Microstructure and oxidation resistance of cryomilled NiCrAlY coating by laser induction hybrid rapid cladding

To further improve the oxidation resistance of NiCrAlY bond coat, the primary NiCrAlY powder processed by mechanical cryomilling was deposited on Ni-based superalloy by laser induction hybrid rapid cladding (LIHRC). The mechanical cryomilling induced the formation of γ′-Ni3Al and the dissolution of β-NiAl in cryomilled NiCrAlY powder, which in turn was only composed of γ/γ′ (γ: Ni, Cr-rich phase). The cryomilled and non-cryomilled NiCrAlY coatings were also composed of γ/γ′, but the former was characterized by columnar growth and the latter presented the dendritic and equiaxed structure. After oxidation, although the oxide products formed on the surface of cryomilled and non-cryomilled coatings were predominantly composed of α-Al2O3, Cr2O3, NiCr2O4 and AlYO3, the thermally grown oxide (TGO) on the surface of cryomilled coating had relatively smaller thickness, less weight gain and lower intensities of XRD peaks than that on the surface of non-cryomilled coating. It was demonstrated that the mechanical cryomilling resulted in a significant improvement in oxidation resistance of NiCrAlY coating by LIHRC. This was because the diffusion pathways could be reduced in the coating consisting of columnar dendrites, through which the mass transport was decreased.