Edge dislocation mobilities in bcc Fe obtained by molecular dynamics

Abstract

In the traditional picture of plasticity in bcc metals, edge dislocations have been assumed to play a minor role due to their high mobility with respect to screw dislocations, which then control plastic flow. $\frac{1}{2}\ensuremath{\langle}111\ensuremath{\rangle}{110}$ edge dislocations indeed fit this description, as it has been shown by way of numerous atomistic simulations. However, $\frac{1}{2}\ensuremath{\langle}111\ensuremath{\rangle}{112}$ edge dislocations have been comparatively much less studied. The recent discovery of a possible regime where they move slowly via thermally activated kink-pair nucleation may have implications in the plastic behavior of bcc materials. Because dislocation mobilities are very difficult to measure experimentally, in this paper, we provide comprehensive mobility laws for both types of edge dislocations as a function of temperature and stress using molecular dynamics simulations. Our results confirm the existence of clearly delimited thermally activated and phonon drag dynamic regimes for $\frac{1}{2}\ensuremath{\langle}111\ensuremath{\rangle}{112}$ edge dislocations and of a single viscous drag regime for their $\frac{1}{2}\ensuremath{\langle}111\ensuremath{\rangle}{110}$ counterparts. We also provide an analysis to relate the difference in mobility to the dislocation core properties. Our fitted mobility laws may be used in dislocation dynamics simulations of plastic flow involving millions of segments.