Transient liquid phase (TLP) bonding of Ti-6Al-4V/UNS 32750 super duplex stainless steel

Dissimilar metal joining between Ti-6Al-4 V and UNS 32750 super duplex stainless steel (SDSS) alloys was carried out by TLP bonding with a Cu interlayer at 890, 920, 950 and 980 degrees C for a bonding time of 60 min. In addition to microstructural survey, the microhardness and shear strength of different bonded specimens were also investigated. The results confirmed that the isothermal solidification zone (ISZ) was extended with the rising temperature up to 980 degrees C. Moreover, the formation of intermetallic compounds (IMCs) like TiCu, Ti2Cu, Cr2Ti, Fe2Ti and FeTi was demonstrated in TLP joints by SEM/EDS examinations. It was found that increasing the bonding temperature promoted the formation of IMCs by increasing the diffusion of Ti, Cu and Fe, which resulted in degradation of shear strength of the joints. Mechanical characterizations indicated that the joint made at 890 degrees C had the highest shear strength (271 MPa), which was equal to 0.49 strength of Ti-6Al-4 V, as well as 0.47 of UNS 32750. Furthermore, the average hardness of the bonded zone was superior than that of the base metals. Also, the SDSS side exhibited high hardness values in the range of 420-460 HV, while the Ti-6Al-4 V side revealed lower hardness values (330-370 HV).