Effects of TiC0.4 on microstructure and properties of WC composites

Abstract

WC composites with 5 wt% TiC0.4 were fabricated by spark plasma sintering (SPS) at sintering temperature of 1400–1700 °C for 10 min under an external pressure of 50 MPa. It can be observed that the WC-5 wt% TiC0.4 composites mainly consisted of WC phase and non-stoichiometric (W1−x, Tix)Cn solid solution phase and the amount of WC dissolving in TiC0.4 increased with sintering temperature. The (W1−x, Tix)Cn solid solutions uniformly distributed around WC grains and formed a semi-coherency interface with WC, which restricted the growth of WC grains and enhanced mechanical properties of the WC-5 wt% TiC0.4 composites. The average grain size of WC (251.5 ± 201.6 nm) in WC-5 wt% TiC0.4 composite sintered at 1600 ℃ was considerably smaller compared to most of previously reported WC-based composites. The existence of high content of C vacancies in non-stoichiometric TiC0.4 raised remarkably the diffusion rate of W and Ti atoms in the sintering process of WC-5 wt% TiC0.4 composites in contrast with stoichiometric TiC. The WC-5 wt% TiC0.4 composite sintered at 1600 ℃ possessed the optimum properties, with the hardness of 21.9 GPa, fracture toughness of 7.6 MPa·m1/2, flexural strength of 612 MPa and compressive strength of 2.7 GPa. Moreover, it can be confirmed that the oxidation resistance of WC-5 wt% TiC0.4 composite at higher temperature outperformed that below 1218 ℃. In addition, the WC-5 wt% TiC0.4 composite sintered at 1600 ℃ showed higher high-temperature hardness, lower thermal conductivity and better resistance to oxidation than those of conventional WC-Co composites.