Grain boundary structure in B2 Fe-Al ordered alloys: an atomic-scale simulation

2000 ◽  
Vol 652 ◽  
Author(s):  
R. Besson ◽  
C. S. Becquart ◽  
A. Legris ◽  
J. Morillo
Keyword(s):  
Grain Boundary ◽  
Ab Initio ◽  
Coincidence Site Lattice ◽  
Bulk Composition ◽  
Atomic Scale ◽  
Boundary Structure ◽  
Grain Boundary Structure ◽  
Symmetric Tilt ◽  
Ab Initio Potentials ◽  
Ab Initio Approach

ABSTRACTWe calculated the atomic structure of the (310)[001] symmetric tilt grain boundary (GB) in B2 ordered Fe-Al, using empirical and ab initio potentials. Including a proper treatment of the influence of small departures from bulk B2 stoichiometry on chemical potentials through a thermodynamic point-defect model, we obtain low energy GB variants geometrically close to the usual ones deduced from the coincidence site lattice (CSL) theory. In Al-rich alloys, both methods predict GB Al segregation whereas in Fe-rich alloys, the empirical (resp. ab initio) approach leads to Fe (resp. Fe or no) segregation. With both methods, strong GB chemical effects triggered by the bulk composition appear, showing that in B2 Fe-Al, GB properties may be strongly influenced by small bulk composition changes.

Observations and implications of grain boundary dislocation networks in high-angle YBa2Cu3O7−δ grain boundaries

1990 ◽  
Vol 5 (5) ◽  
pp. 919-928 ◽  
Author(s):  
S. E. Babcock ◽  
D. C. Larbalestier
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Weak Link ◽  
Coincidence Site Lattice ◽  
Boundary Structure ◽  
High Angle ◽  
Grain Boundary Structure ◽  
Transmission Electron ◽  
Means Of Transmission ◽  
Regular Networks

Regular networks of localized grain boundary dislocations (GBDs) have been imaged by means of transmission electron microscopy in three different types of high-angle grain boundaries in YBa2Cu3O7-δ, implying that these boundaries possess ordered structures upon which a significant periodic strain field is superimposed. The occurrence of these GBD networks is shown to be consistent with the GBD/Structural Unit and Coincidence Site Lattice (CSL)/Near CSL descriptions for grain boundary structure. Thus, these dislocations appear to be intrinsic features of the boundary structure. The spacing of the observed GBDs ranged from ∼10 nm to ∼100 nm. These GBDs make the grain boundaries heterogeneous on a scale that approaches the coherence length and may contribute to their weak-link character by producing the “superconducting micro-bridge” microstructure which has been suggested on the basis of detailed electromagnetic measurements on similar samples.

Structure of Σ7 grain boundary in Al2O3

1994 ◽  
Vol 52 ◽  
pp. 718-719
Author(s):  
C. C. Chu ◽  
F.-R. Chen ◽  
C.-Y. Wang ◽  
L. Chang
Keyword(s):  
Grain Boundary ◽  
Atomic Structure ◽  
Coincidence Site Lattice ◽  
High Vacuum ◽  
Three Dimensional ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Cubic Symmetry ◽  
Grain Boundary Structure ◽  
Resolution Electron

In the past, extensive high resolution electron microscopy has been applied to the atomic structure of grain boundaries of cubic symmetry. In order to have a better understanding of generalization of the grain boundary theory, it could be fruiful to study grain boundary structure of non-cubic and low symmetry crystals in which case the exact CSL’s may not exist. Al2O3 has a hexagonal crystal structure ( non-cubic). In the case of hexagonal crystals, three dimensional coincidence site lattices (CSL’s) are only possible for rational values of (c/a), except for rotations about the [0001] axis. The (c/a) of α-Al2O3 is very close to a rational number (15/2) such that constrained coincidence-site lattice (CCSL) misorientations can be found. In this research, we study the atomic structure of Σ7 grain boundary. The misonentation of Σ7 is [011]/180°. The bicrystals of Σ7 were made by diffusion bonding in high temperature and high vacuum.Figs. 1 (a) and (b). show typical HRTEM images of Σ7 Al2O3 boundary recorded at the underfocus values -48 nm and -96 nm, respectively. The beam direction is parallel to a common axis [20].

The hierarchy of grain boundary structures in SiC bicrystals

1988 ◽  
Vol 46 ◽  
pp. 596-597
Author(s):  
Y. Ishida ◽  
H. Ichinose ◽  
Y. Inomata
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Lattice Theory ◽  
Coincidence Site Lattice ◽  
Boundary Structure ◽  
Geometrical Theory ◽  
Site Lattice ◽  
Atomic Structures ◽  
Grain Boundary Structure ◽  
Predictive Role

The standard geometrical theory having been developed to describe periodically ordered grain boundaries in metals, ie coincidence-site lattice theory faces a new frontier to be expanded in terms of hierarchy of atomic structures in low energy grain boundaries of polytype SiC bicrystals. The unit translation lattice of the polytype crystal is large and elongated in the direction perpendicular to the basal plane. With the elongated translation lattice, the coincidence-site lattice is generally very large. Often too large to be physically significant, although the predictive role of the coincidence-site lattice theory in specifying the orientation of periodically ordered interface was still preserved. Such periodically ordered boundaries were indeed found to occur in the present SiC bicrystals as is predicted by the geometrical theory. A dual description of the grain boundary structure in terms of hierarchy of atomic structures is shown useful in characterizing the bicrystal boundaries.High purity SiC bicrystals were produced by sublimation-deposition method by cooling the encapseled SiC slowly from 2800K.

Direct Determination of Grain Boundary Atomic Structure in SrTiO3

1994 ◽  
Vol 357 ◽  
Author(s):  
M.M. McGibbon ◽  
N.D. Browning ◽  
A.J. McGibbon ◽  
M.F. Chisholm ◽  
S.J. Pennycook
Keyword(s):  
Grain Boundary ◽  
Atomic Structure ◽  
Light Element ◽  
Direct Determination ◽  
Atomic Scale ◽  
Boundary Structure ◽  
Structure Property ◽  
Contrast Imaging ◽  
Grain Boundary Structure ◽  
Tilt Boundaries

AbstractIn the electroceramic SrTiO3 the grain boundary atomic structure governs a variety of electrical properties such as non-linear I-V characteristics. An understanding of this atomic structure-property relationship for individual grain boundaries requires a technique which probes both composition and chemical bonding on an atomic scale. Atomic structure models for [001] tilt boundaries in SrTiO3 bicrystals have been determined directly from experimental data, by combining high-resolution Z-contrast imaging to locate the cation columns at the boundary, with simultaneous electron energy loss spectroscopy to examine light element coordination at atomic resolution. In this paper we compare and contrast the grain boundary structure models of symmetric and asymmetric boundaries in SrTiO3.

Grain Boundary Structure in ARB Processed Copper

2006 ◽  
Vol 503-504 ◽  
pp. 925-930 ◽  
Author(s):  
Kenichi Ikeda ◽  
Naoki Takata ◽  
Kousuke Yamada ◽  
Fuyuki Yoshida ◽  
Hideharu Nakashima ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Structural Unit ◽  
Md Simulation ◽  
Boundary Structure ◽  
Dislocation Model ◽  
Grain Boundary Structure ◽  
Transmission Electron ◽  
Symmetric Tilt ◽  
The Difference

Grain boundary structures in the Accumulative roll-bonding (ARB) processed copper (ARB-Cu) have been studied. The grain boundary structures were observed by high-resolution transmission electron microscopy (HRTEM). In order to clarify the difference between the grain boundaries in ARB-Cu and equilibrium boundaries, calculated atomic structure of symmetric tilt grain boundaries with <110> common axis (<110> symmetric tilt grain boundary; <110> STGB) in Cu were used. The near 14° boundary in the ARB-Cu could be described by the dislocation model, but the dense dislocation region existed near the grain boundary. The high angle boundaries in ARB-Cu could be described by the structural units which were obtained by molecular dynamics (MD) simulation. Furthermore, in the 2 cycles and 6 cycles ARB-Cu (2cARB-Cu and 6cARB-Cu), the deformation twin boundaries could be observed and described by the structural unit. Therefore, it was concluded that the grain boundary structure in the ARB-Cu was not much different from the normal equilibrium grain boundary and explained by conventional dislocation and structural unit models.

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