Role of the rare-earth elements effect in transforming the oxidation behavior of Al CoCrFeNi high entropy alloys

The immersion method leading to the formation of nano-dispersion of Gd 2 O 3 on the surface of Al x (CoCrFeNi) 100 −x alloys ( x = 3; 6; 9) is used to improve their corrosion resistance in air at 900 °C. Gd-modified samples' mass gains are greatly reduced and scales' spallation is nearly suppressed during thermal cyclic oxidation. Scales of the modified samples are much simpler, consisting mainly of Cr 2 O 3 , and spinel precipitates, with very low thickness (<5 µm) even after long exposures. Analysis of the oxidation products confirms the radically different oxidation behavior of the modified samples, proving the effectiveness of the reactive elements effects in HEAs. • Influence of Gd on high-temperature oxidation behavior of Al x CoCrFeNi alloys is studied. • Modification with Gd suppresses the scale degradation under thermal cycling conditions. • Additionally, significant changes in the scales' composition and thickness are observed. • Transformation of oxidation behavior from unsatisfactory to highly protective is achieved.