Microstructure and wear behavior of spherical NbC hardmetals with nickel-based binders on AISI 4145H steel

To investigate the effect of spherical NbC particles on the wear resistance of nickel-based coatings, five groups of samples were tested. The microstructure of nickel-based coatings reinforced by spherical NbC particles was examined through X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. The wear behavior of samples was analyzed by microhardness, coefficient of friction, 2D profile across the wear track and summary of tribological properties, respectively. The results shows that in the microstructure of nickel-based coatings reinforced by spherical NbC particles, γ-Ni solid solution and Cr23C6 dominated the coating, and complex carbides (NbC, Cr7C3 and a small amount of Cr3C2) and borides (Cr2B) were also detected. The hardness of the nickel-based coating was 400HV0.2. With the increase of the NbC content in the coating, the hardness gradually increased, reaching the maximum when the content was 40% NbC, which was 610HV0.2. The average friction coefficient of AISI 4145H steel was 0.473, and the average friction coefficient of nickel-based coating was 0.573. With the increase of NbC content in the coating, the friction coefficient of the coating gradually decreased, reaching the lowest at a NbC content of 40%, which was 0.470. Although the friction coefficient of the coating changed slightly with the addition of NbC, in the friction and wear of the nickel-based coating, the coating was adhesively worn, and there were many abrasive dust, scratches and grooves on the surface of the coating. By the way, there were only a few scratches on the surface after friction and wear of the nickel-based coating containing 40% NbC. The wear rate of the coating with 40% NbC content was about 1.6% of AISI 4145H steel or one-tenth of the nickel-based coating.