A Study of Oxidation Behaviour of WC-Co, Cr3C2-NiCr And TiC-Ni-Based Materials in Thermal Spray Processes

In this paper the oxidation behaviour of WC, Cr₃C₂, and TiC and their composites with binder metals is compared on the basis of literature data and some oxidation experiments. It was found that the oxidation mechanisms in air, which are more or less equal to service conditions of coatings, seem to be totally different from those in the spray process in the case of WC, but similar in the case of TiC and Cr₃C₂. Oxide layer scale adhesion strengths and, possibly, the high volatility of WO₃ seem to be responsible for this difference. It can also be assumed, that the problem of oxidation of TiC-based materials and Cr3C2-NiCr is that of local oxidation on the surface of the spray powder particles during the spray process. Cr₃C₂-NiCr and TiC-based materials are characterized by a high oxidation resistance in air. Plain WC-Co oxidizes readily in the temperature range 400-600°C, but alloying with Cr, as for instance in WC-CoCr and WC-(W,Cr)₂-Ni spray powders increases the oxidation resistance.