Transverse-Rupture Strength and Adhesion of Layer in Coated Cemented Carbide by PVD Process

TiC, Ti(C, N) and TiN layers were coated by PVD (ion plating) process at 573∼853K on HIP-treated WC-10%Co substrates, after the surface of substrate was ground or polished. The transverse-rupture strength (TRS) of specimens at room temperature and the adhesion between the layer and the substrate were mainly studied. The TRS of each coated specimen decreased with increasing PVD temperature. The surface state of substrate (ground or polished) did not affect the strength of each coated specimen. The specimens fractured from the coated layer, when PVD temperature was over about 773 K. However, the specimens coated at lower temperatures than 773 K were apt to fracture from the inside of substrate with no decrease in TRS. Annealing treatments of the coated specimens caused the decrease in TRS, the strength decrease being larger with decreasing PVD temperature. The results of strength tests showed that sufficient adhesion appeared to be obtained between the layer and substrate independently of PVD temperature, sort of coated layers and substrate surface-state. However, according to the results of cutting and scratch tests, the adhesion of coated layer to the ground substrate appeared to be inferior to that to the polished substrate. This was attributed to the fact that the surface of substrate changed in its quality during grinding by diamond wheel.