High temperature oxidation resistance of Al0.25CoCrFeNiMn and Al0.45CoCrFeNiSi0.45 high entropy alloys

High-entropy alloys (HEAs) provide a wide chemical composition window to design novel materials with tailorable properties for harsh environment, especially for high temperature oxidation applications. This paper studies both theoretically and experimentally the oxidation behavior of Al0.25CoCrFeNiMn and Al0.45CoCrFeNiSi0.45 HEAs in the temperature range of 700 degrees C-1000 degrees C for 10 h in air atmosphere. Both samples exhibited a dendritic microstructure which underwent different phase evolution during 10 h of heating at 900 degrees C. Al0.45CoCrFeNiSi0.45 HEA oxidized at 900 degrees C exhibited only about 0.1 mg/cm2 weight gain after 10 h, while this value was about 1 mg/cm2 for Al0.25CoCrFeNiMn HEA oxidized at 900 degrees C. The superior resistance to hightemperature oxidation of Al0.45CoCrFeNiSi0.45 HEA was mainly ascribed to the formation of a protective Al2O3-SiO2 rich oxide layer on the surface of the alloy. For Al0.25CoCrFeNiMn HEA, the formation of noncompact oxide layer containing transition elements could not provide sufficient protection against oxidation at elevated temperatures. Finally, a fair correlation between thermodynamic calculations and experimental analysis of oxidation behavior was realized.