Vacuum brazing of Ti2AlNb and TC4 alloys using Ti-Zr-Cu-Ni and Ti-Zr-Cu-Ni + Mo filler metals: Microstructural evolution and mechanical properties

Two kinds of filler metal, Ti-Zr-Cu-Ni and Ti-Zr-Cu-Ni + Mo, were used to vacuum braze Ti2AlNb and TC4 alloys. The interfacial microstructures and the room temperature (RT) and elevated temperature shear strengths of the brazed joints were analysed. Moreover, the effects of the brazing parameters and filler metal Mo content on the microstructure and corresponding mechanical properties of the brazed joints were investigated. The results showed that the typical brazed joint mainly contained α-Ti, (Ti,Zr)2(Cu,Ni), β-Ti, and Ti-rich phases. The addition of the Mo particles was beneficial to inhibit the eutectoid transformation of β-Ti during cooling, resulting in the formation of residual β-Ti instead of α-Ti. In addition, Mo particles can also make the microstructure more homogeneous. The highest RT shear strength of the joints brazed with the Ti-Zr-Cu-Ni filler metal was 351 MPa when the joint was brazed at 980 °C for 10 min. Under the same brazing parameters, the RT shear strength reached 437 MPa with the addition of 8 wt.% Mo particles to the filler metal. Moreover, the shear strengths of the joints brazed with the Mo-free and 8 wt.% Mo filler metals tested at 600 °C were 272 MPa and 393 MPa, respectively.