Investigation of hot corrosion resistance of bare and Ni-20%Cr coated superalloy 825 to Na2SO4-60%V2O5 environment at 900°C

Abstract

Abstract The present study aims to compare the hot corrosion resistance of bare and Ni-20%Cr coated Ni-Fe based superalloy 825 in Na2SO4-60%V2O5 molten salt environment at 900°C. Superalloy 825 was thermal spray coated with Ni-20%Cr by high-velocity oxy-fuel (HVOF) coating process. During hot corrosion study, weight measurement was done at the end of each cycle to obtain the corrosion kinetics by thermogravimetric technique. Surface morphology study, surface chemical analysis and phase identification of the corrosion products were carried out using scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. Cross-sectional analysis was performed on the hot corroded specimens to determine oxide layer thickness and depth of corrosion attack. Elemental distributions on the cross-sectioned hot corroded specimens were studied using X-ray mapping analysis. The Ni-20%Cr coated specimen showed better corrosion resistance than the bare specimen. Spallation and cracking of scale was observed on the uncoated specimen with progress of corrosion reaction.