High throughput preparation and oxidation behavior of Al_xCr_y(TiTaNi)_100-x-y high entropy alloy film

Al_xCr_y(TiTaNi)_100−x−y high-entropy alloy (HEA) thin films with a continuous composition gradient were prepared using a high-throughput magnetron sputtering co-deposition method with three targets. The as-deposited films covered a compositional range of 12.7–38.5 at% Al, 9.8–30.0 at% Cr, and 47.0–72.1 at% TiTaNi and exhibited a predominantly amorphous structure with a small fraction of nanocrystals. High-temperature oxidation behavior was systematically investigated in dry air at 900 °C for 24 h. All films followed parabolic oxidation kinetics, with parabolic rate constants ranging from 1.15 × 10⁻⁵ to 5.47 × 10⁻⁵ mg²·cm⁻⁴·s⁻¹. Four composition-dependent oxidation regions were identified across the film, exhibiting different oxide scale characteristics ranging from mixed oxides (Al₂O₃, Cr₂O₃, TiO₂ and Ta₂O₅) to the formation of a continuous protective Al₂O₃ layer. The compositional range supporting the formation of a protective Al₂O₃ scale was determined to be 27.5–38.5 at% Al, 9.8–15.2 at% Cr and 51.7–59.9 at% TiTaNi. The oxidation mechanism was clarified by correlating composition variations with oxide scale evolution.