The grain-boundary structural unit model redux

2017 ◽  
Vol 133 ◽  
pp. 186-199 ◽  
Author(s):  
Jian Han ◽  
Vaclav Vitek ◽  
David J. Srolovitz
Keyword(s):  
Grain Boundary ◽  
Structural Unit ◽  
Unit Model

Atomic structure of a Σ = 21 grain boundary

1990 ◽  
Vol 5 (11) ◽  
pp. 2658-2662 ◽  
Author(s):  
William Krakow
Keyword(s):  
Electron Microscope ◽  
Grain Boundary ◽  
Atomic Structure ◽  
Structural Unit ◽  
Defect Structures ◽  
Atomic Column ◽  
Unit Model ◽  
Tilt Grain Boundary

An electron microscope structure image of a σ = 21/[111] tilt grain boundary in Au was obtained and atomic column positions identified to yield a structural unit model of the interface consisting of repeating polyhedron shapes. This result represents the smallest projected spacings at a grain boundary containing defect structures imaged by an electron microscope and interpreted atomistically.

scholarly journals Effect of Grain Boundary Structure on Grain Boundary Diffusivities in the Au/Ag System

1990 ◽  
Vol 209 ◽  
Author(s):  
Qing Ma ◽  
R. W. Balluffi
Keyword(s):  
Thin Film ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Tilt Angle ◽  
Structural Unit ◽  
Boundary Structure ◽  
Grain Boundary Structure ◽  
Unit Model ◽  
Tilt Boundaries ◽  
Accumulation Method

ABSTRACTGrain boundary chemical diffusivities for a series of symmetric [001] tilt boundaries in the Au/Ag system were measured by the surface accumulation method using newly developed thin-film multi-crystal specimens, in which the grain boundaries feeding the accumulation surface were all of the same type. Possible effects due to segregation at the grain boundaries and surfaces were avoided. CSL boundaries of low-Σ ( i.e., 5, 13, 17, 25) and also more general boundaries with tilt angles between the low-Σ orientations were selected. The diffusivities were found to vary monotonically with tilt angle ( i.e., no cusps at low-Σ's were found) in a manner consistent with the Structural Unit model.

Computer simulation on surfaces and [001] symmetric tilt grain boundaries in Ni, Al, and Ni3Al

1989 ◽  
Vol 4 (1) ◽  
pp. 62-77 ◽  
Author(s):  
S. P. Chen ◽  
D. J. Srolovitz ◽  
A. F. Voter
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Structural Unit ◽  
Boundary Energy ◽  
Boundary Structure ◽  
Grain Boundary Energy ◽  
Local Composition ◽  
Embedded Atom ◽  
Grain Boundary Structure ◽  
Unit Model

We have used “local volume” (embedded atom) type potentials to study the surfaces and grain boundaries of Ni, Al, and Ni3Al. The simulations show that with appropriately fit potentials, the surface and grain boundary structure can be realistically calculated. The surface rippling and relaxation show good agreement with experiments. The energies of most surfaces and grain boundaries also agree with existing data. The structural unit model for grain boundaries in Ni3Al shows the same generic units as in pure metals, but with large variations due to distortions and multiplicity. The utility of the structural unit model is thus more limited for alloys. The grain boundary energies were found to be the highest for Al-rich Ni3Al grain boundaries, and depend significantly on the local composition of the grain boundary. The cusps in the grain boundary energy as a function of misorientation angle are different for different grain boundary stoichiometries. The Ni3Al grain boundaries have approximately the same grain boundary energy and cohesive energy as that of Ni.

Structural Unit Models for High Angle Symmetrical Tilt Boundaries in Ordered Compounds with the Ll2 Structure

1984 ◽  
Vol 39 ◽  
Author(s):  
D. Farkas
Keyword(s):  
Grain Boundary ◽  
Structural Unit ◽  
Boundary Energy ◽  
Coordination Shell ◽  
Interatomic Potentials ◽  
Two Phase ◽  
Fcc Metals ◽  
Tilt Boundaries ◽  
Hard Sphere Models ◽  
Fcc Materials

ABSTRACTHard sphere models were used to determine densest configurations in symmetrical [100] and [110] tilt boundaries in compounds with the Ll2 structure. The minimum allowed interatomic distances used in these models were estimated from interatomic potentials and the structures of the intermetallic phases in the binary system. The structural unit model is used to analyze the possible ground states for ordering.Two different cases were analyzed corresponding to compounds with “soft” potentials (i.e. Cu3 Au) and “hard” potentials (i.e. Ni3Al). For the Cu3Au type the grain boundary structures obtained were similar to those reported by other investigators for pure fcc metals. Several boundaries were found to be a “two phase” structure, differing in composition and ordering state. This leads to a certain degree of clustering in the boundaries. The contribution of clustering to the grain boundary energy is calculated in a point approximation based on the first coordination shell.For compounds of the Ni3Al type the structures that are densest were found to be generally diffetent from the low energy configurations of boundaries in, pure fcc metals and Cu3 Au. These configurations preserve order, but are much less dense. The possibility of grain boundary “phases” that are not present in other fcc materials may constitute an explanation for the extreme GB weakness observed in Ni3Al and other Ll2 compounds with high ordering energy.

The structure of a near Σ=27 tilt grain boundary in Ge

1992 ◽  
Vol 50 (1) ◽  
pp. 214-215
Author(s):  
Stuart McKernan ◽  
C. Barry Carter
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Structural Unit ◽  
Perfect Crystal ◽  
Boundary Plane ◽  
Boundary Structure ◽  
Structural Units ◽  
Grain Boundary Plane ◽  
Grain Boundary Structure ◽  
Complex Structural

The modeling of tilt grain boundaries in terms of repeating structural units of varying separation is now a well established concept. High-resolution electron microscope (HREM) images of different tilt grain boundaries in many materials display a qualitative similarity of atomic configurations of the grain boundary structure. These boundaries are frequently described in terms of characteristic structural units, which may be separated from each other by regions of ‘perfect’ crystal (as, for example, in low-angle grain boundaries), or may be contiguous, forming ordered arrays of the structural units along the boundary. In general there will be a different arrangement of the structural units or an arrangement of different structural units, according to the precise geometry of the particular grain boundary. The structure of some special grain boundaries has been examined and these are found to exist in several different configurations, depending on the orientation of the grain boundary plane among other parameters. Symmetry-related symmetric tilt grain boundaries and asymmetric tilt grain boundaries with one grain having a prominent, low-index facet, are commonly observed, low-energy configurations. Structural multiplicity of these configurations along the same grain boundary has been observed in some systems. Defects in the perfect ordering of the structural units may be caused by deviations of the grain boundary plane away from the perfect tilt orientation. Deviations of grain boundary structure away from the exact orientation will also produce defects in the repeating structural unit configuration. These deviations may have a regular and well-defined structure, producing a more complex structural unit.

Atomistic Structure of High Index Surfaces

1996 ◽  
Vol 440 ◽  
Author(s):  
Batsirai Mutasa ◽  
Diana Farkas
Keyword(s):  
Structural Unit ◽  
Structural Features ◽  
Low Energy ◽  
High Index ◽  
Interatomic Potentials ◽  
Embedded Atom ◽  
Unit Model ◽  
Ordered Alloys ◽  
Energy Surfaces ◽  
Atomistic Structure

AbstractInteratomic potentials of the embedded atom (EAM) type were used to study the atomistic structure of high index surfaces in metals and ordered alloys. The results show that a structural unit model can be developed to model the structure of the high index surfaces on the basis of the structure of a few low energy surfaces. The model can predict the structural features and give an estimate of the energies of the higher index surfaces. We present examples of Fe, B2 FeAl and NiAl.

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