High-temperature oxidation of AlCrFeNi-(Mn or Co) high-entropy alloys: Effect of atmosphere and reactive element addition

Highlights: • Different oxidation mechanisms of Al_0.5CrFeNiMn alloy in oxygen and steam with much higher oxidation rate in oxygen. • Selective oxidation of Al and protective alumina scale established on Al_0.5CrFeNiCo alloy in both oxygen and steam atmospheres. • Beneficial effects of Y addition but detrimental effects of Zr addition with the same doping level of ~1 wt% on oxidation performance. The effects of atmosphere (oxygen and steam) and reactive element addition (Zr and Y) on high-temperature oxidation behavior of Al_0.5CrFeNiMn and Al_0.5CrFeNiCo high-entropy alloys at 1000 °C and 1200 °C were studied. The Al_0.5CrFeNiMn alloy displayed different oxidation mechanisms in oxygen and steam owing to differing oxygen partial pressures and preferential oxidation of Mn. A protective alumina scale established on Al_0.5CrFeNiCo alloy in both atmospheres and the beneficial effects of Y addition are seen by remarkably improved oxide scale adherence and suppression of convoluted oxide scale morphology. However, doping with 1 wt% Zr deteriorates the oxidation resistance with substantial Al+Zr internal oxidation.