A novel C-free Co-based alloy for high temperature tooling applications

The principle failure mechanism in thixoforming dies is thermal fatigue as the mechanical loading is modest owing to a mushy feedstock. A novel C-free Co-based alloy was submitted to thermal cycling under conditions which mimic thixoforming of steels. The eutectic carbides, typical of Stellite alloys, are replaced in this alloy with Mo-rich coarse secondary phase particles dispersed predominantly at interdendritic sites. Its response to thermal cycling is remarkable with at least a threefold service life extension with respect to the Stellite 6 alloy, identified to be the best die material for steel thixoforming until today. The superior thermal fatigue performance of the present alloy is attributed to its resistance to high temperature oxidation, to a Co-based matrix free of brittle carbides and to its potential to retain its mechanical strength at elevated temperatures.