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

The oxidation behavior of WC-TiC-TaC-Co hard materials was investigated at 300-900 degrees C. The results indicate that the oxidation reactions have been occurred as low as 350 degrees C. The mass gain is slight at 350-600 degrees C but increases significantly above 600 degrees 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 degrees 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. (C) 2014 Elsevier Ltd. All rights reserved.