Hot corrosion studies of HVOF sprayed Cr 3C 2–NiCr and Ni–20Cr coatings on nickel-based superalloy at 900 °C

Abstract

The high velocity oxy-fuel (HVOF) process is widely adopted by many industries due to its flexibility, cost effectiveness, handiness for use and the superior quality of the coatings produced. The present work is a comparative study of HVOF sprayed Cr 3C 2–NiCr and Ni–20Cr coatings on a Ni-based superalloy in a molten salt environment of Na 2SO 4–60%V 2O 5 at 900 °C under cyclic conditions. The thermogravimetric technique was used to establish the kinetics of corrosion. X-ray diffraction, scanning electron microscopy/energy-dispersive analysis and electron probe microanalysis techniques were used to analyse the corrosion products. The hot corrosion resistance of Ni–20Cr coating was better than Cr 3C 2–NiCr coating. The hot corrosion resistance of both coatings may be attributed to the formation of oxides and spinels of nickel and chromium. These oxides might have blocked the pores and splat boundaries, and acted as diffusion barriers to the inward diffusion of oxidizing species.