Oxidation Behavior and Creep Resistance at 1100°C of Cast MC-Strengthened CoNiFeMnCr HEAs

To explore cast HEAs reinforcement by MC carbides three equimolar CoNiFeCrC alloys without or with Carbon and either hafnium or tantalum were investigated. Their microstructures were specified and tests at 1100°C in oxidation by air and flexural creep tests were carried out. The HEAbase was single–phased. The HEAhfc and HEAtac contained eutectic script HfC and TaC carbides respectively, in the interdendritic spaces. After oxidation for 50h at 1100°C all alloys were covered by a (Cr,Mn)2O3 scale with various proportions in Cr and Mn. HfO2 or CrTaO4 also formed. The subsurface was depleted in Cr and especially in Mn. The HEAbase alloy deformed quickly. The MC carbides greatly improved the creep resistance, and divided deformation by five to ten times.