scholarly journals Complex Frank Loops and Fault Climb

1969 ◽  
Vol 22 (3) ◽  
pp. 393 ◽  
Author(s):  
AJ Morton ◽  
LM Clarebrough
Keyword(s):  
Electron Microscope ◽  
Aluminium Alloys ◽  
Stacking Fault ◽  
The Other ◽  
Dislocation Loops ◽  
Main Loop ◽  
Triangular Region ◽  
Microscope Images

The Burgers vectors of the dislocations bounding steps in the stacking fault in Frank dislocation loops in quenched silver and copper-aluminium alloys have been identified by comparison of experimental electron microscope images and images computed using the Head-Humble technique. The steps in the fault are generally acute, faulted, and bordered by t<llO) stair-rod dislocations. However, obtuse unfaulted steps bordered by t<1l2) Shockley dislocations have also been observed. A characteristic configuration for a stepped loop consists of a triangular region within the main loop with one edge, a dissociated Frank dislocation, forming an edge of the main loop, and the other two edges, acute fault bends bordered by t<llO) dislocations, forming steps in the fault.

scholarly journals The Determination of Stacking Fault Energy by the Tetrahedron Method

1968 ◽  
Vol 21 (6) ◽  
pp. 941 ◽  
Author(s):  
P Humble ◽  
CT Forwood
Keyword(s):  
Electron Microscope ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
The Other ◽  
Dislocation Loops ◽  
The Third ◽  
Wide Range ◽  
Length Measurements ◽  
Incomplete Theory

At present there are three methods for obtaining values of the stacking fault energy y of face-centred cubic (f.c.c.) materials by direct observation of dislocationstacking fault configurations in the electron microscope. These are based on measurements of extended three-fold dislocation nodes (e.g. Whelan 1958; Brown and ThOlen 1964), faulted dipole configurations (e.g. Haussermann and Wilkens 1966; Steeds 1967), and triangular Frank dislocation loops and stacking fault tetrahedral (e.g. Silcox and Hirsch 1959; Loretto, Clarebrough, and Segall 1965). The main advantages of the third method over the other two are that it is applicable to materials of a very wide range of stacking fault energy and involves only simple length measurements of defects that are easily recognized. However, it has suffered from the disadvantage that the values of y deduced from these measurements relied on an incomplete theory. The present authors have reconsidered this problem and, subject to the limitations of isotropic linear elasticity, have taken into account the major variables that may affect the values of y. It is the purpose of this note to present the results of this theory in a form in which values of y may easily be obtained from measurements of Frank dislocation loops and stacking fault tetrahedral without the resources of a large digital computer.

Contrast From Point Defects in The Infinitesimal Approximation

1980 ◽  
Vol 38 ◽  
pp. 350-351
Author(s):  
L. J. Sykes ◽  
J. J. Hren
Keyword(s):  
Electron Microscope ◽  
Point Defects ◽  
Broad Class ◽  
Stacking Fault ◽  
Crystalline Solids ◽  
Dislocation Loops ◽  
Analytical Expression ◽  
Stacking Fault Tetrahedra

In electron microscope studies of crystalline solids there is a broad class of very small objects which are imaged primarily by strain contrast. Typical examples include: dislocation loops, precipitates, stacking fault tetrahedra and voids. Such objects are very difficult to identify and measure because of the sensitivity of their image to a host of variables and a similarity in their images. A number of attempts have been made to publish contrast rules to help the microscopist sort out certain subclasses of such defects. For example, Ashby and Brown (1963) described semi-quantitative rules to understand small precipitates. Eyre et al. (1979) published a catalog of images for BCC dislocation loops. Katerbau (1976) described an analytical expression to help understand contrast from small defects. There are other publications as well.

The climb of dislocation loops in zinc

1966 ◽  
Vol 293 (1434) ◽  
pp. 423-431 ◽  
Keyword(s):  
Zinc Oxide ◽  
Electron Microscope ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Surface Oxide Layer ◽  
Chemical Stress ◽  
Dislocation Loops ◽  
Foil Surface ◽  
A Value ◽  
Normal Manner

The annealing behaviour of faulted dislocation loops in quenched zinc has been studied with the aid of the electron microscope. On annealing, it is observed that some of the loops grow rather than shrink, and this has been attributed to the growth of zinc oxide on the foil surface, which results in the formation of vacancies. Loops which shrink on annealing are considered to lie beneath breaks in the surface oxide layer such that these regions are able to act in the normal manner as vacancy sinks. An estimation of the vacancy supersaturation near such shrinking loops shows that the chemical stress is low, and the climb rate of loops shrinking in the presence of a negligible chemical stress has been analysed to give a value for the stacking fault energy, y. An analysis of the climb rate of a faulted loop based on the emission of vacancies as the controlling process gives a value of 290 erg/cm 2 . A more reliable value of y, which is thought to be independent of the rate-controlling process, is obtained by comparing the climb rate of a faulted loop with that of a prismatic loop. A stacking fault energy value for zinc of 220 erg/cm 2 is deduced.

Electron microscope image contrast of small dislocation loops and stacking-fault tetrahedra

1979 ◽  
Vol 292 (1397) ◽  
pp. 523-537 ◽  
Keyword(s):  
Electron Microscope ◽  
Numerical Solutions ◽  
Preceding Paper ◽  
Stacking Fault ◽  
Image Contrast ◽  
Dislocation Loops ◽  
Displacement Fields ◽  
Microscope Image ◽  
Stacking Fault Tetrahedra ◽  
Electron Microscope Image

With the use of the method described in the preceding paper (to be referred to subsequently as I) for constructing the displacement fields, the electron microscope image contrast of small dislocation loops and of stacking-fault tetrahedra has been computed from numerical solutions of the Howie-Whelan (1961) equations. The computer-simulated images, displayed in the form of half-tone pictures, have been used to identify the nature and geometry of such defects in ion-irradiated foils. A systematic study of the contrast of small Frank loops in Cu + ion irradiated copper under a wide variety of diffraction conditions is reported. In particular the variations of the contrast of loops edge-on and inclined to the electron beam with the operating Bragg reflexion, the thickness and inclination of the foil, depth of the defect in the foil and deviation from the Bragg-reflecting condition have been studied. Methods of obtaining useful information, such as the diameters of the loops, are suggested. The contrast of stacking-fault tetrahedra, and of non-edge perfect dislocation loops in ion-irradiated molybdenum is also investigated.

scholarly journals Diffraction Contrast from Dissociated Frank Dislocations. II. Comparison of Experimental and Computed Electron Micrographs

1969 ◽  
Vol 22 (3) ◽  
pp. 371 ◽  
Author(s):  
LM Clarebrough ◽  
AJ Morton
Keyword(s):  
Electron Micrographs ◽  
Aluminium Alloys ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Dislocation Loops ◽  
Degree Of Dissociation ◽  
Diffraction Contrast

Experimental and computed images for edges of Frank dislocation loops in quenched copper-aluminium alloys and in quenched silver are compared. The comparison shows that Frank dislocations are dissociated in these materials. By matching the computed and experimental images, the degree of dissociation is determined and the stacking fault energy of the various materials is estimated.

The construction of displacement fields of dislocation loops and stacking-fault tetrahedra from angular dislocation segments

1979 ◽  
Vol 292 (1397) ◽  
pp. 513-521 ◽  
Keyword(s):  
Computer Simulation ◽  
Stacking Fault ◽  
Detailed Knowledge ◽  
Image Simulation ◽  
Dislocation Loops ◽  
Displacement Fields ◽  
Burgers Vector ◽  
Stacking Fault Tetrahedra ◽  
Microscope Images ◽  
Stacking Fault Tetrahedron

The computer simulation of electron microscope images of lattice defects requires detailed knowledge of the displacement fields of the defects. By using the method of Yoffe (1960), expressions are derived for the displacement field of a regular N -sided polygonal dislocation loop of arbitrary Burgers vector, and of a stacking-fault tetrahedron, in forms suitable for use in image simulation.

Automatic alignment of stereo images

1994 ◽  
Vol 52 ◽  
pp. 502-503
Author(s):  
John Haselgrove ◽  
Lou Fodor ◽  
Lee Peachey
Keyword(s):  
Electron Microscope ◽  
Rotation Axis ◽  
The Other ◽  
Stereo Images ◽  
Alignment Procedure ◽  
Automatic Alignment ◽  
Microscope Images ◽  
Left And Right ◽  
Digitized Images ◽  
3D Information

Stereoscopic pairs of electron microscope images are used for quantitative 3D information. A prerequisite for the measurement is to position the two images correctly relative to each other and with the stereo rotation axis of each image aligned vertically for viewing. Although this alignment procedure is relatively straightforward to perform using prints of the images, it is not straightforwardto do once the images have been digitized directly from the microscope. We have developed an algorithm for determining the parameters needed for orienting digitized images. Four parameters are needed: The displacements Δx and Δy by which one of the images must be translated to be superimposed on the other, and the angles Θ1 and Θr by which the left and right images must be rotated to bring the stereo-rotation axis vertical.The microscopist first uses an interactive routine to identify the coordinates xl(i),yl(i) and xr(i),yr(i) of a number (N) of fiducial points which can easily be recognized on each image.

Stinging apparatus of apoid wasps and bees as never seen before

ENTOMON ◽  
2020 ◽  
Vol 45 (2) ◽  
pp. 87-92
Author(s):  
Syed Najeer E Noor Khadri ◽  
Rabiya Begum
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
The Other ◽  
Campaniform Sensilla ◽  
Lateral Aspect ◽  
Hunting Behavior ◽  
Sem Images ◽  
Microscope Images ◽  
Ampulex Compressa ◽  
Scanning Electron

The stinging apparatus is expected to vary depending on the type of prey taken and the way it is carried in apoid wasps and the purpose of defense it serves in bees. To understand the differences in sting morphology, members of two apoid wasp families (Ampulicidae and Crabronidae) and a bee family (Halictidae) were studied. Scanning Electron Microscope images of lancets revealed tooth like projections on dorso-lateral aspect in Ampulex compressa (Fabricius, 1781) and blunt barbs on the lancets of Liris aurulentus (Fabricius, 1787) and Tachysphex bengalensis Cameron, 1889 whereas, in Halictus fimbriatellus Vachal, 1894 barbs are arranged in two rows on lancet, which includes four barbs on one side and three barbs on the other side of lancet which are not acutely pointed. The SEM images also indicated the presence of campaniform sensilla on the lancets of compressa. These findings help us to know the possible relationships of hunting behavior and modification of the sting in accordance.

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