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Microstructure and positron lifetimes of zirconium modified aluminide coatings

Romanowska J., Dryzek E., Morgiel J., Siemek K., Kolek Ł., Zagula-Yavorska M.

Archives of Civil and Mechanical Engineering

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2018

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Vol. 18, no. 4

1150--1155

EN

The microstructure of the zirconium modified and non-modified aluminide coatings was examined by the EDS, XRD, TEM and the positron annihilation spectroscopy methods. Both coatings have a double layer structure: β-NiAl phase on the top and γ′-Ni3Al below. Small zirconium nanoparticles were found along grain boundaries in the β-NiAl phase. The positron lifetime in both coatings is the same. The formation of zirconium precipitates neither affects, the number of defects nor the volume diffusion. Zirconium nanoparticles that precipitate along grain boundaries stand against the outward diffusion of Al ions through the coating to the coating/oxygen interface. This “blocking effect” may be responsible for the reduction of the alumina scale growth rate and may delay pore formation on the coating/oxygen interface.

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Positron annihilation studies of high-manganese steel deformed by rolling

Dryzek E., Sarnek M., Wróbel M.

Nukleonika

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2015

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Vol. 60, No. 4, part 1

709--712

EN

Positron annihilation spectroscopy (PAS) has been used to study the annealing behavior of cold rolled Fe – 21 wt% Mn steel with 0.05 wt% C. After the initial annealing of defects shown by Doppler broadening of the annihilation line, a slight increase in the annihilation line shape parameter, i.e., the so-called S parameter and then its decrease in the temperature range between 225◦C and 450◦C indicates generation of new defects and their subsequent annealing. This temperature range coincides with X-ray diffraction measurements, which indicate reversion of deformation-induced ε-martensite. However, for annealing in this temperature range with slow cooling of the sample, the formation of ferrite already starts. The results are compared with our previous results for deformed austenitic stainless steel 1.4301 (EN) where only reversion of deformation-induced α'-martensite was detected.

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Positron annihilation in liquid crystals

Dryzek E., Juszyńska-Gałązka E.

Nukleonika

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2015

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Vol. 60, No. 4, part 1

703--708

EN

Positron annihilation studies of liquid crystals are reviewed with particular reference to thermotropic liquid crystals with rod-like molecules. The studies of compounds exhibiting smectic A or smectic E phases indicate that local arrangement of dipole molecules play an important role because high electron density at the end group of molecules can influence substantially formation and annihilation of positronium. The obtained ortho-positronium lifetimes in these phases can be explained by antiparallel pairing of molecules in case of the smectic A phase or a structure with a nanosegregation of alkyl chains and others parts of molecules into sublayers and liquid-like state of alkyl chains in case of the smectic E phase.

4

Annealing behaviour of plastically deformed stainless steel 1.4307 studied by positron annihilation methods

Dryzek E., Sarnek M., Siemek K.

Nukleonika

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2013

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Vol. 58, No. 1

215-219

EN

Isochronal and isothermal annealing of stainless steel 1.4307 samples deformed by compression were investigated using Doppler broadening measurements of the annihilation line. We made an attempt to describe the obtained dependencies in terms of vacancy migration and sinking to the grain boundaries. The model assumed spherical grains with a homogeneous initial distribution of vacancies. The model was capable of following the isochronal annealing data quite accurately. However, the obtained activation energy of vacancy migration equal to 0.44 plus or minus 0.05 eV seemed too low. The isothermal annealing dependency was reproduced less precisely. The reason for this may be the presence of the alfa'-martensite particles in the samples, which can introduce additional defects seen by positrons in the temperature range in which the martensite reversion takes place.

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Positron annihilation in bioactive glass/poly(glycolide-co-L-lactide) composites

Dryzek E., Cholewa-Kowalska K., Pamuła E.

Nukleonika

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2010

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Vol. 55, No. 1

79-83

EN

Composites made of bioactive glasses and resorbable polymers are promising biomaterials for bone tissue regeneration. In this study several types of composites produced from bioactive glasses, differing in chemical composition (A2 and S2) and poly(glycolide-co-lactide) (PGLA) were obtained. The resulting composite materials were investigated with positron lifetime spectroscopy and Doppler broadening of annihilation line. It was found that for the composites made of S2 bioglass the intensity of the third positron lifetime component coming from the positronium (Ps) annihilation decreased with increasing in volume fraction of bioglass particles exhibiting behaviour characteristic of microcomposites. For the composites produced from A2 bioglass, such a dependence was not found. The differences obtained may be connected with chemical composition of the bioglass and/or its crystallinity.

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The implantation profile of positrons emitted in beta plus decay of 48V in water

Dryzek J., Horodek P., Dryzek E.

Nukleonika

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2009

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Vol. 54, No. 4

223-226

EN

The experimental technique based on scanning of positron implantation profile, hereafter referred to as the DSIP is used for the determination of linear absorption coefficient for positrons emitted from a 48V source into water. This coefficient is equal to 1/(299š62) mi m–1. The determined value is in agreement with the one obtained from the computer simulations using the well known EGS nrc 4.0 and GEANT4 codes. The experimental technique was used for the determination of linear absorption coefficients for 48V positrons in materials of biological origin. The presented data can be useful for PET studies because of similarities of the 18F and 48V positron implantation profiles.

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Próby zastosowania metod anihilacji pozytonów do badań strukturalnych metalowych materiałów kompozytowych

Dryzek J., Dryzek E., Sobczak J., Darłak P.

Kompozyty

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2005

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R. 5, nr 2

74-80

PL

Praca stanowi próbę zastosowania techniki anihilacji pozytonów do badań struktury kompozytów metalowych na przykładzie aluminiowej osnowy metalowej zbrojonej włóknem krótkim na bazie tlenku glinu. Ze względu na duży ładunek nowości w pracy szczegółowo przedstawiono metodologiczne aspekty zastosowanej techniki eksperymentalnej, wykorzystującej stosunkowo proste i poznane sposoby detekcji promieniowania gamma. W zakresie badawczym omówiono dotychczasowe wyniki zmian przebiegu anihilacji pozytonów w przypadku monolitycznej miedzi i stopów aluminium. Badania własne przeprowadzono na próbkach pobranych z tłoka kompozytowego z siluminu okołoeutektycznego zbrojonego lokalnie preformą ceramiczną typu MORGAN, wytworzonego infiltracją ciśnieniową (squeeze infiltration) preform na bazie 22 š2% obj. tlenku glinu (96% Al2O3, 4% SiO2) stopem AlSi12CuNiMg z krzepnięciem całego odlewu pod docelowym ciśnieniem 230 MPa. Przeprowadzono dwie serie pomiarów czasów życia pozytonów, jedną związaną z obszarem monolitycznym, drugą obejmującą strefę kompozytu. W widmie pomiaru obszaru monolitycznego uzyskano jedną wartość średniego czasu życia pozytonów. W widmie otrzymanym dla kompozytu AlSi12CuNiMg/22% Al2O3 wyodrębniono trzy składowe czasów życia pozytonów. Badania prowadzono na próbkach w stanie lanym i po obróbce cieplnej typu utwardzania dyspersyjnego. Rozważania dotyczące powiązania niektórych składowych czasu życia pozytonów z defektami strukturalnymi zilustrowano obrazami defektów typu nieciągłości strukturalnych (SEM). Proponowana metoda może znaleźć zastosowanie w indykacji defektów strukturalnych trudnych do wychwycenia innymi tradycyjnymi metodami pomiarowymi. Dwoje współautorów (J.D. i E.D.) korzystało w trakcie wykonywania pracy ze wsparcia finansowego otrzymanego dzięki grantowi KBN Nr 2 P03B 008 24.

EN

The work presents the preliminary results of application of the positron annihilation method for characterization of MMCs microstructure using as an example the aluminum matrix composites reinforced with short alumina-based fibers. The detailed analysis of methodological aspects of applied innovative experimental method has been done taking into account the known and relatively simple techniques used for the detection of gamma radiation (Figs 1, 2). The obtained results of the process of positron annihilation have been discusscd on an example of monolithic pure copper and aluminum alloys (Tab. 1, Fig. 3). The investigation has been done on the samples taken from the composite piston, produced from near eutectic alloy AlSi12CuNiMg and locally reinforced with a MORGAN porous ceramic preform by squeeze infiltration and further solidification under a pressure of 230 MPa (Fig. 4). The as-received preform had 22 š2 vol.% short alumina-based fibers (96% Al2O3, 4% SiO2). The comparison measurements of the positron life time have been done in both monolithic part of the piston as well as in its reinforced par (Fig. 5, Tab. 2 and 3). The spectrum corresponding to the monolithic part shows one value for the positron life time while the spectrum taken from the reinforced part and presenting the composite AlSi12CuNiMg/22% Al2O3 indicates the well distinguished fraction of the three positron lifetime components. These measurements have been done on the samples in as-cast condition and after heat treatment (precipitate hardening). The results obtained have been analyzed from viewpoint of the effects of such structural defects as discontinuities noted by SEM characterization (Fig. 6). The proposed method can be recommended for the characterization of structural defects, particularly those, which are difficult to be identified by other methods. The authors express their gratitude to the Committee of Scientifics Research (Poland) which has supported this work within grant.