Oxidation of WC-TiC-TaC-Co hard materials at relatively low temperature

•The oxidation process was performed at temperature range from 300 °C to 900 °C.•The mass change a little bit and increase significantly with temperature increased.•The Co binder and the hard phase own different oxidation initial temperature.•WC oxide shows many defects but solid solution oxide exhibits a compact layer.•The solid solution oxide shows higher thermal stability.

The oxidation behavior of WC-TiC-TaC-Co hard materials was investigated at 300–900 °C. The results indicate that the oxidation reactions have been occurred as low as 350 °C. The mass gain is slight at 350–600 °C but increases significantly above 600 °C. The Co binder is preferential oxidized to CoWO4 due to WC solution. Besides, WC and (W, Ti, Ta)C are oxidized to WO3 and mixture of TiO2 and TaxOy, respectively, until 400 °C. Lots of defects on the surface of WO3 accelerate substrate oxidation. On the contrary, the compact layer of the mixture prevents the inner oxidation and significantly enhances the oxidation resistance. A gradual increase in oxidation temperature causes a rapid growth of Co oxide and also promotes the deterioration of WO3. In contrast, the compact layer of the solid solution shows higher thermal stability.