HREM STUDY OF 45” [loo] QUASIPERIODIC GRAIN BOUNDARY IN ALUMINUM

The structural study of grain boundaries is central to a better understanding of many physical properties of polycrystalline materials. In recent years, there has been remarkable progress in research on the atomic structure of grain boundaries, with the publication of theoretical and experimental structures of many grain boundaries [l-,5] and comprehensive reviews [6,7]. The availability of intermediate voltage electron microscopes (300-400 keV) now provides easy access to atomic resolution images of grain boundaries in many metals and semiconductors in low-index zone axis projections [8]. These studies are complemented by geometrical models of grain boundaries based on the coincident site lattice (CSL) [9], displacementshift-complete (DSC) lattice [lo121 and the O-lattice theories [lo]. These models provide an adequate framework for structural characterization of the atomic-resolution images of grain boundaries. However, this approach i:o studying grain boundary structures has limitations in the sense that it only provides structural information on periodic boundaries. The current body of knowledge on interface structures is almost entirely accumulated from grain boundaries and interfaces with periodic structure. The vast majority of grain boundaries in polycrystalline materials are more general and possess complex atomic structure. Structural information on these grain boundaries remains sketchy because of the lack of theoretical and experimental tools for their structural characterization. It is thus recognized [6] that efforts should be directed to gaining knowledge about the structure. Owing to the complex structure of these boundaries, it seems desirable initially to perform structural investigations on boundaries intermediate to periodic and complex general boundaries. Quasiperiodic grain boundaries do not possess translational periodic@, but have some degree of structural order. Thus, they can be considered as a bridge between periodic and general boundaries, and they offer an opportunity to study structures that may be prototypes of more complex boundaries. The structure of quasiperiodic boundaries can be characterized within the framework of the crystallography of quasicrystals [ 131. So far, only a few structural studies of quasiperiodic boundaries have been reported [ 14161. This paper focuses on quasiperiodic boundaries and presents for the first time an HREM study of a 45 D [ 1001 twist quasiperiodic grain boundary.