Consequences of the additional presence of MC carbides on the behavior in oxidation at 1000°C of a cast Cantor high entropy alloy

Abstract

AbstractMC carbides can be successfully obtained in grain boundaries of some high entropy alloys of the Cantor type, to significantly improve their mechanical properties at high temperatures. They can also not be neutral for oxidation behavior. To explore their possible influence in this field, an equimolar CoNiFeMnCr reference alloy and two versions containing TaC or HfC carbides were prepared by casting and exposed to air at 1000°C. Their oxidation behaviors were studied by the analysis of mass gain kinetics measured in thermobalance and the characterization of the oxidation states of samples exposed in the furnace at the same temperature. The metallographic results show that, for all alloys, Mn is more involved in oxidation than Cr. The formation of a mixed oxide of these two elements is much less protective than chromia, as a result, mass gain much faster than chromia‐forming alloys. The presence of HfC carbides deteriorates again the oxidation behavior, in contrast with TaC which stays neutral in this field. From this point of view as well as for the mechanical one, TaC is to be preferred to HfC for strengthening the Cantor alloy.