Oxidation Behavior of the CrMnFeCoNi High-Entropy Alloy

Oxidation of the Cr20Mn20Fe20Co20Ni20 (at%) high-entropy alloy (HEA) was investigated at 500-900 A degrees C in laboratory air. At 600 A degrees C the oxide was mainly Mn2O3 with a thin inner Cr2O3 layer; at 700 and 800 A degrees C it was mainly Mn2O3 with some Cr enrichment; at 900 A degrees C it was Mn3O4. The oxidation rate was initially linear but became parabolic at longer times with an activation energy of 130 kJ/mol, comparable to that of Mn diffusion in Mn oxides but much lower than that for sluggish diffusion of Mn in the HEA. The diffusion of Mn through the oxide is considered to be the rate-limiting process.