Effects of TaCx on the microstructure and properties of WC composites

Abstract

WC-5vol.%TaCx (where x = 0.5, 0.7, 0.8 and 0.9) binderless cemented carbides with different carbon vacancy contents were prepared by spark plasma sintering (SPS) at a lower sintering temperature of 1800 °C. The phase evolution, microstructure and mechanical properties of these materials were investigated. The results show that the presence of WC, W2C and (Ta1-x, Wx)Cn phases in the sintered body. The formation of (Ta1-x, Wx)Cn solid solution is attributed to the dissolution of WC into TaCx, and the existence of vacancies promotes the atomic diffusion. (Ta1-x, Wx)Cn solid solution was uniformly distributed around the WC matrix, which inhibited the WC grain growth. In terms of fracture mode, the WC-5vol.%TaCx composites exhibit a combination of intergranular and transgranular fracture, with crack deflection and bridging contributing to enhanced fracture toughness. Compared to other WC-TaCx composites with varying carbon vacancy content, the WC-5vol.%TaC0.8 composite possesses the smallest average particle size and highest intrinsic hardness. Additionally, a semi-coherent interface is formed between (Ta1-x, Wx)Cn and WC, leading to improved mechanical properties such as highest hardness (24.4GPa) and fracture toughness (8.5MPa·m1/2). The WC-5vol.%TaC0.8 composite, however, exhibits the lowest oxidation onset temperature attributed to its relatively smaller grain size. The introduction of carbon vacancies serves to facilitate atom diffusion and lower the densification temperature, while also functioning as a toughening agent.