High-resolution transmission electron microscopy (HRTEM) observations are presented of a/3[111] grain-boundary dislocations in an aluminum sigma =3[011] bicrystal. These dislocations are present on both (111) (coherent twin) and (211) (incoherent twin) facets of the bicrystal boundary. The dislocations on the coherent twin facet migrate by a climb process that increases the thickness of the twinned material. These dislocations originate on a sigma =3 (211) incoherent twin boundary where they are closely spaced and dissociated in a wide core configuration. Atomistic calculations of the defect structure and interaction of multiple a/3[111] grain boundary dislocations are discussed.
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