Improving high-temperature oxidation behavior by modifying Al and Co content in Al-Co-Cr-Fe-Ni high-entropy alloy

Composition modification was introduced to improve the oxidation resistance by varying Al and excluding Co from the Al-Co-Cr-Fe-Ni system. Since adjusting the composition shifted the valence electron concentration (VEC) of the alloys, the dual-phase structure of the alloys is expected to be more stable. At low temperatures (T < 1273 K), the alloys formed mixed oxide products. As oxidation temperature increased, only Cr2O3 or Al2O3 dominated the alloy's surface. Compared to equiatomic AlCoCrFeNi (5-Equi), non-equiatomic AlCoCrFeNi (5-B 40) and four-component AlCrFeNi (4-B 2013) had better oxidation resistance due to monocrystalline-Al2O3 formation. Besides the role of oxide formation, maintaining BCC and B2 phases within the alloys is also beneficial to supporting the stable Cr2O3 or Al2O3.