High temperature fracture mechanism of ultrafine WC-Co cemented carbides containing (Ti,W)C

Ultrafine WC-Co cemented carbides containing different (Ti,W)C content were fabricated by spark plasma sintering and the fracture mechanism and transverse rupture strength at high temperature were investigated. At ambient temperature, the strength of cemented carbides gradually decreases with the increasing (Ti,W)C. Meanwhile, the fracture behavior presents a mixed mode of intergranular fracture of WC grain boundaries and cleavage fracture of (Ti,W)C. As the temperature increases, the strength of all cemented carbides gradually decreases. At 900 °C, the degradation of materials caused by oxidation leads to a rapid reduction of strength. Compared to WC-Co, samples containing higher (Ti,W)C content present relatively gentle decrease trends of strength. In the substrate (non-oxidized part beneath oxide scales), the (Ti,W)C inhibits the oxygen diffusion at crack tips, which reduces fracture paths along oxidized grain boundaries. At high temperature, the oxidation damage of grain boundaries and brittle-ductile transition of substrate have important effects on the fracture behavior.