Hot corrosion behaviour of HVOF-sprayed NiCrBSi coatings on Ni- and Fe-based superalloys in Na2SO4-60% V2O5 environment at 900 °C

The investigation of high-temperature corrosion-resistant coatings is required so that the service lifetime of components used at higher temperatures in corrosive environments can be prolonged. This study is concerned with the performance evaluation of high-velocity oxy-fuel (HVOF)-sprayed NiCrBSi coatings on Ni- and Fe-based superalloys in a molten salt (Na2SO4-60% V2O5) environment at 900 °C under cyclic oxidation conditions. The thermogravimetric technique was used to establish the kinetics of corrosion. X-ray diffraction, scanning electron microscopy/energy-dispersive analysis and electron probe microanalysis techniques were used to characterise the as-sprayed coatings and corrosion products. The bare superalloys, in general, suffered accelerated corrosion under the given environmental conditions and showed spalling/sputtering of the oxide scale. The hot corrosion resistance of Ni-based superalloys was found to be better than that of Fe-based superalloys. The NiCrBSi coating was found to be very effective in decreasing the corrosion rate in the given molten salt environment at 900 °C. The hot corrosion resistance imparted by NiCrBSi coatings may be attributed to the formation of oxides of silicon, chromium and nickel and spinels of nickel and chromium.