Vacuum brazing of Ti6Al4V alloy to 316L stainless steel using a Ti-Cu-based amorphous filler metal

The effect of brazing parameters on the interfacial microstructure and mechanical properties of Ti6Al4V titanium alloy/316 L stainless steel brazed joint was investigated. The joint presented sectionalized interfacial microstructure by forming four reaction zones. The diffusion of Cu and Fe into Ti6Al4V titanium alloy substrate caused beta-Ti transformation and its dissolution. Raising the brazing temperature promoted the dissolved blocky beta-Ti to migrate to 316 L stainless steel side. Compared to the brazing temperature, the brazing time had relatively less impact on the microstructure of joint. The diffusion of Ti into steel substrate led to the formation of the transition zone which contained three different reaction layers-Fe2Ti, tau + alpha-(Fe, Cr), and gamma-(Fe, Ni) + sigma. With the increase of brazing temperature, the transition zone gradually thickened. The optimized joint shear strength was 65 MPa obtained at 960 degrees C/5 min. Contraction difference between two base metals generated stress concentration at Ti-Cu-Fe/Fe2Ti interface, which was a liquid/solid interface upon solidification. During shear test, cracks initiated at the Ti-Cu-Fe/Fe2Ti interface, and then mainly propagated within the reaction layers of Fe2Ti and tau + alpha-(Fe, Cr).