Dislocation core structure and motion in pure titanium and titanium alloys: A first-principles study

The deformation mode of some titanium (Ti) alloys differs from that of pure Ti due to alloying elements in the alpha-phase. Herein, we investigated all possible slip modes in pure Ti and the effects of Al and V solutes as typical additive elements on the dislocation motion in alpha-Ti alloys using density functional theory (DFT) calculations. The stacking fault (SF) energy calculations indicated that both Al and V solutes reduce the SF energy in the basal plane. In contrast, Al solute increases the SF energy in the prismatic plane, making the slip motion in different planes more comparable. DFT calculations were subsequently carried out to simulate dislocation core structures. The energy landscape of the transition between all possible dislocation core structures and the barriers for dislocation glide in various slip planes clarified the nature of dislocation motion in pure Ti; i) the energy of prismatic core is higher than the most stable pyramidal core, and thereby dislocations need to overcome the energy barrier of the cross-slip (22.8 meV/b) when they move in the prismatic plane, ii) the energy difference between the prismatic and basal cores is higher (127 meV/b), that indicates the basal slip does not activate, iii) however, the Peierls barrier for motion in the basal plane is not as high (16 meV/b) once the dislocation exists stably in the basal plane. Direct calculations for the dislocation core around solutes revealed that both Al and V solutes facilitate dislocation motion in the basal plane by reducing the energy difference between the prismatic and basal cores. Thus, the effect of solutes characterizes the difference in the deformation mode of pure Ti and alpha-Ti alloys.