About the Microstructural Effects of Polycrystalline Materials and their Macroscopic Representation at Finite Deformation

ABSTRACTSmall amounts of second phase materials can have important effects on the thermoelectric properties of polycrystalline γ-La3-xX4 (X-S, Te; 0<x<l/3). Microscopic examination by SEM of hot pressed La3–xTe4 samples has revealed from 1–5 vol. % of La202Te, an amount which is not detected by x-ray powder diffraction measurements. This amount of La202Te resulting from oxygen contamination can reduce the concentration of electrons by as much as 10% to 75% below the electron concentration calculated for single phase La3–xTe4 in the composition range of greatest interest. Small amounts of second phase materials can also lower the lattice thermal conductivity by scattering low frequency phonons These results indicate that microstructural effects should be considered when electrical and thermal properties of polycrystalline materials are analyzed.

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High Voltage Transmission Microscopy of Surveyor III Camera Shrouds

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100064748 ◽

1971 ◽

Vol 29 ◽

pp. 138-139

Author(s):

W. R. Duff ◽

L. E. Thomas ◽

R. M. Fisher ◽

S. V. Radcliffe

Keyword(s):

Alloy Sheet ◽

Transmission Microscopy ◽

Television Camera ◽

Window Method ◽

Transmission Electron ◽

Microstructural Effects ◽

Lunar Environment ◽

Successful Retrieval ◽

Materials Used ◽

Abrasive Paper

Successful retrieval of the television camera and other components from the Surveyor III spacecraft by the Apollo 12 astronauts has provided a unique opportunity to study the effects of a known and relatively extensive exposure to the lunar environment. Microstructural effects including those produced by micro-meteorite impact, radiation damage (by both the solar wind and cosmic rays) and solar heating might be expected in the materials used to fabricate the spacecraft. Samples received were in the form of 1 cm2 of painted unpainted aluminum alloy sheet from the top of the camera visor (JPL Code 933) and the sides (935,936) and bottom (934) of the lower camera shroud. They were prepared for transmission electron microscopy by first hand-grinding with abrasive paper to a thickness of 0.006". The edges were lacquered and the sample electropolished in 10% perchloric methanol using the “window” method, to a thickness of ~0.001". Final thinning was accomplished by polishing 3 mm punched disks in an acetic-phosphoric-nitric acid solution.

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Observation of secondary slip systems in tungsten bicrystals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100112361 ◽

1984 ◽

Vol 42 ◽

pp. 478-479

Author(s):

J. R. Fekete ◽

R. Gibala

Keyword(s):

Stress Field ◽

Grain Boundaries ◽

Deformation Behavior ◽

Stress Axis ◽

Polycrystalline Materials ◽

Slip Systems ◽

Metallic Materials ◽

Twist Boundary ◽

Secondary Slip ◽

Plane Normal

The deformation behavior of metallic materials is modified by the presence of grain boundaries. When polycrystalline materials are deformed, additional stresses over and above those externally imposed on the material are induced. These stresses result from the constraint of the grain boundaries on the deformation of incompatible grains. This incompatibility can be elastic or plastic in nature. One of the mechanisms by which these stresses can be relieved is the activation of secondary slip systems. Secondary slip systems have been shown to relieve elastic and plastic compatibility stresses. The deformation of tungsten bicrystals is interesting, due to the elastic isotropy of the material, which implies that the entire compatibility stress field will exist due to plastic incompatibility. The work described here shows TEM observations of the activation of secondary slip in tungsten bicrystals with a [110] twist boundary oriented with the plane normal parallel to the stress axis.

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Low-temperature annealing of YBa2Cu3O7-x

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100120849 ◽

1992 ◽

Vol 50 (1) ◽

pp. 88-89

Author(s):

R.L. Sabatini ◽

Yimei Zhu ◽

Masaki Suenaga ◽

A.R. Moodenbaugh

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Low Temperature ◽

Oxygen Diffusion ◽

Diffusion Rate ◽

Oxygen Depletion ◽

Low Temperature Annealing ◽

Transmission Electron ◽

Microstructural Effects ◽

Oxygen Diffusion Rate

Low temperature annealing (<400°C) of YBa2Cu3O7x in a ozone containing oxygen atmosphere is sometimes carried out to oxygenate oxygen deficient thin films. Also, this technique can be used to fully oxygenate thinned TEM specimens when oxygen depletion in thin regions is suspected. However, the effects on the microstructure nor the extent of oxygenation of specimens has not been documented for specimens exposed to an ozone atmosphere. A particular concern is the fact that the ozone gas is so reactive and the oxygen diffusion rate at these temperatures is so slow that it may damage the specimen by an over-reaction. Thus we report here the results of an investigation on the microstructural effects of exposing a thinned YBa2Cu3O7-x specimen in an ozone atmosphere using transmission electron microscopy and energy loss spectroscopy techniques.

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The structure of amorphous and polycrystalline materials using energy-filtered RDF analysis

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100130584 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1190-1191

Author(s):

David Cockayne ◽

David McKenzie

Keyword(s):

Electron Diffraction ◽

Diffraction Pattern ◽

Density Function ◽

Electron Diffraction Pattern ◽

Polycrystalline Materials ◽

Nearest Neighbour ◽

X Ray ◽

Selected Area Electron Diffraction ◽

Reduced Density ◽

System F

The technique of Electron Reduced Density Function (RDF) analysis has ben developed into a rapid analytical tool for the analysis of small volumes of amorphous or polycrystalline materials. The energy filtered electron diffraction pattern is collected to high scattering angles (currendy to s = 2 sinθ/λ = 6.5 Å-1) by scanning the selected area electron diffraction pattern across the entrance aperture to a GATAN parallel energy loss spectrometer. The diffraction pattern is then converted to a reduced density function, G(r), using mathematical procedures equivalent to those used in X-ray and neutron diffraction studies.Nearest neighbour distances accurate to 0.01 Å are obtained routinely, and bond distortions of molecules can be determined from the ratio of first to second nearest neighbour distances. The accuracy of coordination number determinations from polycrystalline monatomic materials (eg Pt) is high (5%). In amorphous systems (eg carbon, silicon) it is reasonable (10%), but in multi-element systems there are a number of problems to be overcome; to reduce the diffraction pattern to G(r), the approximation must be made that for all elements i,j in the system, fj(s) = Kji fi,(s) where Kji is independent of s.

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Morphology and atomic structure of segregated grain boundaries in Cu-Sb

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100121673 ◽

1992 ◽

Vol 50 (1) ◽

pp. 254-255

Author(s):

R. W. Fonda ◽

D. E. Luzzi

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Intergranular Fracture ◽

Atomic Structure ◽

Copper Alloys ◽

Polycrystalline Materials ◽

Grain Boundary Embrittlement ◽

Boundary Embrittlement

The properties of polycrystalline materials are strongly dependant upon the strength of internal boundaries. Segregation of solute to the grain boundaries can adversely affect this strength. In copper alloys, segregation of either bismuth or antimony to the grain boundary will embrittle the alloy by facilitating intergranular fracture. Very small quantities of bismuth in copper have long been known to cause severe grain boundary embrittlement of the alloy. The effect of antimony is much less pronounced and is observed primarily at lower temperatures. Even though moderate amounts of antimony are fully soluble in copper, concentrations down to 0.14% can cause grain boundary embrittlement.

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Interface structures in polycrystalline ceramic materials

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100143900 ◽

1986 ◽

Vol 44 ◽

pp. 468-471

Author(s):

K. J. Morrissey

Keyword(s):

Electron Microscopy ◽

Analytical Electron Microscopy ◽

Physical And Mechanical Properties ◽

High Resolution Electron Microscopy ◽

Ceramic Materials ◽

Polycrystalline Materials ◽

Transmission Electron ◽

Resolution Electron ◽

Interface Structures

Grain boundaries and interfaces play an important role in determining both physical and mechanical properties of polycrystalline materials. To understand how the structure of interfaces can be controlled to optimize properties, it is necessary to understand and be able to predict their crystal chemistry. Transmission electron microscopy (TEM), analytical electron microscopy (AEM,), and high resolution electron microscopy (HREM) are essential tools for the characterization of the different types of interfaces which exist in ceramic systems. The purpose of this paper is to illustrate some specific areas in which understanding interface structure is important. Interfaces in sintered bodies, materials produced through phase transformation and electronic packaging are discussed.

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