Microstructure and tribological behavior of Ni60+35WC-Ni coating produced by laser cladding

Ni60+35WC-Ni self-fluxing alloy coating with high hardness and wear resistance was prepared on 20Cr substrate by laser cladding and compared with Ni60 coating. The microstructure, elemental composition and phase constitution of the coatings were observed and analyzed through scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Microhardness distribution from substrate to coating was tested, and ball-on-disc dry sliding wear test on the coatings was performed at 20 and 300℃. The morphology and composition of the worn surface were observed through SEM and EDS. The results showed that Ni60+35WC-Ni coating mainly contained phases of Fe-Ni, Cr₇C₃ and WC. The hard phases of WC and Cr₇C₃ were beneficial to the hardness and wear resistance of the coating. The average microhardness of Ni60+35WC-Ni coating was about three times that of 20Cr substrate. Compared with Ni60 coating, the average microhardness of Ni60+35WC-Ni coating was higher and contained hard phase of WC which contributed to the lower wear loss. At the same temperature, the friction coefficients of Ni60+35WC-Ni and Ni60 coatings were close. For both coatings, the friction coefficients at 300℃ were obviously lower than those at 20℃, but the wear losses increased with the temperature increasing.