High-Temperature Oxidation Behavior of the FeCoNiCr0.8Al0.2 High-Entropy Alloy in Air

In this work, the oxidation behavior of the FeCoNiCr_0.8Al_0.2 high-entropy alloy (HEA) in air was systematically studied by the isothermal oxidation tests at 800, 900, and 1,000 °C. The results show that FeCoNiCr_0.8Al_0.2 HEA has excellent oxidation resistance, and the oxidation kinetics follow the parabolic law at all three temperatures. The oxide layer area of the alloy can be divided into the surface oxide layer and the oxide transition layer. When the temperature is 800 °C, the oxide region of the alloy only consists of the surface oxide layer mainly composed of Cr₂O₃ and Al₂O₃. With the increase of oxidation temperature, the alloy begins to appear oxide transition layer. When the temperature is 900°C and 1,000°C, the oxidation region of the alloy is composed of a surface oxide layer and an oxide transition layer. As the oxidation temperature increases, in the oxide layer region, Fe, Co, and Ni elements gradually diffuse outward, and NiFe₂O₄ and CoCr₂O₄ spinel oxide layers begin to appear in the phase composition of the surface oxide layer of the alloy. In the transition region, the Al oxides inside the alloy gradually increase.