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 degrees 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 degrees C possess three interfacial layers and mainly consist of alpha(2)-Ti3Al, tau(3)-Al3NiTi2 and Ti2Ni, but the brazing seams are no longer layered and Ti2Ni is completely replaced by the uniformly distributed tau(3)-Al3NiTi2 at 1200 and 1220 degrees C due to the destruction of alpha 2-Ti3Al barrier layer. This transformation at 1200 degrees 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.