Microstructure and bonding strength of WC reinforced Ni-base alloy brazed composite coating

A tungsten carbide (WC) reinforced NiCrBSi(Co) composite coating was produced on mild steel by high temperature vacuum brazing. The microstructure, phases present and the interface diffusion have been investigated. The cobalt coated on the surface of WC particles dissolved into the liquid nickel-base alloy but the WC was not decomposed severely during the vacuum brazing process. Microanalysis showed that the composite coating matrix was composed of γ-Ni solution and γ-Ni+(Ni,Co)3B lamellar eutectic. Diffusion and metallurgical reaction occurred at the WC/NiCrBSi(Co) interface and composite coating/substrate interface. A 6-μm thick brazing seam or interfacial bonding zone was found between the coating and the substrate as the coated sample cooled down. Bonding strengths of the WC/NiCrBSi(Co) interface and the composite coating/substrate interface reached 100–140 MPa and 300–360 MPa, respectively, which are far higher than those of thermal spray coating. The abrasive wear resistance of brazed composite coating also appears to be better than that of the flame overlaid at the same composition.