Quantitative insights of competitive plastic deformation mechanisms in metastable β-Ti Alloys: integrated experimental observations and a first-principles approach

Precise control of deformation mechanisms in metastable β-Titanium alloys is essential for optimizing their mechanical properties. While conventional semi-empirical d-electron theory offers qualitative predictions, it falls short in quantifying the influence of alloying elements on deformation pathways. This study investigates the competitive deformation mechanisms in a multicomponent Ti-8Mo-5 W-1Fe alloy using integrated experimental characterization and first-principles calculations. The addition of Fe suppresses the β → α’’ martensitic transformation during early-stage deformation (ε < 2 %), promoting {332}〈113〉_β twinning as the dominant mechanism, coupled with SI-ω/α’ phase transformations (ε, 2–10 %). First-principles calculations, employing virtual crystal approximation and nudged elastic band methods, quantify these deformation modes’ energy profiles and driving forces. The results show that the β → α’’ transformation is driven by a smaller absolute energy difference (−44 meV/atom) in Ti-8Mo-5 W-1Fe compared to Ti-12Mo (−92 meV/atom) and Ti-9Mo-6 W (−56 meV/atom). Conversely, SI-ω/α’ transformations have the highest energy difference (−107 meV/atom and −93 meV/atom) in the ternary alloy. Formation energy analysis further reveals that reduced Mo and increased W content thermodynamically favor ω phase and α’ martensite formation. The delayed α’’ formation and preferential activation of twinning and SI-ω/α’ mechanisms enhance strain hardening in Ti-8Mo-5 W-1Fe, sustaining a high hardening rate (>2 GPa) up to 15 % strain while maintaining an excellent strength-ductility balance. This study provides a quantitative framework for alloy design, advancing the understanding of deformation mechanisms in metastable β-Ti alloys beyond traditional semi-empirical approaches.