Effects of Ta content on microstructure and oxidation behavior of AlCoCrFeNiYTa_x high entropy alloy

The oxidation behavior of the AlCoCrFeNiYTa_x high entropy alloy (HEA) doped with different Ta contents at 1100 °C is investigated. In this study, different reasons for the spallation of the oxide scales of HEAs without/with excessive Ta addition after 1000 h of oxidation are discussed, and the most suitable Ta doping content for this HEA is explored, in which the HEA exhibits both an exceptionally low oxidation rate, and the formation of oxide scales composed of intact α-Al₂O₃. Meanwhile, it is found that the addition of Ta can effectively inhibit the phase transition of β phase, which makes the surface of the oxide scale smoother. By combining our experimental results with Wagner–Hauffe theory, the influence of Ta drag effect on oxide scale growth is explained, which provides some theoretical guidance for the subsequent design of AlCoCrFeNi HEAs, and can lead to the development of thermal barrier coatings at higher service temperature.