Effects of TaC on microstructure and mechanical properties of coarse grained WC-9Co cemented carbides

Coarse grained WC-9Co cemented carbides with 0-1.0% TaC (mass fraction) were fabricated by HIP-sintering and gas quenching. The effects of TaC on the microstructures and mechanical properties were investigated using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), X-ray diffractometry (XRD) and mechanical properties tests. The results show that the maximum values of hardness and strength are HV 1124 and 2466 MPa respectively when 0.4% TaC is added. When the content of TaC is more than 0.6%, the grain size of WC is no longer affected by the amount of TaC, and (W,Ta)C occurs as well. Moreover, the strength and fracture toughness increase and the (Ta+W) content decreases with the increase of TaC content. The dependence of (Ta+W) content on the mechanical properties indicates that (Ta+W) content in Co should be decreased as low as possible to improve the mechanical properties of coarse grained WC-TaC-9Co cemented carbides with the microstructure of WC+gamma two phase regions.