Tuning bias voltage to enhance oxidation resistance of AlCoCrNi high-entropy alloy coatings at 1000 ℃

AlCoCrNi-based high-entropy alloy (HEA) coatings have emerged as promising alternatives to conventional MCrAlY coatings due to their exceptional antioxidation properties. In this study, a series of AlCoCrNi HEA coatings were synthesized by DC magnetron sputtering under various bias voltages, and their antioxidation performance were evaluated at 1000 °C in air. The applied bias voltage was found to markedly influence the coatings` grain size and residual stresses—parameters critical to their antioxidative behavior. The grain size is directly correlated with the diffusion-controlled depletion of Al, which is pivotal for the genesis and thickening of the protective α-Al ₂O ₃ layer during high-temperature oxidation. Furthermore, the residual stress of the as-deposited HEA coatings impacts the compatibility of stress between the HEA coating and thermally grown oxide (TGO) layer, thereby affecting the TGO layer integrity and protective efficacy. Notably, the coating deposited under the bias voltage of −50 V exhibits superior oxidation resistance compared to other coatings by generating a robust and dense TGO layer with large grain size. This study delves into the intrinsic mechanisms underlying the bias-induced improvement in oxidation resistance of HEA coating.