Strengthening mechanism of Ti65/Ti₂AlNb diffusion bonded joint by direct-current-assisted hot-pressure bonding

Heterogeneous high-temperature titanium-alloy blisks play a crucial role in the weight reduction of aeroengines. However, vacuum solid-state diffusion bonding technologies are time-consuming and demand stringent processes. In this study, a Ti65/Ti₂AlNb diffusion joint is successfully fabricated using direct-current-assisted hot-pressure bonding technology. The interfacial microstructure and mechanical properties of the joint are systematically investigated at various temperatures, and the strengthening mechanism of the joint is elucidated. The results indicate that the thickness of the interfacial diffusion layer increases progressively with rising bonding temperature. The joint achieves a maximum shear strength of 646.09 MPa, when bonded at 980 °C at a lower pressure of 2 MPa, owing to the phase transformations, including β → α₂, O → β, and O → α₂ occuring at the bonding interface. The α₂ phase manifests as pin-shaped α phases, which exhibit three-dimensional interlocking at the interface. This configuration forms a structure akin to a “wall” effectively restricting the dislocation glide and climb, increasing the dislocation path length, and enhancing the performance of the bonding joint. The direct-current-assisted hot-pressure bonding technology generates substantial Joule heat at the join interface, promoting plastic deformation and significantly reducing the bonding pressure required while improving the bonding efficiency. This innovative approach holds promise for the fabrication and post-treatment of other dissimilar metal-welded joints.