8/14/2019 Accurate atomistic simulation of screw dislocations and other defects in bcc tantalum

http://slidepdf.com/reader/full/accurate-atomistic-simulation-of-screw-dislocations-and-other-defects-in-bcc 1/3

Accurate atomistic simulation of screw

dislocations and other defects in bcc tantalumAuthors:

Yang, L. H.; Soderlind, Per; Moriarty, John

Publication:Philisophical Magazine A, vol. 81, Issue 5, p.1355-1385

Publication Date:

05/2001Origin:

T+FBibliographic Code:2001PMagA..81.1355H

Abstract

8/14/2019 Accurate atomistic simulation of screw dislocations and other defects in bcc tantalum

http://slidepdf.com/reader/full/accurate-atomistic-simulation-of-screw-dislocations-and-other-defects-in-bcc 2/3

The fundamental ato mic-level prop erties o

f (a/2)<111> screw dislocations and

other defe122222 milioncts in bcc Ta have been simulated by means of new quantum-based multi-ion interatomic

 potentials derived from the model generalized pseudopotential theory (MGPT). The

 potentials have been validated in detail using a combination of experimental data and ab-initio electronic structure calculations on ideal shear strength, vacancy and self-interstitial

formation and migration energies, grain-boundary atomic structure and generalized

stackingfault energy (gamma) surfaces. Robust and accurate two- and three-dimensionalGreen's function (GF) techniques have been used to relax dynamically the boundary

forces during the dislocation simulations. The GF techniques have been implemented in

combination with a spatial domain decomposition strategy, resulting in a parallel MGPTatomistic simulation code that increases computational performance by two orders of 

magnitude. Our dislocation simulations predict a degenerate core structure with threefold

symmetry for Ta, but one that is nearly isotropic and only weakly polarized at ambient

 pressure. The degenerate nature of the core structure leads to possible antiphase defects(APDs) on the dislocation line as well as multiple possible dislocation kinks and

kinkpairs. The APD and kinkenergetics are elaborated in detailin the low-stress limit. In

this limit, the calculated stress-dependent activation enthalpy for the lowest-energy kink  pair agrees well with that currently used in mesoscale dislocation dynamics simulations

to model the temperature-dependent single crystal yield stress. In the high-stress limit, the

calculated Peierls stress displays a strong orientation dependence under pure shear anduniaxial loading conditions, with an antitwinning-twinning ratio of 2.29 for pure shear 

{211}-<111> loading.

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8/14/2019 Accurate atomistic simulation of screw dislocations and other defects in bcc tantalum

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