Effect of vacuum pre-oxidation on oxidation behavior of NiCoCrAlY coating prepared by cold spray

A NiCoCrAlY coating was prepared by cold spray. After deposition, the pre-oxidation of the coating was performed by vacuum heat treatment. The microstructure and phase structure of the coating were characterized by XRD, SEM and EDS. The effect of vacuum heat treatment on the oxidation behavior of NiCoCrAlY coatings at 1050°C was also studied. The results show that the as-sprayed coating presents a dense structure with low porosity (less than 0.36%) and low oxygen content (0.25% mass fraction). Vacuum heat treatment converts the single-phase (γ) as-sprayed coating to a two-phase γ/β microstructure, and a continuous, uniform and dense α-Al₂O₃ layer is formed, with an average thickness of 0.47μm. After oxidation for 200h at 1050°C, a dense and continuous thermally grown oxide(TGO), mainly composed of α-Al₂O₃, is formed on the surface of as-sprayed and vacuum heat-treated coating. Vacuum heat treatment can postpone the formation of spinel in a certain time (100h) and decrease the growth rate of TGO.