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.

GRAIN-SIZE DEPENDENCE OF FRACTURE IN COPPER–ALUMINIUM ALLOYS EMBRITTLED BY MERCURY

1967 ◽  
Vol 45 (2) ◽  
pp. 1235-1249 ◽  
Author(s):  
F. W. J. Pargeter ◽  
M. B. Ives
Keyword(s):  
Aluminium Alloys ◽  
Cellular Network ◽  
Size Dependence ◽  
Network Formation ◽  
Pure Copper ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Aluminium Content ◽  
Α Phase ◽  
Stacking Fault Energies

Polycrystalline specimens of α-phase copper–aluminium alloys of varying composition, amalgamated with mercury, have been deformed in tension in a soft tensile machine. In all cases, brittle intergranular failure occurred at stresses and strains below those required for fracture in air, the degree of embrittlement increasing with increasing aluminium content. The alloys having stacking-fault energies less than '~8 erg/cm2 were found to obey quite well the Petch–Stroh relation:[Formula: see text]The other alloys showed deviations from this relation which became more marked with increasing stacking-fault energy. Values of the fracture energy, varying from ~48 erg/cm2 for pure copper to ~470 erg/cm2 for Cu −8 wt.% Al, have been obtained for all of the alloys. These values are only applicable for relatively small grain sizes.The deviation from the Petch–Stroh relation in the high stacking-fault energy alloys is thought to be due to their tendency to show cross-slip and cellular-network formation, rather than coplanar arrays of dislocations as required by the Stroh model. The low stacking-fault energy alloys typically show well-defined pileups and so obey the Petch–Stroh relations, as expected.

scholarly journals Diffraction Contrast from Dissociated Frank Dislocations. I. Computed Electron Micrographs

1969 ◽  
Vol 22 (3) ◽  
pp. 351 ◽  
Author(s):  
LM Clarebrough ◽  
AJ Morton
Keyword(s):  
Electron Microscope ◽  
Electron Micrographs ◽  
Degree Of Dissociation ◽  
Diffraction Contrast ◽  
Microscope Images

The influence of degree of dissociation on the diffraction contrast from a Frank dislocation for lll, 220, and 020 reflections has been investigated using the technique devised by Head and Humble for computing electron microscope images.

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.

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.

Stacking Faults in Crystals

1968 ◽  
Vol 26 ◽  
pp. 250-251
Author(s):  
P. C. J. Gallagher
Keyword(s):  
Stacking Faults ◽  
Elastic Equilibrium ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Major Influence ◽  
Face Centered Cubic ◽  
Degree Of Dissociation ◽  
Partial Dislocations ◽  
Layer Structures ◽  
Face Centered

Stacking faults are an important substructural feature of many materials, and have been widely studied in layer structures (e.g. talc) and in crystals with hexagonal and face centered cubic structure. Particular emphasis has been placed on the study of faulted defects in f.c.c. alloys, since the width of the band of fault between dissociated partial dislocations has a major influence on mechanical properties.Under conditions of elastic equilibrium the degree of dissociation reflects the balance of the repulsive force between the partials bounding the fault, and the attractive force associated with the need to minimize the energy arising from the misfits in stacking sequence. Examples of two of the faulted defects which can be used to determine this stacking fault energy, Υ, are shown in Fig. 1. Intrinsically faulted extended nodes (as at A) have been widely used to determine Υ, and examples will be shown in several Cu and Ag base alloys of differing stacking fault energy. The defect at B contains both extrinsic and intrinsic faulting, and readily enables determination of both extrinsic and intrinsic fault energies.

Interaction between Dislocation Sliding and Damage Structure in Ion-irradiated Stainless Steels

2008 ◽  
Vol 1125 ◽  
Author(s):  
Terumitsu Miura ◽  
Katsuhiko Fujii ◽  
Koji Fukuya
Keyword(s):  
Shear Strength ◽  
Plastic Strain ◽  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Dislocation Loops ◽  
Number Density ◽  
Damage Structure

ABSTRACTThe interaction between dislocation sliding and damage structure in ion-irradiated austenitic stainless steels was investigated. Solution annealed type 316 and 304 stainless steels (316SS and 304SS) were irradiated with 2.8 MeV Fe2+ ions at 300 °C up to 10 dpa and tensiled to 2% plastic strain at 300 °C. Dislocations moving from unirradiated matrix were prevented due to the interactions with the damage structures consisted of dislocation loops and voids in the damage region. The prevention of dislocation movements by the damage structures became strong in 304SS compared in 316SS; probably due to lower stacking fault energy in 304SS. The prevention of dislocation movements was weak for Fe ion-irradiated specimens in which the increase in shear strength calculated from the size and number density of the defects was small compared to He ion-irradiated specimens.

scholarly journals The Influence of Impurity Content on Thermal Stability of Low Stacking Fault Energy Silver Processed by Severe Plastic Deformation

2012 ◽  
Vol 729 ◽  
pp. 222-227 ◽  
Author(s):  
Zoltán Hegedűs ◽  
Jenő Gubicza ◽  
Megumi Kawasaki ◽  
N.Q. Chinh ◽  
Z. Fogarassy ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Elevated Temperatures ◽  
Lattice Defect ◽  
Impurity Content ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Dislocation Loops ◽  
Boundary Frequency ◽  
Angular Pressing ◽  
Thermal Stability Of

The effect of the impurity content on the evolution of the ultrafine-grained (UFG) microstructure in low stacking fault energy Ag and its stability at room and elevated temperatures were investigated. Samples of silver having high (99.995%) and somewhat lower (99.99%) purity levels were processed by equal-channel angular pressing (ECAP) at room temperature (RT) up to 16 passes. Although, the minimum grain size achieved by ECAP was ~200 nm for both series, the lattice defect structure was strongly influenced by the impurity content. In the samples processed by 4-16 passes of ECAP a self-annealing occurred during storage RT that was promoted by the higher twin boundary frequency. Both room-and high-temperature thermal stability of 99.99% purity Ag were much better due to the pinning effect of impurities. It was found that a large number of dislocation loops remained in the microstructure even after recrystallization at high temperatures.

FAULTED DEFECTS AND STACKING-FAULT ENERGY

1967 ◽  
Vol 45 (2) ◽  
pp. 1135-1146 ◽  
Author(s):  
L. M. Clarebrough ◽  
P. Humble ◽  
M. H. Loretto
Keyword(s):  
Direct Methods ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Face Centered Cubic ◽  
Dislocation Loops ◽  
Cubic Metals ◽  
The Third ◽  
Stacking Fault Tetrahedra ◽  
Dislocation Energy ◽  
Face Centered

Four direct methods of obtaining values of stacking-fault energy from observation of faulted defects in pure face-centered cubic metals are discussed. It is shown that there is essential agreement between the method based on the observation of threefold nodes and that based on the observation of triangular Frank dislocation loops and stacking-fault tetrahedra in deformed f.c.c. metals, in the range where both methods are applicable. On the other hand, it is shown that the third method, based on the collapse size of stacking-fault tetrahedra in quenched metals, cannot yield even an upper limit. New experimental results show that the fourth method, based on the annealing rate of faulted loops, is applicable only to metals of high stacking-fault energy and then only if jog nucleation and propagation are not rate controlling; for low stacking-fault energy metals, these factors, together with the dislocation energy, must be considered, and cannot be completely taken into account.

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