Vacuum brazing of Ti₃Al-based alloy to TiAl using TiZrCuNi(Co) fillers

A traditional Ti13Zr21Cu9Ni (wt.%) filler metal was used to join Ti₃Al-based alloy and TiAl intermetallics, and the joints brazed at 1213-1233 K for 600 s presented a shear strength of 113-149 MPa at room temperature. For the improvement of the joint strength a TiZrCuNiCo filler metal was designed. The shear strength of the joints brazed with the TiZrCuNiCo filler at 1283 K for 300 s reached 278 MPa, increased about 86.6% compared with the TiZrCuNi system filler. The overall hardness in the joint brazed with the TiZrCuNiCo filler was uniformly lower than the joint brazed with TiZrCuNi filler. The Ti₃Al/TiAl joint brazed with Ti-ZrCuNi mainly consisted of Ti₂Al, α₂-Ti₃Al and the residual filler metal of Ti(Cu, Al)₂ + CuZr. The phase sequence within the Ti₃Al/TiAl joint brazed with TiZrCuNiCo filler from TiAl side to Ti₃Al side can be described as the follows: TiAl substrate/Ti₂Al +α₂-Ti₃Al/α₂-Ti₃Al + Ti-rich phase/residual filler metal/Ti-rich phase/Ti-rich phase + O-Ti₂AlNb/Ti₃Al substrate, and the fracture surface of the corresponding joint was characterized by Ti-rich phase, indicating that compared with the traditional TiZrCuNi filler the joint ductility was increased to a great extent.