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Thermodynamic study, elaboration and high temperature oxidation of alloys highly strengthened by tantalum carbides. Part 1: Case of a Co-30Cr-1C-15Ta alloy

Laura Corona, Patrice Berthod

Many alloys designed for wear resistance are composed of ametallic matrix and a high fraction of carbides. When the matrix is based on cobalt there are often chromium carbides or tungsten carbides which play the role of hard phases. In this work a newalloy, based on cobalt and rich in chromium, elaborated by foundry and wished to contain great fraction of another type of carbide: TaC, was considered. With high amounts in both carbon and tantalum, respectively 1 wt.% and 15 wt.%, great volume fractions in tantalum carbides were obtained. Most of them are script-like eutectic carbides situated in the interdendritic spaces, amicrostructure feature known to be favourable to general mechanical resistance at high temperature, and additional compact TaC carbides were also present. The obtained hardness is of a good level (about 440 Hv30kg) and the resistance to high temperature oxidation, evaluated during 46 hours at 1150°C, was good with an obvious chromia-forming behaviour and the development of only a limited carbidefree zone from the surface.