The role of Nb on the high temperature oxidation behavior of CoCrFeMnNbxNi high-entropy alloys

The high temperature oxidation behavior of CoCrFeMnNbxNi high-entropy alloys in air was studied. As-cast CoCrFeMnNb0.25Ni alloy is a duplex-phase structure of FCC plus Laves phase. The oxidation kinetics of alloys followed parabolic rate law and the corresponding oxidation rate constants were calculated. In the oxidation process, Nb plays a dual role: On the one hand, the new Laves phase at the oxidation scale/alloy interface hinders the outward diffusion of active metal cations and improves the oxidation resistance; On the other hand, the Laves phase inside the alloy becomes the channel for oxygen ions to diffuse inward and forms internal oxidation.