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.

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.

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.

Correlation between structure, energy, and ideal cleavage fracture for symmetrical grain boundaries in fcc metals

1990 ◽  
Vol 5 (8) ◽  
pp. 1708-1730 ◽  
Author(s):  
D. Wolf
Keyword(s):  
Phase Space ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Cleavage Fracture ◽  
Good Description ◽  
Random Boundary ◽  
Free Surfaces ◽  
Symmetrical Tilt ◽  
Boundary Model ◽  
Twist Boundaries

The misorientation phase space for symmetrical grain boundaries is explored by means of atomistic computer simulations, and the relationship between the tilt and twist boundaries in this three-parameter phase space is clucidated. The so-called random-boundary model (in which the interactions of atoms across the interface are assumed to be entirely random) is further developed to include relaxation of the interplanar spacings away from the grain boundary. This model is shown to include fully relaxed free surfaces naturally, thus permitting a direct comparison of the physical properties of grain boundaries and free surfaces, and hence the determination of ideal cleavage-fracture energies of grain boundaries. An extensive comparison with computer-simulation results for symmetrical tilt and twist boundaries shows that the random-boundary model also provides a good description of the overall structure-energy correlation for both low- and high-angle tilt and twist boundaries. Finally, the role of the interplanar spacing parallel to the grain boundary in both the grain-boundary and cleavage-fracture energies is elucidated.

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.

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.

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.

TEM Study of a Tilt Boundary in Hot-Pressed Silicon

1981 ◽  
Vol 39 ◽  
pp. 160-161
Author(s):  
C. B. Carter ◽  
J. Rose ◽  
D. G. Ast
Keyword(s):  
Electron Diffraction ◽  
Imaging Technique ◽  
Interface Structure ◽  
Large Area ◽  
Weak Beam ◽  
Lattice Fringe ◽  
Electron Diffraction Technique ◽  
Tilt Boundaries ◽  
Beam Technique ◽  
Twist Boundaries

The hot-pressing technique which has been successfully used to manufacture twist boundaries in silicon has now been used to form tilt boundaries in this material. In the present study, weak-beam imaging, lattice-fringe imaging and electron diffraction techniques have been combined to identify different features of the interface structure. The weak-beam technique gives an overall picture of the geometry of the boundary and in particular allows steps in the plane of the boundary which are normal to the dislocation lines to be identified. It also allows pockets of amorphous SiO2 remaining in the interface to be recognized. The lattice-fringe imaging technique allows the boundary plane parallel to the dislocation to be identified. Finally the electron diffraction technique allows the periodic structure of the boundary to be evaluated over a large area - this is particularly valuable when the dislocations are closely spaced - and can also provide information on the structural width of the interface.

High-resolution microscopy of twin boundaries in gold

1987 ◽  
Vol 45 ◽  
pp. 260-261
Author(s):  
William Krakow ◽  
David A. Smith
Keyword(s):  
High Resolution ◽  
Specimen Preparation ◽  
Gold Films ◽  
Boundary Area ◽  
Transmission Electron ◽  
Recent Developments ◽  
Tilt Boundaries ◽  
High Resolution Microscopy ◽  
Twist Boundaries

Recent developments in specimen preparation, imaging and image analysis together permit the experimental determination of the atomic structure of certain, simple grain boundaries in metals such as gold. Single crystal, ∼125Å thick, (110) oriented gold films are vapor deposited onto ∼3000Å of epitaxial silver on (110) oriented cut and polished rock salt substrates. Bicrystal gold films are then made by first removing the silver coated substrate and placing in contact two suitably misoriented pieces of the gold film on a gold grid. Controlled heating in a hot stage first produces twist boundaries which then migrate, so reducing the grain boundary area, to give mixed boundaries and finally tilt boundaries perpendicular to the foil. These specimens are well suited to investigation by high resolution transmission electron microscopy.

Microstructures of a-axis oriented YBCO films made by hybrid plasma sputtering

1995 ◽  
Vol 10 (4) ◽  
pp. 803-809 ◽  
Author(s):  
W. Ito ◽  
A. Oishi ◽  
S. Mahajan ◽  
Y. Yoshida ◽  
T. Morishita
Keyword(s):  
Electron Microscopy ◽  
Grain Boundary ◽  
Anisotropic Growth ◽  
Plan View ◽  
Plasma Sputtering ◽  
Transmission Electron ◽  
Hybrid Plasma ◽  
Tilt Boundaries ◽  
Symmetrical Tilt ◽  
Twist Boundaries

Microstructures of a-axis oriented YBa2Cu3O7−x films made by newly developed de 100 MHz hybrid plasma sputtering were investigated using transmission electron microscopy (TEM). The films deposited on (110) NdGaO3 and (100) SrTiO3 substrates were found to grow in a perfect epitaxial fashion and with clear interface. The plan view of the TEM image showed that both films were comprised of two kinds of grains having the c axis aligning along two perpendicular directions in the plane with equal probability. The structures of the grain boundary, however, were found to be very different for the two films from the plan views. The film on NdGaO3 showed a lot of twist boundaries, while the film on SrTiO3 consisted of many symmetrical tilt boundaries and basal-plane-faced tilt boundaries. The type of grain boundary is determined by the anisotropic growth rates of the film between c direction and a-b direction.

Atomic Structure and Property Correlation in Pulsed Laser Deposited High -Tc Films

1998 ◽  
Vol 526 ◽  
Author(s):  
R. Kalyanaraman ◽  
S. Oktyabrsky ◽  
K. Jagannadham ◽  
J. Narayan
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Grain Boundaries ◽  
Atomic Structure ◽  
Substrate Surface ◽  
Pulsed Laser ◽  
Structure And Property ◽  
Transmission Electron ◽  
Tilt Boundaries ◽  
Z Contrast

AbstractThe atomic structure of grain boundaries in pulsed laser deposited YBCO/MgO thin films have been studied using transmission electron microscopy. The films have perfect texturing with YBCO(001)//MgO(001), giving rise to low-angle [001] tilt boundaries from the grains with the c-axis normal to substrate surface. Low angle grain boundaries have been found to be aligned preferentially along (100) and (110) interface planes. The energy of (110) boundary planes described by an alternating array of [100] and [010] dislocation is found to be comparable to the energy of a (100) boundary. The existence of these split dislocations is shown to further reduce the theoretical current densities of these boundaries indicating that (110) boundaries carry less current as compared to (100) boundaries of the same misorientation angle. Further, Z-contrast transmission electron microscopy of a 42° asymmetric high-angle grain boundary of YBCO shows evidence for the existence of boundary fragments and a reduced atomic density along the boundary plane

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