Pre-plating Cu on the WC–Co surface to inhibit Co-depletion zone and enhance the shear strength of WC–Co/40Cr joints

The Co-depletion zone in WC–Co brazed joints is the main zone of joint failure, so it is crucial to explore novel processes to inhibit the Co-depletion zone and enhance the joint shear strength. In this study, a composite process of pre-plating Cu on the WC–Co surface + brazing was designed. Co-depletion zone reduces from 6 μm to 1 μm due to the Cu plating. Meanwhile, the formation of a plating fusion zone in the filler layer transforms TiCo with a thickness of 2.5 μm into a small number of TiCo particles. Moreover, the high concentration of Cu atoms in the vicinity of the WC particles at the interface changes the Co-segregation layer in the WC into a Cu-rich layer. The concentration of Cu in the filler layer leading to precipitation of TiCu and Ti 2 Cu particles. Ti 2 Cu particles encapsulated by ductile Ag–Cu–In ternary eutectic contribute to inhibit the cracks propagation. The shear strength of the joints was enhanced by 51.3 % to 295 MPa. The composite process of pre-plating on the base material surface + brazing has positive significance in inhibiting the excessive diffusion of elements from the base materials to the filler layer.