Metastability engineering for TWIP-dominated plasticity with localized α” martensite activity in ω-strengthened metastable β Ti-6311 alloy

In metastable β titanium alloys, the primary deformation behavior is governed by the stability of the β phase, which controls the activation of dislocation slip, twinning-induced plasticity (TWIP), and transformation-induced plasticity (TRIP). In this study, a novel metastable β titanium alloy with a nominal composition of Ti-6Mo-3Cr-1Zr-1Fe (Ti-6311) was designed using d-electron theory, average electron-to-atom ratio (e/a‾) and atomic radius difference (Δr‾) criteria to achieve controlled β phase metastability near the β/(β+ ω) dislocation slip boundary, enabling a TWIP-dominated deformation response. Short-time low-temperature aging (STLTA) was employed to introduce nano-precipitations of ω_iso phase, which act as strong pinning sites for dislocations, thereby enhancing precipitation strengthening. The results indicate that plastic deformation proceeds through the sequential activation of multiple mechanisms, with TWIP being the primary deformation mode, while sporadic twin-interface-assisted α” martensite and dislocation slip provide limited auxiliary strain accommodation. The early activation of {332}<113‾> twins, along with their interactions with grain boundaries (GBs) and twin boundaries (TBs), facilitates dislocation accumulation and induces significant strain hardening. Continued deformation leads to the formation of secondary {332}<113‾> twins inside primary twins, together with sporadic twin-interface-assisted α” martensite and the gradual consumption of ω_iso phase, resulting in ω_iso-depleted regions. The synergistic interactions between the ω_iso phase, twin domains, and α” martensite enhances the capacity for dislocation accumulation and storage. Consequently, the alloy aged at 423K (AG423) achieves a yield strength of 680 MPa, a 19.29% improvement compared with the water quenched (WQ) alloy (570 MPa), while maintaining a total elongation of 31.9%, thus preserving its plasticity. This work provides a viable alloy design and aging route for metastable β-Ti alloys, where tuning β phase stability and ω_iso strengthening jointly control deformation and mechanical performance.