Oxidation behavior of AlCoCrFeNiSi x high-entropy alloys at 1100 ℃

Highlights: • Oxidation behavior of AlCoCrFeNiSi_x high entropy alloys at 1100℃ was investigated. • Microstructure of the alloys changed from single BCC to BCC + Silicide with addtion of Si. • Si_0.2 alloy exhibited best oxidation resistance due to formation of single and compact Al₂O₃ scale after 200 h oxidation. • Excessive Si addition imposed an adverse affect on the oxidation resistance of the alloys. AlCoCrFeNiSi_x high-entropy alloys containing different Si contents (x = 0, 0.2, 0.5, 0.8, 1.0 in molar ratio) were prepared by vacuum arc-melting. The microstructure and oxidation behavior of these alloys at 1100℃ for 200 h were investigated. After adding Si, the alloys mainly consist of BCC and Si-rich precipitates, and both the size and quantity of the Si-rich precipitates increase with increase in the Si content. A suitable content of Si in the alloys improves the oxidation resistance for promoting the formation of a dense single Al₂O₃ scale, while excessive Si imposes an adverse effect by forming easy-peeling scales composed of Al₂O₃ outer layer and mixed oxides inner layer. Formation and failure mechanisms of the oxide scales on these alloys during oxidation have been discussed.