Metadislocations in the structurally complex orthorhombic alloy Al13Co4

The existence of metadislocations in the complex, orthorhombic phase metallic alloy Al13Co4 has been postulated [Phil. Mag. 86 985 (2006)]. The present work is a microstructural characterization of defects in this phase by means of transmission electron microscopy. A dislocation core region and associated planar defects were investigated in a plastically deformed sample. The planar defects were shown to be (0 0 1) slabs of a monoclinic phase in the orthorhombic Al13Co4 matrix. Microstructural investigations reveal the presence of an edge dislocation. The strain at the dislocation core is partially compensated by the introduction of the monoclinic phase. A structural model of the core region, based on a tiling description, is developed. The Burgers vector of the dislocation yields -2.9 angstrom [0 1 0], which is a small irrational fraction of the lattice constant. A comparison with metadislocations and dislocations in Laves phases is made and a definition of a metadislocation, including metadislocation glide, is established.