COMPARATIVE STUDY OF HOT CORROSION BEHAVIOR OF HVOF AND PLASMA SPRAYED NI20CR COATING ON SA213(T22) BOILER STEEL IN NA2SO4-60%V2O5 ENVIRONMENT

Material deterioration is a major issue in various high temperature applications. So it is important to understand the mechanism of hot corrosion in metals/alloys at high temperatures and to provide the protective coating for their economic, reliable and safe operation. Nickel based coatings are commonly used for the enhancement of resistance against the hot corrosion. These coatings can be developed by using different thermal spray techniques. The present investigation is an attempt to compare the resistance offered against hot corrosion by Nickel based coating sprayed by two different thermal spray techniques. Coating powder containing 80%Ni20%Cr was deposited on SA-213 (T22) using two thermal spray techniques, HVOF and Plasma spray. Hot corrosion studies were performed in Na2SO4-60%V2O5 environment at 900oC under cyclic conditions on bare and coated specimens. Thermo-Gravimetric, Scanning Electron Microscope SEM/EDS and X-ray diffraction tests were performed to examine the hot corrosion behavior. It was found that both thermal spray techniques used in the present study were successful in controlling the hot corrosion of 80Ni20Cr coated specimens. Mass gain in HOVF sprayed coated specimen was minimum, followed by Plasma coating and bare metal. From the results of various analysis techniques used, it may be suggested that the HVOF sprayed coating provided the better resistance to hot corrosion than plasma sprayed coating in the given environment