Microstructure and mechanical properties of joints prepared by vacuum brazing on TC4 titanium alloy with Ag as filler metal

Vacuum brazing on TC4 (Ti–6Al–4V) titanium alloy was performed by using Ag foil as the filler metal. Two steps were designed, in which the TC4/Ag/TC4 samples were brazed at 1000 °C for 10 min and followed by a diffusion process at 800 °C for 60–360 min. The microstructural characteristics and the mechanical properties of joints were analyzed. The results indicated that the reaction zones of the joints mainly consisted of α+β lamellar structures with the distributions of acicular and micron-sized particle phases of TiAg attached to Ti₂Ag. As the diffusion time increased, the characteristics of the intermetallic compounds (IMCs) at the joints changed accordingly, as the morphology of IMCs became spherical from acicular, and the amount of IMCs was decreased. Furthermore, the microhardness test results indicated that the lowest hardness values were observed at the centers of the joints. A maximum tensile strength of 864.5 MPa was obtained for the joint diffused at 800 °C for 120 min, and its fracture path was more curved than those of the other joints. Based on the shear test results and fracture analysis, regardless of diffusion time, the joints were fractured at the region of the reaction zone along the IMCs.