Atomistic simulation of pressure-dependent screw dislocation properties in bcc tantalum

Abstract

The pressure-dependent core properties of a/2 〈1 1 1〉 screw dislocations in bcc Ta have been simulated by means of quantum-based, multi-ion interatomic potentials derived from model generalized pseudopotential theory (MGPT). We have considered both ambient-pressure behavior and the change in core properties under high-pressure of 10 Mbar. Robust two- and three-dimensional Green’s function techniques have been used to dynamically relax the boundary forces during the simulations. Our results show that the predicted degenerate core structure is sensitive to pressure, being nearly symmetric and only weakly polarized at ambient pressure, while becoming highly polarized with a distinctive three-fold spread out along 〈1 1 2〉 directions at high-pressure. At the same time, the pure-shear Peierls stress is found to scale linearly with the pressure-dependent 〈1 1 1〉 shear modulus G. The degenerate nature of the core structure leads to multiple possible kinks and kink pairs that can form on the dislocation line at finite temperature. The pressure variation of the lowest kink-pair formation energy reveals a very approximate scaling behavior in terms of G and the Burgers vector.