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1

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

100%

Melichova O., Vostrý P., Procházka I., Cieslar M., Stulíková I., Faltus J.

Acta Physica Polonica A

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1999

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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.

2

Microstructure, Thermal and Mechanical Properties of Non-Isothermally Annealed Al-Sc-Zr and Al-Mn-Sc-Zr Alloys Prepared by Powder Metallurgy

84%

Vlach M., Stulíková I., Smola B., Císařová H., Piešová J., Daniš S., Gemma R., Tanprayoon D., Neubert V.

Acta Physica Polonica A

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2012

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vol. 122

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issue 3

439-443

EN

This paper reports results of a study aimed at understanding the precipitation processes occurring during the annealing of two Al-Sc-Zr-based alloys with and without Mn prepared by powder metallurgy with subsequent hot extrusion at 350°C. Samples were isochronally annealed up to ≈ 570°C. Precipitation behaviour was studied by electrical resistometry and differential scanning calorimetry. Mechanical properties were monitored by microhardness HV1 measurements. Transmission electron microscopy examinations and X-ray diffraction of specimens quenched from temperatures of significant resistivity changes helped to identify the microstructural processes responsible for these changes. Fine (sub)grain structure develops and fine coherent Al_3Sc and/or Al_3(Sc,Zr) particles precipitate during extrusion in both alloys. The distinct changes in resistivity (at temperatures above ≈ 330°C) of the Al-Mn-Sc-Zr alloy are mainly caused by precipitation of Mn-containing particles. The easier diffusion of Mn atoms along the (sub)grain boundaries is responsible for the precipitation of the Al_6Mn and/or Al_6(Mn,Fe) particles at relatively lower temperatures compared to the temperature range of precipitation of these particles in the classical mould-cast Al-Mn-Sc-Zr alloys The apparent activation energy for precipitation of the Al_3Sc and Al_6Mn particles in the Al-Mn-Sc-Zr alloy was determined as (106 ± 10) kJ mol^{-1} and (152 ± 33) kJ mol^{-1}, respectively.

3

Defects in Ultra-Fine Grained Mg and Mg-Based Alloys Prepared by High Pressure Torsion Studied by Positron Annihilation

84%

Čížek J., Procházka I., Smola B., Stulíková I., Kužel R., Matěj Z., Cherkaska V., 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

738-744

EN

Despite the favourable strength and thermal stability, a disadvantage of the Mg-based alloys consists in a low ductility. Recently it has been demonstrated that ultra fine grained metals with grain size around 100 nm can be produced by high pressure torsion. A number of ultra fine grained metals exhibit favourable mechanical properties consisting in a combination of a very high strength and a significant ductility. For this reason, it is highly interesting to examine microstructure and physical properties of ultra fine grained Mg-based light alloys. Following this purpose, microstructure investigations and defect studies of ultra fine grained pure Mg and ultra fine grained Mg-10%Gd alloy prepared by high pressure torsion were performed in the present work using positron annihilation spectroscopy combined with X-ray diffraction, TEM observations, and microhardness measurements. Positrons are trapped at dislocations in Mg and Mg-10%Gd alloy deformed by high pressure torsion. A number of dislocations increases with the radial distance r from the centre to the margin of the sample. No microvoids (small vacancy clusters) were detected. Mg-10%Gd alloy deformed by high pressure torsion exhibits a homogeneous ultra fine grained structure with a grain size around 100 nm and high dislocations density. On the other hand, pure Mg deformed by high pressure torsion exhibits a binomial type of structure which consists of "deformed regions" with ultra fine grained structure and a high dislocation density and dislocation-free "recovered regions" with large grains. It indicates a dynamic recovery of microstructure during high pressure torsion processing.

4

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

68%

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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4 Acta Physica Polonica A

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2 Cieslar M.

2 Islamgaliev R.

2 Kulyasova O.

2 Kužel R.

2 Čížek J.

1 Anwand W.

1 Brauer G.

1 Císařová H.

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1 Faltus J.

1 Gemma R.

1 Matĕj Z.

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1 Melichova O.

1 Neubert V.

1 Piešová J.

1 Tanprayoon D.

1 Vlach M.

1 Vostrý P.

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

Microstructure, Thermal and Mechanical Properties of Non-Isothermally Annealed Al-Sc-Zr and Al-Mn-Sc-Zr Alloys Prepared by Powder Metallurgy

Defects in Ultra-Fine Grained Mg and Mg-Based Alloys Prepared by High Pressure Torsion Studied by Positron Annihilation

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