Experimental and Thermodynamic Exploration of the High-Temperature Microstructures of Co-30 wt.% Cr- (2.5-5.0 wt.%) C Alloys
Résumé
Cobalt alloyed with high contents in Cr and C potentially may lead to hard alloys candidate for high temperature applications involving wear degradations. The Co-30%wt-xC system was explored from x=2.5 to 5wt.% by both experiments and thermodynamic calculations. The stable microstructures at 1000, 1100 and 1200°C and the temperatures of solidus and liquidus were of interest. When the carbon content is between 2.5 and 3.5 the alloys display (hypo-)eutectic microstructures composed of FCC Co-based matrix and M 7 C 3 carbides. Between 4 and 5wt.%C, the microstructures contain coarse pro-eutectic M 7 C 3 carbides, leading to a total volume fraction of M 7 C 3 close to 50% or higher. The C-richest alloys also contain graphite, instead cementite as predicted by calculations. A better agreement between experiments and calculations about microstructures and solidus temperature can be obtained by forbidding cementite in the calculation conditions. The obtained hardness level is about 650Hv but decreases when the heat-treatment temperature increases.
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