Effect of Brazing Temperature on γ-TiAl Joint Brazed with Ti-Ni-TiB₂ Filler Metal

Ti-Ni-TiB₂ cast filler metal prepared by electromagnetic levitation melting was employed to vacuum braze Ti-47Al-2Nb-2Cr-0.15B (at%)alloy under the brazing temperature of 1170-1210 ℃for 1 min.The interfacial microstructure of the TiAl alloy brazed joints and the effect of the brazing temperature on the microstructure, shear strength of the welded joint were studied, and the shear fracture morphology of the brazed joints were observed.The results show that all the brazed joints are mainly divided into three reaction layers, marked by diffusion layer (Ti₃Al), interfacial reaction layer (Ti₃Al+Al₂NiTi)and center brazing layer(Al₂NiTi+Ti₂Ni+TiB₂+TiB).With the increase of the brazing temperature, the thickness of the diffusion layer and the shear strength of the TiAl brazed joint increase firstly and then decrease, and the interfacial microstructure becomes more uniform. The maximum shear strength of 348 MPa is obtained at 1200 ℃and the fracture is quasi-cleavage facture. The in-situ synthesized TiB whiskers in TiAl brazeds joint make the crack deflect, and adjust the gradient of thermal expansion coefficient, which realizes the strengthening and toughening of the TiAl brazed joint.