Microstructural characteristics and mechanical properties of WC-Co/steel joints diffusion bonded utilizing Ni interlayer

In this study, diffusion bonding of WC-Co cemented carbides to a tool steel was realized utilizing Ni foils as the interlayer in a vacuum. The effects of bonding temperature and Ni interlayer thickness on interfacial microstructure and mechanical properties of the joint were studied. The research results revealed that brittle phases and cracks were suppressed due to the Ni interlayer. Moreover, the coherent relationship of [1 2 0]_WC//[1 0 1]_Ni and (0 0 1)_WC//(0 2 0)_Ni was observed at the interface of WC grains and Ni interlayer, and it greatly contributed to the bonding strength of WC-Co/steel joint. As the bonding temperature increased, the atoms diffused sufficiently, and the interfacial defect dimensions decreased. Then, the Ni interlayer was transferred to solid solutions, resulting in the high shear strength of the bonded joint. The optimum shear strength (444.7 MPa) was achieved when the bonding was carried out at 1050 °C for 1 h with a 4-μm-thick Ni interlayer. The cracks were propagated in the interlayer and the WC-Co substrate near the bonding seam.