Crystal-Lattice Images of End-On Dislocations in Deformed Aluminum

Abstract

Of particular interest in the theory of dislocations is the magnitude and extent of the perturbation to the atomic structure in the center of a dislocation and in its immediate vicinity. In the present work, two‐beam crystal‐lattice images have been used to directly examine the perturbing influence of end‐on dislocations on the 2.34 Å spacing of (111) planes in deformed aluminum. The crystal‐lattice images were obtained using a high‐vacuum, short‐focal‐length (2.1 mm) Siemens Elmiskop 1 operated at 100 kV with pointed filaments. The experimental observations very clearly illustrate several fundamental properties of dislocations in crystals. As for the core region of a dislocation, the strains were observed to be nonuniform and high with a maximum of ∼0.15. A detailed examination of two end‐on edge dislocations in a low‐angle tilt boundary revealed dislocation core widths of 6.8 and 8.5 b. These widths agree favorably with the 7.3 b width predicted by isotropic‐elasticity theory. Outside the dislocation core, the observed strain field agrees with that expected from elasticity theory, except for the existence of small‐scale expansions and contractions of the lattice which are observed over a distance of 20 to 30 Å from the center of a dislocation.