Interfacial Microstructure and Shear Strength of Ti50Al50 Joint Vacuum Brazed with Ti-Cu-Ni-Nb-Al-Zr-Hf Amorphous Filler Alloy

Abstract:

Amorphous Ti-9.5Cu-8Ni-8Nb-7Al-2.5Zr-1.8Hf (wt%) filler alloy was employed to vacuum braze Ti₅₀Al₅₀ (at%) alloy at the brazing temperatures ranging from 1140 to 1220 °C for 30 min. The effect of brazing temperature on the microstructure and shear strength of the brazed joints was investigated. Results show that all the brazed joints are mainly divided into three reaction layers regardless of the brazing temperature, and both of α₂-Ti₃Al and Ti₂Cu(Ni) phases exist in each reaction layer, but their size and distribution change significantly with brazing temperature, especially the Ti₂Cu(Ni) phase in isothermal solidification layer Ⅱ. The continuous α₂-Ti₃Al layer Ⅰ is stable below 1200 °C but breaks and loses its barrier effect above 1200 °C. It is notable that the α₂-Ti₃Al precipitated in the brazed seam can act as a nucleation inhibitor and refine the crystal grain. Shear test results show that the average shear strength of Ti₅₀Al₅₀ brazed joints first increases and then decreases with brazing temperature and the maximum shear strength of 184 MPa is obtained at 1180 °C. α₂-Ti₃Al mainly occupies the fracture surface with cleavage characteristics.