Monte Carlo-Discrete Dislocation Dynamics: a technique for studying the formation and evolution of dislocation structures

Abstract

A novel Monte Carlo (MC) based solver for discrete dislocation dynamics (DDD) has been developed, by which dislocation lines are inserted to the system in succession subject to a user-defined acceptance criterion. Utilizing this solver, dislocation structure evolution can be examined in a controlled fashion that is not possible using conventional DDD methods. The outcomes of the MC-DDD simulations establish for the first time that dislocation wall structures can adopt a characteristic width that naturally arises from elastic interactions within the network. This characteristic width does not alter as additional dislocation lines are inserted and the density in the wall increases, meaning it is independent of the mean dislocation spacing. However, the wall width is influenced by the acceptance criterion used during MC steps; the wall gets thinner as the interactions within the wall become more attractive. Finally, we demonstrate that algorithmic aspects of MC-DDD simulations can provide insights into structure evolution. Overall, this new MC-DDD technique will allow systematic studies of dislocation structures, providing unprecedented insight into the underlying mechanics.

An interplay between a hydrogen atmosphere and dislocation characteristics in BCC Fe from time-averaged molecular dynamics

“…Despite extensive studies using both continuum models 11 and atomistic approaches such as molecular statics, 12 Monte Carlo, 10 and first-principles 13 calculations, our current understanding of hydrogen effects on dislocation energies remains poor. The primary knowledge gaps include: (1) continuum models have not considered the hydrogen effects on dislocation core energies; (2) previous atomistic simulations mostly treat hydrogen atoms as frozen atoms whereas hydrogen atoms in experiments always exhibit a ''cloud'' nature due to their high mobilities; (3) past studies of dislocation energies are mostly focused on face-centered-cubic (FCC) materials 14,15 and behavior in body-centered-cubic (BCC) materials is relatively less explored 16,17 ; and (4) while discrete dislocation dynamics (DDD) [18][19][20] is effective in revealing the dislocation behavior on a mesoscale, dislocation energies in DDD simulations are typically constructed from isotropic elasticity theory and the impact of this approximation has never been explicitly explored.…”