Study on diffusion bonded titanium alloy to stainless steel with Ni+Nb interlayers

Vacuum diffusion bonding between titanium alloy TC4 and austenitic stainless steel 1Cr18Ni9Ti was carried out by using conventional and ladder-like processing methods with Ni+Nb as interlayers. The microstructure and elements distribution of the joints were analyzed by OM, SEM and EDS. The mechanical properties of the joints were characterized by tensile strength test. Meanwhile the fracture surfaces were analyzed too. The results showed that Ni+Nb interlayers successfully prevent the formation of Fe-Ti intermetallic compounds, the microstructures of the transient joint from 1Cr18Ni9Ti to TC4 are Fe-Cr-Ni solid solution, Ni-Nb reaction layer, residual Nb and Nb-Ti solid solution. The weld quality of ladder-like processing joints are superior to the conventional processing joints. The maximum strength of 396 MPa at 900°C was achieved by using ladder-like processing method. The fractures occurred on the mixed reaction layer that was formed by Ni₃Nb and a small amount Ni₆Nb₇ between Ni and Nb, and this layer played a crucial role to the joint.