Remarkable contribution of stress-induced martensitic transformation to strain-hardening behavior in Ti- Mo-based metastable β-titanium alloys

The role of stress-induced beta -> alpha '' martensitic transformation in contributing to the exceptional strain-hardening behavior of a Ti-11Mo (wt. %) model alloy was studied. The results reveal that the alpha ''-martensite plates, undergoing relatively high transformation strains upon formation, act as effective barriers against dislocation motion. As deformation proceeds, the progressive generation of these plates dynamically reduces the dislocation mean free path (dynamic Hall-Petch effect), while simultaneously encouraging the accumulation of dislocations. These dual effects substantially enhance the flow stress with increasing strain, thereby resulting in remarkable strain-hardenability, a crucial factor for maintaining excellent ductility. This study presents innovative experimental evidence elucidating the mechanism of the transformation-induced plasticity effect in metastable beta-ti- tanium alloys, while also offering insights for designing novel alloys with superior strain-hardenability and ductility.