Microstructure and bending behavior of Ni-Co/WC-Graphite composite coatings fabricated through vacuum cladding

The Ni-Co/WC-Graphite composite coating was fabricated by vacuum cladding. The microstructure and composition of the composite coating were characterized and analyzed by SEM and XRD. The bending behavior was studied through three point bending test, and the fracture characteristics, elements analysis and fracture mechanism were discussed. The results show that the whole composite coating consists of composite area, transition area, diffusion-fusion strip and heat-affected area. The WC particles well-distribute among the composite coating and form a 3D reticular microstructure characteristic. The main phases are Cr₇C₃, Cr₂₃C₆, Ni₃Si, CrB, WC, C and γ-Ni-Co solid solution in the composite coating. The pearlite is the main phase at heat-affected area. There are γ-Ni-Co solid solution and intermetallics in fusion area and transition area. Three point bending test show that the load-distance curve presents linear change at the initial state, and then the slope of curve decreased. The composite coating debacle happens as the load reaches a maximum when the composite coating bears compress stress, and fracture happens as the load reaches a maximum when the composite coating bears tensile stress. The load increases slowly after the composite coating failure because of the forming of the transition area, diffusion-fusion strip and heat-affected area. The fracture characteristics present intergranular or transgranular at composite coating area. The fracture presents fan cleavage characteristics at the heat-affected area, and there are many dimples at substrate area.