Effect of Nature Aging on Positron Lifetime Spectroscopy in Casting and Wrought Al-alloys

2007 ◽  
Vol 265 ◽  
pp. 13-18 ◽  
Author(s):  
M.A. Abdel-Rahman ◽  
M. Abdel-Rahman ◽  
N.A. Kamel ◽  
M.S. Abdallah ◽  
Emad A. Badawi
Keyword(s):  
Aluminum Alloys ◽  
Positron Annihilation ◽  
Point Defects ◽  
Positron Lifetime ◽  
Natural Aging ◽  
Al Alloys ◽  
Isochronal Annealing ◽  
Mean Lifetime ◽  
Positron Lifetime Spectroscopy

Positron annihilation has been performed in order to study the isochronal annealing of wrought (2024, 7075) and cast (AlSi11.35Mg0.23, AlSi10.9Mg0.17Sr0.06) aluminum alloys, at temperatures ranging from RT to 773K, after having been deformed at RT to 25% deformation. Two annealing stages of the microstructures were distinguished, which were attributed to recovery in (2024, AlSi11.35Mg0.23, AlSi10.9Mg0.17Sr0.06) due to point defects and dislocations, respectively, and only one (due to dislocations) in (7075). Also, natural aging for up to more than 650 days was studied as a function of mean lifetime.

A STUDY OF RECOVERY STAGES IN SOME PLASTICALLY DEFORMED ALUMINUM ALLOYS BY POSITRON LIFETIME SPECTROSCOPY

2005 ◽  
Vol 12 (02) ◽  
pp. 203-207 ◽  
Author(s):  
M. A. ABDEL-RAHMAN ◽  
M. S. ABDALLAH ◽  
EMAD A. BADAWI
Keyword(s):  
Aluminum Alloys ◽  
Positron Annihilation ◽  
Room Temperature ◽  
Positron Lifetime ◽  
Isochronal Annealing ◽  
Temperature Range ◽  
Positron Lifetime Spectroscopy

Positron annihilation was performed to study the isochronal annealing of wrought (2024, 7075) and casting ( AlSi 11.35 Mg 0.23, AlSi 10.9 Mg 0.17 Sr 0.06) aluminum alloys in the temperature range from room temperature to 773 K after they had been deformed at room temperature with 25% deformation. Two annealing stages of microstructures were distinguished which were attributed to recovery in 2024, and AlSi 11.35 Mg 0.23, AlSi 10.9 Mg 0.17 Sr 0.06 due to point and dislocations respectively, and only one due to dislocations in 7075.

An Investigation of Point Defects in NiAl Using Positron Annihilation Techniques

1998 ◽  
Vol 552 ◽  
Author(s):  
Werner Puff ◽  
Bernd Logar ◽  
Adam G. Balogh
Keyword(s):  
Positron Annihilation ◽  
Point Defects ◽  
Proton Irradiation ◽  
Positron Lifetime ◽  
Composition Range ◽  
Isochronal Annealing ◽  
Doppler Broadening ◽  
Positron Lifetime Spectroscopy ◽  
Induced Defects

ABSTRACTVacancy-like defects in NiAl in the composition range 47 at.-% < CNi < 53 at.-% are investigated by means of positron lifetime spectroscopy and Doppler-broadening measurements. The observed lifetimes in the annealed samples confirm that defects are quenched-in during the production of the samples. Isochronal annealing of samples quenched at 1600°C and after proton irradiation show that the induced defects are quite different.

scholarly journals Vacancies in electron irradiated 6H silicon carbide studied by positron annihilation spectroscopy

2003 ◽  
Vol 792 ◽  
Author(s):  
C. H. Lam ◽  
C. C. Ling ◽  
C. D. Beling ◽  
S. Fung ◽  
H. M. Weng ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Positron Annihilation ◽  
Electron Irradiation ◽  
Room Temperature ◽  
Positron Lifetime ◽  
Positron Annihilation Spectroscopy ◽  
Isochronal Annealing ◽  
Positron Lifetime Spectroscopy ◽  
Irradiation Process ◽  
Positron Lifetime Measurement

ABSTRACTPositron lifetime spectroscopy was employed to study the as-electron-irradiated (10 MeV, 1×1018 cm-2) n-type 6H silicon carbide sample in the measuring temperature range of 15 K to 294 K. Isochronal annealing studies were also performed up to the temperature of 1373 K by carrying out the room temperature positron lifetime measurement. Negatively charged carbon vacancies and VCVSi divacancy were identified as the major vacancy type defects induced by the electron irradiation process. The concentration of the VCVSi divacancy was found to decrease dramatically after the 1973 K annealing.

Defects Distribution of Pr2Fe14B Hard Magnetic Magnet from Amorphous to Nanostructures Characterized by Positron Annihilation Spectroscopy

2005 ◽  
Vol 475-479 ◽  
pp. 2123-2126
Author(s):  
Yu Cheng Wu ◽  
W. Sprengel ◽  
K. Reimann ◽  
K.J. Reichle ◽  
D. Goll ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Grain Growth ◽  
Melt Spinning ◽  
Positron Lifetime ◽  
Positron Annihilation Spectroscopy ◽  
Amorphous Structure ◽  
Defect Distribution ◽  
Positron Lifetime Spectroscopy ◽  
Positron Lifetimes ◽  
Shape And Size

The defect distributions have been investigated using positron lifetime spectroscopy on amorphous and nanocrystalline Pr2Fe14B samples, produced by melt-spinning and nanocrystallization route. The main two components can be concluded that were ascribed to vacancy-like defects in the intergranular layers or the interfaces, and microvoids or large free volumes with size compared to several missing atoms at the interactions of the atomic aggregates or the crystallites. The remarkable changes in the positron lifetimes from the amorphous structure to the nanocrystalline with varied sizes can be interpreted, indicating that the structural transformation and the grain growth induce the defect distribution changes occurring at the interfaces with different shape and size.

Dislocation Recovery in Casting Alloy by Positron Lifetime Technique

2008 ◽  
Vol 280-281 ◽  
pp. 113-119
Author(s):  
M.A. Abdel-Rahman ◽  
M.S. Abdallah ◽  
N.A. Kamel ◽  
Emad A. Badawi
Keyword(s):  
Annealing Temperature ◽  
Positron Lifetime ◽  
Activation Enthalpy ◽  
The Other ◽  
Isochronal Annealing ◽  
Casting Alloy ◽  
Perfect Lattice ◽  
Mean Lifetime ◽  
Recovery Behavior ◽  
Fast Cooling

Recovery behavior of 20% plastically deformation of casting AlSi11.35Mg0.23 in various stages of isochronal annealing has been investigated by positron Lifetime (LT). The experimental results show that the positron mean lifetime is a function of annealing temperature. Lifetime of the positron annihilating in perfect lattice is 187.3ps and in 20% deformed is 229.8 ps. There are two regions in the isochronal annealing, one of them relating to the point defect and the other to the dislocation. The activation enthalpy for the dislocation is calculated from the isothermal study in the dislocation region from (575-675) K by slow and fast cooling as 0.16±0.02 and 0.53±0.06 eV respectively.

Positron spectroscopy of bulk and near-surface defects in semiconductors

1989 ◽  
Vol 67 (8) ◽  
pp. 813-817
Author(s):  
P. Hautojārvi
Keyword(s):  
Positron Annihilation ◽  
Positron Lifetime ◽  
Surface Defects ◽  
Positron Beam ◽  
Near Surface ◽  
Slow Positron ◽  
Positron Spectroscopy ◽  
Positron Lifetime Spectroscopy ◽  
Defects In Semiconductors ◽  
Ion Implanted

The use of positron annihilation to study defects in semiconductors is discussed. Positron-lifetime spectroscopy reveals As vacancies in as-grown GaAs and gives information on ionization levels. The vacancy profiles in ion-implanted Si are investigated by slow positron beam.

Activation Enthalpy of Dislocation Migration in Aircraft (Aerospace) (2024) Alloy by Positron Spectroscopy

2008 ◽  
Vol 278 ◽  
pp. 11-14 ◽  
Author(s):  
M.A. Abdel-Rahman ◽  
M.S. Abdallah ◽  
N.M. Hassan ◽  
Emad A. Badawi
Keyword(s):  
Activation Energy ◽  
Aluminum Alloys ◽  
Positron Annihilation ◽  
Point Defects ◽  
Isothermal Annealing ◽  
Activation Enthalpy ◽  
Positron Annihilation Lifetime ◽  
Nuclear Techniques ◽  
Positron Spectroscopy ◽  
2024 Alloy

Positron annihilation lifetime is one of the most important nuclear techniques, used to study the isochronal and isothermal annealing in one of the most important engineering aluminum alloys which is 2024 alloy. Samples of 25 % deformation have been used for these studies. Two recovery stages during the isochronal annealing [1] were observed which were ascribed to the recovery of point defects and dislocations introduced by the deformation. The isothermal annealing measurements were performed at 583, 603, 623 and 643 K from which the activation energy obtained was 1.24 ± 0.08 eV.

The 3d Electrons and Microdefects in Binary Ti-Al Alloys Studied by Positron Annihilation

2011 ◽  
Vol 399-401 ◽  
pp. 99-102
Author(s):  
Wen Deng ◽  
Xiao Lei Guo ◽  
Bing Xie ◽  
Ding Kang Xiong ◽  
Yu Yang Huang
Keyword(s):  
Grain Boundary ◽  
Positron Annihilation ◽  
Free Electron ◽  
Positron Lifetime ◽  
Al Alloys ◽  
Doppler Broadening ◽  
Al Content ◽  
Open Volume ◽  
Ti Content ◽  
Coincidence Doppler Broadening

The behavior of 3d electrons and microdefects in binary Ti-Al alloys with Al contents from 47at.% to 53at.% have been studied by coincidence Doppler broadening and positron lifetime techniques. It has been found that the 3d electron signals in the spectra of binary Ti-Al alloys increase with Ti content. In Al-rich Ti-Al alloys, on increasing Al content, the open volume of defect on grain boundary increases while the density of free electron decreases. On the contrary, in Ti-rich Ti-Al alloys, on increasing Ti content, the open volume of defect on grain boundary decreases, and the electron density of the grain boundary increases.

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