The effect of heat treatment on the oxidation resistance of cobalt-based superalloys

Degradation of the mechanical integrity of cobalt-based superalloys can occur as the carbide network is progressively oxidised during high temperature service. In this study, a heat-treatment aimed at redistributing the carbides was tested on two similar commercial Co-based superalloys, one with high C content (Co-101) and one with low C content (Stellite-21), to determine its influence on oxidation resistance. It was found that the carbide phases in the lower C-containing alloy could be solutioned more readily than the higher C-containing alloy, enabling the continuity of the carbide network to be reduced. This resulted in a reduced attack of the carbides down the interdendritic channels during oxidation testing, but increased thickness of the oxide overscale.