Microstructure and hot corrosion characteristics evaluation of high-velocity oxy-fuel sprayed Ni–20%Cr coating on AISI 321 steel with Na2SO4–60%V2O5 salt deposits

The high-temperature corrosion is a crucial issue of stainless-steel components such as boilers and superheaters in power plant industries when it operates at elevated temperatures due to impurities in the environment, which deteriorate the properties of the materials. The current research work goal is to investigate the cyclic corrosion characteristics of the bare and Ni–20%Cr, a high-velocity oxy-fuel sprayed coating on AISI 321 steel in Na2SO4–60%V2O5 salt atmosphere at 900 °C. Thermogravimetric study was used to examine the corrosion kinetics by weight change technique. Surface morphology and compositions of the coating and oxide scale morphology were characterized. X-ray diffraction analysis divulges that Fe2O3 is the primary scale in the uncoated specimen. Corrosion attack across the depth and scale thickness is analyzed by a cross-sectional study. More oxide scales spalling could be observed in the uncoated specimen during the corrosion study due to nonprotective Fe2O3 formation. Compared with the bare specimen, the coated steel provides superior corrosion resistance at 900 °C. This is ascribed to the occurrence of NiO, NiCr2O4, and Cr2O3 scales in the coated specimen, which provides sufficient protection to the specimen.