Characteristics of 〈a〉 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 〈a〉 screw dislocation in pure α-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 〈a〉 prismatic stacking fault (SF) is lower in energy than the basal intrinsic I2 SF. Two stable core structures for the 〈a〉 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 〈a〉 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 〈a〉 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.