Effect of brazing temperature on microstructure and tensile strength of γ-TiAl joint vacuum brazed with micro-nano Ti−Cu−Ni−Nb−Al−Hf filler

A novel micro-nano Ti−10Cu−10Ni−8Al−8Nb−4Zr−1.5Hf filler was used to vacuum braze Ti−47Al− 2Nb−2Cr−0.15B alloy at 1160−1220 °C for 30 min. The interfacial microstructure and formation mechanism of TiAl joints and the relationships among brazing temperature, interfacial microstructure and joint strength were emphatically investigated. Results show that the TiAl joints brazed at 1160 and 1180 °C possess three interfacial layers and mainly consist of α₂-Ti₃Al, τ₃-Al₃NiTi₂ and Ti₂Ni, but the brazing seams are no longer layered and Ti₂Ni is completely replaced by the uniformly distributed τ₃-Al₃NiTi₂ at 1200 and 1220 °C due to the destruction of α₂-Ti₃Al barrier layer. This transformation at 1200 °C obviously improves the tensile strength of the joint and obtains a maximum of 343 MPa. Notably, the outward diffusion of Al atoms from the dissolution of TiAl substrate dominates the microstructure evolution and tensile strength of the TiAl joint at different brazing temperatures.