Improved interfacial strength of Ti/Ti ultrasonic welds by introducing // heterogeneous bonding interface

We investigated ultrasonic welding (USW) of pure alpha-Ti sheets, which exhibited an insufficient weldability due to the extensive formation of cracks caused by sliding friction during the USW. To overcome this issue, an alpha/beta/alpha heterogeneous interfacial microstructure was designed by introducing a thin Fe interlayer, a beta stabilizer, between alpha-Ti sheets. The diffusion of Fe interlayers triggered the formation of a continuous beta-Ti thin layer (similar to 1-2 mu m) without Fe-Ti intermetallics near the bonding interface after USW. The continuous thin beta-Ti layer exhibited a significant improvement in the joining of the brittle alpha-Ti, where the bonding strength was increased from 350 to 1700 N. This study provides a potential approach to design an interfacial microstructure that promotes the formation of a deformable phase, overcoming the inherent brittleness of hexagonal close-packed metals and enabling production of strong joints.