The atomistic structure of the  = 3 (111) grain boundary was determined by means of quantitative high-resolution transmission electron microscopy. In this B2 structure, such a grain boundary constituted an incoherent twin boundary. By using atomic resolution microscopy, images of the grain-boundary structure were obtained with a point resolution of 0.105nm. In order to deduce the quantitative atomistic structure from these images, a new digital image processing method was used. This yielded the positions of Ni and Al columns, in the grain boundary core, with a precision of 0.015nm. The refined structure had Al atoms on the boundary plane. When compared with a geometrical model, the real boundary was found to contain excess volume. Except for the region close to the boundary, the atomic configuration exhibited mirror symmetry with respect to the boundary plane. However, when near to the boundary, lateral relaxation of the atomic positions broke the mirror symmetry. The common building principle which determined these features seemed to be a strong repulsion between closely spaced Al atoms. Due to the relaxation of atomic positions, the boundary core had an open structure; thus suggesting a tendency to intrinsic weakness and brittle fracture.

K.Nadarzinski, F.Ernst: Philosophical Magazine A, 1996, 74[3], 641-64