High temperature oxidation behavior of atmosphere plasma sprayed AlCoCrFeNi high-entropy alloy coatings

In this work, AlCoCrFeNi high-entropy alloy (HEA) coating was prepared by atmosphere plasma spraying (APS) and the oxidation behavior at 800, 900, 1000 °C was studied. A new passivation mechanism based on element migration and oxidation process was proposed. Results showed that the weight gain curve of HEA coating was a two-stage parabola. The steady-state oxidation of Al was dominant at all temperatures within 50 h. Al migrated laterally and longitudinally to form a dense Al2O3 passivation layer with mesh structure, which effectively prevents the internal diffusion of O. High temperature induced BCC to FCC phase transformation of HEA alloy thus resulted in the formation of Fe-Ni-rich spinel oxides. The proposed mechanism indicated that increasing Al content in AlCoCrFeNi coating would improve its oxidation-resistance.