Influence of WC replacement by TiC and (Ta,Nb)C on the oxidation resistance of Co-based cemented carbides

At 600 °C, the oxidation kinetics obeys a linear function and the increasing content of (Ta,Nb)C causes a reduction of the oxidation rate, which is significantly further decreased by alloying with TiC. In contrast, at 800 °C, the oxidation kinetics follows a parabolic law. In addition, results reveal that an improvement of oxidation resistance at 800 °C is only attained by TiC addition. The oxide scale consists mainly of Co3O4, WO3 and CoWO4. Inclusions of TiO2 within the scale were observed for TiC contents above 14 mol%. Thus, the main factor affecting the oxidation resistance is the content of WC after the replacement by the mixed carbides and the passivation effect of the Ti, Ta and Nb oxides.