Characterization of the Structure and Wear Resistance of Ni65-Based Coatings via HVOF Flame Spraying and Its Application to Potato Digging Shovels

To improve the tribological properties of a potato digging shovel (PDS), Ni65-based coatings with rare earth oxides additions were fabricated on 65Mn# steel via High-Velocity Oxygen-Fuel (HVOF) flame spraying, the effect of macroscopic surface shape of PDSs on their wear resistance of PDSs was examined, and finally a kind of PDS with a specific macroscopic surface shape and satisfied wear resistance was obtained. The addition of CeO2 and Y2O3 decreased the defects in coatings, refined the microstructure, made hard phases distributed more uniformly and ultimately improved coating properties. According to the XRD analysis results, the Ni65-based coatings were composed of the matrix phase gamma-Ni and hard phases formed by Cr, Fe and Ni with B, C and Si. More Cr7C3 phases were detected in coating B than in coating A, but the phases related to Y and Ce were also not detected because of the low content in both EDS and XRD analyses. Heat treatment and HVOF flame sprayed coatings both increased the hardness of specimens, and coating A (621HV(1.0)) provided a hardness nearly equivalent to that of the heat treatment specimens (617HV(1.0)), while coating B provided the highest hardness (664HV(1.0)). For all specimens, laser surface texturing (LST) structures weakened their corrosion resistance. However, the Ni65-based self-fluxing alloy coatings significantly improved the corrosion resistance of specimens, and coating B provided the best corrosion resistance. SEM images show that the main wear mechanism for worn specimens was abrasive wear, and less wear signs were observed on the surface of coating B. Abrasive wear examinations indicate that specimen BJ had the best wear resistance and, compared with specimen W, the mass loss of specimen BJ decreased by 28.56% and 20.83% at relative sliding speeds of 2.35 m/s and 3.02 m/s, respectively. However, considering the negative effect of LST structures on the corrosion resistance of specimens, the processing techniques of specimen A and specimen B are more applicable to PDSs. The macroscopic surface shapes affected the wear resistance of PDSs and ZF had the lowest mass loss but the highest draught force; comparatively, YS had a better balance on the draught force reduction and wear resistance. Finally, YS with coating B, which decreased the mass loss by more than 27.17%, is recommended in this paper. On the whole, the conclusions in this paper provide a reference for the design of potato digging shovels with lower draught force and better tribological properties.