Atomic-scale arrangement of dislocations at grain-boundary facet junctions

This study investigates the atomic-scale arrangement of dislocations at grain-boundary facet junctions. We focus on the junctions between Σ3 {112} grain-boundary facets (often termed "incoherent" or "lateral" twin boundaries) in face-centered-cubic metals. Planar Σ3 {112} boundaries have long been modeled as dense arrays of Shockley partial dislocations distributed on adjacent {111} planes. Here, we analyze how such dislocations must be arranged at grain-boundary facet junctions. We find that these junctions constrain the sequences of dislocations that can allow for motion of the junctions through coordinated, conservative glide, a result we investigate with complementary molecular-dynamics simulations. For some facet arrangements, namely those for which facets are terminated at both ends by junctions of the same sense, the Shockley partial dislocations must change planes at the junctions, forming a 2 〈 110 〉 unit jogs. Because the unit jogs require the absorption or emission of point defects to move, they will limit motion of facet junctions. Such considerations offer insights into the mechanisms governing grain-boundary junction behavior.