The main cause of boiler tube failure in high-temperature thermal power plants is molten sulphate-vanadate-induced hot corrosion. Applying thermal spray coatings on alloy steels can reduce hot corrosion. This study aims to examine the impact of nano yttria stabilized zirconia (YSZ) reinforcement on Ni-20Cr composite coatings on hot corrosion behaviour of T22 steel in a corrosive environment of Na2SO4-60%V2O5 at 650 °C over 50 cycles.
The coatings were deposited using a high velocity oxyfuel technique. The samples were subjected to hot corrosion in a Silicon tube furnace at 650 °C for 50 cycles. Weight gain data after each cycle were used to analyse the kinetics of corrosion behaviour. Corrosion products were examined using X-ray diffraction, scanning electron microscopy, energy dispersive and cross-sectional analytical methods.
During investigation, nano YSZ-reinforced Ni-20Cr composite coatings on T22 steel were discovered to give superior corrosion resistance in a molten salt environment at 650 °C. Throughout the experiment, the coatings gained less weight and formed protective oxide scales. Increased YSZ concentration in the coating matrix resulted in better protection against hot corrosion.
The inclusion of nano YSZ reduced porosity in Ni-20Cr coatings by filling voids and interlocking particles, as well as blocking the penetration of corroding species, hence improving the corrosion resistance of composite coatings. The corrosion rate decreased with increasing YSZ content in the coating matrix.
It should be noted that the high temperature corrosion behaviour of thermally sprayed nano YSZ-Ni-20Cr composite coatings has never been investigated and is not documented in the literature. As a result, the current study can provide useful information for the application of nano YSZ-reinforced coatings in high-temperature fuel combustion conditions.
