Dislocation emission at junctions between Σ=3 grain boundaries in gold thin films

Abstract

The interaction of dislocations with grain boundary junctions plays an important role during plastic deformation and stress relaxation in polycrystalline thin films. In the present work, arrays of secondary grain boundary dislocations (SGBDs) and their behavior at junctions between orthogonal Σ=3{111} and Σ=3{112} grain boundaries in Au thin films have been studied using room temperature and in situ transmission electron microscopy (TEM). Through diffraction contrast experiments, we find that these dislocations have Burgers vectors of the type a/6 112 . In situ TEM experiments conducted at elevated temperature show that the arrays of SGBDs on {111} twin planes originate in the {112} boundaries where they accommodate a small rotational misorientation from the exact coincident-site-lattice (CSL) orientation. We propose that the discontinuous distribution of SGBDs in the {112} boundary produces a climb stress that drives the dislocation motion. As the dislocations in the grain boundary increase their separation, the climb stress and the misorientation between grains is reduced. To test the plausibility of this explanation, we consider the balance between the reduction in energy due to motion in response to the climb stress and the increase in energy due to the lengthening of dislocation line on the {111} twin plane.