Low-Σ twist and tilt grain boundaries in cubic materials

2011 ◽  
Vol 44 (6) ◽  
pp. 1152-1156 ◽  
Author(s):  
A. Morawiec
Keyword(s):  
Grain Boundaries ◽  
Tilt Boundary ◽  
Polycrystalline Materials ◽  
Two Dimensional ◽  
Special Boundary ◽  
Cubic Symmetry ◽  
Cubic Materials ◽  
Boundary Properties ◽  
Tilt Boundaries ◽  
Twist Boundaries

Knowledge of the geometry of grain boundaries in polycrystalline materials is essential for predicting boundary properties. The issue of cataloging the geometrically characterized groups of twist and tilt boundaries is addressed. All distinct types of pure-twist and pure-tilt boundaries are determined for misorientations corresponding to highly coincident (3 ≤ Σ ≤ 13) lattices of cubic symmetry. For these particular misorientations, the number of distinct twist boundaries and zones of tilt boundaries ranges from 5 (Σ = 3) to 11 (Σ = 9 or 11). Maps displaying the locations of twist and tilt boundary planes indicate boundaries having particular geometries with two-dimensional periodicities. This is of significance for identification of special boundary structures. Moreover, the maps allow for relating peaks on experimentally determined grain boundary distributions to particular types of twist or tilt boundaries.

High-resolution x-ray analysis of dislocation networks nn tilt boundaries

1988 ◽  
Vol 46 ◽  
pp. 612-613
Author(s):  
J. R. Michael ◽  
C. H. Lin ◽  
S. L. Sass
Keyword(s):  
Grain Boundaries ◽  
Analytical Electron Microscopy ◽  
Solute Segregation ◽  
X Ray ◽  
Periodic Arrays ◽  
Analytical Electron ◽  
Primary Dislocation ◽  
Tilt Boundaries ◽  
Polycrystalline Solids ◽  
Twist Boundaries

The segregation of solute atoms to grain boundaries in polycrystalline solids can be responsible for embrittlement of the grain boundaries. Although Auger electron spectroscopy (AES) and analytical electron microscopy (AEM) have verified the occurrence of solute segregation to grain boundaries, there has been little experimental evidence concerning the distribution of the solute within the plane of the interface. Sickafus and Sass showed that Au segregation causes a change in the primary dislocation structure of small angle [001] twist boundaries in Fe. The bicrystal specimens used in their work, which contain periodic arrays of dislocations to which Au is segregated, provide an excellent opportunity to study the distribution of Au within the boundary by AEM.The thin film Fe-0.8 at% Au bicrystals (composition determined by Rutherford backscattering spectroscopy), ∼60 nm thick, containing [001] twist boundaries were prepared as described previously. The bicrystals were analyzed in a Vacuum Generators HB-501 AEM with a field emission electron source and a Link Analytical windowless x-ray detector.

Frequencies of Tilt and Twist Boundaries among Random Grain Boundaries

2010 ◽  
Vol 160 ◽  
pp. 95-99 ◽  
Author(s):  
Adam Morawiec
Keyword(s):  
Computer Program ◽  
Grain Boundaries ◽  
Random Boundary ◽  
Small Deviations ◽  
Tilt Boundaries ◽  
The Difference ◽  
Twist Boundaries

There are a number of classifications of homophase grain boundaries. It is quite common to divide them into twist, tilt and general boundaries. As in the case of the classification into coincident lattice (CSL) boundaries and non-CSL boundaries, one may ask about the possible frequencies of incidence of tilt and twist boundaries in a set of “random” boundaries. The proba¬bilities of occurrence of these particular boundary types are clearly defined if small deviations from pure twist and tilt conditions are allowed. We estimated the probabilities numerically for the cases of cubic and hexagonal holohedries. For a given randomly generated boundary, a computer program searched for the nearest pure-tilt and pure-twist boundaries. All symmetrically equivalent representations of the random boundary were processed, and the smallest distance was taken as the result. The distance was based on both the difference in misorientations and the deviation between boundary inclinations. The findings concerning tilt boundaries turned out to be striking. For instance, if the allowed deviation from pure-tilt conditions is only 1°, then as many as 39.0% and 21.2% of random boundaries have near-tilt character for the cubic and hexagonal cases, respectively. If the limiting deviation is raised to 5°, the frequencies of near-tilt boundaries reach 98.6% and 77.0%, respectively.

The Structure of Dislocations in Low-Angle Grain Boundaries in the Diamond Cubic Lattice

1981 ◽  
Vol 5 ◽  
Author(s):  
C.B. Carter
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Faults ◽  
Burgers Vector ◽  
Cubic Lattice ◽  
Partial Dislocations ◽  
Tilt Boundaries ◽  
P Type ◽  
Twist Boundaries

ABSTRACTDislocations in low-angle tilt boundaries exhibit a wide variety of Burgers vector including a/2<112> a<001> and a<111>. The dislocations are usually dissociated: Shohkley, stair-rod and Frank partial dislocations may each be formed together with associated intrinsic and extrinsic stackingfaults. Dislocations in low-angle {111} twist boundaries are usually assumed to dissociated by a glide mechanism to give two types of extended nodes, known as P–type and K–type, which contain intrinsic and extrinsic stacking-faults respectively. It is shown that dissociation by climb actually occurs for both types of grain boundary.

Anisotropic Behaviour of Grain Boundaries

2005 ◽  
Vol 482 ◽  
pp. 63-70 ◽  
Author(s):  
Václav Paidar ◽  
Pavel Lejček
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Polycrystalline Materials ◽  
Grain Boundary Engineering ◽  
Interfacial Dislocation ◽  
Special Character ◽  
Boundary Properties ◽  
Properties Of Materials ◽  
Boundary Classification ◽  
Boundary Chemistry

Grain boundaries are decisive for many properties of materials. Due to short-range stress field their influence is primarily based on their atomic structure. Special character of grain boundary properties related to their structure, follows from the nature of atomic arrangements in the boundary cores, from the interfacial dislocation content and from the boundary mobility. All those aspects of boundary behaviour are strongly influenced by the boundary chemistry including various segregation phenomena. Approaches to the boundary classification and the interpretation of recent experimental results are discussed in the context of the complex relationship between microstructure and material properties. Such findings are essential for Grain Boundary Engineering proposed to improve the performance of polycrystalline materials.

Structure of grain boundaries in hexagonal close-packed metals

1987 ◽  
Vol 45 ◽  
pp. 264-267
Author(s):  
A.H. King ◽  
Fu-Rong Chen
Keyword(s):  
Grain Boundaries ◽  
Coincident Site Lattice ◽  
Low Energy ◽  
Site Lattice ◽  
Cubic Symmetry ◽  
Hexagonal Close Packed ◽  
Cubic Materials ◽  
Dislocation Arrays ◽  
And Behaviors ◽  
Electron Microscopist

The structures and behaviors of grain boundaries in cubic materials have been studied extensively by electron microscopists for almost two decades, and much of this work has been related to the geometrical theories of Bollmann. Grain boundaries separating crystals that are close to coincident site lattice (CSL) misorientations have received extensive attention because they appear to have unusual properties and they also have relatively easily resolved structures which can be described in terms of dislocation arrays embedded in low-energy atomic configurations. When we start to deal with materials of lower than cubic symmetry, however, new problems arise and considerable difficulties beset the electron microscopist: in order to tackle some of these problems, we have begun by studying grain boundaries in hep metals.

A new method for preparing tilt grain boundaries in thin vapor-deposited films

1987 ◽  
Vol 45 ◽  
pp. 280-281
Author(s):  
William Krakow ◽  
Victor Castaño
Keyword(s):  
Grain Boundaries ◽  
Boundary Migration ◽  
Ion Milling ◽  
The Past ◽  
Single Crystal Films ◽  
Crystal Films ◽  
Tilt Boundaries ◽  
Deposited Films ◽  
Twist Boundaries

In the past the electron microscope samples used to study tilt grain boundaries and interfaces were prepared from bulk samples grown from the melt which were then cut, polished and thinned by ion milling or chemical jet etching. This technique is also employed routinely in preparing crossectional semiconductor materials and metals. Another technique to prepare tilt boundaries in metals is to fuse two thin single crystal films each on substrates by heating and forming twist boundaries (e.g. Au (100)). Then, the boundary which forms at the composite film midplane, migrates to one of the two films surfaces having many island grains separated by tilt boundaries perpendicular to the foils’ surface. One of the present authors has carried this technique further by being able to perform this process directly in the microscope and observe the boundary migration when the total film thickness, in the case of Au, was ∼250Å. The technique is limited to this composite thickness because small holes develop in thinner films which thin rapidly become discontinuous when heated in-situ.

Excess Free Volume of High Angle Grain Boundaries in Aluminium

2006 ◽  
Vol 519-521 ◽  
pp. 1557-1562 ◽  
Author(s):  
V.A. Ivanov ◽  
Dmitri A. Molodov ◽  
Lasar S. Shvindlerman ◽  
Günter Gottstein ◽  
D. Kolesnikov ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Free Volume ◽  
Pressure Range ◽  
Boundary Energy ◽  
Tilt Boundary ◽  
Triple Junctions ◽  
High Angle ◽  
Absolute Value ◽  
Excess Free Volume ◽  
Tilt Boundaries

A new method is introduced to determine the absolute value of the boundary excess free volume. Along with the boundary energy the excess free volume belongs to the major thermodynamic properties of grain boundaries. The method utilizes the dependence of the contact angle at triple junctions of grain boundaries in Al-tricrystals on hydrostatic pressure. We investigated <111> tilt boundaries in the pressure range up to 14 kbar. In particular, for a 40° <111> tilt boundary with 2° twist component the boundary free volume was found to be equal to 5.03×10-11 m3/m2.

scholarly journals Near–atomic-scale observation of grain boundaries in a layer-stacked two-dimensional polymer

2020 ◽  
Vol 6 (33) ◽  
pp. eabb5976 ◽  
Author(s):  
Haoyuan Qi ◽  
Hafeesudeen Sahabudeen ◽  
Baokun Liang ◽  
Miroslav Položij ◽  
Matthew A. Addicoat ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Atomic Scale ◽  
Great Promise ◽  
Formation Mechanisms ◽  
Two Dimensional ◽  
Transmission Electron ◽  
2D Polymers ◽  
Tilt Boundaries ◽  
2D Polymer ◽  
Grain Coalescence

Two-dimensional (2D) polymers hold great promise in the rational materials design tailored for next-generation applications. However, little is known about the grain boundaries in 2D polymers, not to mention their formation mechanisms and potential influences on the material’s functionalities. Using aberration-corrected high-resolution transmission electron microscopy, we present a direct observation of the grain boundaries in a layer-stacked 2D polyimine with a resolution of 2.3 Å, shedding light on their formation mechanisms. We found that the polyimine growth followed a “birth-and-spread” mechanism. Antiphase boundaries implemented a self-correction to the missing-linker and missing-node defects, and tilt boundaries were formed via grain coalescence. Notably, we identified grain boundary reconstructions featuring closed rings at tilt boundaries. Quantum mechanical calculations revealed that boundary reconstruction is energetically allowed and can be generalized into different 2D polymer systems. We envisage that these results may open up the opportunity for future investigations on defect-property correlations in 2D polymers.

Nucleation and propagation of cracks at grain boundaries in zinc bicrystals

1989 ◽  
Vol 4 (5) ◽  
pp. 1182-1194 ◽  
Author(s):  
H. A. Schmitz ◽  
D. Dew-Hughes ◽  
J. C. Bilello
Keyword(s):  
Surface Energy ◽  
Crack Propagation ◽  
Grain Boundaries ◽  
Surface Defects ◽  
Crack Nucleation ◽  
Effective Surface ◽  
Crack Penetration ◽  
Fatigue And Fracture ◽  
Tilt Boundaries ◽  
Twist Boundaries

A study has been made of fatigue and fracture in zinc bicrystals. It is shown that cleavage cracks are nucleated, both under tension and as a result of fatigue, in regions of multiple slip adjacent to grain boundaries at stresses below those for crack nucleation in single crystals. The nature of crack penetration through the boundary is observed as a function of orientation across the boundary. Low angle tilt boundaries are barriers to crack propagation, increasing effective surface energies for crack propagation by 1.6–2 times. Twist boundaries, due to the tearing that accompanies penetration, can result in a twelvefold increase in effective surface energy. Nonbasal cleavage is associated with a twinning mechanism, and an even higher surface energy is required to propagate a crack into a crystal oriented for this type of cleavage. The results carry the implication that, in the absence of surface defects, fatigue, failure in polycrystalline zinc is nucleated at the first internal grain boundary and not at the surface.

Faceted Twin Boundaries in an Mg-Al Spinel

1982 ◽  
Vol 40 ◽  
pp. 550-551
Author(s):  
T. M. Shaw ◽  
C. B. Carter
Keyword(s):  
Grain Boundaries ◽  
Atomic Structure ◽  
Ceramic Materials ◽  
Amorphous Layer ◽  
Fundamental Importance ◽  
Polycrystalline Materials ◽  
Detailed Structure ◽  
Twin Boundaries ◽  
Lattice Fringe ◽  
Tilt Boundaries

The atomic structure of grain boundaries is of fundamental importance in determining their behavior and thus the properties of polycrystalline materials. There have been several studies (eg. refs 1-4) of the detailed structure of pure tilt boundaries using lattice-fringe and structure imaging. These studies have mainly been concerned with metals and semiconductors. There have been some reports on the detailed structure of grain boundaries in ceramic materials (eg. 5,6) but most effort there has been directed towards identifying and understanding the nature of the thin amorphous layer which appears often to be present. The present paper presents results of a new study on the structure of twin boundaries in an Mg-Al spinel. The spinel studied is the non-stoichiometric MgO.2Al2O3 in which the oxygen atoms form an fcc sublattice and the cations sit in the tetrahedral and octahedral intersticies.

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