Grain boundary structure analysed by a coincidence‐site‐lattice pattern for a layer stacking structure of the 4H‐type Laves phase

A coincidence-site-lattice (CSL) model is applied to the 4H-type layer stacking structure of Mg(Cu,A1) 2 alloys of the Laves phase, in order to analyse the structure of densely packed plane (DPP) boundaries which are observed by high-resolution electron microscopy (HREM). In this analysis 'lattice point' is used in a wide sense, including all the origins of the repeating unit in every layer. Owing to this extension, extra coincidence sites of lattice points (CSL-points) occur in the interpenetrating lattices and produce a characteristic pattern which is called a CSL-pattern in this paper. The CSL-pattern gives a satisfactory model for the boundary structure of layer stacking structures such as the Laves phase. Basis vectors of the displacement-shiftcomplete (DSC) lattice obtained here are smaller than those of the usual DSC-lattice and explain well the Burgers vectors of grain boundary dislocations (GBD's). Step vectors and step heights associated with the GBD's are also discussed in detail for the DPP-boundary.