Positron Lifetime Calculation for Plastic Deformed Nanocrystalline Copper

2017 ◽  
Vol 373 ◽  
pp. 31-34
Author(s):  
Kai Zhou ◽  
Ting Zhang
Keyword(s):  
Positron Annihilation ◽  
Deformation Mechanism ◽  
Positron Lifetime ◽  
Experimental Information ◽  
Point Of View ◽  
Nanocrystalline Copper ◽  
Mean Grain Size ◽  
Positron Lifetimes ◽  
Boundary Deformation

Positron lifetime calculation has been performed on a computer-generated nanocrystalline copper with a mean grain size of 9.1 nm during its deformation. For the undeformed and deformed nanocrystalline copper, calculated positron lifetimes are around 157 ps which come from the positron annihilation in the free volume in grain boundaries. Due to the grain-boundary deformation mechanism, no vacancies or vacancy clusters will be induced in grains during the plastic deformation of the nanocrystalline copper, which is different to the deformation of the conventional polycrystal. From this point of view, in-situ positron annihilation measurements can provide important experimental information on the deformation mechanism of nanocrystalline metals.

scholarly journals Positron Annihilation Study of Deformation in a Two-phase (α+β) Cu - Zn Alloy

1996 ◽  
Vol 49 (6) ◽  
pp. 1181
Author(s):  
CQ Tang ◽  
LH Yu
Keyword(s):  
Positron Annihilation ◽  
Deformation Mechanism ◽  
Positron Lifetime ◽  
Special Structure ◽  
Two Phase ◽  
Degree Of Deformation ◽  
The Mean ◽  
Positron Lifetimes ◽  
Positron Annihilation Study ◽  
Zn Alloy

Positron lifetimes have been measured as a function of the degree of deformation ε in a two-phase (α+τ) Cu–Zn alloy. In this alloy the increase of the mean positron lifetime τm with ε is slower and the saturation effect occurs at a larger deformation than that in most simple metals and alloys. With increasing ε the positron lifetime parameters τ1 Ι1 and Ι2 exhibit a rise or fall near ε ≈ 4% and 35%, and they change slowly for 4% < ε < 35%. These results are explained by the special structure of the α and β phases and the particular deformation mechanism in this alloy.

Preliminary Positron Lifetime Results on Free Volumes in Cyclodextrins

2010 ◽  
Vol 666 ◽  
pp. 99-102 ◽  
Author(s):  
Maria Fatima Ferreira Marques ◽  
A.M.G. Moreira Da Silva ◽  
P.M. Gordo ◽  
Z. Kajcsos
Keyword(s):  
Positron Annihilation ◽  
Free Volume ◽  
Positron Lifetime ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Source ◽  
Lifetime Component ◽  
Positron Annihilation Lifetime ◽  
Long Lifetime

Positron annihilation lifetime spectroscopy was used to study the free-volume parameters in various pure -, - and -cyclodextrins samples and, in the case of β-cyclodextrin, with inclusion of S-carvone and thymoquinone. The results clearly indicate the presence of long lifetime components related to Ps-formation. The data show that the addition of S-carvone to β-cyclodextrin results in a decrease of o-Ps lifetime that we ascribe to a reduction of free volume holes from 81.8 to 63.7 Å3. The long lifetime component disappears when thymoquinone is added to -cyclodextrin, indicating this substance acts as an o-Ps quencher. For all samples studied, a decrease in the long lifetime component values was observed with increasing source in situ time, a result that might be attributed to the irradiation of the sample by the 22Na positron source.

Ni-Substitution Induced Inversion in ZnFe2O4 Seen by Positron Annihilation

2012 ◽  
Vol 733 ◽  
pp. 219-223 ◽  
Author(s):  
P.M.G. Nambissan ◽  
O. Mondal ◽  
C. Chakrabarty ◽  
M. Pal
Keyword(s):  
Positron Annihilation ◽  
Spinel Structure ◽  
Positron Lifetime ◽  
Drastic Change ◽  
Doppler Broadening ◽  
Positron Trapping ◽  
Normal Spinel ◽  
Ni Substitution ◽  
Positron Lifetimes ◽  
Coincidence Doppler Broadening

We report in this work about the inversion of the spinel structure of ZnFe2O4induced by the substitution of Zn2+by Ni2+ions. Positron lifetimes were measured in Zn1-xNixFe2O4with different concentrations (x) of doped Ni2+ions and a drastic change across x = 0.4 – 0.6 was observed, which is attributed to this transformation. The interchange of positions of the cations on doping leaves a fraction of them unoccupied and these vacancies act as positron trapping centres. Since Ni2+is smaller in size than Zn2+, defects due to non-stoichiometry are less in NiFe2O4than in ZnFe2O4. The increase in positron lifetime implies the trapping of positrons being shifted from A- to B-sites and is an indication of the transformation from inverse to normal spinel configuration. Coincidence Doppler broadening measurements supported these findings.

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.

Positron Lifetime Studies of Polyaniline Conducting Polymers

1995 ◽  
Vol 413 ◽  
Author(s):  
C. M. Huang ◽  
J. Liu ◽  
T. C. Sandreczki ◽  
Y. C. Jean
Keyword(s):  
Positron Annihilation ◽  
Room Temperature ◽  
Positron Lifetime ◽  
The Other ◽  
Chemical Compositions ◽  
Lifetime Measurements ◽  
Positron Annihilation Lifetime ◽  
Positron Lifetimes ◽  
Lifetime Studies ◽  
Made In

ABSTRACTPositron annihilation lifetime measurements are made in a series of polyaniline polymers with different chemical compositions and protonation ratios at room temperature. Two positron lifetimes are observed in these materials: one is assigned to annihilation in the bulk and the other to voids created due to protonation. A relationship between conductivities and positron annihilation probabilities is found.

Examination of Neutron-Irradiated Pressure-Vessel Steel Using Positron Annihilation Lifetime Spectrosopy

1998 ◽  
Vol 540 ◽  
Author(s):  
Stephen E. Cumblidge ◽  
Arthur T. Motta ◽  
Gary L. Catchen
Keyword(s):  
Positron Annihilation ◽  
Pressure Vessel ◽  
Positron Lifetime ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Positron Annihilation Lifetime ◽  
Annealing Temperatures ◽  
Neutron Damage ◽  
Reactor Temperature ◽  
Positron Lifetimes

AbstractOn a variety of pressure-vessel (PV) steels, we have observed changes in the average positron lifetime with increasing (near end-of-life) neutron fluences. Samples were irradiated at reactor-temperature and subjected to post-irradiation annealing, and they were examined using positron annihilation lifetime spectroscopy (PALS). The measured average positron lifetimes in high-temperature (2900 C-300° C) irradiated PV steels decrease with increasing neutron damage up to fluences of 8.5×1018 cm−2 and increase again at higher fluences. Annealing of high-fluence, 300° C irradiated ASTM A508 PV steel samples produces an initial decrease in average positron lifetimes with increasing annealing temperatures of up to 400° C, followed by an increase in average positron lifetime with higher annealing temperatures, when samples were annealed in successive 24-hour steps. A sample of weld steel, irradiated to 2.2×1019 cm−2 at 290° C, shows similar behavior in which the minimum lifetime occurs at ≈ 450° C. These trends are similar to those seen in previous studies performed on VVER and other ferritic steels.

Microstructure and Positron Lifetimes of Aluminide Coatings on Inconel 713

2019 ◽  
Vol 803 ◽  
pp. 65-68
Author(s):  
Jolanta Romanowska ◽  
Ewa Dryzek ◽  
Maryana Zagula-Yavorska
Keyword(s):  
Positron Annihilation ◽  
Double Layer ◽  
Positron Lifetime ◽  
Layer Structure ◽  
Positron Annihilation Spectroscopy ◽  
Aluminide Coatings ◽  
Double Layer Structure ◽  
Nial Phase ◽  
Lifetime Value ◽  
Positron Lifetimes

The microstructure of the palladium modified and non-modified aluminide coatings was examined by the EDS and the positron annihilation spectroscopy methods. Both coatings have a double layer structure: β-NiAl phase or β-(Ni,Pd)Al phase on the top and the interdiffusion zones with the chromium and molybdenum rich phases in the β-NiAl or or β-(Ni,Pd)Al phase below. Palladium, that forms the β-(Ni,Pd)Al phase and substitutes for nickel atoms causes the increase of the positron lifetime value due to the increase in the number of open volume defects in the lattice which are jogs or vacancies on dislocation lines.

scholarly journals In situ TEM study of a new grain boundary deformation mechanism in olivine

2021 ◽  
Author(s):  
Patrick Cordier ◽  
Ihtasham Ul Haq ◽  
Vahid Samae ◽  
Hosni Idrissi ◽  
Dominique Schryvers
Keyword(s):  
Grain Boundary ◽  
Deformation Mechanism ◽  
In Situ Tem ◽  
Boundary Deformation

scholarly journals Positron Annihilation Lifetime Spectroscopy in the study of defects in materials

2019 ◽  
Vol 24 ◽  
pp. 235
Author(s):  
K. Triantou ◽  
K. Mergia ◽  
I. E. Stamatelatos
Keyword(s):  
Positron Annihilation ◽  
Electron Density ◽  
Positron Lifetime ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Vacancy Defects ◽  
Positron Annihilation Lifetime ◽  
Defect Site ◽  
Experimental Apparatus ◽  
Valuable Method ◽  
Positron Lifetimes

The Positron Annihilation Lifetime Spectroscopy (PALS) is a valuable method for the study of the open volume defects in materials. The reduced electron density at the vacant/defect site increases the positron lifetime, and positron lifetime increases as the size of defect increases. In the current paper the experimental apparatus for the measurement of the positron lifetime in materials is described and the spectra from W and Cd specimens are analyzed. The presence of dislocations and vacancy defects is found, since the positron lifetimes of specimens are higher than the defect-free (bulk) values.

In situ TEM studies of irradiation effects for materials improvement

1991 ◽  
Vol 49 ◽  
pp. 452-453
Author(s):  
Charles W. Allen
Keyword(s):  
Nuclear Reactor ◽  
Austenitic Stainless Steels ◽  
High Energy ◽  
Point Of View ◽  
In Situ Tem ◽  
Irradiation Effects ◽  
Tem Analysis ◽  
Radiation Induced ◽  
Analytical Tools

Irradiation effects studies employing TEMs as analytical tools have been conducted for almost as many years as materials people have done TEM, motivated largely by materials needs for nuclear reactor development. Such studies have focussed on the behavior both of nuclear fuels and of materials for other reactor components which are subjected to radiation-induced degradation. Especially in the 1950s and 60s, post-irradiation TEM analysis may have been coupled to in situ (in reactor or in pile) experiments (e.g., irradiation-induced creep experiments of austenitic stainless steels). Although necessary from a technological point of view, such experiments are difficult to instrument (measure strain dynamically, e.g.) and control (temperature, e.g.) and require months or even years to perform in a nuclear reactor or in a spallation neutron source. Consequently, methods were sought for simulation of neutroninduced radiation damage of materials, the simulations employing other forms of radiation; in the case of metals and alloys, high energy electrons and high energy ions.

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