Screw-dislocation constrictions in face-centered cubic crystals
E Martinez and JP Hirth, PHYSICAL REVIEW B, 90, 064102 (2014).
We show, using molecular statics and dynamics simulations along with dislocation dynamics calculations, that the structure of a screw dislocation in a thin film or at a free surface for face-centered cubic Cu differs from that found in bulk. In agreement with earlier work, a screw dislocation at the surface is observed to dissociate in two different 111 planes, forming a constriction at the site where the glide plane changes. We analyze in detail the energetics of the structure and conclude that the constricted configuration is stable due to the long-range elastic interactions. We have also performed shear stress simulations and compared to bulk stress to understand how the constriction modifies the response of the dislocation to an applied load. We found that such constriction represents a strong pinning point, substantially increasing the yield stress required for the dislocation to glide. In contrast, the configuration provides a barrierless source for the dislocation to cross slip.
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