Microstructure evolution, diffusion behavior and fatigue properties of TC4 titanium alloy joints brazed with Ti–Zr-based filler

TC4 titanium alloy was brazed with Ti–18Zr–15Cu–10Ni (wt%) filler in a vacuum brazing furnace. The effects of the brazing time on the microstructure and tensile properties of the brazed joints were investigated, and the microstructure evolution during the brazing process and the high-cycle fatigue properties were further analyzed. The interfacial microstructure of the brazed joint at 940 °C for 60 min consists of coarse acicular α Ti, (Ti/Zr) 2 (Cu/Ni) intermetallics, eutectoid α Ti, and residual β Ti. The nucleation and growth of α Ti cause the component segregation, resulting in the rich of Cu, Ni, and V in β Ti to form β rich Ti, which in turn leads to the eutectoid decomposition reaction of β rich Ti, and the formation of granular intermetallic compounds at the edge of residual β Ti. The tensile strength increases first and then decreases with the brazing time, the maximum tensile strength (984.90 MPa) is obtained at 940 °C for 60 min, and the elongation at break increases with the prolongation of the brazing time; the maximum elongation at break (12.39%) is obtained at the brazing time of 90 min due to the large size of the α p phase. The fatigue limit of the brazed joints at 940 °C for 60 min is 492 MPa. The location of fracture is highly dependent on the fatigue load stress amplitude, and the growth rate of the fatigue crack is greatly affected by the microstructure of the fracture area.