The oxidation mechanisms of Pt and reactive elements modified AlCoCrFeNi2.1 eutectic high-entropy alloy at high temperature

AlCoCrFeNi 2.1 eutectic high-entropy alloys (EHEAs) show great potential in high-temperature applications due to the dual-phase lamellar structure. In this work, the high-temperature oxidation behavior and scaling mechanisms of three AlCoCrFeNi 2.1 EHEAs (EHEA, Y–Hf EHEA, Pt–Y-Hf EHEA) were studied. It was found that the oxide formed on AlCoCrFeNi 2.1 EHEA peel off over a large surface area after a short-term oxidation. The diffusion-induced voids accumulate at the oxide/alloy interface cause the spallation of oxide on the influence of thermal stress. In contrast, a continuous and adherent Al 2 O 3 scale formed on the Y–Hf EHEA and Pt–Y-Hf EHEA. Internal oxidation of Y, Hf reactive elements is found in Y–Hf EHEA, which induce an abnormal rapid growth of surrounding oxides. Pt element in the Pt–Y-Hf EHEA suppressed the over-doping effect of Y and Hf element, resulting in the growth of a more homogeneous and protective α-Al 2 O 3 scale.