Corrosion behavior of wire arc sprayed Ni-based coatings in extreme environment

The current study represents the corrosion behavior of wire arc sprayed Ni-based (Ni-5Al and Ni-20Cr) coatings on commonly used boiler tube steels (T11 and Gr A1). A cyclic hot corrosion behavior of the samples has been carried out at 900 °C for 50 cycles with the application of Na2SO4-60%V2O5 salt. The coatings offered excellent corrosion resistance in comparison to bare steel. The surface and cross sectional analysis of coated samples before and after corrosion has been carried out using SEM/EDS and XRD analysis. It was observed that Ni-20Cr coating exhibited better corrosion resistance for both T11 and Gr A1 steel than a Ni-5Al coating. The Ni-20Cr coating has shown 87% and 75% better corrosion resistance in terms of weight change in comparison to bare T11 and Gr A1 boiler steel, while Ni-5Al offered 86% and 73% better corrosion resistance to bare steels respectively. This may be due to the formation of protective Cr2O3 oxide in the top oxide layer, lower porosity of coatings and high micro hardness.