Birefringence images of screw dislocations viewed end‐on in cubic crystals

1991 ◽  
Vol 69 (11) ◽  
pp. 7556-7564 ◽  
Author(s):  
Chuan‐zhen Ge ◽  
Nai‐ben Ming ◽  
K. Tsukamoto ◽  
K. Maiwa ◽  
I. Sunagawa
Keyword(s):  
Screw Dislocations ◽  
Cubic Crystals

Birefringence images of screw dislocations viewed end on in cubic crystals containing a long‐range stress field

1993 ◽  
Vol 74 (1) ◽  
pp. 139-145 ◽  
Author(s):  
Chuan‐Zhen Ge ◽  
Hai‐Wen Wang ◽  
Nai‐Ben Ming
Keyword(s):  
Stress Field ◽  
Long Range ◽  
Screw Dislocations ◽  
Cubic Crystals

Measurement of the Displacement Across a Coincidence Grain Boundary

1977 ◽  
Vol 35 ◽  
pp. 124-125
Author(s):  
J. W. Matthews ◽  
W. M. Stobbs
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Fault ◽  
The Other ◽  
Measuring Technique ◽  
High Angle ◽  
Twin Boundaries ◽  
Rigid Displacement ◽  
Cubic Crystals ◽  
Lattice Displacement

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

In situ Tensile Experiments at Low Temperatures on Niobium Single Crystals by H.V.E.M.

1975 ◽  
Vol 33 ◽  
pp. 58-59
Author(s):  
F. H. Louchet ◽  
L. P. Kubin
Keyword(s):  
Electron Microscope ◽  
Transition Temperature ◽  
Low Temperature ◽  
Slip System ◽  
Low Temperatures ◽  
Tensile Axis ◽  
Image Intensifier ◽  
Screw Dislocations ◽  
Source Operation

Experiments have been carried out on the 3 MeV electron microscope in Toulouse. The low temperature straining holder has been previously described Images given by an image intensifier are recorded on magnetic tape.The microtensile niobium samples are cut in a plane with the two operative slip directions [111] and lying in the foil plane. The tensile axis is near [011].Our results concern:- The transition temperature of niobium near 220 K: at this temperature and below an increasing difference appears between the mobilities of the screw and edge portions of dislocations loops. Source operation and interactions between screw dislocations of different slip system have been recorded.

Observation of dislocations in dynamically loaded Cu-SiO2

1986 ◽  
Vol 44 ◽  
pp. 424-425
Author(s):  
D. S. Pritchard
Keyword(s):  
Electron Microscope ◽  
Strain Rate ◽  
Single Crystal ◽  
Transmission Electron Microscope ◽  
Volume Fraction ◽  
Screw Dislocations ◽  
Spherical Inclusions ◽  
Transmission Electron ◽  
Crystal Dispersion ◽  
Strain Rate Loading

The effect of varying the strain rate loading conditions in compression on a copper single crystal dispersion-hardened with SiO2 particles has been examined. These particles appear as small spherical inclusions in the copper lattice and have a volume fraction of 0.6%. The structure of representative crystals was examined prior to any testing on a transmission electron microscope (TEM) to determine the nature of the dislocations initially present in the tested crystals. Only a few scattered edge and screw dislocations were viewed in those specimens.

Freeze-fracture TEM of the helical smectic A* phase

1992 ◽  
Vol 50 (1) ◽  
pp. 278-279
Author(s):  
K.J. Ihn ◽  
R. Pindak ◽  
J. A. N. Zasadzinski
Keyword(s):  
Liquid Crystal ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Freeze Fracture ◽  
Smectic Phase ◽  
Layer Spacing ◽  
Screw Dislocations ◽  
Smectic A ◽  
Smectic Phases ◽  
Discrete Amount

A new liquid crystal (called the smectic-A* phase) that combines cholesteric twist and smectic layering was a surprise as smectic phases preclude twist distortions. However, the twist grain boundary (TGB) model of Renn and Lubensky predicted a defect-mediated smectic phase that incorporates cholesteric twist by a lattice of screw dislocations. The TGB model for the liquid crystal analog of the Abrikosov phase of superconductors consists of regularly spaced grain boundaries of screw dislocations, parallel to each other within the grain boundary, but rotated by a fixed angle with respect to adjacent grain boundaries. The dislocations divide the layers into blocks which rotate by a discrete amount, Δθ, given by the ratio of the layer spacing, d, to the distance between grain boundaries, lb; Δθ ≈ d/lb (Fig. 1).

Microtwinning Evidence For The Apparent Five-Fold Symmetry in T2(Al6Li3Cu)

1987 ◽  
Vol 45 ◽  
pp. 24-25
Author(s):  
Kenneth S. Vecchio ◽  
David B. Williams
Keyword(s):  
Stable Equilibrium ◽  
Equilibrium Phase ◽  
Convergent Beam Electron Diffraction ◽  
Icosahedral Structure ◽  
Cubic Crystals ◽  
Icosahedral Phases ◽  
Heat Treated ◽  
Zero Layer ◽  
Convergent Beam ◽  
Zr Alloy

Since the discovery in 1984 by Shechtman et al. of crystals which display apparent five-fold symmetry, extensive effort has been given to establishing a theoretical basis for the existence of icosahedral phases (eg.2.). Several other investigations have been centered on explaining these observations based on twinning of cubic crystals (eg.3.). Recently, the existence of a stable, equilibrium phase T2Al6 Li3Cu) possessing an icosahedral structure has been reported in the Al-Li-Cu system(4-6).In the present study an Al-2.6wt.%Li-l.5wt.%Cu-0.lwt.%Zr alloy was heat treated at 300°C for 100hrs. to produce large T2 precipitates. Convergent Beam Electron Diffraction (CBED) patterns were obtained from two-fold, three-fold, and apparent five-fold axes of T2 particles. Figure 1 shows the five-fold symmetric zero layer CBED pattern obtained from T2 particles.

MISORIENTATION DISTRIBUTION FUNCTION FOR CUBIC CRYSTALS

2019 ◽  
Vol 85 (5) ◽  
pp. 28-32
Author(s):  
A. S. Kolyanova ◽  
Y. N. Yaltsev
Keyword(s):  
Distribution Function ◽  
Grain Boundaries ◽  
Orientation Distribution ◽  
Recrystallization Annealing ◽  
Misorientation Distribution ◽  
Cubic Crystals ◽  
Special Boundaries ◽  
Pole Figures ◽  
Two Samples ◽  
Euler Space

A calculation method for obtaining the misorientation distribution function (MDF) for cubic crystals which can be used to estimate the presence or absence of special boundaries in the materials is presented. The calculation was carried out for two samples of Al-Mg-Si alloy subjected to various mechanical and thermal treatments: the first sample is subjected to rolling; the second sample is subjected to recrystallization annealing. MDF is calculated for each sample; the results are presented in the Euler space and in the angle-axis space. The novelty of the method consists in the possibility of gaining data on the grain boundaries from X-ray texture analysis without using electron microscopy. A calculation involving only mathematical operations on matrices was performed on the basis of the orientation distribution function restored from incomplete pole figures. It is shown that no special boundaries are observed in the deformed sample, whereas in the recrystallized alloy, special boundaries are detected at Ʃ = 23, 13, and 17. The shortcoming of the proposed method can be attributed to the lack of accurate data on grain boundaries, since all possible orientation in the polycrystal should be taken into account in MDF calculation.

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