Microstructure and properties of Ni-WC gradient composite coating prepared by laser cladding

In this study, an Ni-based gradient composite coating reinforced with WC was prepared on a Q345R steel substrate by laser cladding. The Ni-WC composite coating was designed as a multilayer structure with gradient composition. The coating started with a layer of C276 alloy with 10 wt% WC on the substrate, and the subsequent layers were composed of Ni60 alloy with different WC contents (10, 30, and 50 wt% WC). The overall morphology, phase composition, and microstructure of the coatings were investigated. The microhardness and the wear properties of each layer of the coatings were also evaluated. The results showed that the gradient composition design was beneficial for reducing the cracking tendency. The coating was composed of an Ni-based matrix, WC, and multiple carbides and borides hard phases. With increasing WC content in the layers, the hard phases exhibited regional distribution characteristics. The WC reinforcement particles underwent different types of dissolution during the cladding process. From the surface to the substrate, the average microhardness of the coating was 1053.5 HV0.2, 963.4 HV0.2, 859.0 HV0.2, 441.7 HV0.2, and 260.5 HV0.2. The wear tests revealed that the coefficient of friction and the wear loss values of the four layers were all lower than those of the substrate, demonstrating enhanced wear resistance.