High-temperature oxidation behavior of AlCoCrFeNi2.1 eutectic high-entropy alloy: Microstructure evolution and microhardness

In this work, the high-temperature oxidation behavior at 820 °C of an AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) prepared by vacuum induction melting was studied, while the evolution of microstructure and microhardness at different oxidation times (1 h, 3 h, 5 h, 10 h, 20 h, 30 h, and 50 h) were also investigated. The prepared AlCoCrFeNi2.1 EHEA shows a typical FCC/BCC bi-phase microstructure with Cr-rich precipitation phase. Compared to 304 stainless steels, the AlCrCoFeNi2.1 EHEA exhibits a better oxidation resistance, which is due to the continuous and dense Al2O3 generated during high-temperature oxidation process. The AlCoCrFeNi2.1 EHEA also has an excellent high-temperature structure stability, proved by that the phase composition and elemental composition of each phase remain almost unchanged with the increase in oxidation time. After high-temperature oxidation, the microhardness of AlCoCrFeNi2.1 EHEA decreases as expected, however, with the increase in oxidation time, the microhardness shows a noticeable increasing trend due to the solid solution strengthening of the σ phase and formation of the α-Cr phase.