Oxidation behavior of titanium carbonitride-based materials

The oxidation behaviour of two different Ti(C,N)-WC based materials (a ceramic type, containing 0.9 wt% Co and a cermet type, containing (6.2Ni + 2.9Co) wt %), was tested at 900 and 1000°C in static laboratory air. The values of the mass gain (~53 mg/cm2 after 100 hours) and extended microstructural modifications demonstrated that these materials are rather unstable under oxidizing conditions. After an initial transitory period where the mass change results from the competition between the weight gain due to formation of solid TiO2 and the weight loss due to evaporation of tungsten oxide that form, the oxidation process obeys to a linear law in function of the oxidation time, i.e. it is governed by the chemical reaction at the interface of the Ti based carbonitrides into TiO2. Oxidation kinetics and mechanisms are discussed in terms of the phase composition, the presence of metal binder phases at grain boundaries, the residual porosity of the starting materials.