The role of HVOF coatings in improving hot corrosion resistance of ASTM-SA210 GrA1 steel in the presence of Na2SO4-V2O5 salt deposits

Cr2C3-NiCr, NiCr, WC-Co and stellite-6 metallic coatings were sprayed on ASTM SA-210 grade A1 steel by the HVOF process. LPG was used as the fuel gas. The porosity measurements were carried out to assess the coating characteristics. Hot corrosion studies were conducted on the uncoated as well as HVOF sprayed specimens after exposure to molten salt at 900 °C under cyclic conditions. The thermo-gravimetric technique was used to establish kinetics of corrosion. XRD, SEM/EDAX and EPMA techniques were used to analyse the corrosion products. All these overlay coatings showed better resistance to hot corrosion as compared to that of uncoated steel. NiCr Coating was found to be most protective followed by Cr2C3-NiCr coating. WC-Co coating was least effective to protect the substrate steel. It is concluded that the formation of Cr2O3, NiO, NiCr2O4, and CoO may contribute to the development of hot corrosion resistance in the coatings. The uncoated steel suffered corrosion in the form of intense spalling and peeling of the scale, which may be due to the formation of unprotective Fe2O3 oxide scale.