Residual stresses and HRTEM phase interface structures of AlN structured PVD coatings on plate-grained WC–Co substrate

Abstract

A fine plate-like grained WC–12Co based alloy with (0001)WC texture coefficient of 2.73 for the sinter skin was used as the substrate. Single layer Al0.66Cr0.34N and two layers Al0.65Cr0.30Si0.04W0.01N/Al0.66Cr0.34N (AlCrSiWN/ AlCrN) approximate 1.6 μm in total thickness for each were separately deposited on the substrate in an industrial-scale arc evaporation system. This study aims to investigate the strengthening mechanism for the adhesion and the resistance against cohesive failure of the films and to prove a hypothesis of stress buffering function of the binder phase in the substrate to the film. Accordingly, coating related phase structure and residual stress change in the substrate and HRTEM phase interface structures of the film/substrate system were investigated. The results show that stress buffering by the Co phase (binder phase) is realized by energy absorption in a form of residual stress build-up and fcc to hcp phase transformation, accompanied by an atomic disorder Co zone in several atomic layer thickness adjacent to the AlCrN/Co interface. Coherent and semi-coherent epitaxial growth of AlCrN on WC surfaces is observed and the superiority of plate-grained WC–Co substrate is confirmed. Methods of exploiting the potential of the stress buffering function are proposed.