Observation of dislocation arrays in low angle tilt boundaries in gold

Abstract

AbstractTechniques were developed for studying the structure of low angle tilt boundaries by transmission electron microscopy. Boundaries were observed: 1) at normal incidence in bicrystals prepared by welding single crystal films together face‐to‐face at predetermined misorientations, 2) edge‐on in polycrystals obtained by the annealing of welded thin‐film bicrystals initially containing only twist boundaries. Symmetric (100) boundaries with [001] tilt axes consisted of either: a) arrays of uniformly spaced single edge dislocations running parallel to [001] with Burgers vectors b = a [100]; or b) arrays of uniformly spaced close pairs of dislocations running parallel to [001] with the dislocations in each pair having b = a/2 [110] and b = a/2 [110]. A choice between possibilities a) and b) could not be made on the basis of either the experimental observations or simple energy considerations. Symmetric (110) boundaries with [001] tilt axes consisted, as expected, of arrays of single edge dislocations parallel to [001] with b = a/2 [110]. Dislocation structures in (100) and (110) boundaries which possessed particularly small tilt angles and tilt axes lying along directions other than [001] in the boundary plane were also studied. In many cases, when the tilt axes were in certain favorable ranges of orientation, the dislocations broke up into segments in the boundary planes along directions which allowed them to dissociate on {111} planes into partial dislocations and stacking fault ribbons.