Characterizations and hot corrosion resistance of Cr3C 2-NiCr coating on Ni-base superalloys in an aggressive environment

Abstract

In the current study, Cr3C2-NiCr coating was deposited on the Ni-base superalloys by using high velocity oxyfuel (HVOF) process for high temperature corrosive environment applications. Optical microscopy (OM), x-ray diffraction (XRD), scanning electron microscopy/energy- dispersive analysis (SEM/EDAX), microhardness tester, and electro probe microanalyzer (EPMA) techniques were used to characterize the coating with regard to coating thickness, porosity, microhardness, and microstructure. The thermogravimetric technique was used to establish kinetics of corrosion. The hot corrosion behaviors of the bare and Cr3C2-NiCr coated superalloys were studied after exposure to aggressive environment of Na 2SO4-60%V2O5 salt mixture at 900 °C under cyclic conditions. The structure of the as-sprayed Cr 3C2-NiCr coating mainly consisted of 7-nickel solid solution along with minor phases of Cr7C3 and Cr 2O3. Coating has porosity less than 1.5% and microhardness in the range of 850-900 Hv (Vickers hardness). Some inclusions, unmelted and semimelted powder particles were observed in the structure of the coatings. The Cr3C2-NiCr coating has imparted necessary resistance to hot corrosion, which has been attributed to the formation of oxides of nickel and chromium, and spinel of nickel-chromium. © ASM International.