Review: Precipitate-phase regulation of the strength–ductility balance in metastable β titanium alloys—plasticity effects

Metastable β titanium alloys exhibiting transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects are promising structural materials because of their low density, high specific strength, and excellent work-hardening capability. However, the reduced β-phase stability required to activate martensitic transformation or deformation twinning often results in insufficient yield strength, limiting their engineering application. Precipitate-phase regulation provides an effective route to address this limitation by strengthening the matrix while adjusting the activation of TRIP/TWIP mechanisms. This review summarizes recent progress in precipitate-mediated strength–ductility regulation in metastable β titanium alloys, with particular emphasis on ω and α phases. The formation and mechanical roles of athermal/isothermal ω precipitates, ω-assisted α precipitation, hierarchical α structures, and their effects on deformation mode selection are discussed. The coupling among alloy composition, heat treatment, precipitate evolution, β-phase stability, and mechanical response is highlighted. Finally, unresolved issues and future directions are proposed, including quantitative precipitate control, in situ characterization of deformation–precipitation interactions, and scalable processing strategies for engineering applications.