The formation and growth of vacancy loops in magnesium

1968 ◽  
Vol 307 (1488) ◽  
pp. 71-81 ◽  
Keyword(s):  
Surface Oxidation ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Dislocation Loops ◽  
Temperature Range ◽  
Vacancy Loops ◽  
A Value ◽  
Thin Foils ◽  
Contrast Analysis ◽  
Kinetics Of

Single, double and multi-layered dislocation loops have been observed in thin foils of quenched magnesium, and the structure of the loops established by contrast analysis. On annealing in the temperature range 150 to 200°C the loops are observed to grow as a result of the production of vacancies by surface oxidation of magnesium. The kinetics of loop growth have been analysed and a value of 125 ± 25 erg/cm 2 for the stacking fault energy obtained.The reliability and significance of the value in governing the properties of magnesium is discussed.

The annealing of faulted loops in magnesium and zinc

1966 ◽  
Vol 292 (1429) ◽  
pp. 240-263 ◽  
Keyword(s):  
Oxide Film ◽  
Metal Surface ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Stacking Sequence ◽  
Nearest Neighbour ◽  
Dislocation Loops ◽  
Factors Influencing ◽  
Thin Foils ◽  
Kinetics Of

It has been shown that dislocation loops can be nucleated and grown in thin foils made from quenched specimens of magnesium and zinc. Observations are presented which indicate that the surfaces of the thin foils are sealed with an oxide film. Freely diffusing vacancies can only escape from the foil where this oxide film has become locally ruptured, exposing the metal surface. The loops are usually faulted, with b = R = 1/6 <2023>. Occasionally unfaulted loops, with b = <0001>, are observed. An analysis of the kinetics of climb of the faulted loops provides estimates of the stacking fault energy (corresponding to a single violation of the next-nearest-neighbour stacking sequence). These values are, for magnesium, 280 ± 100 erg/ cm 2 and, for zinc, 300 ± 150 erg/cm 2 . Factors influencing the climb rate are discussed.

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.

Defects in ion implanted silicon

1978 ◽  
Vol 36 (1) ◽  
pp. 386-387
Author(s):  
J.A. Lambert ◽  
P.S. Dobson
Keyword(s):  
Defect Structure ◽  
Dislocation Loops ◽  
Frank Loop ◽  
Burgers Vector ◽  
Temperature Range ◽  
Perfect Dislocation ◽  
Contrast Analysis ◽  
Image Position ◽  
Ion Implanted

The defect structure of ion-implanted silicon, which has been annealed in the temperature range 800°C-1100°C, consists of extrinsic Frank faulted loops and perfect dislocation loops, together with‘rod like’ defects elongated along <110> directions. Various structures have been suggested for the elongated defects and it was argued that an extrinsically faulted Frank loop could undergo partial shear to yield an intrinsically faulted defect having a Burgers vector of 1/6 <411>.This defect has been observed in boron implanted silicon (1015 B+ cm-2 40KeV) and a detailed contrast analysis has confirmed the proposed structure.

Kinetics of the hydrolysis of cellobiose and p-nitrophenyl-β-D-glucoside by cellobiase of Trichoderma viride

1977 ◽  
Vol 55 (1) ◽  
pp. 19-26 ◽  
Author(s):  
R. James Maguire
Keyword(s):  
Steady State ◽  
Trichoderma Viride ◽  
Solution Temperature ◽  
Temperature Range ◽  
A Value ◽  
Steady State Kinetics ◽  
Decreasing Ph ◽  
Ph Curve ◽  
Kinetics Of ◽  
Hydrolysis Of

Cellobiase has been isolated from the crude cellulase mixture of enzymes of Trichoderma viride using column chromatographic and ion-exchange methods. The steady-state kinetics of the hydrolysis of cellobiose have been investigated as a function of cellobiose and glucose concentrations, pH of the solution, temperature, and dielectric constant, using isopropanol–buffer mixtures. The results show that (i) there is a marked activation of the reaction by initial glucose concentrations of 4 × 10−3 M to 9 × 10−2 M and strong inhibition of the reaction at higher initial concentrations, (ii) the log rate – pH curve has a maximum at pH 5.2 and enzyme pK values of 3.5 and 6.8, (iii) the energy of activation at pH 5.1 is 10.2 kcal mol−1 over the temperature range 5–56 °C, and (iv) the rate decreases from 0 to 20% (v/v) isopropanol.The hydrolysis by cellobiase (EC 3.2.1.21) of p-nitrophenyl-β-D-glucoside was examined by pre-steady-state methods in which [Formula: see text], and by steady-state methods as a function of pH and temperature. The results show (i) a value for k2 of 21 s−1 at pH 7.0 (where k2 is the rate constant for the second step in the assumed two-intermediate mechanism [Formula: see text]) (ii) a log rate–pH curve, significantly different from that for hydrolysis of cellobiose, in which the rate increases with decreasing pH below pH 4.5, is constant in the region pH 4.5–6, and decreases above pH 6 (exhibiting an enzyme pK value of 7.3), and (iii) an activation energy of 12.5 kcal mol−1 at pH 5.7 over the temperature range 10–60 °C.

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.

A comment on ‘The annealing kinetics of double dislocation loops in thin foils'

1976 ◽  
Vol 34 (5) ◽  
pp. 903-906
Author(s):  
P. M. Marquis ◽  
R. E. Smallman
Keyword(s):  
Dislocation Loops ◽  
Thin Foils ◽  
Kinetics Of

Atomistic Simulation of Mobile Defect Clusters in Metals

1998 ◽  
Vol 540 ◽  
Author(s):  
Yu.N. Osetsky ◽  
D.J. Bacon ◽  
A. Serra
Keyword(s):  
Stacking Fault ◽  
Atomic Scale ◽  
Dynamics Simulation ◽  
Structure Stability ◽  
Dislocation Loops ◽  
Fcc Metals ◽  
Thermally Activated ◽  
Vacancy Loops ◽  
Mobile Defect ◽  
The Difference

AbstractThe structure, stability and thermally-activated motion of interstitial and vacancy clusters in Fe and Cu have been studied using atomic scale computer simulation. All studied interstitial clusters and perfect interstitial loops (PILs) in Fe are mobile whereas their mobility in Cu can be suppressed at large sizes (bigger than 49–61 self-interstitials depending on the temperature) due to dissociation. A comparative study of relaxed configurations has shown that the structure of small perfect dislocation loops of vacancy and self-interstitial nature is very similar. Molecular dynamics simulation has demonstrated that small perfect vacancy loops (PVLs) in Fe consisting of more than 37 vacancies are stable over a wide temperature range and produce atomic displacements by a thermally-activated movement in the direction of the Burgers vector. The mechanism is qualitatively similar to that of SIA clusters studied earlier. Motion of vacancy loops in Cu does not occur because they transform into sessile configurations similar to stacking fault tetrahedra. These results point to the possibly important contribution of vacancy loop mobility to the difference in radiation damage between bcc and fcc metals, and between fcc metals with different stacking fault energy.

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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