Characteristics of ⟨α⟩ screw dislocations and their slip on prismatic and pyramidal planes in pure α titanium from atomistic simulations

Molecular statics and dynamics simulations were carried out to characterize the core structure and calculate the critical resolved shear stress (CRSS) of an <alpha > screw dislocation in pure alpha-Ti using a recent modified embedded atom method spline like potential developed for Ti-Nb alloys. Firstly, it is shown that the generalized stacking fault energy (GSFE) curves calculated using this potential agree well with density functional theory (DFT) and nudged elastic band + DFT computations for the basal, prismatic-I and pyramidal-I planes. In particular, this potential predicts that the <alpha > prismatic stacking fault (SF) is lower in energy than the basal intrinsic 1(2) SF. Two stable core structures for the <alpha > screw dislocations were identified by this potential, one dissociates on the pyramidal-I plane, and the other on the prismatic-I plane. The pyramidal-I core is found to be the ground state core structure, while the prismatic-I core is metastable with an excess energy of 18.8 meV/b, which is in good agreement with published DFT calculations. Also, it is shown that the basal dissociation of the <alpha > screw dislocation is not stable and upon relaxation this core reconstructs directly to the pyramidal-I ground state structure. Finally, the CRSS for the slip of a prismatic <alpha > screw dislocation core on the prismatic-I plane is computed as a function of temperature between 0 and 300 K. It is found that screw dislocations glide by kink-pair mechanism on the prismatic-I planes, and the calculated CRSSs are in good agreement with experimental measurements.