Linking Atomistic and Continuum Modeling of Dislocation Core Properties

The Peierls-Nabarro (PN) model provides an ideal framework for a multiscale study of dislocation core properties. The strength of the model, when combined with ab initio calculations for the energetics, is that it produces essentially an atomistic simulation for dislocation core properties without suffering from the uncertainties associated with empirical potentials. Therefore, this method is particularly useful in providing insight into alloy design when empirical potentials are not available or not reliable for such multi-element systems. Various core properties, including the core width, dissociation behavior, core energetics, and Peierls stress for different dislocations have been investigated. The correlation between the core energetics and the Peierls stress with the dislocation character has been explored. The effect of hydrogen on the dislocation core properties of aluminum will be discussed. We find that H not only facilitates dislocation emission from the crack tip but also enhances dislocation mobility dramatically, leading to macroscopically softening of the material ahead of the crack tip. We observe strong binding between H and dislocation cores, with the binding energy depending on dislocation character. This dependence can directly affect the mechanical properties of Al by inhibiting dislocation cross-slip and developing slip planarity. Finally, I will discuss extension of the original planar PN model to study dislocation spreading at more than one slip planes, such dislocation cross-slip and junctions. The model is applied to study the external stress assisted dislocation cross-slip and constriction process in two fcc metals, Al and Ag, exhibiting different deformation properties. We find that the screw dislocation in Al can cross-slip spontaneously in contrast with that in Ag, where the screw dislocation splits into two partials that cannot cross-slip without first being constricted. The dislocation response to an external stress is examined in detail. The dislocation constriction energy and the critical stress for cross-slip are determined, and from the latter, we estimate the cross-slip energy barrier for straight screw dislocations.