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

• Ultrasonic welding (USW) is applied in joining of less ductile hexagonal close-packed metals. • The intrinsic brittleness of α-Ti inhibited the increase in joint strength in USW. • A deposition of a thin Fe interlayer purposefully introduced an α-to-β transformation. • A β-Ti layer formed by Fe diffusion without obvious Fe–Ti intermetallics after USW. • A strong Ti/Ti bond was obtained with a continuous α/β/α interfacial microstructure. We investigated ultrasonic welding (USW) of pure α -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 α /β/ α heterogeneous interfacial microstructure was designed by introducing a thin Fe interlayer, a beta stabilizer, between α -Ti sheets. The diffusion of Fe interlayers triggered the formation of a continuous β-Ti thin layer (⁓1–2 μm) without Fe–Ti intermetallics near the bonding interface after USW. The continuous thin β-Ti layer exhibited a significant improvement in the joining of the brittle α -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. [Display omitted] [ABSTRACT FROM AUTHOR]