Extraneous grain boundary dislocations in low and high angle (001) twist boundaries in gold

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Abstract
A study of extraneous grain boundary dislocation (GBD) structures in low and high angle (001) twist boundaries in gold was carried out by transmission electron microscopy using bicrystal specimens prepared by welding evaporated single crystal thin films together face-to-face. GBD structures were observed which could be explained by the introduction of dislocations with lattice Burgers vectors ±a/2[101], ±a/2[101], ±a/2[011], or ±a/2[011] into the boundaries and the subsequent interactions of these dislocations with the networks of misfit screw GBD's which are associated with the intrinsic equilibrium structure of the twist boundaries (Schober and Balluffi 1970 b). In many cases the interactions in the boundary essentially eliminated the components of the Burgers vectors of the extraneous GBD's in the plane of the boundary and produced effective Burgers vectors almost (or exactly) perpendicular to the boundary. In all cases the components normal to the boundary of the effective Burgers vectors were of magnitude a/2 (a=lattice parameter). It was suggested that most of the extraneous GBD structures originated from lattice dislocations which impinged on the boundaries during plastic deformation which occurred during the specimen preparation. The roles of such GBD's in supporting grain boundary point defect source (or sink) action and boundary migration are pointed out.