Microstructure and mechanical properties of vacuum diffusion bonded joints between Ti-6Al-4V titanium alloy and AISI316L stainless steel using Cu/Nb multi-interlayer

Dissimilar joining of Ti-6Al-4V titanium alloy and AISI316L stainless steel was investigated in the current study by diffusion bonding using Cu/Nb multi-interlayer. Effects of the bonding temperature and bonding time on microstructure and mechanical properties were studied in the range of 850-950 °C. Microstructural characterization was carried out through optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Results showed that when the bonding temperature is 900 °C or below, the formation of intermetallic compounds was successfully prevented and strong TiA/α-β Ti/Nb/Cu/SS diffusion bonding joints were achieved by inserting a Cu/Nb multi-interlayer. A minimum hardness value of 99 HV was measured in the joint zones and maximum tensile strength of 489 MPa is accomplished when the joints processed at 900 °C for 90 min. Fracture analysis results showed different fracture morphologies at different bonding temperatures. Fracture took place though Cu/Nb interface at lower parameters then transferred to remnant Cu layer at 900 °C for 90 min with extensive dimples on the surfaces, displaying a ductile nature. However, bonded at 950 °C for 90 min, joints fractured along the intermetallic compounds upon tensile tests, indicating a brittle nature.