Strength-ductility synergy mechanism in dual-titanium heterogeneous structures fabricated by multi-material laser powder bed fusion and tailored heat treatments

Heterogeneous design offers a promising pathway to overcome the strength-ductility trade-off. However, current additively manufactured multi-material titanium systems critically lack compatible post-processing strategies and frequently suffer from severe interfacial strain localization, leading to premature fracture. To address this fundamental research gap, we engineered a novel dual-titanium architecture combining Ti64 (Ti-6Al-4V) and Ti55511 (Ti-5Al-5Mo-5V-1Cr-1Fe) via multi-material laser powder bed fusion (MM-LPBF), paired with a pioneering compatible solution-quench-age treatment. The heat-treated structure achieves an exceptional ultimate tensile strength of 1143.7 ± 13.2 MPa and an elongation of 11.26 ± 0.64% (increasing by 51.5% and 286.5% over monolithic Ti64 and Ti55511, respectively). This strength-ductility synergy originates from a ∼200 μm continuous interfacial transition band with coupled compositional and microstructural gradients, evolving smoothly from α-dominated basketweave Ti64 to β-dominated bimodal Ti55511. During deformation, the architecture exhibits pronounced strain partitioning and sequential yielding. This hetero-deformation induced (HDI) strengthening is quantitatively supported by the dynamic evolution of long-range back stress, evidenced by the unloading-reloading hysteresis loop width expanding from 0.015% at 2% strain to 0.027% at 4% strain, alongside the continuous accumulation of geometrically necessary dislocations (GNDs). While the current investigation is limited to quasi-static room-temperature conditions, this work demonstrates that leveraging intrinsic strength contrasts via MM-LPBF and precise thermal control effectively breaks the strength-ductility trade-off, establishing a robust framework for developing high-performance multi-material titanium structures for advanced aerospace applications.