Oxidation Resistance of AlCoFeNiCux High Entropy Alloys

The oxidation behavior of as-cast AlCoFeNiCux (x = 0.6–3.0) high entropy alloys was studied by isothermal annealing in flowing synthetic air at 1000 °C. A formation of an external protective Al2O3 scale has been found. The oxidation kinetics followed a parabolic rate law. The rate constants were increasing with increasing Cu concentration in the alloys. A scale spallation on the alloys with higher Cu concentration was observed. The spallation facilitated a penetration of oxygen through the scale and promoted the formation of CuO and CuAl2O4. The oxidation mechanism of the AlCoFeNiCux alloys is discussed and compared with previously studied high entropy alloys.