Effect of copper interlayer thickness on shear strength, microstructure and fracture mechanism of activated transient liquid-phase bonded YG6X cemented carbide-45 steel

Abstract To reveal the influence mechanism of copper (Cu) interlayer thickness on the bonding performance of activated transient liquid phase (A-TLP) bonded YG6X cemented carbide-45 steel dissimilar joints, five A-TLP bonding schemes were designed with Cu interlayer thicknesses of 50, 100, 500, 1000 and 2000 μ m (fixed thicknesses of Ti and BNi2 interlayers in the laminated structure at 50 μ m each), and a comparative BNi2 brazing experiment was conducted under the same conditions. A-TLP bonding was performed at 1050 °C for 30 min under a vacuum of ⩽2 × 10 ⁻³ Pa and an applied pressure of 0.3 MPa, with the A-TLP joints adopting a ‘YG6X/Ti/Cu/BNi2/steel’ structure and the brazed joints using a ‘YG6X/BNi2/steel’ configuration. The shear strength, microstructure and elemental diffusion behavior of the joints were systematically characterized by an electronic universal testing machine, scanning electron microscope and energy dispersive x-ray spectrometer. Results show that the Cu interlayer thickness exerts a significant regulatory effect on the shear strength of A-TLP joints, which first increases and then decreases with increasing Cu thickness, reaching a maximum of 176.37 MPa at 100 μ m–59.8% higher than the 110.35 MPa of BNi2 brazed joints. This excellent performance is attributed to the uniform, dense microstructure, sufficient interfacial elemental diffusion and favorable interfacial deformation compatibility enabled by the intrinsic ductility of the 100 μ m Cu interlayer. This work provides a practical reference for parameter optimization of A-TLP bonding of cemented carbide-steel dissimilar joints.