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Study of deformation mechanisms in extruded magnesium alloys containing neodymium and yttrium
Hojnoš, Peter ; Minárik, Peter (advisor) ; Chmelík, František (referee)
Submitted work shows results of the investigation of ternary (WN43) and two binary magnesium alloys containing neodymium (2Nd) and yttrium (4Y) extruded at two different extrusion rates (2 and 5 mm/s). Microstructure of the investigated samples was analysed by light microscope. Additionally, texture of all samples was measured by X-ray diffraction. Mechanical properties were studied by compression deformation tests with two different deformation directions with respect to the processing direction. Acoustic emission was recorded during the deformation tests in order to correlate deformation behaviour with the micros- tructure. Analysis of the acoustic emission helps to identify deformation micro- mechanisms acting during the mechanical straining. Additionally, effect of sample size and deformation rate on the deformation mechanisms was investigated. 1
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Study of deformation processes in hexagonal materials
Čapek, Jan
The deformation mechanisms of commercially pure magnesium using advanced in-situ methods were investigated in the present work. Compression and tensile test were done at room temperature. Simultaneously, the neutron diffraction was measured and the acoustic emission was recorded. The microstructure of the deformed material was also studied by means of optical microscopy and electron back-scattered diffraction. These measurements provided information about twin nucleation and growth, microstructure changes and the influence of the orientation of grains on the number of twins and their shape. The values obtained were compared to the Elasto-Plastic Self-Consistent model, which provides information about the activity of deformation mechanisms. We focused on clarifying the influence of twinning activity on asymmetry between tensile and compression deformation. Powered by TCPDF (www.tcpdf.org)
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Study of deformation processes in hexagonal materials
Čapek, Jan ; Mathis, Kristián (advisor) ; Karlík, Miroslav (referee)
The deformation mechanisms of commercially pure magnesium using advanced in-situ methods were investigated in the present work. Compression and tensile test were done at room temperature. Simultaneously, the neutron diffraction was measured and the acoustic emission was recorded. The microstructure of the deformed material was also studied by means of optical microscopy and electron back-scattered diffraction. These measurements provided information about twin nucleation and growth, microstructure changes and the influence of the orientation of grains on the number of twins and their shape. The values obtained were compared to the Elasto-Plastic Self-Consistent model, which provides information about the activity of deformation mechanisms. We focused on clarifying the influence of twinning activity on asymmetry between tensile and compression deformation.
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An Acoustic Emission Study of Deformation Mechanisms in Novel Magnesium Alloys at Uniaxial and Low Cyclic Loading
Horváth, Klaudia ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
This work is focused on the study of the relationship between microstructure and deformation mechanisms in magnesium (Mg) alloys during uniaxial (tension, compression) and low cyclic loading by the acoustic emission (AE) technique. The main attention is paid to the study of tension-compression yield asymmetry and twinning-detwinning process during changes in deformation mode in novel aluminium-free Mg alloys, where the deformation texture influences the activation of various deformation mechanisms. The results contribute to the understanding of dislocation processes and twin activation (especially of twinning-detwinning process) during cyclic loading. These processes are of great importance because they influence significantly the fatigue life of Mg alloys.
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The numerical analysis of interactions between twins and precipitates in magnesium alloys
Bogdan, Miloš ; Gröger, Roman (referee) ; Šiška, Filip (advisor)
Hlavním cílem této práce je analýza napěťových polí, indukovaných dvojčatěním ovlivněných přítomností precipitátu před čelem dvojčete. Zvolený případ popisuje tahové dvojče {1012} 101 1 s lamelarními precipitáty v hořčíkové slitině AZ31. Systém je modelován metodou konečnýh prvků jako 2D elastická eliptická inkluze, se dvěmi elastickými precipitáty tyčovitého tvaru, nacházející se před čelem elipsy obklopené plastickou matricí modelovanou pomocí krystalové plasticity. Analýza dvojčat a precipitátů s různou tlouštkou ukazje inhibující účinek precipitátů na růst tloušťky dvojčat. Velikost tohoto účinku se mění s tloušťkou dvojčete v důsledku komplexní interakce mezi dvojčetem precipitátem a indukovanou plastickou zónou.
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Observation of twin boundaries in Ni-Mn-Ga alloys
Čech, Jan ; Jan, Vít (referee) ; Zelený, Martin (advisor)
This bachelor’s thesis is focused on observation of twin boundaries in a magnetic shape memory alloy based on Ni2MnGa with 10M martensitic structure. Theoretical part of the thesis describes materials with shape memory effect, their response on mechanical or magnetic loading, phenomenon of twinning, which is closely connected to the shape memory effect, and various levels of twinning. Experimental part studies different types of twin boundaries in monocrystal of alloy Ni49.2Mn30.4Ga20.4 using optical and electron microscopy. The thesis also deals with detection of structural orientations in different twin variants. A holder of samples was designed and constructed for real time observation of twin-boundary movement by optical microscopy. Deformation by pressure shows, that stress necessary for movement of Type II twin boundaries is ~0.2 MPa, whereas it is ~0.6 MPa for movement of Type I.
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