Abstract:
High-velocity-oxy-fuel (HVOF) spray and detonation-gun (D-gun)
spray techniques were used to deposit Ni–20Cr coatings on a commonly used boiler
steel ASTM-SAE 213-T22. The specimens, with and without coating, were subjected to molten salt (Na2SO4–60%V2O5) deposition in a laboratory furnace at
900 C to determine hot-corrosion resistance. Specimens were also exposed to the
superheater zone of a thermal power plant boiler at an average temperature of
700 C under cyclic conditions to ascertain their erosion-corrosion (E-C) behavior.
Mass-change measurements were taken to approximate the kinetics of corrosion and
erosion-corrosion. In the case of E-C, the thickness lost data were also taken at the
end of the exposure. The exposed specimens were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy/energy dispersive
spectroscopy (FE-SEM/EDS). The HVOF-sprayed coating was found to be intact
during exposure to both given environments; whereas the D-gun coating showed
spallation of its oxide scale during exposure to the molten salt environments. An
overall analysis of the results indicated that the HVOF-sprayed Ni–20Cr coating
should be a better choice for the given boiler applications
