High-value regeneration of high-oxygen/nitrogen titanium scraps through heterogeneous microstructure design for exceptional strength-ductility synergy

The sustainable recycling and high-value utilization of titanium alloy scraps are severely hindered by their inherently high oxygen and nitrogen contents, which induce catastrophic interstitial embrittlement and critically deteriorate the material's plasticity. To overcome this recycling bottleneck, herein, we engineered a TA1/TA15 mixed alloy containing extreme impurity levels (2549 ppm O, 1985 ppm N) derived from high-impurity scraps via high-temperature sintering and slow cooling. Driven by impurity-induced thermodynamic β-transus shifts, a heterogeneous quasi-bimodal microstructure was successfully constructed, comprising solid-solution-strengthened coarse α laths and flexible intergranular β films. Consequently, the alloy achieves an exceptional synergy of ~900 MPa yield strength and ~15% elongation, breaking the conventional strength-ductility trade-off. Microstructural analyses reveal that the ultrahigh strength originates from severe multiaxial lattice distortions coupled by interstitial and substitutional solutes. Furthermore, a multi-stage accommodation mechanism governs the extraordinary ductility: early-stage strain partitioning within the soft β phase effectively blunts potential microcracks, while extreme local stresses at the ultimate deformation stage drive dynamic lattice rotation, forcing the activation of high-energy <c+a> multi-slip systems and triggering dynamic subgrain refinement. This hierarchical mechanism provides a robust theoretical paradigm for the direct structural regeneration of highly contaminated titanium scraps.