Shear-induced hexagonal close-packed to face-centered cubic phase transition in pure titanium processed by equal channel angular drawing

The hexagonal close-packed (HCP) to face-centered cubic (FCC) phase transition has recently been identified in commercial purity titanium under cryogenic plane-strain compression or conventional rolling. To verify whether the shear deformation could induce this unique HCP-to-FCC phase transition or not, we performed equal channel angular drawing (ECAD) on pure Ti and observed the microstructure changes after deformation by transmission electron microscopy. The results show that the ECAD deformation can induce this phase transition easily. The orientation relationship between the HCP matrix and FCC phase is the well-known prismatic relation \( {\left\langle {0001} \right\rangle_{HCP}} / /\left\langle {001} \right\rangle \) and \( {\left\{ {10\bar 10} \right\}_{HCP}} / /{\left\{ {1\bar 10} \right\}_{FCC}} \) after ECAD at room temperature. Meanwhile, the FCC–Ti phase processed by ECAD exhibits a high thermal stability with a transus temperature of about 600 °C according to the differential scanning calorimetry technique and annealing tests. However, the FCC-structured Ti has unexpectedly poor stability under high-energy electron beam irradiation, and the FCC-to-HCP reverse transition is attributed to the shear-shuffle mechanism.