Effect of vacuum pre-oxidation on microstructure and hot corrosion behavior of CoNiCrAlY coating prepared by cold spray

CoNiCrAlY coatings were prepared by cold spray process. After deposition, the pre-oxidation of the coating was performed by vacuum heat-treatment. The microstructure and phase constituent of coating were characterized by XRD, FE-SEM and TEM. The corrosion behavior and mechanisms of as-sprayed and pre-oxidized coatings in molten 75%Na₂SO₄+25%NaCl (mass fraction, the same below) at 900°C were also studied. The results show that the as-sprayed coating presents a nanocrystalline structure with low porosity (less than 0.28% volume fraction) and low oxygen content (0.12%). Vacuum pre-oxidation treatment improves the bonding status of particle interface and forms a continuous, uniform and dense α-Al₂O₃ layer, with an average thickness of 0.26 μm. As-sprayed and pre-oxidized coatings can protect the substrate from hot corrosion due to the formation of the continuous and dense α-Al₂O₃ layer. Moreover, the vacuum pre-oxidation treatment can alleviate the diffusion of S and Cl into coating and thus lead to an increase of one time in the hot corrosion resistance than the as-sprayed coatings.