Designing Ductile 2-GPa Yielding Titanium Alloys via Multifunctional Subgrain Boundaries and Nanoprecipitates

Abstract

Ductile titanium alloys yielding at 2 GPa are rarely achieved via strengthening of hexagonal close-packed α-nanoprecipitates, which suffer from the planar glide softening to cause strain localization for insufficient work hardening capability. In this study, by engineering multifunctional β-subgrain boundaries, an unprecedented combination of ultra-high yield strength ≈1929 MPa and ultimate strength ≈2014 MPa, along with a notable uniform elongation ≈6.2%, is successfully achieved in a Ti-4Al-5Mo-3V-5Cr-1Fe alloy. This superior mechanical performance is enabled by a unique microstructure featured with ultrafine β-subgrains containing intragranular α-nanoprecipitates and intergranular discrete α-nanolaths. The resulting complex, multiscale hierarchical architecture effectively impedes and regulates dislocation motion, thereby endowing the alloys synergistic strengthening and ductilizing. Furthermore, local chemical heterogeneities combined with high stress-driven elemental partitioning exert strong nanoscale segment detrapping effects on mobile dislocations, contributing to a sustained work hardening rate and thus large uniform elongation. This multifunctional subgrain boundary strategy holds significant promise for extension to other metallic materials, particularly these additively manufactured alloys with dense dislocation cells, toward achieving ultrastrong-yet-ductile performance.