INDUSTRIAL MATERIALS

Development of “ACE-COAT AC510U/AC520U” for Machining of Exotic Materials

Akihiko SHIBATA*, Haruyo FUKUI and Keiichi TSUDA

The application of exotic materials like and heat resistant is increasing more and more, especially in the aircraft industry. Such exotic materials are difficult to machine because of their good mechanical properties and high temperature during machining. Newly developed AC510U and AC520U are high-toughness carbide grades with “Super ZX Coat”, an exclusive physical vapor deposition (PVD) coating. Super ZX Coat is super-multi layered coating consisting of nanometer-thin layers of TiAlN and AlCrN alternately stacked up to 1,000 layers. Its hardness is improved 40%, and the oxidation temperature is 200˚C higher as compared with conventional coating. And also the chipping resistance is improved by controlling its residual stress. Therefore, AC510U and AC520U show superior wear and thermal resistance in exotic material machining, and provide longer tool life and higher productivity.

1. Introduction 2. Features of Super ZX Coat

Aircraft demand has dropped and remained stag- AC510U and AC520U are coated with Super ZX nant since year 2000. However, announcements made Coat, which is Sumitomo Electric Hardmetal’s propri- by the two leading commercial aircraft manufacturers etary newly developed physical vapor deposition (PVD) Boeing and Airbus about their new aircraft models coating (2). As shown in Fig. 1, Super ZX Coat is a super- (B787 and A380, respectively) created a significant turn- multilayer coating that is formed by alternately layering around in aircraft orders in 2005, and currently the air- super-thin TiAIN and AlCrN films, each having a craft industry is experiencing an unprecedented boom. nanometer-order thickness (a nanometer is one-bil- Exotic materials such as titanium alloys and heat- lionth of a meter), until the number of layers reaches resistant alloys are widely used for aircraft manufactur- approximately one thousand. It is a wear- and heat-resis- ing. These materials that are generally defined as “hard- tant coating that is 40% higher in hardness compared to-cut” have excellent mechanical and thermal proper- with conventional coatings. This high hardness is due to ties, which mean that they have following drawbacks the increased and optimized amount of aluminum addi- when being cut. tive. The oxidation temperature is raised to 200°C by 1) Low thermal conductivity resulting in the gener- adding (Table 1). ation of high temperatures during cutting Figure 2 shows the results of thermogravimetric 2) Formation of work-hardened surface layers analysis of Super ZX Coat and conventional coating. 3) High reactivity (affinity) to cutting tools The weight change during temperature rise in the These factors create an extremely harsh operating atmosphere was measured by using samples prepared by environment for cutting tools (1). It is therefore impor- coating a 3-µm-thick film on Pt substrates. The results tant to reduce the generation of cutting heat when machining hard-to-cut materials, and thus machining of exotic materials is commonly practiced under low speed, low feed, and wet cutting conditions. Because of the upturn in aircraft orders, the need TiAlN to machine these exotic materials is expected to further (dark-colored area) increase in the future. Accordingly, there is a rising demand for cutting tools designed for exotic material AlCrN cutting applications that exhibit stable long life and (light-colored area) offer higher machining efficiency for production lead time reduction. This report describes the features and use case TiAlN examples of the new turning insert grades AC510U and AlCrN AC520U that were developed by Sumitomo Electric TiAlN 10nm Hardmetal Corporation for cutting of exotic materials AlCrN to meet the needs of the market. TiAlN

Fig. 1. Cross-sectional TEM image and structural diagram of Super ZX Coat

SEI TECHNICAL REVIEW · NUMBER 67 · OCTOBER 2008 · 7 Table 1. Characteristics of Super ZX Coat In addition, controlling the compressive residual Oxidation stress was found to be effective to improve the chipping Coating Hardness Residual stress temperature resistance of a coating. As indicated in Fig. 4, by optimiz- Conventional ing the coating conditions along with the growth of the 40GPa 950˚C -0.7 GPa coating coating so that the compressive residual stress in the coat- Super ZX ing becomes larger from the carbide substrate toward the 56GPa 1150˚C -1.9 GPa Coat surface, the chipping resistance can be successfully improved without sacrificing the peeling-resistance.

Complete oxidation

1.0 Coating Substrate

0.8 Conventional Super ZX Coat coating 0 0.6

0.4 -1 Weight change (a.u.) Weight 0.2 Compressive Tensile -2 0 Residual stress (GPa) 750 850 950 1050 1150 Temperature (˚C) -3 012345 Fig. 2. Thermogravimetric analysis results Probing depth (µm)

Fig. 4. Depth profile of residual stress show that while the sample with conventional coating started to oxidize at about 850°C and completely oxi- dized at 950°C, the sample with Super ZX Coat started 3. Features of AC510U/AC520U to oxidize at about 960°C and progressed slowly until reaching the complete oxidation at 1150°C, which is AC510U and AC520U are made by applying Super 200°C higher than the case of the sample with conven- ZX Coat on special high-toughness cemented carbide. tional coating. They are more resistant to wear and heat and can fur- Figure 3 shows the results of thermal effusivity ther withstand fractures than conventional grades. analysis using the light-pulse heating thermo-reflectance Therefore, these new grades drastically reduce damages method. Thermal effusivity is a property that correlates caused by exotic material machining such as localized strongly with thermal conductivity. Materials with low wear induced by extremely high cutting heat and result- thermal effusivity have low thermal conductivity. As the ing accidental chipping, as well as notch wear or break- analysis results show, Super ZX Coat has a lower thermal age caused by the work-hardened surface layer of the effusivity than the conventional coating, which also material. AC510U and AC520U fulfill the market needs means a lower thermal conductivity. Therefore it can be for stable long tool life and high cutting efficiency. said that Super ZX Coat offers high heat resistance. The applicable areas and recommended machining conditions of AC510U and AC520U are indicated in Fig. 5. AC510U is a general-purpose grade that delivers high cutting performance in a wide range of machining oper- 6000 ations from rough to finish machining. AC520U is a

5000 ) -1 K -2

m 4000 Cutting type Finish cutting Medium cutting Rough cutting -0.5 Recommended cutting conditions vc=50-80 vc=40-70 vc=30-60 3000 Speed: vc (m/min) f=0.1-0.2 f=0.15-0.3 f=0.2-0.35 Feed: f (mm/rev) 2000 AC510U 1000 Thermal effusivity (Js Grade 0 Conventional Super ZX Coat AC520U coating

Fig. 3. Thermal effusivity analysis results Fig. 5. Application range and recommended cutting conditions

8 · Development of “ACE-COAT AC510U/AC520U” for Machining of Exotic Materials grade whose key feature is high strength and is suited Figure 8 shows a case example of rough turning of for use in machining applications such as heavy inter- iron-based heat-resistant alloys using AC510U. After machin- rupted cutting that require high cutting-edge strength. ing the same number of work pieces, the competitor product showed notch wear at its cutting edge that is seen specifically after machining exotic materials while AC510U did not. This means that AC510U has a longer 4. Case examples of machining using life span. AC510U/AC520U Figure 9 shows a case example of high-speed machining of 718 using AC510U. After machin- Figure 6 shows a case example of turning of titani- ing the work pieces at a cutting speed twice the conven- um alloys (Ti-6Al-4V) using AC510U. While the conven- tional speed of 50 m/min (100 m/min), the competitor tional PVD-coated grade showed significant wear and product developed severe cutting-edge damage that damage after turning for over 10 minutes, AC510U reduced its life to a third. AC510U, on the other hand, showed less wear after turning for up to 20 minutes, pro- was capable of machining up to three work pieces at 100 viding stable machining. m/min without showing breakage, thus achieving high Figure 7 shows a case example of turning of Inconel machining efficiency. 718 using AC510U. While the PVD-coated grade of a Figure 10 shows a case example of rough turning of competitor showed large notch wear and crater wear Inconel 718 using AC520U. After machining the same after turning for 7 minutes, AC510U exhibited less number of work pieces, the competitor product showed notch damage and crater wear even after turning for large flank wear and crater wear at its cutting edge. By more than twice longer time, thus achieving a stable and contrast, AC520U showed less wear, thus achieving long tool life. longer tool life span.

AC510U Competitor PVD grade 0.5 AC510U Conventional grade After machining the same number of work pieces 0.4 Notch wear Breakage 0.3 AC510U 0.2 Conventional grade

Frank wear (mm) wear Frank 0.1

0 0 5 10 15 20 25 Stable machining without notch wear Cutting time (min) Material: Iron-based heat-resistant alloy Insert: CNMG120412N-MU Cutting conditions: vc=30m/min, f=0.35mm/rev, Material: Ti-6Al-4V Insert: CNMG120408N-EX ap=4.0mm, dry Cutting conditions: vc=80m/min, f=0.25mm/rev, ap=0.5mm, wet Fig. 8. AC510U cutting performance (Rough turning of iron-based heat-resistant alloy) Fig. 6. AC510U cutting performance(Turning of Ti-6Al-4V)

Competitor PVD grade vc=50m/min vc=50m/min

Competitor vc=100m/min 0.3 AC510U Competitor PVD grade Decrease 0.25 PVD grade vc=100m/min 0.2 AC510U 0.15 AC510U vc=100m/min 0.1 Competitor PVD grade 0.05 13AC510U

Flank wear width (mm) Flank wear vc=100m/min 0 Tool life (pieces machined) 0 5 10 15 20 Life span equal to conventional grade Cutting time (min) even at a twice higher machining speed

Material: Inconel 718 Insert: CNMG120412N-UP Material: Inconel 718 Insert: CNMG120408N-EX Cutting conditions: vc=100m/min, f=0.2mm/rev, Cutting conditions: vc=80m/min, f=0.12mm/rev, ap=0.5mm, wet ap=0.8mm, wet

Fig. 9. AC510U cutting performance Fig. 7. AC510U cutting performance(Turning of Inconel 718) (High speed turning of Inconel 718)

SEI TECHNICAL REVIEW · NUMBER 67 · OCTOBER 2008 · 9 Figure 11 shows a case example of heavy-interrupt- ed cutting of iron-based heat-resistant alloys using AC520U Competitor PVD grade AC520U. While the competitor product showed break- After machining the same number of work pieces age due to wear after turning two work pieces, AC520U was capable of turning twice larger number of work pieces. Also, the wear on AC520U after machining was small, indicating possible further life expansion.

Possible tool life extension 5. Conclusion Material: Inconel 718 Insert: CNMG120412N-EX Cutting conditions: vc=55m/min, f=0.18mm/rev, This report described the features and use case ap=2.5mm, wet examples of AC510U and AC520U, the new turning insert grades for exotic materials. Fig. 10. AC520U cutting performance(Rough turning of Inconel 718) A future increase in the use of exotic materials is expected to increase not only in the aircraft industry but also in industries such as automobile and petroleum. AC510U and AC520U featuring more stable and longer life and higher cutting efficiency will contribute to AC520U reducing the tooling costs, production costs (by reduc- AC520U ing machining time,) and environmental burden.

Competitor Breakage Competitor PVD grade References PVD grade (1) Katsuyoshi Karino, Tool Engineer(Sep-2007),.10-20 24 (2) Haruyo Fukui et al., “Development of TiAlN/AlCrN Super Multi- layer Coating ‘Super ZX Coat’ and Application to Cutting Tools” Tool life (pieces machined) SEI Technical Review, No.169, P.60-64 (3) Akihiko Shibata, “‘ACE-COAT AC510U/AC520U’ for exotic Material: Iron-based heat-resistant alloy material machining”, Mechanical Engineering(Dec-2007),P.145 Insert: CNMG120412N-EX Cutting conditions: vc=60m/min, f=0.22mm/rev, ap=0.6mm, wet

Fig. 11. AC520U cutting performance (Heavy interrupted turning of iron-based heat-resistant alloy)

Contributors (The lead author is indicated by an asterisk (*)). A. SHIBATA* • Assistant Manager, Material Development Department, Sumitomo Electric Hardmetal Corp. H. FUKUI • Assistant Manager, Material Development Department, Sumitomo Electric Hardmetal Corp. K. TSUDA • Group Leader, Material Development Department, Sumitomo Electric Hardmetal Corp.

10 · Development of “ACE-COAT AC510U/AC520U” for Machining of Exotic Materials