Vacuum brazing TC4 titanium alloy / 316L stainless steel with Ti_43.76Zr_12.50Cu_37.49-xNi_6.25Co_x amorphous filler metals

Ti-Zr-Cu-Ni-Co amorphous filler metals were designed and prepared for vacuum brazing of TC4 titanium alloy to 316L stainless steel according to the dual-cluster model. The effect of Co content in filler metals on the microstructure, mechanical properties and fracture behavior of brazed joints was investigated. The results showed that the cross section of brazed joint could be divided into TC4/diffusion zone I/brazing seam center zone II/interface zone III/316L. The typical interfacial microstructure of the brazed joints was TC4/β-Ti + Ti₂Cu/(Ti, Zr)₂(Cu, Ni) + Ti₂Cu + Ti₂(Cu, Ni) + TiFe/(Fe, Cr)₂Ti + α-(Fe, Cr) + τ + γ -(Fe, Ni) + σ/316L. The shear strength of brazed joints first increased, then decreased and then increased with the increase of Co content. The maximum shear strength of 310 MPa was obtained at 1.56% Co. When Co element was not added, brazed joints fractured in the center of the brazing seam (zone II). And when the Co content was 1.56 ~ 6.24%, brazed joints fractured near the interface zone (zone III) of 316L base metal. The fracture mode was typical cleavage fracture.