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Study of beta phase in Al-Mg-Si alloys by means of unconventional methods of electron microscopy
Ligas, Aleš ; Julišová, Martina (referee) ; Mikmeková, Šárka (advisor)
Aluminium Al-Mg-Si alloys are the most commonly used in automotive and construction industry. Hexagonal ’-phase is one of the metastable phases occured in this type of alloys. Unlike classic square -phase, this ’-phase is characterized by different crystalographic orientation to the matrix and shape. Standard method used for identification of aluminium alloys is scanning electron microscopy (SEM), because of its quickness and efficiency, but in case of very thin or damaged structures (as a result of metallographic process) it’s insufficient. Scanning low energy electron microscopy (SLEEM) can be appropriate for identification of mentioned precipitates due to its physical principles resulting in many advantages compared to SEM. So the most important benefits are interaction volume reduction (which leads to improvement of surface sensitivity), increase of material contrast (ability to change matrix / precipitates contrast) as well as crystalographic contrast.
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Study of metals by low voltage SEM
Ligas, Aleš ; Jánský, Pavel (referee) ; Mikmeková, Šárka (advisor)
The aim of this thesis is to demonstrate the advantages of the scanning low energy electron microscopy (SLEEM) in the field of materials science. The SLEEM can be very effectively used for investigation of wide range of materials, such as steels, alloys, ceramics and thin films. Experimental part of this work was performed on the scanning electron microscope TESCAN VEGA TS 5310 equipped with cathode lens mode at Institute of Scientific Instruments of the ASCR, v.v.i..
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STUDY OF COMPLICATED CRYSTAL STRUCTURES BY MEANS OF SLOW ELECTRONS
Mikmeková, Šárka ; Kasl, Josef (referee) ; Švejcar, Jiří (referee) ; Frank, Luděk (advisor)
Methods for examination of the crystal structure of crystalline materials include the X-Ray, neutron and synchrotron-radiation diffraction, electron backscattered diffraction in the scanning electron microscope, scanning transmission electron microscopy, transmission electron microscopy and focused ion beam microscopy. The scanning low energy electron microscopy (SLEEM) is less known as yet but already has proven itself very powerful tool for studies of the crystal lattice. By means of very slow electrons reflected from the sample and effectively detected in their full angular and energy distribution the crystalline structure is imaged at high spatial resolution and high contrast is obtained between differently oriented grains in polycrystals. Because of high sensitivity of the image signal to the inner potential distribution in the sample even details like subgrains or twins as well as strain at the microstructural level can be visualized. The aim of this thesis is to demonstrate the scanning low energy electron microscopy as an effective tool for investigation of wide range of materials like steels, non-ferrous alloys and ultra-fine grained materials.
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Study of beta phase in Al-Mg-Si alloys by means of unconventional methods of electron microscopy
Ligas, Aleš ; Julišová, Martina (referee) ; Mikmeková, Šárka (advisor)
Aluminium Al-Mg-Si alloys are the most commonly used in automotive and construction industry. Hexagonal ’-phase is one of the metastable phases occured in this type of alloys. Unlike classic square -phase, this ’-phase is characterized by different crystalographic orientation to the matrix and shape. Standard method used for identification of aluminium alloys is scanning electron microscopy (SEM), because of its quickness and efficiency, but in case of very thin or damaged structures (as a result of metallographic process) it’s insufficient. Scanning low energy electron microscopy (SLEEM) can be appropriate for identification of mentioned precipitates due to its physical principles resulting in many advantages compared to SEM. So the most important benefits are interaction volume reduction (which leads to improvement of surface sensitivity), increase of material contrast (ability to change matrix / precipitates contrast) as well as crystalographic contrast.
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Study of metals by low voltage SEM
Ligas, Aleš ; Jánský, Pavel (referee) ; Mikmeková, Šárka (advisor)
The aim of this thesis is to demonstrate the advantages of the scanning low energy electron microscopy (SLEEM) in the field of materials science. The SLEEM can be very effectively used for investigation of wide range of materials, such as steels, alloys, ceramics and thin films. Experimental part of this work was performed on the scanning electron microscope TESCAN VEGA TS 5310 equipped with cathode lens mode at Institute of Scientific Instruments of the ASCR, v.v.i..
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