Microstructure and strength of brazed joints of Ti₃Al-base alloy with different filler metals

The interfacial microstructure and properties of brazed joints of Ti3Al-based alloy were investigated. The effects of different brazing fillers on interfacial microstructure and shear strength were studied. And the optimum joining parameters were given. The brazed joints were qualitatively and quantitatively analyzed by means of EPMA, SEM and XRD. The results show that using brazing filler NiCrSiB, TiAl₃, AlNi₂Ti and Ni[s,s] are formed at the interface of joint, and the formation of Ti₃Al and AlNi₂Ti decreases the shear strength. Using brazing filler TiZrNiCu, Ti₂Ni, Ti(Cu,Al)₂ and Ti[s,s] are formed at the interface of joint, the formation of intermetallics Ti₂Ni and Ti(Cu,Al)₂ decreases the shear strength. Using brazing filler AgCuZn, TiCu, Ti(Cu,Al)₂ and Ag[s,s] are formed, the shear strength of the joint is decreased because of the formation of TiCu and Ti(Cu, Al)₂. Using brazing filler CuP, Cu₃P, TiCu and Cu[s,s] are formed at the interface of the joint, the former two intermetallics decrease the shear strength. The analysis also indicates that using brazing filler NiCrSiB, the optimum brazing parameters for the joint are joining temperature T=1373 K, joining time t=5 min, and the maximum shear strength is 219.6 MPa. To the brazing filler TiZrNiCu, the optimum parameters are temperature T=l323 K, joining time t=5 min, and the maximum shear strength is 259.6 MPa. To the brazing filler AgCuZn, the optimum parameters are joining temperature T=l173 K, joining time t=5 min, and the maximum shear strength is 125.4 MPa. To the brazing filler CuP, the optimum parameters are joining temperature T=l223 K, joining time t=5 min, and the maximum shear strength is 98.6 MPa.