2 157 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Additional Hazard Class Hazard Statement Number of classification Regulatory and CLP Substance Name and Category Code(s) Notifiers and labelling status Code(s) (labelling) comments Titanium silicon carbide No Information on not available classification and (CAS -) labelling are available. (EC -) Titanium H 302 (harmful if diboride Acute Tox. 4 swallowed) Notified classification (CAS 12045-63- Acute Tox. 4 H 312 (harmful in contact 120 and labelling. 5) Acute Tox. 4 with skin) (EC 234-961-4) H332 (harmful if inhaled)
Not classified 1649
Aluminium oxide H370 (Causes damage to Additional Stot SE 3 44 Notified classification (CAS 1344-28-1) organs) notification are and labelling. available (EC 215-691-6) H 332 (harmful if inhaled) Acute Tox. 4 H 335 (may cause 34 STOT SE 3 respiratory irritation) Chromium Pre registered substance; nitride notified classification (CAS 24094-93- Not classified 3 and labelling according 7) to CLP criteria. (EC 246-016-3)
APPENDIX 2.1.5: ALTERNATIVE 5: Nanocrystalline cobalt phosphorus alloy coating Table 1: Substance IDs and physicochemical properties.
Parameter Value Physicochemical properties Value
Chemical name and Physical state at 20°C and Orthophosphoric acid Liquid, colourless, viscous composition 101.3 kPa EC number 231-633-2 Melting point 41.10 °C (101 kPa) CAS number 7664-38-2 Density 1.87 g/cm³ (20 °C) IUPAC name Phosphoric acid Vapour pressure 4 Pa (20 °C) 5,480 g/L (cold water, pH = Molecular formula H3PO4 Water solubility 0.5) Flammability - Molecular weight 98.00 g/mol Flash Point: - Parameter Value Physicochemical properties Value Chemical name and Physical state at 20°C and Cobalt dichloride Solid, crystalline composition 101.3 kPa EC number 231-589-4 Melting point 737 °C CAS number 7646-79-9 Density 3.37 g/cm³ (25 °C) IUPAC name Cobalt(II)dichloride Vapour pressure 100 hPa (at 818 °C) Molecular formula CoCl2 Water solubility 585.90 g/L (20 °C, pH = 7) Flammability - Molecular weight 129.84 g/mol Flash Point -
158 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Table 2: Hazard classification and labelling
Hazard Hazard Statement Additional Class and Number of Regulatory and Substance Name Code(s) classification and Category Notifiers CLP status labelling comments Code(s) (labelling) H314 (Causes severe skin burns and eye REACH registered. damage) Harmonised Skin Corr. H318 (Causes serious Orthophosphoric Classification- 1B, 1C eye damage) acid Annex VI of Eye Dam. 1 H312 (Harmful in 52 - Regulation (EC) No (EC 231-633-2) Acute Tox. 4 contact with skin) 1272/2008 (CLP (CAS 7664-38-2) STOT SE 3 H335 (May cause Regulation). respiratory irritation) Index Number: 015- H302 (Harmful if 011-00-6 swallowed) H302 (Harmful if swallowed) H317 (May cause an allergic skin reaction) Acute Tox. 4 H334 (May cause allergy or asthma Skin Sens. 1 symptoms or REACH registered. Resp. Sens. breathing difficulties Harmonised 1 if inhaled) Cobalt(II) Classification- dichloride Muta. 2 H341 (Suspected of Annex VI of causing genetic 26 - Regulation (EC) No (EC 231-589-4) Carc. 1B defects) 1272/2008 (CLP Repr. 1B (CAS 7646-79-9) H350i (May cause Regulation). Aquatic cancer by inhalation) Acute 1 Index Number: 027- H360F (May damage 004-00-5 Aquatic fertility) Chronic 1 H400 (Very toxic to aquatic life) H410 (Very toxic to aquatic life with long lasting effects)
APPENDIX 2.1.6: ALTERNATIVE 6: High velocity thermal process Table 1: Substance ID and properties for an exemplary tungsten carbide-cobalt coating.
Parameter Value Physicochemical properties Value
Chemical name and Physical state at 20°C and WC-12Co Solid (grey, odourless) composition 101.3 kPa EC number Multiple components Melting point 3,410°C CAS number Multiple components Density - IUPAC Name Multiple components Vapour Pressure - Molecular Formula Multiple components Water solubility Insoluble in water Flammability - Molecular weight Multiple components Flash Point -
Use number: 2 159 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Table 2: Hazard classification and labelling overview. Hazard Hazard Class Statement Number of Additional classification Regulatory and CLP Substance Name and Category Code(s) Notifiers and labelling comments status Code(s) (labelling)
According to suppliers’ SDS, the following hazard statements are given: WC-12Co May cause eye and skin (commercially Skin Irrit. 2, irritation. Substance is not available product; Eye Irrit. 2, REACH registered. - Contains Material that Multiple STOT SE 3, may cause target organ Hazard information component System) Carc. 2 damage (based on animal from suppliers’ SDS. data) Possible cancer hazard- contains material which may cause cancer (based on animal data).
APPENDIX 2.1.7: ALTERNATIVE 7: Trivalent hard chromium Table 1: Substance ID and physicochemical properties
Parameter Value Physicochemical properties Value Chemical name and Chromium trichloride Physical state at 20°C and Solid (green) composition hexahydrate 101.3 kPa EC number - Melting point 80-83°C CAS number 10060-12-5 Density - Chromium(III) chloride IUPAC name Vapour pressure - hexahydrate
Molecular formula CrCl3 · 6H2O Water solubility 590 g/L (at 20°C) Flammability Non flammable Molecular weight 266.45 g/mol Flash point - Parameter Value Physicochemical properties Value Chemical name and Boric acid (mono Physical state at 20°C and Solid (crystalline, odourless) composition constituent substance) 101.3 kPa No melting point detected below EC number 233-139-2 Melting point 1,000°C CAS number 10043-35-3 Density 1.49 g/cm3 IUPAC name Boric acid Vapour pressure 9.90 . 10-8 kPa (25 °C)
Molecular formula B(OH)3 Water solubility 48.40 g/L (20°C, pH = 3.6) Flammability Non flammable Molecular weight 61.83 g/mol Flash point -
Parameter Value Physicochemical properties Value
Chemical name and Chromium potassium Physical state at 20°C and Solid (purple red) composition bi(sulphate) 101.3 kPa EC number - Melting point 89.0°C CAS number 7788-99-0 Density 1.83 g/cm3
160 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Parameter Value Physicochemical properties Value
Chromium(3+) potassium IUPAC name Vapour pressure - sulfate hydrate (1:1:2:12)
. Molecular formula CrKS2O8 12 H2O Water solubility 250 g/L Flammability Non flammable Molecular weight 499.4 g/mol Flash Point -
Parameter Value Physicochemical properties Value
Chemical name and Formic acid (mono Physical state at 20°C and Liquid composition constituent substance) 101.3 kPa EC number 200-579-1 Melting point 4.0°C CAS number 64-18-6 Density 1.22 g/cm3 (at 20°C) IUPAC name Formic acid Vapour pressure 42.71 hPa (20°C)
Molecular formula CH2O2 Water solubility Miscible in any ratio Flammability Flammable Molecular weight 46.0 g/mol Flash Point 49.5°C (at 1,013 hPa)
Parameter Value Physicochemical properties Value
Chemical name and Physical state at 20°C and Ammonium sulfamidate Solid (colourless) composition 101.3 kPa EC number 231-871-7 Melting point 131-135°C CAS number 7773-06-0 Density 1.00 g/cm3 IUPAC name Ammonium sulphamate Vapour pressure -
Molecular formula H6N2O3S Water solubility 1,666 g/L Flammability Non flammable Molecular weight 114.12 g/mol Flash Point - Parameter Value Physicochemical properties Value Chemical name and Physical state at 20°C and Ammonium chloride Solid (crystalline) composition 101.3 kPa EC number 235-186-4 Melting point 340°C (sublimation) CAS number 12125-02-9 Density 1.53 g/cm3 (at 20°C) IUPAC name Ammonium chloride Vapour pressure -
Molecular formula NH4Cl Water solubility 283 g/L (25°C) Flammability Non flammable Molecular weight 53.5 g/mol Flash Point -
Table 2: Classification and labelling of relevant substances.
Hazard Class Hazard Statement Additional Number of Regulatory and CLP Substance Name and Category Code(s) classification and Notifiers status Code(s) (labelling) labelling comments H 315 (causes skin Skin Irrit. 2 irritation) Chromium H 319 (causes Substance is not REACH serious eye trichloride Eye Irrit. 2 30 registered. hexahydrate irritation) Not included in the CLP
(CAS 10060-12-5) H 335 (may cause Regulation, Annex VI; STOT SE 3 respiratory Included in C&L irritation) inventory Acute H 302 (ha 24 Tox.TOX 4 rmful if swallowed)
Use number: 2 161 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Hazard Class Hazard Statement Additional Number of Regulatory and CLP Substance Name and Category Code(s) classification and Notifiers status Code(s) (labelling) labelling comments Chromium H 315 (causes skin Pre-registered substance potassium irritation) Skin Irrit. 2 Not included in the CLP bi(sulphate) H 319 (causes 5 Regulation, Annex VI; Eye Irrit. 2 dodecahydrate serious eye Included in C&L (CAS 7788-99-0) irritation) inventory Skin Corr. 1A; Harmonised H314: C ≥ 90% classification- Annex VI Skin Corr. 1B; of Regulation (EC) No Formic acid H 314 (causes H314: 10% ≤ C < 1272/2008 (CAS 64-18-6 Skin Corr 1A severe skin burns 90% Included in CLP (EC 200-579-1) and eye damage) Skin Irrit. 2; H315: Regulation, Annex VI 2% ≤ C < 10% (index number 607-001- Eye Irrit. 2; H319: 00-0); 2% ≤ C < 10%
H302 (harmful if Acute Tox. 4 49 swallowed) Pre-registered Substance Ammonium Not included in the CLP sulphamidate Not classified - 46 Regulation, Annex VI; (CAS 7773-06-0) Included in C&L (EC 231-871-7) H 302 (harmful if Acute Tox. 4 inventory swallowed) Aquatic Acute 23 H 400 (very toxic to 1 aquatic life) Harmonised classification- Annex VI H 302 (harmful if Ammonium of Regulation (EC) No swallowed) chloride Acute Tox 4 1272/2008 H 319 (causes (CAS 12125-02-9) Eye Irrit. 2 Included in CLP serious eye Regulation, Annex VI (EC 235-186-4) irritation) (index number 017-014- 00-8);
APPENDIX 2.1.8: ALTERNATIVE 8: Physical vapour deposition Table 1: Substance ID and physicochemical properties.
Parameter Value Physicochemical properties Value Chemical name and Silicon carbide (mono Physical state at 20°C and 101.3 Solid composition constituent substance) kPa Dissociate at 2,700°C into EC number 206-991-8 Melting point graphite and silicon
CAS number 409-21-2 Density 3.22 g/cm³ (at 25°C)
IUPAC name Silicon carbide Vapour pressure - Molecular formula SiC Water solubility Insoluble <0.1 mg/L Flammability Non flammable Molecular weight 40.1 g/mol Flash Point: -
Parameter Value Physicochemical properties Value
Chemical name and Tungsten Carbide (mono Physical state at 20°C and 101.3 Solid (crystalline) composition constituent substance) kPa EC number 235-123-0 Melting point 2,785°C (at 1,013 hPa)
162 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
CAS number 1270-12-1 Density 15.63 g/cm³ (at 23°C) IUPAC name Tungsten Carbide Vapour pressure - Slightly soluble (0.1- Molecular formula WC Water solubility 100 mg/L) Flammability Non flammable Molecular weight 195.9 g/mol Flash Point: - Parameter Value Physicochemical properties Value Chemical name and Physical state at 20°C and 101.3 Chromium nitride Powder (black) composition kPa EC number 246-016-3 Melting point 1,770°C CAS number 24094-93-7 Density 5.90 g/cm³ IUPAC name azanylidynechromium Vapour pressure - Molecular formula CrN Water solubility Insoluble Flammability - Molecular weight 66.00 g/mol Flash Point: - Parameter Value Physicochemical properties Value Chemical name and Titanium nitride (mono Physical state at 20°C and 101.3 Solid (brown) composition constituent substance) kPa EC number 247-117-5 Melting point 2,930°C CAS number 25583-20-4 Density 5.22 g/cm3 IUPAC name Titanium nitride Vapour pressure - Molecular formula TiN Water solubility Insoluble in Water Flammability Non flammable Molecular weight 61.87 g/mol Flash Point -
Table 2: Hazard classification and labelling overview.
Additional Hazard Class Number Substance Hazard Statement Code(s) classification Regulatory and CLP and Category of Name and labelling status Code(s) (labelling) Notifiers comments
Not classified - 604
Carc. 1B H350 (may cause cancer) REACH registered; 50 Silicon carbide STOT RE 1 H372 (causes damage to organs) Not included in the CLP Regulation, (CAS 409-21-2) H315 (causes skin irritation) Annex VI; (EC 206-991-8) Skin Irrit. 2 H319 (causes serious eye Included in C&L Eye Irrit. 2 irritation) 25 inventory STOT SE 3 H335 (may cause respiratory irritation) REACH registered; Tungsten carbide Not included in the CLP Regulation, (CAS 12070- Not classified 94 Annex VI; 12-1) Included in C&L (EC 235-123-0) inventory 11 Pre-registered Not classified Titanium nitride substance; (CAS 25583- Notified Flam. Sol. 2 20-4 ) H 228 (flammable solid) Classification and Skin Irrit. 2 10 labelling according to (EC 247-117-5) H 315 (causes skin irritation) Eye Irrit. 2 CLP criteria.
Use number: 2 163 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Additional Hazard Class Number Substance Hazard Statement Code(s) classification Regulatory and CLP and Category of Name and labelling status Code(s) (labelling) Notifiers comments H 319 (causes serious eye irritation)
Chromium Pre registered nitride substance; (CAS 24094- Not classified 3 Notified 93-7) Classification and labelling according to (EC 246-016-3) CLP criteria.
APPENDIX 2.1.9: ALTERNATIVE 9: Plasma Spraying Table 1: Substance ID and properties for an exemplary tungsten carbide-cobalt coating.
Parameter Value Physicochemical properties Value WC-12Co Chemical name and Physical state at 20°C and Solid (grey, odourless) composition Commercially available 101.3 kPa product EC number Multiple components Melting point 3,410°C CAS number Multiple components Density - IUPAC Name Multiple components Vapour Pressure - Molecular Formula Multiple components Water solubility Insoluble in Water Flammability - Molecular weight Multiple components Flash Point -
Table 2: Hazard classification and labelling overview. Hazard Hazard Class Statement Number of Additional classification Regulatory and CLP Substance Name and Category Code(s) Notifiers and labelling comments status Code(s) (labelling)
According to suppliers’ SDS, the following hazard statements are given: WC-12Co May cause eye and skin (commercially Skin Irrit. 2, irritation. Substance is not available product; Eye Irrit. 2, REACH registered. - Contains Material that Multiple STOT SE 3, may cause target organ Hazard information component System) Carc. 2 damage (based on animal from suppliers’ SDS. data) Possible cancer hazard- contains material which may cause cancer (based on animal data).
164 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
APPENDIX 2.1.10: ALTERNATIVE 10: General laser and weld coating technology Table 1: Substance ID and properties for an exemplary tungsten carbide-cobalt coating.
Parameter Value Physicochemical properties Value
WC-12Co Chemical name and Physical state at 20°C and Solid (grey, odourless) composition Commercially available 101.3 kPa product EC number Multiple components Melting point 3,410°C CAS number Multiple components Density - IUPAC Name Multiple components Vapour Pressure - Molecular Formula Multiple components Water solubility Insoluble in Water Flammability - Molecular weight Multiple components Flash Point -
Table 2: Hazard classification and labelling overview. Hazard Hazard Class Statement Number of Additional classification Regulatory and CLP Substance Name and Category Code(s) Notifiers and labelling comments status Code(s) (labelling)
According to suppliers’ SDS, the following hazard statements are given: WC-12Co May cause eye and skin (commercially Skin Irrit. 2, irritation. Substance is not available product; Eye Irrit. 2, REACH registered. - Contains Material that Multiple STOT SE 3, may cause target organ Hazard information component System) Carc. 2 damage (based on animal from suppliers’ SDS. data) Possible cancer hazard- contains material which may cause cancer (based on animal data).
APPENDIX 2.1.11: ALTERNATIVE 11: Stainless steel and high speed steel Stainless steel is a term that defines a diverse family of alloys, containing iron and a minimum of 10.5% of chromium or in some cases nickel (≥ 8%) and/or molybdenum. Nickel is the only substance of major importance with regard of the hazard classification of stainless steel in solid form. Although, stainless steels are generally considered non-hazardous to human health and the environment and regularly applied in contact with drinking water, food contact materials and medical devices, stainless steels containing more than 10% nickel are in accordance with CLP criteria, classified as STOT RE 1, with 1-10% as STOT RE 2 and with less than 1% nickel they are not classified. Furthermore, stainless steel containing more than 1% of nickel is classified as carcinogen category 2 when classified as a simple mixture. However, no carcinogenic effects resulting from exposure to stainless steels have been reported, either in epidemiological studies or in tests with animals. In addition, IARC has concluded that
Use number: 2 165 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES stainless steel implants are not classifiable as to their carcinogenicity to humans. Stainless steels containing less than 1% Ni are not classified. Since the exact composition of a possible alternative substance is not known, an assessment regarding the overall risk to human health and the environment is not possible.
APPENDIX 2.1.12: ALTERNATIVE 12: Thermal Spray coatings Table 1: Substance ID and properties for an exemplary tungsten carbide-cobalt coating.
Parameter Value Physicochemical properties Value
WC-12Co Chemical name and Physical state at 20°C and Solid (grey, odourless) composition Commercially available 101.3 kPa product EC number Multiple components Melting point 3,410°C CAS number Multiple components Density - IUPAC Name Multiple components Vapour Pressure - Molecular Formula Multiple components Water solubility Insoluble in water Flammability - Molecular weight Multiple components Flash Point -
Table 2: Hazard classification and labelling overview.
Hazard Hazard Class Statement Number of Additional classification Regulatory and CLP Substance Name and Category Code(s) Notifiers and labelling comments status Code(s) (labelling) According to suppliers’ SDS, the following hazard statements are given: WC-12Co May cause eye and skin (commercially Skin Irrit. 2, irritation. Substance is not available product; Eye Irrit. 2, REACH registered. Multiple - Contains Material that STOT SE 3, component may cause target organ Hazard information Carc. 2 System) damage (based on animal from suppliers’ SDS. data)
Possible cancer hazard- contains material which may cause cancer (based on animal data).
166 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
APPENDIX 2.2 - PRE-TREATMENTS: MINERAL ACIDS Table 1: Substance IDs and physicochemical properties are presented (not exhaustive): Physico-chemical Parameter Value Value properties Chemical name and Sulphuric acid (mono Physical state at 20°C and Liquid (odourless) composition constituent substance) 101.3 kPa 10.4-10.5°C EC number 231-639-5 Melting point (pure sulfuric acid) 1.83 g/cm3 (20°C, pure sulphuric CAS number 7664-93-9 Density acid) IUPAC name Sulfuric acid Vapour pressure 0.49 hPa (20°C)
Molecular formula H2SO4 Water solubility Miscible with water Flammability Non flammable Molecular weight 98.08 g/mol Flash point - Physico-chemical Parameter Value Value properties Orthophosphoric acid Chemical name and Physical state at 20°C and Solid (crystalline, if no water (mono constituent composition 101.3 kPa attached) substance) EC number 231-633-2 Melting/freezing point 41.1 °C (101 kPa) CAS number 7664-38-2 Density 1.84 g/cm3 (38°C) IUPAC name Phosphoric acid Vapour pressure 80 Pa (25°C, extrapolated)
Molecular formula H3PO4 Water solubility 5,480g/ L (cold water, pH= 0.5) Flammability Non flammable Molecular weight 98.00 g/mol Flash point - Physico-chemical Parameter Value Value properties Chemical name and Nitric acid (mono Physical state at 20°C and Liquid (fumes in moist air) composition constituent substance) 101.3 kPa EC number 231-714-2 Melting/freezing point - 41.60 °C CAS number 7697-37-2 Density 1.51 g/cm3 (20°C) IUPAC name Nitric acid Vapor pressure 9.00 kPa (25°C)
Molecular formula HNO3 Surface Tension - Molecular weight 63.01 g/mol Water solubility > 1,000g /L (20°C, pH= -1) Flammability Non flammable Molecular structure Flash point - Physico-chemical Parameter Value Value properties Chemical name and Physical state at 20°C and Chromium(III) sulphate Solid composition 101.3 kPa EC number 233-253-2 Melting point 90 °C CAS number 10101-53-8 Density 3.10 g/cm³ (anhydrous) IUPAC name Chromium(III) sulphate Vapour pressure - Insoluble (anhydrous). Soluble as Molecular formula Cr2(SO4)3 Water solubility hydrate. Flammability Non-flammable Molecular weight 392.18 g/mol Flash point - Physico-chemical Parameter Value Value properties
Use number: 2 167 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Physico-chemical Parameter Value Value properties Chemical name and Physical state at 20°C and Iron(II)-sulphate Solid composition 101.3 kPa EC number 231-753-5 Melting point > 300°C (decomposes) CAS number 7720-78-7 Density 3.65 g/cm³ IUPAC name Iron(2+) sulfate Vapour pressure -
Molecular formula FeSO4 Water solubility Very soluble (>10,000 mg/L) Flammability Non flammable Molecular weight 151.9 g/mol Flash point -
Table 2: Hazard classification and labelling overview
Hazard Class Hazard Statement Number Additional classification Regulatory and CLP Substance Name and Category Code(s) of and labelling comments status Code(s) (labelling) Notifiers Specific Concentration H314 (Causes severe limits: skin burns and eye REACH registered; Sulphuric acid damage) Skin Corr. 1A: C ≥ 15%, Skin Corr. 1A H314 Included in CLP (CAS 7664-93-9) H290 (may be n/a Regulation, Annex VI Met. Corr. 1 Skin Irrit. 2: 5% ≤ C < corrosive to metals) (index number 016-020- (EC 231-639-5) 15%, H315 00-8); Eye Irrit. 2: 5% ≤ C <
15%; H319 H314 (Causes severe Skin Corr. 1B skin burns and eye n/a Legal classification. REACH registered; Phosphoric acid damage) Included in CLP (CAS 7664-38-2) Regulation, Annex VI Additional self- (EC 231-633-2) H290 (May be (index number 015-011- Met. Corr. 1 n/a classification according to corrosive to metals) 00-6); REACH registration; H272 (May intensify Ox. Liq. 3 fire; oxidizer) H314 (Causes severe Skin Corr. 1A skin burns and eye n/a damage) Additional classification H290 (May be Met. Corr. 1 according to REACH REACH registered; Nitric acid corrosive to metals) registration. Included in CLP (CAS 7697-37-2) Classification notified to Regulation, Annex VI Not classified - 257 (EC 231-714-2) the C&L inventory. (index number 007-004- 00-1) H315 (Causes skin Skin Irrit. 2 irritation) Classification notified to the C&L inventory. H318 (Causes serious Eye Dam. 1 271 eye damage) Further 163 notifiers classified the substance as H335 (May cause Eye Dam. 1 only. STOT SE 3 respiratory irritation) Currently not REACH Chromium registered; sulphate 1103 notifiers did not Not included in the CLP (CAS 10101-53- Not classified - 1103 classify the substance. Regulation, Annex VI; 8) Included in C&L (EC 233-253-2) inventory
168 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
Hazard Class Hazard Statement Number Additional classification Regulatory and CLP Substance Name and Category Code(s) of and labelling comments status Code(s) (labelling) Notifiers Reach registered H302 (harmful if substance; Harmonised Iron(II) sulphate swallowed) Acute Tox. 4 classification- Annex VI (CAS 7720-78-7) H315 (causes skin of Regulation (EC) No Skin Irrit. 2 - (EC 231-753-5) irritation) 1272/2008 (CLP Eye Irrit. 2 Regulation). H319 (causes serious eye irritation) (Index number: 026- 003-00-7)
Use number: 2 169 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed. ANALYSIS OF ALTERNATIVES
APPENDIX 2.3 – SOURCES OF INFORMATION Information on substance identities, physicochemical properties, hazard classification and labelling are based on online data searches. All online sources were accessed between June and September 2014. The main sources are:
1. European Chemicals Agency: http://echa.europa.eu/de/
2. ChemSpider internet site: http://www.chemspider.com
3. Merck SDS: www.merckgroup.com
4. Sigma Aldrich SDS: http://www.sigmaaldrich.com
5. READE internet site: http://www.reade.com
6. Chemie.de internet site: http://www.chemie.de
7. Alfa Aesar SDS: http://www.alfa.com/content/msds/German/14510.pdf
8. Carl Roth SDS: http://www.carlroth.com
9. MAK Collection for Occupational Health and Safety: http://onlinelibrary.wiley.com
10. Chemical Book internet site: http://www.chemicalbook.com
11. Merck SDS: http://www.merck-performance-materials.com
12. Analytyka SDS: http://www.analytyka.com
13. Airgas.com internet site: http://www.airgas.com/msds/001069.pdf
14. Air Liquide internet site: http://encyclopedia.airliquide.com
15. Air Liquide SDS: http://www.airliquide.de
16. Praxair Surface Technology internet site: www.praxairsurfacetechnologies.com
17. Sciencelab internet site: www.sciencelab.com
170 Use number: 2 Copy right protected – Property of Members of the CTAC Submission Consortium – No copying / use allowed.