David Cereceda, J. Manuel Perlado, Sylvain Queyreau, Alexander Stukowski, Jaime Marian, Lisa Ventelon, M. -Cosmin Marinica
Screw dislocations in bcc metals display non-planar cores at zero temperature which result in high lattice friction and thermally activated strain rate behavior. In bcc W, electronic structure molecular statics calculations reveal a compact, six-fold symmetric core with an associated Peierls stress of approximately 3 GPa. However, a full picture of the dynamic behavior of dislocations can only be gained by using more efficient atomistic simulations based on semiempirical interatomic potentials. In this paper we perform molecular dynamics simulations of screw dislocation motion using five different potentials to understand the effect of different force-fields on the dynamic properties of screw dislocations. Dislocations are seen to display thermally-activated motion in most of the applied stress range, with a gradual transition to a viscous damping regime at high stresses. We find that some potentials predict a core transformation from six- to three-fold symmetric at finite temperature that changes the fundamental energetics of kink-pair production and impacts the mechanism of motion. We rationalize this transformation in terms of the changes with temperature to the free energy barrier to displace a string of atoms along the <111> direction.
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http://arxiv.org/abs/1204.5501
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