The role of Al on microstructure and high-temperature oxidation behavior of AlxMnCrCoFeNi (x=0, 0.2, 0.4, 1) high-entropy alloys

In this study, the effect of Al content on microstructure and high-temperature oxidation behavior of AlxMnCrCoFeNi (x = 0, 0.2, 0.4, 1) high-entropy alloys were investigated. High-entropy alloys with different compositions were synthesized by vacuum melting. Analysis of the microstructure and phase composition was performed by Backscatter Electron Microscopy and X-ray diffraction methods. The microstructures of the alloys were FCC for Al0 and FCC + BCC/B2 for other alloys. Cyclic oxidation tests were performed in an air atmosphere for 120 h at 1000 ?. The oxidation kinetics obeyed the parabolic law, and the main component of the oxide layer was Mn oxide. With increasing Al, a fine and dense Al2O3 oxide film was formed at the bottom of the oxide layer. The parabolic rate constant (K-p) decreased with Al content up to 8 at.%, whereas a further increase in Al concentration to 16 at.% revealed an inverse effect.