Microstructure and high-temperature oxidation behavior of Al2O3/Cr composite coating on Inconel 718 alloy

In this paper, Al2O3/Cr composite coatings were prepared on the surface of Inconel 718 alloy by cathodic liquid plasma electrolytic deposition (CLPED) and double-glow plasma surface alloying (DGPSA) processes. The microstructure and high-temperature oxidation behavior of Al2O3/Cr composite coating were investigated. The results showed that the Al2O3 interlayer surface was fully covered with Cr coating. The interface between the Al2O3 layer and the Cr metal layer presents a mechanical interlock effect, which can absorb the deformation caused by thermal expansion, thereby reducing the adverse effects of thermal stress. The surface roughness of the Al2O3 coatings decreased after depositing Cr coating. The oxidation weight gain of the Al2O3/Cr composite coatings were significantly lower than that of the substrate, indicating that the Al2O3/Cr composite coatings improved the high-temperature oxidation resistance of Inconel 718 alloy. The oxidation weight gain of the Al2O3/Cr composite coatings at different frequencies were similar, while the Al2O3/Cr composite coatings at 400 Hz was lowest. During the high-temperature oxidation process, the Al2O3 interlayer can effectively inhibit the external diffusion of Ni, Fe and other elements in the matrix, which helps to prevent the cracking of the outer oxide film, thereby reducing the oxidation rate.