Hot Corrosion Behavior of Cold-sprayed CoNiCrAlY Coating in Na₂SO₄ Salt

Abstract

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. When corrosion in single Na2SO4 molten salt with the same temperature, the consumption speed of Al is two times of that in high temperate oxidation

Keywords

• <em>M</em>CrAlY coating
• hot corrosion
• cold spray
• vacuum pre-oxidation
• high temperature oxidation