Oxidation of WC-Co, WC-Ni and WC-Co-Ni hard metals in the temperature range 500-800 degrees C

Oxidation of WC-16%Co, WC-8%Co-8%Ni and WC-16%Ni hard metals in the temperature range between 500 and 800 degrees C was investigated by TGA, XRD and SEM methods. The thermodynamics of tungsten carbide oxidation reactions was calculated. Oxidation kinetics of the alloys follows a complex behaviour. The WC-16%Co alloy is oxidized to a lesser degree than the WC-16%Ni alloy in the temperature range 650-800 degrees C. Oxidation resistance of hard metals is governed by phase composition, formation mechanism of the scales and protective properties of the oxidation products (CoO, NiO, WO3 and complex oxides, based on the formula (Ni, Co)WO4).