MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF WC-TIN-CO AND WC-TIN-MO2C-CO(NI) CEMENTED CARBIDES

In the present investigation the microstructure and the mechanical properties of WC-10Co, WC-8.7TiN-12Co and WC-7.5TiN-1.8Mo2C-6Co-6Ni cemented carbides were studied. Introduction of TiN in WC-10Co cemented carbide increased the mean WC grain size and the width of its size distribution. Incorporation of nickel and molybdenum in the binder cobalt improved the wettability of the hard phases with the binder and resulted in a decreased mean grain size of the hard phase and the width of its distribution. A large difference between the microstructures of hexagonal phase (WC) and cubic phase (TiN) was observed after hot isostatic pressing (HIP'ing) of the liquid phase sintered alloys. TiN, being more ductile in nature, had undergone substantial plastic deformation during HIP'ing which led to the formation of shear bands. The modification of the binder cobalt with nickel and molybdenum did not noticeably affect either WC/binder or TiN/binder interfaces. However, TiN containing cemented carbides after HIP'ing showed almost equivalent mechanical properties to that of WC-10Co. The predominant local fracture modes in different cemented carbides were found to be sensitive to the alloy composition.