Studies on the behaviour of stellite-6 as plasma sprayed and laser remelted coatings in molten salt environment at 900 °C under cyclic conditions

Stellite-6 (St-6) coating was obtained on boiler tube steels namely ASTM-SA210-Grade A1 (GrA1), 1Cr–0.5Mo steel ASTM-SA213-T-11 (T11) and 2.25Cr–1Mo steel ASTM-SA213-T-22 (T22) through plasma spray process. Ni–Cr–Al–Y was used as a bond coat before applying St-6 coating. Nd:YAG laser has been used for the post-coating treatment. As sprayed and laser remelted steels were subjected to molten salt environment (Na2SO4–60%V2O5) at 900 °C under cyclic conditions. The samples were visually examined and subjected to weight change measurements at the end of each cycle of study.Techniques like XRD, SEM/EDAX and EPMA analysis have been used to analyse the oxide scale. The coating was found to be effective in decreasing corrosion rate of the boiler tube steels. Protection is higher when GrA1 steel was the substrate steel and lower for T22 base steel. Due to the formation of vertical cracks, laser remelted coatings have indicated slightly higher corrosion rate in the given molten salt environment.