Degradation behaviour and microstructural characterisation of HVOF-sprayed Cr3C2-NiCr cermet coatings in molten salt environment

The present work investigated the cyclic high temperature degradation behaviour of high velocity oxy-fuel (HVOF) sprayed Cr3C2-NiCr coating deposited on 310S stainless steel (310S). The coated as well as uncoated specimens were exposed to molten salt (Na2SO4-60%V2O5) environment at 700 degrees C under cyclic conditions. The kinetics of hot corrosion was established using thermogravimetric technique. The corrosion products were characterised using the techniques such as X-ray diffraction, FE-SEM/EDAX and X-ray mapping for elucidating the corrosion mechanisms. The Cr3C2-25%NiCr coating was found to be successful in maintaining its continuous contact with the alloy substrate during cyclic degradation under simulated laboratory condition. HVOF sprayed Cr3C2-25% NiCr coating on 310S alloy substrate is found to be very effective in reducing the corrosion rate in the aggressive environment at 700 degrees C as observed from the present work. The oxide scales for Cr3C2-25% NiCr coated specimen were found to be intact and spallation-free. The parabolic rate constant of the coated specimen was lower than that of the bare specimen. The better hot corrosion resistance imparted by Cr3C2-NiCr coatings may be attributed to the formation of oxides of chromium, nickel and spinel of nickel and chromium.