High temperature oxidation microstructure analysis of Ni-based P/M superalloy coated with an inorganic aluminum coating

In this paper, TWL12 + TWL20 inorganic salt aluminum coating was sprayed on the surface of Ni-based P/M superalloy. The microstructure changes of inorganic salt aluminum coating and P/M superalloy after high temperature oxidation at 700, 750 ℃ and 800 ℃ were studied by XRD, SEM, EPMA and TEM. The results show that after high temperature oxidation, the surface structure of the coating peels off, and the aluminum in the coating diffuses with the substrate to form a transition layer composed of oxidation zone, diffusion layer and interdiffusion zone. The oxidation zone is the outermost layer, where is mainly enriched with O and Al elements to form Al2O3 layer. The diffusion layer mainly contains Ni and Al elements, forming NiAl phase and α-Cr phase dispersed in it. Finally, the interdiffusion zone rich in Ti, Cr, Co, Ta and other elements exists between the diffusion zone and the matrix, which is mainly composed of Ni2AlTi phase matrix and σ phase dispersed in it. The analysis shows that the thickness of transition layer changes with the increase of oxidation temperature, it is mainly manifested by the increase of the width of the interdiffusion zone, the increase of the size of α-Cr phase in the diffusion layer and σ phase in the interdiffusion zone, and the growth trend of σ phase along the vertical transition zone is intensified. The oxidation weight gain curve shows that the transition layer exhibits good oxidation resistance during high temperature oxidation at 750 ℃ and 800 ℃ after the surface structure of the coating falls off, it indicates that the TWL12 + TWL20 inorganic salt aluminum coating has the potential to provide high temperature oxidation coating protection for advanced P/M superalloy used in aeroengines