Oxidation behavior of titanium carbonitride based materials

The oxidation behavior of two different Ti(C,N)-WC based materials (a ceramic type containing 0.9 wt.% Co and a cermet type containing (6.2Ni + 2.9 Co) wt.%), was tested at 900 and 1000 degreesC in static laboratory air. The values of the mass gain (similar to50 m g/cm(2) after 100 h at 1000 degreesC and extended microstructural modifications demonstrated that these materials are rather unstable under oxidizing conditions. After an initial transitory period where the mass change resulted from the competition between the mass gain due to formation of solid TiO2 and the mass loss due to released volatile tungsten oxides that were formed, the oxidation process obeyed a linear law in function of the exposure time, i.e. it is governed by a chemical reaction at the interface of the titanium based carbonitrides transformed into TiO2. Oxidation kinetics and mechanisms were discussed in terms of the phase composition, presence of metal binder at grain boundaries, and of the residual porosity of the starting materials. (C) 2002 Elsevier Science Ltd. All rights reserved.