Structure and properties of diffusion bonded TA2 to 1Cr18Ni9Ti joints with Ni+Nb composite interlayer

Diffusion bonding in vacuum was carried out between commercially pure titanium TA2 and austenitic stainless steel 1Cr18Ni9Ti by using Ni+Nb composite interlayer at the temperature of 840°C, 880°C and 920°C for 60min under 4 MPa axial pressure. The tensile strengths of the joints were tested, meanwhile the fracture surfaces were analyzed by SEM and XRD. The microstructure and element distribution of the joints were analyzed by OM, SEM and EDS. The results show that Ni+Nb composite interlayer successfully suppresses interdiffusion of Ti and Fe, so that the sound joints were formed. Five reacted-layers are presented at the joint. They are FeCrNi solid solution, residual Ni, Ni₃Nb, residual Nb, TiNb widmanstatten structure from 1Cr18Ni9Ti to TA2. The residual Ni is critical to strength of the joint, the strength reaches up to 261 MPa and changes a less with temperature.