Modification of SS316 steel with the assistance of high velocity oxy fuel (HVOF) process to upsurge its sustainability

Vanadium carbide (VC) is an eminent hard material. However, the same has not been sightsaw as an entrant coating material to provide sustainability for hydromachinery components by mitigating the problem of cavitation erosion. Therefore, in this research work, VC, blended with a 25 wt.% binder, namely CuNi-Cr, has been deposited on hydromachinery SS316 steel using the HVOF spraying process in order to make them sustainable. The obtained VC-based coating was studied with repute to cavitation erosion and further compared with uncoated steel. The cavitation erosion testing was done by using an in-house fabricated high-speed water jet cavitation erosion test rig with variability in impingement parameters comprising of jet velocity (m/s) and stand-off distance (cm) with impingement angle (degree) fixed as normal to jet. Further, microstructure, micro-hardness, porosity, and surface roughness of the developed coating were also investigated to justify the variation in cavitation erosion results. It has been observed that HVOF sprayed 75%VC+25%CuNi-Cr coating possesses dense microstructure with intermediate porosity. The cavitation erosion for coated and uncoated steel was found to be maximum for a combination of impingement variables comprising maximum velocity and transitional stand-off distance. The VC-based coating was found to be sustainable with very small cavitation erosion compared to uncoated SS316 steel for each combination of impingement variables, which can be due to the combined effect of higher micro-hardness and cushioning effect imparted by the coating as compared to SS316 steel. In the case of SS316 steel, multiple overlapped pits were observed; however, in the case of VC-based coating, isolated pits with a smaller area have been reported.