nc-AlTiN/a-Si3N4 and nc-AlCrN/a-Si3N4 nanocomposite coatings as protection layer for PCBN tools in hard machining

The cutting material polycrystalline cubic boron nitride (PCBN) is ideally suited for machining of difficult-to-cut materials. It exhibits properties such as high hardness and high chemical stability at elevated temperatures. However, due to the occurrence of tribo-oxidation and abrasion during machining of hardened steels abrupt tool failure is common. The deposition of coatings offers a possibility to protect the PCBN substrate. Initial research results indicate that nanocomposite coated cutting tools show a significantly improved tool life and process behavior in hard machining. This paper describes the results of machining tests with uncoated and nc-AlTiN/a-Si3N4 and nc-AlCrN/a-Si3N4 nanocomposite coated PCBN tools with regard to the tool life and wear form. Additionally, the wear mechanisms abrasion and tribo-oxidation were investigated in model wear experiments. Furthermore, FEM cutting simulations were used to investigate the thermal interaction between substrate and coating.