Effects of Nb content in Ti-Ni-Nb brazing alloys on the microstructure and mechanical properties of Ti-22Al-25Nb alloy brazed joints

Vacuum brazing was successfully used to join Ti-22Al-25Nb alloy using Ti-Ni-Nb brazing alloys prepared by arc-melting. The influence of Nb content in the Ti-Ni-Nb brazing alloys on the interfacial microstructure and mechanical properties of the brazed joints was investigated. The results showed that the interfacial microstructure of brazed joint consisted of B2, O, τ3, and Ti2Ni phase, while the width of brazing seams varied at different Nb contents. The room temperature shear strength reached 359 MPa when the joints were brazed with eutectic Ti40Ni40Nb20 alloy at 1180 °C for 20 min, and it was 321, 308 and 256 MPa at 500, 650 and 800 °C, respectively. Cracks primarily initiated and propagated in τ3 compounds, and partially traversed B2+O region. Moreover, the fracture surface displayed typical ductile dimples when cracks propagated through B2+O region, which was favorable for the mechanical properties of the brazed joint.