High Temperature Properties of an Equimolar CoNiFeCr Medium Entropy Alloy Added with Titanium

This study investigates the effects of Ti addition on the microstructures, melting temperature ranges, thermal expansion behavior, high temperature creep and oxidation resistances of an equimolar CoNiFeCr alloy of a foundry origin. 1.5 wt.% Ti added did not really change the single–phased state of the reference quaternary alloy but induces a significant decrease of the melting start and melting end temperatures. The thermal expansion coefficient is slightly lowered only while the creep resistance at 1100°C is significantly enhanced. The oxidation at 1200°C is controlled by species diffusion through a continuous chromia layer and the parabolic constant is higher than for the quaternary alloy, due to external and internal Ti oxidation. The presence of a thin layer of titanium oxide covering the chromia scale is suspected to limit chromia volatilization and scale spallation at cooling. Globally Ti demonstrated a globally beneficial influence of the high temperature properties of the alloy.