Microstructure and mechanical properties of TC4/oxygen-free copper joint with silver interlayer prepared by diffusion bonding

Diffusion bonding of two dissimilar materials, Ti-6Al-4V (TC4) and oxygen-free copper (OFC), was investigated at low temperature. A 30-µm silver foil was used as interlayer and the bonding was carried out at various bonding temperatures and times. The diffusion bonded joint microstructures were studied using an S-4800 field emission scanning electron microscope, JXA-8100 electron probe micro-analyzer, and Rigaku Ultima II X-ray diffractometer. Joint tensile strengths were measured by tensile tests. The silver interlayer prevented the formation of Ti-Cu compounds, AgTi and AgTi2 were generated at the TC4/Ag interface and a solid solution formed at the Ag/OFC interface. The tensile strength of the TC4/Ag/OFC joint increased first and decreased with bonding temperature or bonding time. The joint bonded at 700 °C for 120 min at 10 MPa showed a maximum tensile strength of 161.9 MPa. Fracture morphology showed that ductile fracture initiation and propagation took place at the Ag/OFC interface, which was the weak point of the joint.