Sn-triggered nanoscale phase modulation suppresses martensitic transformation in metastable β titanium alloys

This study investigated the influence of Sn addition on phase stability and deformation behavior in metastable β-type Ti–12Mo–xSn (x = 2, 6; wt.%) alloys. The results reveal that increasing Sn concentration suppresses athermal ω phase formation while promoting the emergence of nanoscale O′ phase. The Ti–12Mo–2Sn alloy exhibits pronounced strain hardening associated with stress-induced β→α″ martensitic transformation (SIMT) and deformation twinning, whereas these mechanisms are largely absent in the Ti–12Mo–6Sn alloy, where plasticity is dominated by planar slip. First-principles calculations indicate that increasing Sn concentration facilitates the β→O′ transformation by reducing the required atomic shuffle magnitude and destabilizing the ω phase. The resulting O′ phase impedes SIMT, inducing a transition in deformation mode that markedly enhances yield strength but diminishes ductility. These findings demonstrate that Sn-driven nanoscale phase engineering can effectively modulate deformation mechanisms in metastable β titanium alloys.