Phase composition in cemented carbides and cermets

Abstract

Cemented carbides and cermets of types WC-Co, WC-MC-Co, TiC-TiN-Mo 2C-Ni/Co and (Ti, W, Ta)(C, N)-(Co, Ni) have been studied with atom probe field ion microscopy and analytical electron microscopy. All materials were found to have a hard phase skeleton with grain boundary segregation of binder metal. The binder phase contained metal atoms from hard phases but was almost completely free of C and N. Cobalt binder phase contains W and Mo but little Ti, nickel binder phase Ti and Mo. The amount of Ti did not vary much with N content in the alloy, whereas the Mo content increased substantially with total N content. Materials containing more than one hard phase formed a core-rim structure. No diffusion of metal atoms occurred in the hard phases during sintering, but C and N may diffuse so that the system approaches ( para)-equilibrium with respect to these elements during sintering.