In situ reversed deformation of aluminum single crystals in the HVEM: a new X-Y straining stage

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100137616 ◽

1995 ◽

Vol 53 ◽

pp. 248-249

Author(s):

M. A. Wall ◽

M. E. Kassner

Keyword(s):

Shear Stress ◽

Thin Foil ◽

Dislocation Dynamics ◽

Metal Fatigue ◽

In Situ Experiments ◽

Dislocation Movement ◽

Imaging Conditions ◽

Reversed Deformation ◽

Shear Bending

The metal fatigue phenomenon is poorly understood, partially because the dislocation dynamics of reversed deformation have not been well characterized. Little success has been realized with the direct observation of dislocations during in situ cyclic deformation. Problems associated with buckling of the specimen foil occur during applied shear, bending or compression. Buckling can preclude adequate imaging conditions and further complicate the thin foil stress-state. Recent experiments have shown that dislocation movement can be reversed by tensile stressing in alternate perpendicular directions (i.e. 90° rotation of the tensile stress to X and Y directions results in the reversal of the shear stress). Buckling of the specimen foil is also reduced in these experiments.Results from recent in situ reversed deformation experiments are presented here. The experiments were performed on a new straining stage which is a modification of the Sleeswyk- Kassner X-Y stage. The specimen design and preparation procedures have also been modified to facilitate better and more reproducible in situ experiments. The new X-Y straining stage is illustrated in figure 1.

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Decorrelated Dislocation Movement in the γ-Matrix Channels of a Ni-Based Superalloy: Experiment and Dislocation Dynamics Simulation

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.278.13 ◽

2011 ◽

Vol 278 ◽

pp. 13-18

Author(s):

Florence Pettinari-Sturmel ◽

Joël Douin ◽

Didier Locq ◽

Pierre Caron ◽

Armand Coujou

Keyword(s):

Partial Dislocation ◽

Dislocation Dynamics ◽

Dynamics Simulation ◽

Deformation Mechanisms ◽

Narrow Channels ◽

Microscopic Scale ◽

Transmission Electron ◽

Dislocation Movement ◽

Low Strain Rate

The mechanical behavior of the polycrystalline NR3 Ni-based superalloy has been investigated at the microscopic scale. The elementary deformation mechanisms have been analyzed using transmission electron microscope observations as well as in situ straining experiments. Under low stress and relatively low strain rate conditions, a large variety of shearing micromechanisms has been observed depending on the local microstructure and the local effective stress. The influence of the smallest precipitates on the creep behavior has been enlightened: they induce narrow channels which act as obstacle for the movement of the dislocations. In the case of the narrowest channel, the deformation can operate by the propagation of Shockley dislocations or else, by the only propagation of the leading partial resulting from the partial dislocation decorrelation. The occurrence of the observed micromechanisms has been quantitatively analyzed using a nodal dislocation dynamics simulation.

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Experimental Research On the Performance of a Novel Geo-Filament Anchor For An Earthen Architectural Site

10.21203/rs.3.rs-951337/v1 ◽

2021 ◽

Author(s):

Wang Yulan ◽

Guo Jian ◽

Zhang Weixi ◽

Lei Fan

Keyword(s):

Shear Stress ◽

Performance Studies ◽

Distribution Data ◽

The Novel ◽

Grouting Material ◽

Stress Diffusion ◽

In Situ Experiments ◽

Anchoring System ◽

Earthen Architecture

Abstract An efficient anchoring method, explicitly developed for small sliders, has hitherto been missing in the practice of earthen architecture conservation. Furthermore, anchoring performance studies conducted so far, have failed to fully take into account the soil characteristics of certain targets. To address these concerns, the conservation project conceived for the Gaochang Ruins, Turpan, in China, was selected as the testing ground to design a novel Geotechnical Filament Anchor (GFA) for reinforcing small sliders in the earthen historical ramparts. In-situ experiments were conducted for evaluating six parameters—anchoring length (L), GF thickness (H), bore diameter (D), grouting strength (S), GFA surface status (R), and inclination angle (A). These parameters were varied in order to determine the effect they produce on anchoring performance, as demonstrated by the indicators, including tensile strength, destruction mode, load displacement (P-S) relation, and strain (ζ-L) distribution characteristics of the novel GFA. Data acquired from the experiments, in combination with the conservation specifics of earthen architectural sites, anchoring performance, and safety reserve, were further employed to introduce a calculation formula for computing the designed force value (N) through L. A simplified model depicting the shear stress distribution of the anchoring system under N was devised by extracting the strain distribution data with respect to the GF-grouting interface. Taking into account the soil properties of the above-mentioned site, the shear stress diffusion coefficient (α) was conceptualized, the formula for the shear strength of the grouting material was devised, and the tolerable ranges of L, D, H, R, and S were determined. Thus, a feasible anchoring method for small sliders used in earthen architectural sites is proposed, and validated by strong and reliable experimental and theoretical groundwork.

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Effets of surfaces on precipitate morphology in irradiated thin foils

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100110416 ◽

1978 ◽

Vol 36 (1) ◽

pp. 654-655

Author(s):

D.I. Potter ◽

A. Taylor

Keyword(s):

Ion Irradiation ◽

Dark Field Image ◽

Thin Foil ◽

Dark Field ◽

Al Alloy ◽

Bright Field Image ◽

Dislocation Loops ◽

Precipitate Morphology ◽

Thin Foils

Thermal aging of Ni-12.8 at. % A1 and Ni-12.7 at. % Si produces spatially homogeneous dispersions of cuboidal γ'-Ni3Al or Ni3Si precipitate particles arrayed in the Ni solid solution. We have used 3.5-MeV 58Ni+ ion irradiation to examine the effect of irradiation during precipitation on precipitate morphology and distribution. The nearness of free surfaces produced unusual morphologies in foils thinned prior to irradiation. These thin-foil effects will be important during in-situ investigations of precipitation in the HVEM. The thin foil results can be interpreted in terms of observations from bulk irradiations which are described first.Figure 1a is a dark field image of the γ' precipitate 5000 Å beneath the surface(∿1200 Å short of peak damage) of the Ni-Al alloy irradiated in bulk form. The inhomogeneous spatial distribution of γ' results from the presence of voids and dislocation loops which can be seen in the bright field image of the same area, Fig. 1b.

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An in situ and ex situ TEM study of the formation of thin cobalt silicide films by molecular beam epitaxy on the silicon (100) surface

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010010648x ◽

1988 ◽

Vol 46 ◽

pp. 884-885

Author(s):

D. Loretto ◽

J. M. Gibson ◽

S. M. Yalisove ◽

R. T. Tung

Keyword(s):

Molecular Beam Epitaxy ◽

Molecular Beam ◽

Defect Density ◽

High Vacuum ◽

Ultra High Vacuum ◽

Ex Situ ◽

Metal Base ◽

In Situ Experiments ◽

Potential Applications

The cobalt disilicide/silicon system has potential applications as a metal-base and as a permeable-base transistor. Although thin, low defect density, films of CoSi2 on Si(111) have been successfully grown, there are reasons to believe that Si(100)/CoSi2 may be better suited to the transmission of electrons at the silicon/silicide interface than Si(111)/CoSi2. A TEM study of the formation of CoSi2 on Si(100) is therefore being conducted. We have previously reported TEM observations on Si(111)/CoSi2 grown both in situ, in an ultra high vacuum (UHV) TEM and ex situ, in a conventional Molecular Beam Epitaxy system.The procedures used for the MBE growth have been described elsewhere. In situ experiments were performed in a JEOL 200CX electron microscope, extensively modified to give a vacuum of better than 10-9 T in the specimen region and the capacity to do in situ sample heating and deposition. Cobalt was deposited onto clean Si(100) samples by thermal evaporation from cobalt-coated Ta filaments.

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Influence of ion-milling on the T2 phase in Al-2.5%Li-2.5%Cu alloy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100153415 ◽

1989 ◽

Vol 47 ◽

pp. 288-289

Author(s):

J. R. Reed ◽

D. J. Michel ◽

P. R. Howell

Keyword(s):

Thin Foil ◽

Icosahedral Symmetry ◽

Ion Milling ◽

Cu Alloy ◽

Thin Foils ◽

Heat Treated ◽

Aluminum Solid Solution ◽

In Situ Heating ◽

The Stability

The Al6Li3Cu (T2) phase, which exhibits five-fold or icosahedral symmetry, forms through solid state precipitation in dilute Al-Li-Cu alloys. Recent studies have reported that the T2 phase transforms either during TEM examination of thin foils or following ion-milling of thin foil specimens. Related studies have shown that T2 phase transforms to a microcrystalline array of the TB phase and a dilute aluminum solid solution during in-situ heating in the TEM. The purpose of this paper is to report results from an investigation of the influence of ion-milling on the stability of the T2 phase in dilute Al-Li-Cu alloy.The 3-mm diameter TEM disc specimens were prepared from a specially melted Al-2.5%Li-2.5%Cu alloy produced by conventional procedures. The TEM specimens were solution heat treated 1 h at 550°C and aged 1000 h at 190°C in air to develop the microstructure. The disc specimens were electropolished to achieve electron transparency using a 20:80 (vol. percent) nitric acid: methanol solution at -60°C.

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A method for direct measurement of specimen noise in HREM images

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100148125 ◽

1993 ◽

Vol 51 ◽

pp. 458-459

Author(s):

Sidnei Paciornik ◽

Roar Kilaas ◽

Ulrich Dahmen ◽

Michael Adrian O'Keefe

Keyword(s):

Random Noise ◽

Image Interpretation ◽

Thin Foil ◽

High Resolution Electron Microscopy ◽

Black Dot ◽

Atomic Column ◽

Amorphous Oxide ◽

Resolution Electron ◽

Imaging Conditions ◽

Image Simulations

High resolution electron microscopy (HREM) is a primary tool for studying the atomic structure of defects in crystals. However, the quantitative analysis of defect structures is often seriously limited by specimen noise due to contamination or oxide layers on the surfaces of a thin foil.For simple monatomic structures such as fcc or bcc metals observed in directions where the crystal projects into well-separated atomic columns, HREM image interpretation is relatively simple: under weak phase object, Scherzer imaging conditions, each atomic column is imaged as a black dot. Variations in intensity and position of individual image dots can be due to variations in composition or location of atomic columns. Unfortunately, both types of variation may also arise from random noise superimposed on the periodic image due to an amorphous oxide or contamination film on the surfaces of the thin foil. For example, image simulations have shown that a layer of amorphous oxide (random noise) on the surfaces of a thin foil of perfect crystalline Si can lead to significant shifts in image intensities and centroid positions for individual atomic columns.

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Electron and ion irradiation-induced dissolution of mechanical twins in the intermetalic U3Si: An in situ HVEM study

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100155232 ◽

1989 ◽

Vol 47 ◽

pp. 652-653

Author(s):

Charles W. Allen ◽

Robert C. Birtcher

Keyword(s):

Elevated Temperatures ◽

Ion Irradiation ◽

Ion Beam ◽

National Laboratory ◽

Argonne National Laboratory ◽

Heavy Ion ◽

High Energy ◽

Mechanical Twinning ◽

In Situ Experiments

The uranium silicides, including U3Si, are under study as candidate low enrichment nuclear fuels. Ion beam simulations of the in-reactor behavior of such materials are performed because a similar damage structure can be produced in hours by energetic heavy ions which requires years in actual reactor tests. This contribution treats one aspect of the microstructural behavior of U3Si under high energy electron irradiation and low dose energetic heavy ion irradiation and is based on in situ experiments, performed at the HVEM-Tandem User Facility at Argonne National Laboratory. This Facility interfaces a 2 MV Tandem ion accelerator and a 0.6 MV ion implanter to a 1.2 MeV AEI high voltage electron microscope, which allows a wide variety of in situ ion beam experiments to be performed with simultaneous irradiation and electron microscopy or diffraction.At elevated temperatures, U3Si exhibits the ordered AuCu3 structure. On cooling below 1058 K, the intermetallic transforms, evidently martensitically, to a body-centered tetragonal structure (alternatively, the structure may be described as face-centered tetragonal, which would be fcc except for a 1 pet tetragonal distortion). Mechanical twinning accompanies the transformation; however, diferences between electron diffraction patterns from twinned and non-twinned martensite plates could not be distinguished.

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A computer-control program for TEM in situ fatigue experiments

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100155074 ◽

1989 ◽

Vol 47 ◽

pp. 620-621

Author(s):

Kenneth S. Vecchio ◽

John A. Hunt

Keyword(s):

Slow Crack Growth ◽

Computer Control ◽

Control Program ◽

Video Tape ◽

Computer Control System ◽

Transmission Electron ◽

In Situ Experiments ◽

Tremendous Amount ◽

And Control

In-situ experiments conducted within a transmission electron microscope provide the operator a unique opportunity to directly observe microstructural phenomena, such as phase transformations and dislocation-precipitate interactions, “as they happen”. However, in-situ experiments usually require a tremendous amount of experimental preparation beforehand, as well as, during the actual experiment. In most cases the researcher must operate and control several pieces of equipment simultaneously. For example, in in-situ deformation experiments, the researcher may have to not only operate the TEM, but also control the straining holder and possibly some recording system such as a video tape machine. When it comes to in-situ fatigue deformation, the experiments became even more complicated with having to control numerous loading cycles while following the slow crack growth. In this paper we will describe a new method for conducting in-situ fatigue experiments using a camputer-controlled tensile straining holder.The tensile straining holder used with computer-control system was manufactured by Philips for the Philips 300 series microscopes. It was necessary to modify the specimen stage area of this holder to work in the Philips 400 series microscopes because the distance between the optic axis and holder airlock is different than in the Philips 300 series microscopes. However, the program and interfacing can easily be modified to work with any goniometer type straining holder which uses a penrmanent magnet motor.

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Coliform transport in a pristine reservoir: modeling and field studies

Water Science & Technology ◽

10.2166/wst.1998.0124 ◽

1998 ◽

Vol 37 (2) ◽

pp. 137-144 ◽

Cited By ~ 11

Author(s):

Elisa Garvey ◽

John E. Tobiason ◽

Michael Hayes ◽

Evelyn Wolfram ◽

David A. Reckhow ◽

...

Keyword(s):

Model Development ◽

Fate And Transport ◽

Field Studies ◽

Meteorological Conditions ◽

Reservoir Modeling ◽

Vertical Circulation ◽

Quality Model ◽

Circulation Patterns ◽

In Situ Experiments

This paper reports on field studies and model development aimed at understanding coliform fate and transport in the Quabbin Reservoir, an oligotrophic drinking water supply reservoir. An investigation of reservoir currents suggested the importance of wind driven phenomena, and that both lateral and vertical circulation patterns exist. In-situ experiments of coliform decay suggested dependence on light intensity and yielded an appropriate decay coefficient to be used in CE-QUAL-W2, a two-dimensional hydrodynamic and water quality model. Modeling confirmed the sensitivity of reservoir outlet concentration to vertical variability within the reservoir, meteorological conditions, and location of coliform source.

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