Performance of HVOF and Cold Sprayed Ni-20Cr Coatings in Aggressive Molten Salt Environment at 900°C under Cyclic Condition

Nickel-chromium alloys have been used as coatings to deal with oxidation environments at high temperature. The present work is a comparative study of HVOF and cold sprayed Ni-20Cr coating on a boiler steel (SAE 213-T22) in a molten salt environment of Na₂SO₄-60%V₂O₅ at 900°C under cyclic conditions. The weight change technique was used to establish the kinetics of corrosion. X-ray diffraction, surface and cross-sectional FE-SEM/EDS techniques were used to analyse the corrosion products. The hot corrosion resistance of both the coatings was better than the uncoated steel. This may be attributed to the formation of oxides and spinels of nickel and chromium in the coated steels. These oxides might have blocked the pores and splat boundaries, and acted as diffusion barriers to the inward diffusion of corroding species. Based upon the overall results and subsequent analysis of hot-corrosion data the cold spray process may be recommended as a better choice for the deposition of the Ni-20Cr coating on Mo-containing T22 steel in comparison with the HVOF spray process for hot corrosion protection.