DEFECT CONCENTRATION IN DEFORMED AlSiMgSr BY TRAPPING MODEL OF POSITRON

2005 ◽  
Vol 12 (04) ◽  
pp. 545-547 ◽  
Author(s):  
M. A. ABDEL-RAHMAN ◽  
M. S. ABDALLAH ◽  
EMAD A. BADAWI
Keyword(s):  
Dislocation Density ◽  
Defect Concentration ◽  
Thickness Reduction ◽  
Free State ◽  
Trapping Rate ◽  
Perfect Agreement ◽  
Lifetime Measurements ◽  
Trapping Model

This paper reports the results of lifetime measurements on deformed AlSiMgSr alloy. Using the trapping model, we obtained the value of 196.7 ps for the lifetime of the free state, and 210.5 ps for the trapped state. The specific trapping rate per unit defect concentration was calculated to be 0.2280 cm2 · s-1. The concentration of defects was 5.78×1017 cm -3 when thickness reduction was 18.2%. The dislocation density for the same thickness reduction is 1.63×1010 cm -2. We have compared these values with a previously used method1 and have obtained perfect agreement for both methods, demonstrating that this a very powerful tool for detecting and evaluating defect concentration.

Positron Trapping at Dislocations in Copper

1974 ◽  
Vol 52 (9) ◽  
pp. 759-765 ◽  
Author(s):  
B. T. A. McKee ◽  
S. Saimoto ◽  
A. T. Stewart ◽  
M. J. Stott
Keyword(s):  
Binding Energy ◽  
Defect Concentration ◽  
Trapping Rate ◽  
Positron Trapping ◽  
Trapping Model ◽  
Random Arrays ◽  
Cold Worked ◽  
Positron Lifetimes ◽  
Copper Crystals

Measurements of positron lifetimes in cold worked copper samples show clearly positron trapping by dislocations. The copper crystals were deformed under conditions that would lead to known densities of dislocations in near random arrays and were annealed to remove other defects associated with the deformation. Using a trapping model, the data yields the value of μ = 2.9 × 1015 s−1 for the trapping rate per unit defect concentration, somewhat higher than the rate for trapping by vacancies in copper. The increase in lifetime of positrons trapped at dislocations is 34 ps (26%), about half the change for positrons trapped at vacancies in copper. A discussion of positron trapping at dislocations contrasted to vacancies emphasizes the differences arising from the extended nature of the dislocation. The theoretical picture leads to a trapping rate at dislocations roughly proportional to the binding energy.

STUDY OF TRAPPING RATE AND DEFECT DENSITY IN AlSi11.35Mg0.23 BY POSITRON ANNIHILATION TECHNIQUE

2004 ◽  
Vol 11 (04n05) ◽  
pp. 427-432 ◽  
Author(s):  
M. A. ABDEL-RAHMAN ◽  
M. S. ABDALLAH ◽  
EMAD A. BADAWI
Keyword(s):  
Positron Annihilation ◽  
Defect Density ◽  
Defect Concentration ◽  
Thickness Reduction ◽  
Trapping Rate ◽  
Positron Annihilation Lifetime ◽  
Maximum Value ◽  
Mean Lifetime ◽  
The Mean

The measurements of Positron Annihilation Lifetime Technique (PALT) have been performed on AlSi 11.35 Mg 0.23 Alloys. It has been shown that positrons can become trapped at imperfect locations in solids and their mean lifetime can be influenced by changes in the concentration of such defects. No change has been observed in the mean lifetime values at the saturation of defect concentration. The trapping rates of positrons can be determined for thickness reduction up to 11% for dislocation. The concentration of defect (ρ') range varies from 8.65×1015 to 2.35×1018 cm -3 up to the maximum value of strain (ε) 0.23.

DETECTING DEFECTS IN AIRCRAFT MATERIALS BY NUCLEAR TECHNIQUE (PAS)

2005 ◽  
Vol 19 (22) ◽  
pp. 3475-3482
Author(s):  
EMAD. A. BADAWI
Keyword(s):  
Aluminum Alloy ◽  
Dislocation Density ◽  
Material Science ◽  
Positron Annihilation Spectroscopy ◽  
Defect Concentration ◽  
Nuclear Technique ◽  
Nuclear Techniques ◽  
Mean Lifetime ◽  
The Mean ◽  
7075 Alloy

Positron annihilation spectroscopy (PAS) is one of the nuclear techniques used in material science. The present measurements are used to study the behavior of defect concentration in one of the most important materials — aluminum alloy — which is a 7075 alloy. It has been shown that positrons can become trapped in imperfect locations in solids and their mean lifetime can be influenced by changes in the concentration of such defects. No changes have been observed in the mean lifetime values after the saturation of defect concentration. The mean lifetime and trapping rates were studied for samples deformed up to 58.3%. The concentration of defect range varies (from 1015 to 1018 cm-3) at the thickness reduction, (from 2.3 to 58.3%). The range of the dislocation density varies (from 108 to 1011 cm/cm3).

Identification of Mg Vacancy in MgO by Positron Lifetime Measurements and First-Principles Calculations

2005 ◽  
Vol 242-244 ◽  
pp. 1-8 ◽  
Author(s):  
Masataka Mizuno ◽  
Hideki Araki ◽  
Yasuharu Shirai ◽  
Fumiyasu Oba ◽  
Isao Tanaka
Keyword(s):  
First Principles ◽  
Positron Lifetime ◽  
Dopant Concentration ◽  
Lattice Relaxation ◽  
Single Crystal Sample ◽  
First Principles Calculations ◽  
Lifetime Measurements ◽  
Crystal Sample ◽  
Trapping Model ◽  
Positron Lifetimes

The formation of Mg vacancy induced by ultra-dilute trivalent impurities in MgO is investigated by a combination of positron lifetime measurements and first-principles calculations. The undoped MgO yields the shortest positron lifetime of 140 ps that is shorter than that of a single crystal sample. The positron lifetime of the doped samples increases with the increase of the Al dopant concentration and is saturated at around 180 ps. This result clearly indicates that the formation of Mg vacancy is induced by Al dopant. The concentration of the other trivalent impurities can be evaluated using the result of component analysis of positron lifetimes. The experimental bulk lifetime of 130 ps, which is obtained by employing trapping model, is well reproduced by the theoretical calculation using the semiconductor model. The calculated defect lifetime is about 20 ps longer than the experimental value. This may be due to the lattice relaxation around Mg vacancy associated with the trapping of positrons.

DETECTING DEFECTS IN AIRCRAFT MATERIALS BY NUCLEAR TECHNIQUE (PAS)

2005 ◽  
Vol 12 (01) ◽  
pp. 1-6 ◽  
Author(s):  
EMAD. A. BADAWI
Keyword(s):  
Aluminum Alloys ◽  
Dislocation Density ◽  
Material Science ◽  
Positron Annihilation Spectroscopy ◽  
Defect Concentration ◽  
Nuclear Technique ◽  
Nuclear Techniques ◽  
Mean Lifetime ◽  
The Mean ◽  
7075 Alloy

Positron annihilation spectroscopy (PAS) is one of the nuclear techniques used in material science. The present measurements are used to study the behavior of defect concentration in one of the most important materials aluminum alloys which is the 7075 alloy. It has been shown that positrons can become trapped at imperfect locations in solids and their mean lifetime can be influenced by changes in the concentration of such defects. No changes have been observed in the mean lifetime values after the saturation of defect concentration. The mean lifetime and trapping rates are studied for samples deformed up to 58.3%. The concentration of defect range vary from 1015 to 1018 cm -3 at the thickness reduction from 2.3 to 58.3%. The dislocation density varies from 108 to 1011 cm/cm 3.

Positron annihilation in deformed Co–Ni alloys

1980 ◽  
Vol 58 (2) ◽  
pp. 270-280 ◽  
Author(s):  
S. Dannefaer ◽  
D. P. Kerr ◽  
S. Kupca ◽  
B. G. Hogg ◽  
J. U. Madsen ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Phase Transition ◽  
Dislocation Density ◽  
Defect State ◽  
Annihilation Process ◽  
Trapping Rate ◽  
Ni Alloys ◽  
Transmission Electron ◽  
Hcp Structure ◽  
Positron Lifetimes

Positron lifetimes have been investigated in a series of deformed Co–Ni alloys in an attempt to identify the mechanism involved in the annihilation process at dislocations. Isochronal annealing measurements show that, although the mechanism is complex in the deformed alloys before annealing, a unique defect state may be attained which gives rise to a lifetime of 140 ps, This value is similar to the lifetime related to monovacancies suggesting that annihilation occurs at a vacancy trapped by a dislocation. The dislocation density was determined by transmission electron microscopy and the trapping rate per unit dislocation density was found to be 2 × 1015 s−1. The phase transition between the fcc and hcp structure for two of the alloys is shown to introduce defects.

Defect and Dislocation Density Parameters of 5251 Al Alloy Using Positron Annihilation Lifetime Technique

2012 ◽  
Vol 332 ◽  
pp. 17-25 ◽  
Author(s):  
M.A. Abdel-Rahman ◽  
M. Elsayed ◽  
Ahmed G. Attallah ◽  
A.A. Ibrahim ◽  
Emad A. Badawi
Keyword(s):  
Cross Section ◽  
Positron Lifetime ◽  
Defect Density ◽  
Theoretical Calculations ◽  
Linear Increase ◽  
Trapping Efficiency ◽  
Al Alloy ◽  
Trapping Rate ◽  
Lifetime Measurements ◽  
Positron Annihilation Lifetime

The result of positron lifetime measurements of a defected 5251 Al alloy is reported. Positron lifetime is measured as a function of the thickness reduction of the sample which shows a nearly linear increase and then becomes constant; which can be considered to be a reason for the defect movement saturation. The trapping rate, trapping efficiency, trapping cross-section, defect concentration and defect density of positrons are also measured for the sample concerned. The behaviors of these parameters are matched with theoretical calculations. Data are analyzed using the PATFIT88 computer program.

Positron Lifetime in Deformed AlSi10.9Mg0.17Sr0.06 Alloys

2007 ◽  
Vol 261-262 ◽  
pp. 55-60 ◽  
Author(s):  
M.A. Abdel-Rahman ◽  
M.S. Abdallah ◽  
Emad A. Badawi
Keyword(s):  
Dislocation Density ◽  
Positron Annihilation ◽  
Material Science ◽  
Positron Lifetime ◽  
Defect Concentration ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Annihilation Lifetime ◽  
Nuclear Techniques ◽  
Mean Lifetime ◽  
The Mean

Positron annihilation lifetime spectroscopy (PALS) is one of the nuclear techniques used in material science. (PALT) measurements are used to study the behaviour of the defect concentration in a set of AlSi10.9Mg0.17Sr0.06 alloys. It has been shown that positrons can become trapped at imperfect locations in solids, and that their mean lifetime can be influenced by changes in the concentration of such defects. No changes have been observed in the mean lifetime values following saturation of the defect concentration. The mean lifetime and trapping rates were studied for samples deformed up to 34.9 %. The concentrations of defects range vary from 5.194x1015 to 1.934x1018 cm-3 for thickness reductions of 2.2 to 34.9 %. The range of the dislocation density varies from 1.465x 108 to 5.454x1010 cm/cm3 over the same range of deformations.

Ultrastructural Changes in Patients With Heat Stroke

1970 ◽  
Vol 28 ◽  
pp. 210-211
Author(s):  
O. T. Minick ◽  
M. C. Kew
Keyword(s):  
Liver Damage ◽  
Heat Stroke ◽  
Free State ◽  
Ultrastructural Changes ◽  
Gold Mines

The effects of heat stroke on hepatic structure were studied in 32 Bantu patients who worked underground in the Transvaal and Orange Free State Gold Mines.Judging from biochemical and morphologic findings, liver damage is an invariable complication of heat stroke. In the milder cases (90 per cent) raised enzyme levels, bromsulphalein retention, and increased prothrombin times were the most common abnormalities.

Observations of dislocation interactions with recrystallized grain boundaries

1988 ◽  
Vol 46 ◽  
pp. 628-629
Author(s):  
C. W. Price
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Dislocation Structure ◽  
Hot Deformation ◽  
Static Recrystallization ◽  
High Dislocation Density ◽  
High Angle ◽  
Dislocation Interactions

Little evidence exists on the interaction of individual dislocations with recrystallized grain boundaries, primarily because of the severely overlapping contrast of the high dislocation density usually present during recrystallization. Interesting evidence of such interaction, Fig. 1, was discovered during examination of some old work on the hot deformation of Al-4.64 Cu. The specimen was deformed in a programmable thermomechanical instrument at 527 C and a strain rate of 25 cm/cm/s to a strain of 0.7. Static recrystallization occurred during a post anneal of 23 s also at 527 C. The figure shows evidence of dissociation of a subboundary at an intersection with a recrystallized high-angle grain boundary. At least one set of dislocations appears to be out of contrast in Fig. 1, and a grainboundary precipitate also is visible. Unfortunately, only subgrain sizes were of interest at the time the micrograph was recorded, and no attempt was made to analyze the dislocation structure.

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