Molecular Dynamics Simulations of a<111> Screw Dislocation in Ta

Guofeng Wang, Alejandro Strachan, Tahir Cagin and William A. Goddard III

Abstract

    Using a new, first principles based, Embedded-Atom-Method (EAM) potential for tantalum (Ta), we have carried out atomistic simulations to investigate the core structure, core energy and Peierls energy barrier and stress for a<111> screw dislocation. Equilibrated core structures were obtained by relaxation of dislocation quadrupoles with periodic boundaries. We found that the equilibrium dislocation core has three-fold symmetry and spreads out in three <112> directions on {110} planes. Core energy per Burgers vector b was determined to be 1.36 eV/b. We studied dislocation motion and annihilation via Molecular Dynamics simulations of a periodic dislocation dipole cell, with <112> or <110> dipole orientation. In both cases the dislocations move in zig-zag on primary {110} planes. Atoms forming the dislocation cores are distinguished based on their atomic energy. In this way we can accurately define the core energy and its position not only for equilibrium configurations but also during dislocation movement. Peierls energy barrier was computed to be ~ 0.08 eV/b with a Peierls stress of ~ 0.03 u, where u is the bulk shear modulus of perfect crystal. The preferred slipping system at low temperature is <112> directions and {110} planes.

Results

Fig. 1. Core energy determination from the linear data fitting for different size simulations. Core Energy of 1/2a<111> screw dislocation is 1.36 eV/b

Fig. 2. Peierls potential variation during 1/2a<111> screw dislocation movemnet. Peierls barrier is about 0.73 eV/b

Acknowledgement

    This research was founded by a grant from DOE-ASCI-ASAP. The facilities of the MSC are also supported by grants from NSF (MRI CHE 99), ARO (MURI), ARO (DURIP), NASA, BP Amoco, Exxon, Dow Chemical, Seiko Epson, Avery Dennision, Chevron Corp., Asahi Chemical, 3M and Beckman Institute.