ISSN : 2249-5762 (Online) | ISSN : 2249-5770 (Print) IJRMET Vo l . 3, Is s u e 2, Ma y - Oc t 2013 Recent advancements in Thermal Spray Coatings Baljit Singh Dept. of Mechanical Engineering, DBFGOI, Moga, Punjab, India

Abstract • Flame spraying with a powder or wire, Within most industry segments, significant financial losses may • Electric arc wire spraying, be incurred due to accelerated of various components. In • Plasma Spraying. order to minimize the effects of mechanical wear and extend • High Velocity Oxy-fuel (HVOF) spraying, product life, thermal spray coating solutions introduced into • Spray and fuse. production and is further developing them to meet even more • Detonation Gun. demanding wear applications. Applying coatings using thermal spray is an established industrial method for resurfacing metal III. Detonation Spray Process parts. The process is characterized by simultaneously melting Fig. 1, given below represents the detonation spray process in and transporting sprayed materials, usually metal or ceramics, which a precisely measured quantity of the combustion mixture onto parts. In this paper some studies on Thermal sprayed wear consisting of oxygen and acetylene is fed through a tubular resistant coatings have been reviewed. barrel closed at one end. In order to prevent the possible back firing a blanket of gas is allowed to cover the gas inlets. Keywords Simultaneously, a predetermined quantity of the coating powder Thermal Spray, Detonation Gun, Wear, Wear Resistant is fed into the combustion chamber. The gas mixture inside the Coatings chamber is ignited by a simple spark plug.

I. Introduction is a family of processes that use combustion or plasma energy to heat and accelerate the millions of particles, which impact onto the surface of a target/forming remarkable continuous uniform solid layer [1]. Thermal spraying is an effective and low cost method to apply thick coatings to change surface properties of the component [12]. Coatings are used in a wide range of applications including automotive systems, boiler components, and power generation equipment, chemical process equipment, aircraft engines, pulp and paper processing equipment, Fig. 1: Schematic Diagram of the Detonation Sprays Process bridges, rollers and concrete reinforcements, orthopedics and dental, land-based and marine turbines, and ships [12]. For The combustion of the gas mixture generates high pressure shock depositing wear resistant thermal spray coatings, the commonly waves (detonation wave), which then propagate through the used powders are WC–Co (with Co lying in the range 8–15 wt.). gas stream. Depending upon the ratio of the combustion gases, Previous experimental studies have revealed that the hardness and the temperature of the hot gas stream can go up to 4000 deg C elastic modulus of coatings obtained using the above powders are and the velocity of the shock wave can reach 3500 m/sec. The substantially lower than the hardness and modulus of bulk material hot gases generated in the detonation chamber travel down the of identical composition [5-6]. Indeed, these mechanical properties barrel at a high velocity and in the process heat the particles to a are dependent not only on the nature and distribution of phases plasticizing stage (only skin melting of particle) and also accelerate present in the coating (largely determined by powder composition) the particles to a velocity of 1200 m/sec. These particles then but also on a host of other properties like coating microstructure come out of the barrel and impact the component held by the (layered structure resulting from splat formation during the coating manipulator to form a coating. The high kinetic energy of the hot process), porosity, the nature of residual stress and its magnitude powder particles on impact with the substrate result in a buildup of within the coating and finally the coating-substrate adhesion. The a very dense and strong coating. The coating thickness developed purpose of this paper is to present the development status of the on the work piece per shot depends on the ratio of combustion Thermal spray wear resistant coating with Detonation gun. gases, powder particle size, carrier gas flow rate, frequency and distance between the barrel end and the substrate. Depending on II. Thermal Spray Processes the required coating thickness and the type of coating material Thermal spraying can be used to apply coatings to machine the detonation spraying cycle can be repeated at the rate of 1-10 or structural parts to satisfy a number of requirements: Repair shots per second. The chamber is finally flushed with nitrogen worn areas on parts damaged in service Restore dimension to again to remove all the remaining “hot” powder particles from the mismachined parts Increase a part’s service life by optimizing the chamber as these can otherwise detonate the explosive mixture in physical surface properties The primary advantages of thermal an irregular fashion and render the whole process uncontrollable. spraying include the range of chemically different materials that With this, one detonation cycle is completed above procedure is can be sprayed, a high coating deposition rate, which allows repeated at a particular frequency until the required thickness of thick coatings to be applied economically, and spray equipment coating is deposited. portability. Heath et al [8] have summarized the thermal spray processes that have been considered to deposit the coatings, are VI. Studies Related to Thermal Spray Coatings enlisted below: Wang et al [2] have tried to protect the conticaster rolls which were frequently out of operation due to severe working conditions. Rolls www.ijrmet.com International Journal of Research in Mechanical Engineering & Technology 55 IJRMET Vo l . 3, Is s u e 2, Ma y - Oc t 2013 ISSN : 2249-5762 (Online) | ISSN : 2249-5770 (Print)

were coated with Cr3C2–NiCr detonation spray coating. Using the as the abrasive medium. Finally it was concluded that performance orthogonal test, suitable technological parameters were obtained. of DS coating is slightly better than the HVOF coating possibly They concluded that the coatings were very dense with good due to the higher residual compressive stresses induced by the bonding to substrate as well as high resistance to high temperature former process and WC-based coating has higher wear resistance oxidation and wear. It was concluded from the results (obtained in comparison to Cr3C2-based coating. in service tests at one Steel plant) that the Cr3C2–NiCr detonation Rajasekaran et al [11] has investigated that influence of detonation spray coating produced by authors has at least doubled the roll gun sprayed alumina coating on Al–Mg–Si alloy (AA 6063) test life. samples subjected to cyclic loading with and without fretting. Murthy et al [3] investigating the effect of grinding on the erosion Coated samples were grounded to have coatings of two different behaviour of a WC–Co–Cr coating. As a part of this work a thickness values, 40 and 100 μm. Under plain fatigue loading, comparison has also been brought out between two high velocity 100 μm coated specimens exhibited inferior lives due to the coating processes namely High Velocity Oxy-Fuel (HVOF) and presence of lower surface compressive residual stress compared detonation gun spray process (DS). A WC–10Co–4Cr powder has with uncoated and 40-μm-thick coated samples. Under fretting been sprayed on a medium carbon steel using the above mentioned fatigue loading, uncoated specimens exhibited inferior lives high velocity sprays processes. The coating in both ‘as-coated’ and compared with coated samples owing to the very low hardness ‘as-ground’ conditions has been tested for solid particle erosion of the uncoated specimens). The reason for the superior fretting behaviour. It has been found that surface grinding improved the fatigue lives of 40-μm-thick coated samples compared with 100- erosion resistance. This work presents detailed characterization of μm-thick coated samples was the presence of relatively higher the WC–Co–Cr coating in both ‘as-coated’ and ‘as-ground’ form. surface compressive residual stress in 40-μm-thick coated A detailed analysis indicates that the increase in residual stress specimens. in the ground specimen is a possible cause for the improvement J.P. Singla et al [12] evaluated that wear occurs on both surfaces in erosion resistance. when two surfaces are in contact. Surface coating is a best way Yang et al [4] studied the effects of the powder particle size and to improve surface characteristics like increase the wear and the acetylene/oxygen gas flow ratio during the detonation spray corrosion resistance of steels. Detonation gun coatings are often process on the amount of phase, porosity, and considered to the premier coatings which are having very dense hardness of the coatings using MoB powder were investigated microstructure (0.1- 1% porosity).It is used for coating of ceramics, by X-Ray Diffraction (XRD), Scanning Electron Microscopy , composites, metals & alloys. (SEM), etc. The results show that the presence of metallic Manoj Kumar Singla et al [13] studied the results of CNT (Carbon molybdenum in the coating results from decomposition of MoB nano tubes) reinforced nano composite coatings produced by powder during thermal spray. The compositions of the coatings thermal spray process. It is anticipated that, if properly deposited, are metallic Mo, MoB, and Mo2B, which are different from the nano composite ceramic coatings could also provide improved phases of the original powder. The amount of molybdenum phase properties like wear resistance.Thermal sprayed nano composite increases monotonously with the oxygen/acetylene ratio, but the coatings shows improvement of resistance to wear, erosion, increasing rate for the fine powder is faster than that for the coarse corrosion and mechanical properties. powder. The porosity and hardness of the coating are related to Singh et al [14] Materials are precious resources. Different the amount of molybdenum phase. The phase constitution of the methods are employed to protect the material from degradation. coating is discussed. Thermal spraying is one of the most effective method to protect Kharlamov et al [9] evaluated that detonation gun spraying, the material from wear, high temperature corrosion, stresses and is a technique of thermal spraying, and achieves well-bonded erosion, thus increasing the life of material in use. Detonation dense protective coatings through ultra high velocity, medium gun spraying is one of the thermal spraying techniques known temperature deposition of powders. In this paper the science and for providing hard, wear resistant and dense microstructured technology of detonation spraying reviewed relative to other coatings. This paper summarizes the results of previous research associated methods of thermal spraying (e.g. plasma spraying). done by various authors on different coatings done by detonation Special attention centred on optimization methods for a range gun spraying technique. of engineering applications. The mechanism of formation of Gill et al [15] Various techniques are employed to protect the detonation-sprayed coatings will be discussed. material from degradation. As the wear is a surface phenomenon Sundararajan et al [10] have been deposited wide range of wear and occurs mostly at outer surfaces. Therefore it is more appropriate resistant coatings utilizing the detonation spray process and found and economical to use surface engineering for making surface that tribological performance of thermal spray coatings depends modifications. Detonation gun spraying is one of the thermal on a host of properties like coating composition, nature of phases spraying techniques known for providing hard, wear resistant and and their distribution, microstructure, porosity and residual stress. dense micro structured coatings. This paper reviews the previous The resulting coatings have been characterized in terms of phase research done by various authors on different coatings done by content and distribution, porosity, micro hardness, and evaluated detonation gun spraying technique to increase the wear resistance for erosion, abrasion and sliding wear resistance. in Grey Cast Iron Murthy & Venkataraman [7] in their study deposited the Magdi et al [16] -based coatings are being increasingly -based and carbide-based coatings by high used to combat erosion-corrosion in oil and gas industries such that velocity processes like High Velocity Oxy-Fuel (HVOF) and occurring in offshore piping, production systems and machinery Detonation Gun Spray (DS) techniques which are known to involving fluid and/or slurry flowing corrosive media which provide best wear performance for a variety of wear resistance often contain solid particles such as sand. This leads to material/ applications. They compared the low stress abrasion wear substrate damage caused by the combined surface degradation resistance of these coatings. The abrasion tests were done using mechanisms of erosion and corrosion. This review assesses the a three-body solid particle rubber wheel test rig using silica grits erosion-corrosion resistance and performance of cermet coatings

56 International Journal of Research in Mechanical Engineering & Technology www.ijrmet.com ISSN : 2249-5762 (Online) | ISSN : 2249-5770 (Print) IJRMET Vo l . 3, Is s u e 2, Ma y - Oc t 2013 applied by different thermal spraying methods. Electrochemical [11] B. Rajasekaran , S. Ganesh Sundara Raman ,S.V. Joshi, G. measurements, which monitor the erosion-corrosion mechanisms Sundararajan”, Influence of detonation gun sprayed alumina and coating integrity by themselves and when both erosion and coating on AA 6063 samples under cyclic loading with and corrosion act simultaneously are considered. In addition, surface without fretting”, October 2007. characterization, and the extent of weight loss that covered through [12] J.P.Singla, J.S. Grewal, Vikas Chawla,“A survey of the different combinations of cermet were reviewed. Detonation gun sprayed wear resistant coatings”, Feb. 2010. V. Conclusion [13] Manoj Kumar Singla, Harpreet Singh, Vikas Chawla, It is possible to use the Detonation-Gun Spray system for "Thermal Sprayed CNT Reinforced Nanocomposite developing protective Thermal spray coatings of almost any Coatings”, Vol. 10, No. 8, pp. 717-726, 2011. material like , , metals, hard alloys and composite [14] Lakhwinder Singh, Vikas Chawla, J.S. Grewal,“A Review material powders onto mild steel, and other EN series. There is no on Detonation Gun Sprayed Coatings”, Journal of Minerals doubt that considerable progress has been made in the Detonation & Materials Characterization & Engineering, Vol. 11, No. –Gun Spray process by optimizing the process parameters like 3, pp. 243-265, 2012. Fuel Ratio, Carrier gas flow rate, frequency of detonations, and [15] Harjot Singh Gill, Jawala Parshad, N.K Grover,“Review spray distance over the last few years. Applications of detonated Paper on Enhancing the Wear Resistance of Grey Cast sprayed coated components include gas turbine blades, camshafts, Iron Using D-Spray Process”, International Conference on wire drawing pulleys, ball and gate valves, valve spindles, brake Advanced Research in Mechanical Engineering (ICARME- drums etc. Although Nano-structured coatings have been deposited 2012), 13th May, 2012, Trivendum. by various other thermal spray processes like HVOF and plasma [16] Magdy M. El Rayes, Hany S. Abdo, Khalil Abdelrazek spray, however further studies are necessary to study the detonation Khalil,“Erosion - Corrosion of Cermet Coating”, Int. J. sprayed nano-structured coatings on carbon nano tubes, Use of Electrochem. Sci., 8, pp. 1117 -1137, 2013. Thermally sprayed coatings on boiler steel to increase service life of boiler. Thermal spray coatings apply on grey cast iron to reduce wear and to test microbiological behavior of different Baljit Singh is working as a Assistant Thermal spray coatings. Professor at Desh Bhagat Foundation Group Of Institution, Moga, Punjab, References India. He is working on his Ph.D. in the [1] H Singh, M S Grewal, H S Sekhon, R G Rao,“Sliding wear field of mechanical Engineering.

performance of high-velocity oxy-fuel spray Al2O3/TiO2 and

Cr2O3 coatings”, 29 February 2008 published Vol. 222, Issue 4, pp. 601-610. [2] Jun Wang, Baode Sun, Qixin Guo, Mitsuhiro Nishio and Hiroshi Ogawa,“Wear resistance of a Cr3C2-NiCr detonation spray coating” Vol. 11, 2000, Number 2, pp. 261-265. [3] J.K.N Murthy, D.S Rao, B Venkataraman,“Effect of grinding on the erosion behaviour of a WC–Co–Cr coating deposited by HVOF and detonation gun spray processes”, Vol. 249, Issue 7, July 2001, pp. 592–600. [4] Gao Yang, Hei Zu-kun, Xu Xiaolei, Xin Gang,“Formation of Molybdenum Boride Cermet Coating by the Detonation Spray Process”, Journal of Thermal Spray Technology, Vol 10(3), 2001 [5] G. Barbezat, A. Nicoll, A. Sickinger,“Abrasion, erosion scuffing resistance”, Published in 2001 pp5-6. [6] S.Y.Semenov, B.M. Cetegen,“Experiments and modeling of the deposition of nano-structured alumina–titania coatings by detonation waves”, Mater. Sci. Eng. A Vol. 335, 2002, pp. 67–81. [7] J.K.N. Murthy, B. Venkataraman,“Abrasive wear behaviour

of WC–CoCr and Cr3C2–20(NiCr) deposited by HVOF and detonation spray processes”, Surface & Coatings Technology Vol. 200, 2006, pp. 2642– 2652. [8] R. Heath, P. Heimgartner, G. Irons, R. Miller, S.Gustafsson, Material Science Forum, Vol. 251-254, 1997, pp. 809-816. [9] Kharlamov,“Detonation spraying of protective coatings”, may 2003, Vol. 93, September 1987, pp. 1–37. [10] G. Sundararajan, D. Sen, G. Sivakumar,“The tribological behaviour of detonation sprayed coatings: The importance of coating process parameters”, Wear, Vol. 258, 2005, pp. 377–391. www.ijrmet.com International Journal of Research in Mechanical Engineering & Technology 57