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1
Content available remote

The Influence of Silicon Content on Recrystallization of Twin-Roll Cast Aluminum Alloys for Heat Exchangers

100%
Poková M., Cieslar M., Lacaze J.
Acta Physica Polonica A
|
2012
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vol. 122
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issue 3
625-629
EN
Thin foils of aluminum alloys are commonly used in automotive industry for manufacturing heat exchangers. Use of twin-roll casting instead of direct-chill casting requires modifications in the manufacturing process and use of improved materials. In the present study, the evolution in microstructure and mechanical properties during isochronal annealing of two AW3003-based alloys differing in silicon content was monitored. The silicon influenced both the microhardness and precipitation kinetics during annealing, but not the recrystallization temperature. Precipitation of cubic α-Al_{15}(Mn,Fe)_3Si_2 phase occurred in two steps in the material with higher Si content, while mainly precipitates of Al_6(Mn,Fe) phase formed in the second material in a broad temperature interval, preferentially at grain boundaries.
2
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AFM Observation of Fe-Al Single Crystals under in situ Deformation

100%
Veselý J., Cieslar M., Kopeček J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 3
618-621
EN
Fe-Al single crystals of three different compositions (20, 28 and 40 at.% Al) in single slip orientation were studied. Evolution of their surfaces during deformation at room temperature was observed in situ in atomic force microscope. Atomic force microscopy allows us to investigate slip lines on much finer scale than traditional optical observations. Wavy slip bands in Fe-Al_{20}, cross-slip in Fe-Al_{28} and weak slip line texture in Fe-Al_{40} are described. Post mortem observations of surfaces of Fe-Al_{28} deformed at elevated temperatures (in the range of yield stress anomaly) are presented as well.
3
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The Evolution of Microstructure and Mechanical Properties of Al-Mn-Fe-Si Alloys During Isothermal Annealing

100%
Poková M., Zimina M., Cieslar M.
|
EN
Recrystallization during isothermal annealing is studied in a twin-roll cast Al-Mn-Fe-Si alloy with Zr addition. Al₃Zr precipitates, which are known to improve the recrystallization resistance by exerting the Zener drag on migrating grain boundaries, form during heat treatment at 450°C. Materials with and without Al₃Zr precipitates are subjected to 4 passes of equal channel angular pressing at room temperature and a submicrometric grain size is achieved. In the course of isothermal annealing materials recrystallize at 400°C, 425°C and 450°C. The time required for recrystallization follows an Arrhenius equation. Recrystallization kinetics is similar independently of the presence of Al₃Zr precipitates. Precipitation of α-Al(Mn,Fe)Si particles is thought to increase the recrystallization resistance in the material without Al₃Zr.
4
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Influence of Ceramic Nanoparticles on Thermal Stability of Ultra Fine Grained Copper

88%
Čížek J., Procházka I., Cieslar M., Islamgaliev R., Kulyasova O.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1285-1292
EN
A detailed study of the bulk ultra fine grained pure copper and copper with Al_2O_3 particles was carried out in the present work. The specimens were prepared by the high-pressure torsion and their microstructure was investigated by positron lifetime spectroscopy combined with transmission electron microscopy and microhardness tests. Defects in the as-deformed materials were characterized and the thermal stability of the ultra fine grained microstructure was subsequently examined in annealing experiments. An addition of Al_2O_3 nanoparticles was found to improve significantly the thermal stability of the ultra fine grained structure, the optimum content of Al_2O_3 being ≈0.5 wt.%.
5
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Recrystallization in Multilayer Al99.99/AlMg3 Laminates Prepared by Accumulative Roll-Bonding

88%
Cieslar M., Poková M., Zimina M., Veselý J., Bajer J.
Acta Physica Polonica A
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2015
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vol. 128
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issue 4
487-490
EN
Composite multilayer sheets from Al/AlMg3 with 32 alternating layers of Al and AlMg3 were prepared by accumulative roll-bonding and their thermal stability was studied. Recrystallized 2 mm thick sheets of a commercial twin-roll cast AlMg3 alloy and high purity Al99.99 served as input materials. Electrical resistivity measurements were used for the integral monitoring of solute atoms distribution during annealing. Light optical microscopy was employed for the direct grain-size determination and recrystallization description. Post-mortem electron microscopy observations were performed on as-prepared and annealed specimens and they were combined with in situ heating electron microscopy in order to explain the observed annealing effects. A broadening of Al layers during annealing was observed and related to diffusion of magnesium.
6
Content available remote

Electrical Resistivity and Positron Lifetime Studies of Precipitation Effects in Al-Cu Alloy

76%
Αda P., Cieslar M., Vostrý P., Bečvář F., Νovotný I., Procházka I.
Acta Physica Polonica A
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1995
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vol. 88
|
issue 1
111-117
EN
Decomposition of the supersaturated solid solution of 2 at.% Cu in Al was investigated by means of electrical resistivity and high-resolution positron lifetime measurements. The phase composition of this alloy was determined by transmission electron microscopy. Electrical resistivity measurements were performed by a classical four-point method. Positron lifetime spectra were measured by means of a spectrometer consisting of two BaF_{2} detectors and a standard fast-slow coincidence system. The specimens were first exposed to the solution heat treatment at 783 K for 19 hours with a subsequent quenching. Then the specimens were isochronally annealed in the temperature range 293 ÷ 573 K. Annealing responses of electrical resistivity and positron annihilation were studied. Resistivity measurements as well as transmission electron microscopy observations confirmed the well-known decomposition sequence of the Al-Cu alloy. The decomposition of the alloy was manifested by the decrease in the intensity of positron lifetime component τ_{2} = (207 ±2 ) ps correlated with simultaneous appearance and increase in the intensity of τ_{3} = (180 ± 5) ps component. Component τ_{2} originates from positron annihilation in vacancies trapped at the Guinier-Preston zones while τ_{3} comes from annihilation of the positrons localized in the misfit dislocations at coherent precipitates of the Al_{2}Cu phase. The shortest observed component τ_{1} apparently belongs to annihilation of untrapped positrons.
7
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Electrical Resistivity and Positron Lifetime Studies of Precipitation Effects in Al-Cu-Based Alloys

76%
Melichova O., Vostrý P., Procházka I., Cieslar M., Stulíková I., Faltus J.
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vol. 95
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issue 4
627-631
EN
The improved workability of the commercial automatic machine designed alloy Al-Cu-Bi-Pb is guaranteed by the presence of Pb. Nevertheless, the toxic element Pb reduces some of the alloy properties. Therefore new Pb-free machinable Al-based alloys are developed. The Al-Cu-Bi-Sn alloy belongs to these non-traditional materials. The contribution deals with the investigation of precipitation effects in Al-Cu-Bi-Sn alloy during step-by-step isochronal annealing up to 500°C after previous solution heat treatment by means of positron annihilation spectroscopy completed with electrical resistivity measurements and results of independent transmission electron microscopy studies. The used combination of experimental methods gives the possibility to detect separately the redistribution of Sn and Cu atoms in the matrix and to study the influence of vacancies on this process.
8
Content available remote

Effect of Pressure on Magnetic Properties of TM_3[Cr(CN)_6]_2 · nH_2O Nanoparticles

64%
Zentko A., Zentková M., Kavečanský V., Mihalik M., Mitróová Z., Arnold Z., Kamarád J., Cieslar M., Zeleňák V.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
489-493
EN
Effect of pressure on magnetic properties of magnetic nanoparticles, based on Prussian blue analogues, were studied in pressures up to 1.2 GPa. The Mn_3[Cr(CN)_6]_2·nH_2O and Ni_3[Cr(CN)_6]_2·nH_2O nanoparticles were prepared by reverse micelle technique. Transmission electron microscopy images show nanoparticles with average diameter of about 3.5 nm embedded in an organic matrix. The characteristic X-ray peaks of nanoparticles are more diffused and broader. Systems of nanoparticles behave as systems of interacting magnetic particles. The Curie temperature T_C is reduced from T_C = 56 K for Ni-Prussian blue analogues to T_C = 21 K for Ni-nanoparticles system and from T_C = 65 K for Mn-Prussian blue analogues to T_C = 38 K for Mn-nanoparticles system. One can explain this reduction of the Curie temperature and of the saturated magnetizationμ_s by dispersion of nanoparticles in an organic matrix i.e. by a dilution effect. Applied pressure leads to a remarkable increase in T_C for system of Mn-nanoparticles (ΔT_C/Δp = +13 K/GPa) and to only slight decrease in T_C for system of Ni-nanoparticles (ΔT_C/Δp = -3 K/GPa). The pressure effect follows behavior of the mother Prussian blue analogues under pressure. The increase in saturated magnetization, attributed to compression of the organic matrix, is very small.
9
Content available remote

The Study of the Behavior of Constrained Groove Pressed Magnesium Alloy after Heat Treatment

64%
Zimina M., Bohlen J., Letzig D., Kurz G., Poková M., Knapek M., Zrník J., Cieslar M.
Acta Physica Polonica A
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2015
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vol. 128
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issue 4
775-778
EN
In this work twin-roll cast AZ31 magnesium strip of thickness 5.6 mm was subjected to the heat treatment and further constrained groove pressing. A comparison of the microstructure and microhardness of as-cast, constrained groove pressed and annealed material was carried out. The twin-roll cast strip exhibits an inhomogeneous structure which is replaced by a finer and uniform recrystallized one after aging at 450°C for 10 h. A significant increase of the microhardness was observed accompanied by a pronounce grain refinement. Nevertheless, the distribution of the grain size is unequal along the specimen width. Thermal stability of the deformed structure during subsequent annealing was investigated. It was shown that higher annealing temperatures result in a formation of a more uniform recrystallized structure and in a significant drop of microhardness down to the values obtained for as-cast alloy.
10
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Content available

Ultra Fine-Grained Metals Prepared by Severe Plastic Deformation: A Positron Annihilation Study

52%
Čížek J., Procházka I., Kužel R., Matĕj Z., Cherkaska V., Cieslar M., Smola B., Stulíková I., Brauer G., Anwand W., Islamgaliev R., Kulyasova O.
Acta Physica Polonica A
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2005
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vol. 107
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issue 5
745-752
EN
Recent investigations of ultra fine-grained metals (Cu, Fe, Ni) performed within a Prague-Rossendorf-Ufa collaboration will be reviewed. The specimens were prepared by severe plastic deformation: the high-pressure torsion and equal channel angular pressing. Positron annihilation spectroscopy was used as the main method including (i) the conventional lifetime and the Doppler broadening measurements with ^{22}Na and (ii) the slow-positron implantation spectroscopy with the Doppler broadening measurement. Other methods were also involved: transmission electron microscopy, X-ray diffraction, and microhardness. First, the mean grain size was determined and defects were identified in the as-deformed materials. Defects concentration and spatial distribution were studied in detail. Dislocations situated in distorted regions along grain boundaries, and a few-vacancy clusters distributed homogeneously inside dislocations-free grains, were observed in the ultra fine-grained Cu, Fe, and Ni. Subsequently, the thermal evolution of the ultra fine-grained structures during isochronal annealing was studied.
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