Kink-pair mechanisms for a/2 〈111〉 screw dislocation motion in bcc tantalum

The structure, energetics, and multiplicity of kinks on an a/2 〈111〉 screw dislocation in bcc Ta have been studied in detail via atomistic computer simulation, using quantum-based multi-ion interatomic potentials derived from model generalized pseudopotential theory (MGPT) together with a robust Greenʹs function simulation technique. The stable core structure of the rigid screw dislocation is predicted to be weakly polarized and spread out on three {110} planes in 〈112〉 directions, with two energetically equivalent configurations. This double degeneracy leads to the possibility of anti-phase defects forming on the dislocation line as well multiple kinks and kink pairs. The zero-stress formation energies of 16 possible kink-pair configurations for bcc Ta have been calculated and are in the range 0.67–1.84 eV. The lowest kink-pair energy of the perfect screw is in good agreement with the best current empirical estimate. Under an applied stress, the corresponding kink–kink interaction energy displays a λ−1 elastic attraction when the separation λ is larger than 7b=20 Å, while the stress needed to maintain the kink pair varies as λ−1.5.