Properties of TaN Coating Film Deposited on WC-Co-Based Cemented Carbide Using Magnetron Sputter Ion Plating

Abstract

Various methods of surface modification technology are available for yielding high function characteristics such as wear-resistance, lower or higher friction coefficient, corrosion-resistance and thermal-resistance on the surface of the material. Generally, the coating of a hard material like ceramic on the surface of a material is a popular surface modification technology. The physical vapor deposition (PVD) method, which is one of the coating technologies, is widely used because it can be coated at a lower treatment temperature of 470K – 870K. In cutting, e.g. turning, milling, drilling and tapping, coated cemented carbide tools, which have good fracture toughness and wear resistance, seem to be effective tool materials. In this case, the titanium based films (e.g. TiN, Ti(C,N), (Ti,Al)N) are generally used as the coating film. However, the tantalum based films (e.g. TaN, TaC) are not applied as the coating film for cutting tools because the melting point of TaC is higher than that of TiC. Moreover, it is unclear whether TaN coating film can be used as a coating film of WC-Co cemented carbide cutting tools. In this study, to clarify the effectiveness of tantalum (TaN) coating film, we measured the thickness, hardness and scratch strength (critical load measured by scratch tester) of TaN coating film formed on the surface of the substrate which was a cemented carbide ISO K10 by the magnetron sputter ion plating process. The hardened steel ASTM D2 (JIS SKD11) was turned with the TaN and the (Ti,Al)N coated cemented carbide tools. The tool wear of the TaN coated cemented carbide tool was experimentally investigated and compared with that of the (Ti,Al)N coated tool. The following results were obtained: (1) Droplets on the surface of the TaN coating film, which has the K10 substrate, were negligible. (2) The micro-hardness of TaN coating film 2510HV was higher than that of TiN coating film 2090HV, and there was little difference in hardness between the TaN 2510HV and (Ti,Al)N 2710HV. (3) The critical scratch load of TaN coating film over 130N was higher than that of TiN coating film 68N or (Ti,Al)N coating film 73N. (4) In cutting the hardened steel using TaN and (Ti,Al)N coated tools, the wear progress of the TaN coated carbide tool was almost equivalent to that of the (Ti,Al)N coated carbide tool. The above results clarify that the TaN coating film, which is a new type of coating film, has both high hardness and good adhesive strength, and can be used as a coating film of WC-Co cemented carbide cutting tools.