Some properties of TiC-coated cemented tungsten carbides

Abstract

Results of a series of investigations into the behaviour of TiC-coated cemented carbide cutting tools under conditions of abrasive, adhesive, oxidation, and diffusion wear are reported. The coated tools had excellent resistance to all of these wear conditions. Hardness and transverse (bend) rupture strength of the coating in relation to its microstructure were also investigated. It wasfound that the elongated grains of the coating were oriented normal to the substrate surface and were responsiblefor the relatively low transverse rupture strength of the coated tools. The coating also cracked readily under thermal shock because of the mismatch in the coefficients of thermal expansion of the coating and the substrate. Examination of diffusion couples suggests that a thin η-carbide layer which develops just beneath the coating during the production process is partially responsible for the unexpected but continued good performances of coated tools even after portions of the coating have failed.