Hot corrosion behaviour of plasma and d-gun sprayed coatings on t91 steel used in boiler applications

Abstract

Material degradation by salt induced hot corrosion is a serious threat to Coal fired Boiler components. Corrosion resistant thermal spray coatings is a proven solution for this problem. Thiswork compares the hot corrosion behaviour of a NiCoCrAlY coating on T91 boiler steel deposited using two different thermal spray methods namely Atmospheric Plasma Spray (APS) and Detonation Gun (D-Gun) spray. The coated samples were exposed to 650C for 100 cycles (1 cycle being 1 hour holding plus 20 minutes cooling in air) in a thermal cycling furnace under a mixed deposit containing Na2SO4, K2SO4 and Fe2O3 to simulate the real time coal ash environment. The exposed coatings were examined using FESEM/EDS and XRD to analyze the extent and nature of corrosion attack. The results indicate that the D-Gun sprayed coatings provided superior corrosion resistance over their APS sprayed counterparts. NiO and Spinel oxide NiCr2O4 which offers corrosion resistance were formed in both the coatingswith the APS sprayed coatingbeing rich in the fast growing NiO which affected its corrosion performance. The enhanced corrosion resistance of the D-Gun sprayed coatings was attributed to its dense microstructure with minimal porosity and good intersplat bonding which minimized corrosion ingress. © Published under licence by IOP Publishing Ltd.