Simultaneously enhancing strength-ductility synergy in the Ti₂AlNb diffusion bonding joint via heterogeneous high-entropy interface design

Brittle defects, such as continuous intermetallic compounds and straight bonding line composed of grain or phase boundaries, often form at the interface of dissimilar metals joints, resulting in the premature cracking at the interface. Therefore, bonding interfaces with excellent strength and ductility are attractive for application in welding structural components. However, increasing strength usually comes at the expense of ductility, which is known as strength-ductility trade-off. In this work, we explored a novel interface design strategy by introducing multi-scale grains into the bonding interface of the Ti₂AlNb-based alloy using a heterogeneous refractory high entropy alloy. The interface was composed of the multi-sized grains, which successfully eliminated the brittle defects. Through this approach, the strength and ductility of the joint synergistically improved to 877 MPa and 11.54 %, respectively. Both strength and ductility exceeded 98 % of the mechanical performances of the base metal. The exceptional strength-ductility combination was benefiting from cooperative strain hardening mechanisms, which increased the interfacial hardening capability via in situ refinement of free path of dislocations motion. This hetero-interface strategy could expand the design ideas for the bonding interface of intermetallic compound-based alloys, and provides a new approach to synergistically increase the mechanical performance.