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Acoustic Emission Study of Plastic Instabilities in AlSi1MgMn

100%
Molnárová O., Dobroň P., Chmelík F.
Acta Physica Polonica A
|
2015
|
vol. 128
|
issue 4
801-804
EN
The influence of the strain rate and heat treatment on the occurrence of plastic instabilities in a cast AlSi1MgMn alloy was studied. The samples were uniaxially loaded in compression at various strain rates and at room temperature. The tests were done with concurrent acoustic emission monitoring and the acoustic emission parameters are correlated to the microstructure and to the stress-strain curves in order to better understand the patterns of plastic deformation. All samples exhibited the Portevin-Le Chatelier effect of different types, dependently on the heat treatment and the applied strain rate. The occurrence of the Portevin-Le Chatelier effect is manifested by acoustic emission signals with high amplitudes. Statistical analysis of the acoustic emission signals shows the power-law probability distribution.
2
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The Influence of Rolling Conditions on Deformation Behavior of Magnesium Alloy Sheets

88%
Drozdenko D., Bohlen J., Chmelík F., Letzig D., Dobroň P.
Acta Physica Polonica A
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2015
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vol. 128
|
issue 4
795-800
EN
The influence of texture on deformation behavior was investigated for conventionally rolled magnesium alloy slabs and rolled twin roll cast magnesium alloy strips in the form of sheets. The Mg-Zn based sheets were deformed at room temperature with the tensile axis oriented in the rolling and transversal directions. The texture with respect to different rolling conditions was characterized by X-ray diffraction. In the case of Mg-Zn-rare earth alloy sheets, the basal pole intensity, aligned with the sheet normal direction, is lower for conventionally rolled sheet in comparison to the rolled twin roll cast strip. Difference in angular distribution of basal planes influences on the mechanical behavior of the sheets. The yield strength is higher for the tension along rolling direction than along transversal direction for the conventionally rolled sheets, whereas the opposite deformation behavior is observed for the rolled twin roll cast strips. Furthermore, the planar anisotropy of the yield strength is less pronounced for the rolled twin roll cast strips. The deformation behavior of the sheets was also investigated by the acoustic emission technique. The acoustic emission signal analysis correlates the microstructure and the stress-time curves with active deformation mechanisms. It highlights the activity of a basal slip and tensile twinning, particularly during the transverse direction tension.
3
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Acoustic Emission Study of the Deformation Behavior of Mg-Mn Alloys Containing Rare Earth Elements

88%
Illkova K., Dobroň P., Chmelík F., Letzig D., Bohlen J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 3
634-638
EN
Magnesium-manganese (Mg-Mn) based alloys with various chemical composition were processed by indirect extrusion at two different speeds. Alloying with Mn and rare earth elements has significant influence on the microstructure and on the texture of the alloys under investigation. This paper deals with the acoustic emission analysis of the deformation behavior of the extruded Mg-Mn alloys. The acoustic emission measurements were performed during the uniaxial tension and compression tests, and the obtained results are discussed with respect to the influence of rare-earth elements on the deformation behavior, particularly in terms of the activation of dislocation glide and twinning.
4
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On the Effect of the Extrusion Speed on Microstructure and Plastic Deformation of ZE10 and ZEK100 Magnesium Alloys - an Acoustic Emission Study

88%
Dobroň P., Chmelík F., Parfenenko K., Letzig D., Bohlen J.
Acta Physica Polonica A
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2012
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vol. 122
|
issue 3
593-596
EN
Mg-Zn-based alloys ZE10 and ZEK100 have been extruded at different speeds varying from 1 m/min to 20 m/min. Specimens taken in the extrusion direction were uniaxially loaded in tension and compression at room temperature. The results are discussed using concurrent acoustic emission monitoring during mechanical testing and the acoustic emission signal analysis that correlates the microstructure and the stress-strain curves to the possible deformation mechanisms. In all tests, the acoustic emission response exhibited a large acoustic emission peak at the beginning of plastic deformation. A small local maximum on the onset of the acoustic emission activity was frequently observed, i.e. at very low stresses. For the alloys with bimodal grain structure tested in compression, an additional acoustic emission peak appeared at larger strains. This peculiar behavior can be explained by interplay of (10-12)-twinning and dislocation slip in samples with various grain size distributions.
5
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Influence of Pre-Compression on Tensile Behaviour in Wrought Mg-Zn-Ce Alloy Studied by the Acoustic Emission Technique

76%
Dobroň P., Drozdenko D., Bohlen J., Yi S., Letzig D., Chmelík F.
Acta Physica Polonica A
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2015
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vol. 128
|
issue 4
790-794
EN
Wrought Mg-Zn-Ce alloy (ZE10) has been pre-compressed and subsequently subjected to tensile loading. Due to a fibre texture of the samples, the level of pre-compression stress significantly influences the subsequent tensile behaviour. The acoustic emission technique was used for monitoring active deformation mechanisms during mechanical testing. The obtained acoustic emission results are correlated to the stress-time curves and the differences in the acoustic emission count rate were used to reveal changes in underlying deformation mechanisms. Firstly, a compression-tension cycle was monitored by the acoustic emission technique. Then, the samples were deformed to specific points on the stress-time curve, where acoustic emission exhibits strong changes in the activity. The following microstructure analysis of the samples, deformed to different strain-levels, by using electron back scattered diffraction method brought a detailed insight into active deformation mechanisms. Twinning during the pre-compression was followed by detwinning during the tensile loading. Two consecutive acoustic emission peaks, which appeared at larger strains, are explained by interplay of detwinning and dislocation slip and a nucleation of compression twins, respectively.
6
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Acoustic Emission During Firing of the Illite-Based Ceramics with Fly Ash Addition

76%
Knapek M., Húlan T., Dobroň P., Chmelík F., Trník A., Štubňa I.
Acta Physica Polonica A
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2015
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vol. 128
|
issue 4
783-786
EN
In this work, illite-based ceramic body with power plant fly ash addition (60 wt.% of illite, 30 wt.% of fly ash and 10 wt.% of illite fired at 1100°C) was investigated by the thermal analysis techniques (differential thermal analysis, thermodilatometry and thermogravimetry) and the acoustic emission technique. The green body was heated up to 1100°C at three different rates 2.5, 5, 10 K/min. The most intense acoustic emission was recorded at the highest rate 10 K/min. Mutual correlations between thermal analyses and acoustic emission data were also examined. The first acoustic emission response appears at 430°C, corresponding to a small endotherm on the DTA curve, where the thermal decomposition of mineral portlandite takes place. In the temperature range from 600 to 900°C, high acoustic emission activity correlates with dehydroxylation and expansion of the sample. At temperatures higher than 800°C, the source of acoustic emission signals is the thermal decomposition of calcite. The amorphous phase created from illite at 920°C becomes pyroplastic, therefore it is not documented by the acoustic emission technique.
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