Shear-strain induced β phase transformed by high pressure torsion process at room temperature in pure Ti

Shear-strain induced α (hcp) phase to β (bcc) plus ω (simple hexagonal, space group P6/mmm) phase transformation in pure titanium (Ti) occurs during high pressure torsion (HPT) deformation at the pressure of 5 GPa and rotation speed of 0.2 rpm at room temperature. Notably, the β phase remains metastable at ambient temperature and pressure after the HPT load is released. In contrast, prior studies report that the β phase in pure Ti typically forms only at temperatures exceeding 1155 K under ambient pressure or under pressures potentially surpassing 52 GPa at ambient temperature. The present findings provide further insights into shear-strain induced allotropic transformations in pure Ti, providing the basis for understanding the formation and stabilization of high temperature phase or high pressure phase under ambient conditions.