Microstructure and wear-resistant properties of NiCr–Cr₃C₂ coating with Ni45 transition layer produced by laser cladding

NiCr–Cr₃C₂ metal–ceramic composite coating is commonly produced on metal substrate by laser cladding to be used as wear-resistant coating under medium- or high-temperature working conditions. The coating has high hardness, generally over three times that of the substrate. In order to make the hardness increase gradually from substrate to coating surface, the nickel-based alloy Ni45 was chosen as the transition layer and NiCr–Cr₃C₂ coating was indirectly cladded on 20Cr2Ni4A substrate. Microstructure and composition of the coating were characterized by scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Microhardness of the cross section of the coating was measured. Friction and wear behavior of NiCr–Cr₃C₂ coating and substrate were investigated through sliding against the SiC ball at 20, 100 and 300 °C. The morphologies of worn surfaces were analyzed by SEM and EDS. The results show that the hardness of Ni45 transition layer is between that of the substrate and NiCr–Cr₃C₂ coating, which avoids hardness jump and stress concentration of the coating. NiCr–Cr₃C₂ coating contains hard phases of Cr₃C₂ and Cr₇C₃ which enhance the wear resistance. With the temperature increasing, friction coefficient and wear rate of the substrate increase significantly. Compared with the substrate, NiCr–Cr₃C₂ coating has lower friction coefficient and wear rate at 100 and 300 °C, which verifies the good wear resistance of NiCr–Cr₃C₂ coating.