Brazing properties and mechanism of YG8/42CrMo joints regulated by BNi-2+Ni interlayer

Cemented carbide, valued for its superior hardness and impact resistance, is widely used in critical industrial applications. Achieving reliable bonding between cemented carbide and steel remains challenging due to residual stresses and brittle interfacial phases. In this study, YG8 cemented carbide and 42CrMo steel were brazed using BNi-2 filler metal with varying thicknesses of a Ni interlayer (0–400 μm). The results demonstrate that the Ni interlayer thickness critically regulates both microstructure and mechanical performance. The joint with a 100 μm Ni interlayer exhibited the highest shear strength of 299.4 MPa—a 15.2% improvement over the Ni-free joint. Microstructural analysis revealed that the bonding interface primarily consists of CrWSi and Co_0.5Ni_0.5 phases, while the brazed seam is dominated by a ductile (Fe, Ni)s,s. The optimal Ni thickness promoted element diffusion, suppresses brittle phase formation, and alleviates residual stress, as confirmed by finite-element simulations. Conversely, excessive Ni thickness (>200 μm) leads to microcracking, and strength degradation. This work clarifies the thickness-dependent role of the Ni interlayer in microstructural evolution and stress relief, providing a practical approach for strengthening cemented carbide/steel brazed joints.