The failure behavior of thermally grown oxide of the AlCoCrFeNi bond coating prepared by atmospheric plasma spray at 900–1000 °C

Abstract

The AlCoCrFeNi high entropy alloy bond coating was prepared by atmospheric plasma spray. The growth process and failure behavior of the thermally grown oxide (TGO) layer during the oxidation of the AlCoCrFeNi bond coating at 900–1000 °C were investigated. Results show that the AlCoCrFeNi bond coating generates a protective TGO layer composed of Al2O3 at 900–1000 °C, which effectively reduces the oxidation rate of the coating. The oxidation kinetic curves of the AlCoCrFeNi coating at 900–1000 °C exhibited a parabolic pattern. Until 50h oxidation, the TGO layer at 900 °C remained complete. In contrast, the TGO layer exfoliated at 1000 °C, associated with the thermal mismatch stress between the TGO layer and the AlCoCrFeNi coating. The growth of the TGO layer is primarily controlled by the outward diffusion of Al ions, which causes the generation of Al ion vacancies within the coating, consequently developing into visible pores. The presence of pores exacerbates the possibility of TGO layer exfoliation. The control of the outward diffusion process of Al ions, which can reduce the growth rate of the TGO layer and the amount of pores in the coating, is an important idea to improve the oxidation resistance of AlCoCrFeNi coating.