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As-Cast Microstructures and Hardness of Chromium-Rich Cobalt-Based Alloys Reinforced by Titanium Carbides

Khair M and Berthod P

Three cobalt-based alloys containing chromium for good chemical resistance at high temperature and both carbon and titanium in quantities great enough for expecting developing significant TiC network to mechanically reinforce them at high temperature, were synthesized by foundry. This Co-25Cr-0.25C or 0.50C-1Ti or 2Ti (all contents in wt%) were successfully obtained, thanks to the fusion and solidification both in inert atmosphere. The obtained microstructures were composed of a dendritic matrix and of interdendritic carbides, mainly of the TiC composition in the three alloys but chromium carbides are also present, notably in the Co-25Cr-0.50C-1Ti. The titanium carbides are of the script-like morphology and are imbricated with matrix in the interdendritic spaces, seemingly forming a eutectic compound with it. The higher the carbon content, the more numerous the carbides whatever their nature, and the higher the titanium content the more numerous the titanium carbides. The hardness is of about 300Hv10 Kg for the 0.25C-containing alloy and of about 370Hv10 kg for the two 0.5C-containing ones. Some particles looking more or less as titanium carbides are rather titanium carbonitrides Ti(C,N) et the presence of titanium oxides was observed in some locations in the bulk. Obviously the elaboration protocol using commercial argon is not well adapted to the strong tendency of titanium to react with O and N.