Hot corrosion behavior of cold-sprayed CoNiCrAlY coating in Na₂SO₄ salt

CoNiCrAlY coatings were prepared by cold spray process. After deposition, the pre-oxidation treatment of the coating was performed by vacuum heat-treatment. The microstructure and phase constituent of coating were characterized by XRD, SEM and EDS. The hot corrosion behavior of as-sprayed and pre-oxidized CoNiCrAlY coatings in molten Na₂SO₄ at 900℃ was also studied. The results show that the as-sprayed coating presents a dense structure with low porosity (less than 0.28%, volume fraction) and low oxygen content (0.12%, mass fraction). Vacuum pre-oxidation treatment forms a continuous and dense α-Al₂O₃ layer on the coating surface, with an average thickness of about 0.26μm. As-sprayed and pre-oxidized coatings can protect the substrate from hot corrosion due to the formation of a continuous and dense α-Al₂O₃ layer. Moreover, the vacuum pre-oxidation treatment can alleviate the diffusion of S and O into coating, and thus the hot corrosion resistance of coating is improved. The damage of hot corrosion plays a more important role than high temperature oxidation.