Phase transformation mediated anomalous plasticity of titanium under severe loading conditions

Titanium (Ti) with ω phase is always considered brittle and non-deformable. Therefore, little is known of the role of ω phase in the anomalously high plasticity of titanium alloys undergoing severe plastic deformation. The deformation mechanisms of shocked Ti samples in uniaxial compression and severe shear deformation was investigated by using molecular dynamics (MD) simulations. Results show that anomalous plasticity of Ti is accommodated by a forward and reverse α-ω martensitic transformation and subsequent twin-twin interactions, rather than conventional dislocation activity. The dislocation-free deformation mechanism in ω-Ti is due to an energy barrier that favors ω→α martensitic transformation compared to dislocation-based slip. Moreover, the α↔ω martensitic transformation process is accompanied by grain/domain refinement, which can be explained by the symmetry change during the phase transformation. This work advances the understanding of the interplay between phase transformation and plastic deformation in titanium under extreme loading conditions.