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

Abstract

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 Ti2Cu particles. Ti2Cu 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.