DEVELOPMENT OF EROSION AND CQRROSION RESISTANT COATING BASED ON NICKEL AND COBALT BASED INTERMETALLICS

Abstract

In the present investigation boiler steels SA213-T1 1, SA213-T22 have been taken as candidate materials. Specimens have been subjected to erosion in silica slurry for 4 cycles of 6hr. duration and the erosion rate for two has been compared. It has been found that the steel SA213-T1 1 shows higher resistance compared to SA213-T22. The SA213-T22 steel has been plasma spray coated with Ni3A1 by taking a mixture of 3:1 nickel and aluminum. Formation of Ni3A1 was conformed by XRD analysis. The coating was uniform and adherent. A Stellite 6 coating was obtained by spraying commercially available stellite 6 composition. The SEM micrographs of eroded SA213-Tl 1, SA213-T22, and coated specimen indicated that the uncoated steel show large scale indentation where as in case of coatings indentation is very less. Hot corrosion study under cyclic condition. of SA213-T22 boiler steel and the same coated with Ni3A1 and stellite 6 in Na2SO4 — 30% V205 salt environment at 900° C was carried out for 40 cycles. It can be inferred that both the coatings provide resistance to hot-corrosion by above environment. The overall weight gain is decreased by 73% and 78% for Ni3A1 and Stellite 6 respectively when compared with SA213-1 22 The phases identified were Ni3A1, NiO, A1203 for Ni3A1 coating and CoO, Cr203. whereas in case of SA213-122 the main phase identified was Fe203.