Sequential obstacle interactions with dislocations in a planar array

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The strengthening of metals by nano-scale obstacles is mainly attributed to the impediment to glide dislocations offered by these obstacles. It is important to understand the mechanisms for dislocation bypass of obstacles having nano-scale dimension, including the atomic-scale structure changes sustained by both obstacles and dislocations after the bypass process. Recently, atomic-scale modeling has provided much insight into obstacle interactions involving a single dislocation. However, the more naturally occurring scenarios involving a sequence of encounters with arrays of moving dislocations are not as well understood owing to prohibitively large length scale requirements for atomistic models. In this study, we utilize a novel multiscale concurrent atomistic-continuum method to simulate a sequence of interactions between glide dislocations in an array with a spherical nano-obstacle (either a void or an impenetrable precipitate) in Al. In the case of a void, the bypassing array of dislocations progressively weakens the void until it splits the originally spherical void into two hemispheres. In the case of a large impenetrable precipitate, sequential dislocations in the array bypass via alternating mechanisms of Orowan looping and Hirsch looping. The residual dislocation loop created around the precipitate by the bypass of the first dislocation is completely removed by the passage of the subsequent dislocation. These mechanisms can benefit the design of materials that are reinforced with nanophase inhomogeneities to achieve ultra high strength.