| Abstract | The combined effects of high-temperature and long-term exposure to oxidation environment on an AlCoCrFeNi-based high entropy alloy (HEA) are investigated. The alloy has a composition of Al₁₀Co₂₀Cr₂₀Fe₂₀Ni₃₀ (at%) and is oxidized in lab air at 1000 °C for 1000 h to emulate working conditions and long operation cycles of gas turbines. The microstructure and oxide formation of the HEA are characterized using scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. The performance of the HEA is compared to that of Inconel 625 and Hastelloy X and shows slower oxidation kinetics than Inconel 625 until 750 h. The HEA has the thinnest oxide layer of the three alloys and exhibits a triplex structure with a continuous Cr₂O₃ outer scale, a semi-continuous Al₂O₃ subscale, and deep AlN precipitates. The matrix shows signs of Cr and Al depletion after 1000 h, leading to its inability to replace the degraded oxide scales that evaporated or spalled, and decreases its long-term oxidation resistance. Overall, the HEA shows good oxidation resistance until 750 h, but may benefit from a higher Al content on the surface to form a longer-lasting Al₂O₃ subscale that would remain protective beyond 750 h. |
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