Effects of ultrafine WC on the densification behavior and microstructural evolution of coarse-grained WC-5Co cemented carbides

The effect of ultrafine WC on the macroscopic shrinkage behavior and microstructural evolution of coarse-grained WC-Co cemented carbides during sintering was studied. WC-Co composite powders containing mixture of ultrafine (300 nm) and coarse (6.0 pm) WC powders were prepared using a novel sol-gel process. The results indicate that ultrafine WC addition enhanced shrinkage in the composite powder compacts during solid state sintering, while its influence on densification process in liquid-phase sintering can be ignored. The microstructural evolution confirmed that ultrafine WC addition promote the spreading of cobalt binder and the formation of WC-Co agglomerate in initial state of sintering. And, ultrafine WC addition resulted in a more uniform densification in the solid state sintering. Mechanisms of the enhanced shrinkage include the accelerated spreading of Co due to shortened diffusion distances and the increased surface diffusion velocity, and the activated sintering of WC skeleton due to grain boundary sliding.