Diffusion of potassium in single crystals and polycrystalline aggregates of molybdenum

1966 ◽  
Vol 8 (5) ◽  
pp. 412-414
Author(s):  
G. P. Benediktova ◽  
G. N. Dubinin ◽  
M. G. Karpman ◽  
G. V. Shcherbedinskii
Keyword(s):  
Single Crystals ◽  
Polycrystalline Aggregates

scholarly journals The diffraction of electrons by single crystals

1931 ◽  
Vol 133 (821) ◽  
pp. 1-25 ◽  
Keyword(s):  
Single Crystals ◽  
Present Theory ◽  
Simple Theory ◽  
Complete Agreement ◽  
Surface Films ◽  
Wave Mechanics ◽  
Fast Electrons ◽  
Polycrystalline Aggregates ◽  
Slow Electrons ◽  
Cleavage Face

The Diffraction of Electrons by Single Crystals . 1. The diffraction of electron waves has been observed both with single crystals and with polycrystalline aggregates. So far most of the work with single crystals has been done with slow electrons of a few hundred volts energy. While the results are in general agreement with wave mechanics, they differ considerably from the predictions of the simple theory, even when the latter is extended to include a consideration of the inner potential of the crystal. Part of the discrepancy is caused by undue simplification of the theory, and better results have been got with the more elaborate theory of Morse, but there are a number of cases in which beams corresponding to half order spectra and reflection by “forbidden” crystal planes have been recorded, and for these the present theory is quite unable to account. Experiments with fast electrons on polycrystalline aggregates have shown results in full agreement with the simple theory, and it is hoped that electron diffraction will become a valuable method for the study of surface films Clearly, however, this cannot be done satisfactorily as long as there is any doubt of the ability of the existing theory to explain the diffraction by known structures. It is therefore of importance to see whether any abnormalities exist for single crystals with fast electrons. So far the only work in this connection is that of Kikuchi and others on mica, that of Niskikawa and Kikuchi on calcite, and some work by Emslie at Aberdeen on galena and calcite. Kikuchi’s work shows complete agreement with theory, but has unusual features on account of the large spacing of mica across the cleavage face. The work on calcite is complicated by charging up of the crystal, and galena, as the present author has found, changes under the influence of the rays, so that it is difficult to draw precise conclusions. No metals have been investigated. The present work has, therefore, been undertaken. It consists of a detailed investigation of the diffraction of electrons of from 30,000 to 50,000 volts by single crystals of rocksalt, copper and silver.

scholarly journals Prediction of Localized Necking Based on Crystal Plasticity: Comparison of Bifurcation and Imperfection Approaches

2016 ◽  
Vol 716 ◽  
pp. 779-789
Author(s):  
Holanyo K. Akpama ◽  
Mohamed Ben Bettaieb ◽  
Farid Abed-Meraim
Keyword(s):  
Mechanical Behavior ◽  
Single Crystals ◽  
Large Strain ◽  
Micromechanical Model ◽  
Initial Imperfection ◽  
The Self ◽  
Forming Limit ◽  
Localized Necking ◽  
Self Consistent ◽  
Polycrystalline Aggregates

In the present work, a powerful modeling tool is developed to predict and analyze the onset of strain localization in polycrystalline aggregates. The predictions of localized necking are based on two plastic instability criteria, namely the bifurcation theory and the initial imperfection approach. In this tool, a micromechanical model, based on the self-consistent scale-transition scheme, is used to accurately derive the mechanical behavior of polycrystalline aggregates from that of their microscopic constituents (the single crystals). The mechanical behavior of the single crystals is developed within a large strain rate-independent constitutive framework. This micromechanical constitutive modeling takes into account the essential microstructure-related features that are relevant at the microscale. These microstructural aspects include key physical mechanisms, such as initial and induced crystallographic textures, morphological anisotropy and interactions between the grains and their surrounding medium. The developed tool is used to predict sheet metal formability through the concept of forming limit diagrams (FLDs). The results obtained by the self-consistent averaging scheme, in terms of predicted FLDs, are compared with those given by the more classical full-constraint Taylor model. Moreover, the predictions obtained by the imperfection approach are systematically compared with those given by the bifurcation analysis, and it is demonstrated that the former tend to the latter in the limit of a vanishing size for the initial imperfection.

Electron Microscopy of Diamond Synthesized by Explosive Shock

1968 ◽  
Vol 26 ◽  
pp. 444-445
Author(s):  
Lucien F. Trueb
Keyword(s):  
Single Crystals ◽  
High Explosive ◽  
Average Width ◽  
Metal Mixtures ◽  
Flat Surfaces ◽  
Large Numbers ◽  
Diamond Single Crystals ◽  
New Type ◽  
Polycrystalline Aggregates

The microstructure of early shock-synthesized diamond was discussed in a previous report; this paper is concerned with the characterization of improved material which is now available from E. I. du Pont de Nemours & Company in various size ranges suitable for lapping and polishing.This new type of synthetic industrial diamond is produced by shocking dense graphite-metal mixtures at high explosive pressures. It consists of two types of particles which are shown in Figure 1; polycrystalline aggregates which are rounded and have a mottled surface, and single crystals or fragments thereof which have straight edges and flat surfaces. Figure 2 shows the two types of particles in transmission; they both partly consist of the hexagonal modification of diamond. Single crystals have either a cubic or a hexagonal habit and they often contain large numbers of stacking faults. Polycrystalline particles consist of densely aggregated bundles of acicular crystallites having an average width of 150 A and a length varying between 0.05 and 0.3 p.; a strong preferred orientation is invariably present (Figure 3).

Linking Meso- and Macroscale Simulations: Crystal Plasticity of hcp Metals and Plastic Potentials

2007 ◽  
Vol 539-543 ◽  
pp. 1741-1746
Author(s):  
Dirk Steglich ◽  
Stéphane Graff ◽  
Wolfgang Brocks
Keyword(s):  
Slip System ◽  
Single Crystals ◽  
Crystal Plasticity ◽  
Yield Function ◽  
Crystal Plasticity Model ◽  
Plastic Deformation Behavior ◽  
Polycrystalline Aggregates ◽  
Tension Compression Asymmetry ◽  
Rolled Plates

A crystal plasticity model has been used to simulate channel die experiments on both, pure magnesium single crystals and polycrystalline textured rolled plates. Deformation mechanisms and slip system activity can be identified by FE-analyses of single crystals. The role of twinning can be understood and modeled phenomenologically by an additional slip system. Simulations of polycrystalline aggregates are used to obtain a representation of the material's phenomenological yield function in order to describe the plastic deformation behavior using the framework of continuum mechanics. This allows for accounting for the specific texture and thus for its optimization. The tension- compression asymmetry, which is typical for mechanically processed magnesium material, can be reproduced by means of the crystal plasticity and a phenomenological model.

ELASTIC PROPERTIES OF SINGLE CRYSTALS OF ANHYDRITE

1965 ◽  
Vol 2 (6) ◽  
pp. 673-683 ◽  
Author(s):  
W. M. Schwerdtner ◽  
J. C.-M. Tou ◽  
P. B. Hertz
Keyword(s):  
Single Crystals ◽  
Elastic Properties ◽  
Uniaxial Compression ◽  
Electrical Resistance ◽  
Strain Gauges ◽  
Compression Tests ◽  
Polycrystalline Aggregates

The nine moduli of compliance for anhydrite were obtained in uniaxial compression tests. The displacements were measured by strain gauges of an electrical resistance variety (Budd MetalFilm). Geophysical constants for the polycrystalline aggregates were also computed.

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