Microstructure evolution and mechanical properties of Ti2AlNb/TC17 joints brazed with Ti-Zr-Cu-Ni filler metal

TC17 and Ti2AlNb alloys were bonded by vacuum brazing using Ti-Zr-Cu-Ni filler metals. Microstructure and mechanical properties of joints were comprehensively investigated by the scanning electron microscopy (SEM), transmission electron microscope (TEM) and shear tests. The brazing joint was composed of solid solution (SS) 13-Ti, & alpha;-Ti+(Ti,Zr)2(Ni,Cu), bulk (Ti,Zr)2(Ni,Cu) and SS 13-Ti. Increasing the brazing temperature gradually eliminated the intermetallic compound (IMC). When the joint was brazed at 970 degrees C for 30 min, the homogeneous solid solution formed at the brazing interface without the precipitation of IMC, resulting in the maximum shear strength of 529.2 MPa. The microstructure evolution of joints was attributed to the mutual diffusion of elements. The residual molten filler metal formed the successive bulk IMC at brazing interface during the cooling solidi-fication. Higher brazing temperature promoted the atomic diffusion, decreasing the amount of residual liquid filler metals and further inhibiting the formation of IMC. Furthermore, a microstructure-based finite element model (FEM) was applied to investigate stress distribution of brazed joints during the shear deformation. As a result, the formation of uniform solid solution at the interface effectively relieves the stress concentration, thereby promoting the mechanical performance improvement of the joint.