Atomic-scale study of dislocation glide in a model solid solution

Abstract

International audienceBased on atomic scale simulation techniques, we study the dislocation pinning mechanism in a dilute Ni(Al) model solid solution. For a solute concentration between 1 and 10 at. %, we found that the pinning of the dislocation on obstacles made of Al pairs is an interaction that operates significantly. The statistics of the dislocation motion is then modified accordingly to the nature of the obstacles and follows a modified Mott-Nabarro statistics. Finally, a method to address thermal activation is proposed and exemplified on a periodic row of solute

Solute strengthening in random alloys

“…Numerical simulations of solute strengthening has lead to the identification of important trends and understandings: contribution to the strength of solutes in planes away from the glide plane, role of the screw vs. edge dislocations, role of solute pairs when the solute concentration increases and the reference is taken from a pure elemental matrix, etc. [37,38,81,109,110]. However, MD simulations, even using empirical potentials, suffer from important limitations, which make difficult to compare simulation results to (i) analytical models and (ii) real material strength.…”

Depinning of a discrete elastic string from a two-dimensional random array of weak pinning points

“…The recent developments of three-dimensional atomistic simulations (3D-AS) allowed to work on more realistic models for dislocations in solid solutions [23,24,25,26,27,28,29,30]. Though 3D-AS confirmed that a large part of the dislocation pinning hinges on the impurities situated in the crystal planes that bounds the dislocation glide plane [23], the simulations revealed also the complexity of the dislocationobstacle interaction.…”

“…In fcc alloys, the geometry of the dislocation core, dissociated in two Shockley partials separated by a (111) stacking fault ribbon undermines the simple picture of an elastic line in interaction with a single type of obstacles, as stated in the basic version of SSH theory. Instead, the pinning forces differ according to partials and to the obstacle positions, i.e., above or below the glide plane [25,28].On the other hand, the nanometric scale of the atomistic simulations, a stringent limit imposed by the computational load, hinders the direct extrapolation of simulation results to macroscopic samples. A multi-scale approach is thence required to link the atomistic studies to the realm of materials sciences.…”

“…Within analytical theory for SSH, the dislocation is thought of as a continuous elastic string impinged on a two-dimensional (2D) random static potential. The depinning transition in such a model is a typical issue of statistical physics, belonging to a broad class of problems concerned with extended interfaces motion in heterogeneous materials [10,11,12,13,14,15,16,17,18,19,20,21,22].The recent developments of three-dimensional atomistic simulations (3D-AS) allowed to work on more realistic models for dislocations in solid solutions [23,24,25,26,27,28,29,30]. Though 3D-AS confirmed that a large part of the dislocation pinning hinges on the impurities situated in the crystal planes that bounds the dislocation glide plane [23], the simulations revealed also the complexity of the dislocationobstacle interaction.…”

“…The parameter w fixes how the interaction de- creases in the vicinity of the force maximum. Both f M and w can be extracted from atomistic data as those reported in [25,28].The dimensionless over-damped Langevin dynamics for the chain node k is given by:where x k is the position of the node k, τ is the external force and s k,i is the coordinate of the ith obstacle in the kth row. For the weak pinning forces we are concerned with, the chain strain remains very small such that the anharmonic terms in the spring tension have been neglected.…”