Superior oxidation resistance of a Y-Hf co-doped Al 18 Co 30 Cr 10 Fe 10 Ni 32 eutectic high-entropy alloy at 1100-1300 ° C

We report a study on the oxidation behavior of Al 18 Co 30 Cr 10 Fe 10 Ni 32 eutectic high -entropy alloy co -doped with reactive elements (RE) Y and Hf at 1100-1300 degrees C. The highly stable eutectic microstructure of gamma' / beta phases within this alloy contributes to a low coefficient of thermal expansion, thus a low residual stress in the Al 2 O 3 scale. The spinel with a low thickness is formed at the top of Al 2 O 3 scale at 1100 degrees C due to the low Al diffusion coefficient of gamma'- phase and low aspect ratio of beta- phase in maze -like eutectic region. As the oxidation temperature increases, the oxidation products transition to exclusive Al 2 O 3 at 1200 degrees C and 1300 degrees C, facilitated by the increased Al diffusion coefficient. The Al 2 O 3 scale exhibits a dominated columnar grain microstructure at 1100-1300 degrees C, suggesting that the inward O diffusion plays more critical role than Al diffusion and thus leads to the low oxidation rate. Besides, the segregation of S to scale/metal interface is inhibited by the uniform RE distribution in the alloy resulting from the fine eutectic microstructure in the alloy. Overall, this alloy exhibits low residual stress in the oxide scale, slow oxidation rate, and the lack of interfacial sulfur segregation, thus contributing to its superior oxidation resistance. The strong oxidation resistance of Y-Hf co -doped Al 18 Co 30 Cr 10 Fe 10 Ni 32 eutectic highentropy alloy makes it a potential candidate for advanced oxidation -resistant alloy or coating applications.