Engineered ω_iso phase enable deformation-induced mechanisms strength and plasticity synergy in a novel Ti-531 metastable β titanium alloy

Metastable β-Ti alloys are known for their high strain hardening rates and excellent plasticity through the combined effects of transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) effects, yet their relatively low yield strength restrict structural applications. Improving yield strength without sacrificing ductility is thus a key challenge in these alloys. To address this long-standing strength-plasticity dilemma, we designed a novel metastable β-Ti alloy, Ti-5Mo-3Cr-1Zr (Ti-531), guided by d-electron theory, average electron-to-atom ratio (e/a‾) and atomic radius difference (Δr‾) criteria. By engineering nanoscale ω_iso phase precipitations, a strategy is demonstrated to concurrently strengthen the yield response and preserve high ductility in the Ti-531 alloy. The results show that these ω_iso particles substantially strengthen the alloy and activate a synergistic deformation-induced strengthening mechanism. This mechanism involves a sandwich-type composite twin/stress-induced ω (SI_ω) structures, interactions between twin/SIM (α”), and development of dislocation channels largely devoid of ω_iso phase synergistically accommodate localized strain. These dislocation channels facilitate to accelerate dislocation accumulation, promote forest hardening and suppress the impeding effect of ω_iso phase. As a result, the alloy aged at 423 K (A423) outperforms the hot-rolled solution-treated alloy (R1123) in yield strength (∼642 MPa, ∼28 % higher) with merely a slight (∼1.1 %) reduction in elongation, thus combining high strength with largely preserved ductility. This work introduces instability-control paradigm that harmonizes twin/ SI_ω/SIM-assisted deformation and dislocation channels strengthening to engineer high performance metastable β-Ti alloys.