Gradient Microstructure Induced by Surface Mechanical Attrition Treatment in Grade 2 Titanium Studied Using Positron Annihilation Spectroscopy and Complementary Methods

Microstructural changes in grade 2 titanium generated by surface mechanical attrition treatment (SMAT) were studied using positron annihilation lifetime spectroscopy and complementary methods. A significant increase in the mean positron lifetime indicated many lattice defects introduced by SMAT. Two positron lifetime components were resolved in the positron lifetime spectra measured. The longer lifetime revealed the presence of vacancy clusters containing about 3 or 4 vacancies, while the shorter one was attributed to the annihilation of positrons trapped at dislocations. The changes of the positron lifetime indicated a decreasing dislocation density and the presence of a deeper layer with a higher concentration of vacancy clusters at the distance from the treated surface for which the microhardness approached the value for the strain-free matrix. Electrochemical impedance spectroscopy showed the positive effect of SMAT on the corrosion resistance of the titanium studied in a saline environment also after removal of the original oxide layer that was formed during the SMAT.

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Gradient Microstructure Induced by Surface Mechanical Attrition Treatment (SMAT) in Magnesium Studied Using Positron Annihilation Spectroscopy and Complementary Methods

Materials ◽

10.3390/ma13184002 ◽

2020 ◽

Vol 13 (18) ◽

pp. 4002

Author(s):

Konrad Skowron ◽

Ewa Dryzek ◽

Mirosław Wróbel ◽

Paweł Nowak ◽

Marianna Marciszko-Wiąckowska ◽

...

Keyword(s):

Positron Annihilation ◽

Positron Lifetime ◽

Electron Backscatter Diffraction ◽

Electrochemical Corrosion ◽

Positron Beam ◽

Corrosion Current ◽

Surface Mechanical Attrition Treatment ◽

Mechanical Attrition ◽

Gradient Microstructure ◽

The Mean

Surface mechanical attrition treatment (SMAT) was used to generate a gradient microstructure in commercial grade magnesium. Positron annihilation lifetime spectroscopy and variable energy positron beam measurements, as well as microhardness tests, electron backscatter diffraction, X-ray diffraction, and electrochemical corrosion tests, were used to investigate the created subsurface microstructure and its properties. It was found that SMAT causes an increase in dislocation density and grain refinement which results in increased hardness of the subsurface zone. The mean positron lifetime values indicate trapping of positrons in vacancies associated with dislocations and dislocation jogs. The increase of the SMAT duration and the vibration amplitude influences the depth profile of the mean positron lifetime, which reflects the defect concentration profile. Electrochemical measurements revealed that the structure induced by SMAT increases the susceptibility of magnesium to anodic oxidation, leading to the enhanced formation of hydroxide coverage at the surface and, as a consequence, to the decrease in corrosion current. No significant effect of the treatment on the residual stress was found.

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Thermal kinetics of micro-defects in He-ion implanted W and W5Re alloys

Tungsten ◽

10.1007/s42864-021-00074-w ◽

2021 ◽

Author(s):

Yong-Li Liu ◽

Ya-Min Song ◽

Lei Li ◽

Ruo-Yu Bai ◽

Peng Zhang ◽

...

Keyword(s):

Positron Annihilation ◽

Annealing Temperature ◽

Thermal Evolution ◽

Ion Irradiation ◽

Positron Annihilation Spectroscopy ◽

Vacancy Cluster ◽

Dislocation Loops ◽

Positron Annihilation Lifetime ◽

Vacancy Clusters ◽

Nucleation Sites

AbstractTo investigate the thermal evolution of vacancy-type defects in He-ion irradiated W and W5Re alloy, different isochronal annealing treatments from 373 to 1273 K were conducted on the irradiated materials. Positron annihilation spectroscopy including positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy were mainly used to characterize the micro-defects evolution. The results showed that the thermal evolution characteristics of defects in both W and W5Re were similar. After He-ion irradiation, mono-vacancies with positron annihilation lifetime of ~ 190 ps were detected in W, together with a large amount of dislocation loops with positron annihilation lifetime of ~ 150 ps in W5Re alloys. The coarsening of vacancy clusters at the expense of small vacancy clusters was the main thermal evolution feature of vacancy-type defects in both W and W5Re when annealing temperature increased to 1073 K. In this progress, the positron annihilation lifetime increased to ~ 350 ps (clusters composed of 4 –8 mono-vacancies) in both W and W5Re. As the temperature increased to 1273 K, the positron annihilation lifetime decreased to ~ 240 ps, which was attributed to a significant population reduction of the dislocation loops, the dissociation of large HenVm complexes and the annealing of micro-voids in both W and W5Re. The vacancy-type defects in W5Re were more susceptible to the annealing temperature because of the formation of vacancy cluster-Re complexes. Re clusters in irradiated W5Re alloy could serve as the nucleation sites of He bubbles, which promoted the swelling and protrusion formation on the surface.

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First Stages of Nano-Crystallization of Amorphous Fe75.5Cu1Si12.5B8 Studied by the Positron Annihilation Lifetime Technique

MRS Proceedings ◽

10.1557/proc-321-245 ◽

1993 ◽

Vol 321 ◽

Author(s):

A. J. Kruk ◽

H. Schut ◽

J. Sietsma ◽

A. Van Veen

Keyword(s):

Positron Annihilation ◽

Crystallization Process ◽

Positron Lifetime ◽

Early Stage ◽

Average Density ◽

Crystalline Material ◽

Positron Annihilation Lifetime ◽

Resistivity Measurements ◽

Nano Crystalline ◽

Crystallisation Process

ABSTRACTThe first stages of the nano-crystallization process of amorphous Fe75.5Cu1Nb3Si12.5B8 into a nano-crystalline structure are investigated by the positron annihilation lifetime technique. Samples have been isothermally annealed at 643 K for times varying between 600 and 105 seconds. The positron lifetime spectra have been analyzed allowing for three lifetimes. The shortest and the longest lifetime, τ1 = 150 ± 2 ps and τ3 = 1500–2000 ps respectively, are attributed to annihilation of positrons in the amorphous phase and to the formation and annihilation of ortho-positronium at the surface of the stacked foils and did not change significantly upon the annealing. The intermediate positron lifetime τ2 increased from 324 ps to 387 ps. The intensity of this component increased from 5 to 15%. Comparison with resistivity measurements indicates that the change of this lifetime component occurs at an early stage in the crystallisation process, i.e. when the fraction of crystalline material is on the order of 10−3. The increase of τ2 is attributed to positrons annihilating in a region with lower average density surrounding the small crystallite.

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Annihilation Lifetime Spectroscopy Using Positrons from Bremsstrahlung Production

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.331.41 ◽

2012 ◽

Vol 331 ◽

pp. 41-52 ◽

Cited By ~ 3

Author(s):

Andreas Wagner ◽

Wolfgang Anwand ◽

Maik Butterling ◽

Thomas E. Cowan ◽

Fine Fiedler ◽

...

Keyword(s):

Positron Annihilation ◽

Linear Accelerator ◽

Electron Accelerator ◽

Positron Annihilation Spectroscopy ◽

Doppler Broadening ◽

Electron Linear Accelerator ◽

Positron Annihilation Lifetime ◽

Electron Bremsstrahlung ◽

New Type ◽

Set Up

A new type of a positron annihilation lifetime spectroscopy (PALS) system has been set up at the superconducting electron accelerator ELBE [ at Helmholtz-Zentrum Dresden-Rossendorf. In contrast to existing source-based PALS systems, the approach described here makes use of an intense photon beam from electron bremsstrahlung which converts through pair production into positrons inside the sample under study. The article focusses on the production of intense bremsstrahlung using a superconducting electron linear accelerator, the production of positrons inside the sample under study, the efficient detector setup which allows for annihilation lifetime and Doppler-broadening spectroscopy simultaneously. Selected examples of positron annihilation spectroscopy are presented.

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Preliminary Positron Lifetime Results on Free Volumes in Cyclodextrins

Materials Science Forum ◽

10.4028/www.scientific.net/msf.666.99 ◽

2010 ◽

Vol 666 ◽

pp. 99-102 ◽

Cited By ~ 3

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.

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Positron Annihilation Lifetime Measurements in Collagen Biopolymer

MRS Proceedings ◽

10.1557/proc-530-33 ◽

1998 ◽

Vol 530 ◽

Cited By ~ 1

Author(s):

S. Siles ◽

G. Moya ◽

X.H. Li ◽

J. Kansy ◽

P. Moser

Keyword(s):

Positron Annihilation ◽

Amorphous Region ◽

Positron Annihilation Spectroscopy ◽

Lifetime Data ◽

Spectroscopy Technique ◽

Lifetime Measurements ◽

Lifetime Distributions ◽

Positron Annihilation Lifetime ◽

Coincidence System ◽

Three Components

AbstractLifetime measurement in Positron Annihilation Spectroscopy (PAS) is applied to the study of free-volume collagen characteristics as a function of concentration. The lifetimes of positrons were obtained by a conventional fast-fast coincidence system. All lifetime data are fitted in three components by using the computer program POSITRON FIT and resolved. For each concentration, lifetime distributions were analyzed in order to obtain the different components, thus we have observed three components of which a long component τ3. This long lived component can be associated with a pick-off annihilation of ortho-positronium (o-Ps) trapped in free volumes of amorphous region. This investigation shows the potential of the positron annihilation spectroscopy technique in the study of biopolymer microstructures.

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

Materials Science Forum ◽

10.4028/www.scientific.net/msf.475-479.2123 ◽

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.

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POSITRON INTERACTION IN POLYMERS

International Journal of Modern Physics A ◽

10.1142/s0217751x04020208 ◽

2004 ◽

Vol 19 (23) ◽

pp. 3951-3959 ◽

Cited By ~ 2

Author(s):

CORINE BAS ◽

N. DOMINIQUE ALBÉROLA ◽

MARIE-FRANCE BARTHE ◽

JÉRÉMIE De BAERDEMAEKER ◽

CHARLES DAUWE

Keyword(s):

Positron Annihilation ◽

Chemical Structure ◽

Positron Beam ◽

Positron Annihilation Spectroscopy ◽

Hole Size ◽

Doppler Broadening ◽

Positron Source ◽

Positron Annihilation Lifetime ◽

Doppler Broadening Spectra ◽

Variable Energy

A series of dense copolyimide membranes was characterized using positron annihilation spectroscopy. The positron annihilation lifetime spectroscopy performed on film with a classical positron source gives informations on the positronium fraction formed and also on the hole size within the film. The Doppler broadening spectra (DBS) of the gamma annihilation rays coupled with a variable energy positron beam allow the microstructural analyses as a function of the film depth. Experimental data were also linked to the chemical structure of the polyimides. It was found that the presence of the fluorine atoms strongly affects the positron annihilitation process and especially the DBS responses.

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Micro Structural Changes in Welded AlCuLi-Alloys by Positron Annihilation Spectroscopy, SAXS and DSC

Materials Science Forum ◽

10.4028/www.scientific.net/msf.877.387 ◽

2016 ◽

Vol 877 ◽

pp. 387-392

Author(s):

Danny Petschke ◽

Torsten E.M. Staab

Keyword(s):

Positron Annihilation ◽

Structural Changes ◽

Base Material ◽

Positron Annihilation Spectroscopy ◽

Weld Nugget ◽

Scanning Calorimetry ◽

Positron Annihilation Lifetime ◽

Friction Stir ◽

X Ray Scattering ◽

Type Size

We follow changes in the micro structure at several distances from the weld nugget of friction stir welded AlCuLi-alloy (AA2198) plates occurring due to the tool movement and the created heat by employing different methods: Small Angle X-ray Scattering (SAXS), giving information on type, size and density of precipitates, Differential Scanning Calorimetry (DSC), giving information on formed precipitates by their dissolution signal, and positron annihilation lifetime spectroscopy (PALS), being sensitive to vacancies and dislocations as well as to the formation and growth of precipitates. We start by characterizing the base material as a reference and proceed via the heat-affected zone to the weld nugget. By the use of complementary methods, we obtain information on structure, kind and distribution of precipitates and correlate this with hardness measurements.

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Study of multiblock polyamide-6/Poly-(isoprene) copolymers by positron annihilation spectroscopy

Open Chemistry ◽

10.2478/s11532-008-0073-9 ◽

2008 ◽

Vol 6 (4) ◽

pp. 575-580 ◽

Cited By ~ 1

Author(s):

R. Bryaskova ◽

R. Mateva ◽

N. Djourelov ◽

M. Krasteva

Keyword(s):

Positron Annihilation ◽

Free Volume ◽

Main Chain ◽

Positron Annihilation Spectroscopy ◽

Polyamide 6 ◽

Positron Annihilation Lifetime Spectroscopy ◽

Degree Of Crystallinity ◽

Doppler Broadening ◽

Annihilation Line ◽

Positron Annihilation Lifetime

AbstractPositron annihilation lifetime spectroscopy (PALS) has been used to determine the free volume in multiblock polyamide-6/poly-(isoprene) copolymers (PA-6/PI), synthesized via activated anionic bulk copolymerization. The diisocyanate functionalized telechelic PI, blocked with caprolactam (CL) has been used as a commoner and an activator at the same time. The elastic PI block incorporated into the main chain of PA-6 affects the amorphous and crystal phase of the copolymer leading to changing in degree of crystallinity. The positron annihilation lifetime spectroscopy (PAL) and Doppler broadening of annihilation line (DBAL) technique in a set of pure PA-6 and PA-6/PI copolymers with two different compositions have been applied and evaluation of the size of free-volume holes (pores), localized mainly in the disordered regions of the PA-6/PI copolymer by measuring the o-Ps lifetime (τ3) and o-Ps intensity (I3) has been performed.

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