Ultrafine cemented carbides with superhigh fracture strength - Optimization of carbon content and grain growth inhibitor

The carbon content was optimized in the synthesis of WC-Co composite powder by in-situ reactions. The particle sizes were optimized for the grain growth inhibitors (GGI) of VC and Cr₃C₂. A series of experiments were performed using various GGI with different particle sizes. The effects of carbon content and GGI characteristics on the properties of cemented carbide bulks prepared by sinter-HIP were studied. A transverse rupture strength higher than 5100 MPa was achieved in the ultrafine WC-12Co cemented carbide bulk, which had the best combination of carbon content in the in-situ synthesis of composite powder and GGI particle size in the sintered material. It was found that with decreasing the Cr₃C₂ particle size, the toughness and strength of the sintered bulk materials increased significantly and reached a maximum. The opposite trend appeared when decreasing the VC particle size. Moreover, addition of nanoscale VC particles caused inhomogeneous microstructure and hence deteriorated the fracture strength. The weakening of wettability of WC grains towards Co binder by the VC nanoparticles was considered the reason.