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Investigation of the dynamics of the deformation processes in Mg-RE alloys using in-situ experimental methods
Farkas, Andrea ; Mathis, Kristián (advisor)
In this present work, the dynamics of deformation mechanisms activated in binary magnesium-gadolinium alloys with respect to amount of Gd were investigated with in-situ experimental methods. Cast alloys are characterized by random texture. Compression test were done at room temperature with simultaneous record of acoustic emission response. The acoustic emission signal was subsequently analysed using advanced clustering method providing information about the dominant deformation mechanisms. High speed camera was used to study the dynamics of twinning, including estimation of the velocity of twin propagation with respect to Gd concentration. The deformation tests were repeated in a chamber of scanning electron microscope (in-situ SEM) with concurrent following the microstructure development using secondary electrons and electron back-scattered diffraction (EBSD) in different stages of the deformation. Main goal of this measurements was to identify active slip systems and the progress of twin volume fraction during deformation. Keywords: magnesium alloy, deformation tests, acoustic emission, high-speed camera, electron microscopy, twinning
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Experimental study of the deformation mechanisms in cobalt by advanced in-situ techniques
Greš, Adam ; Knapek, Michal (advisor) ; Mathis, Kristián (referee)
The behaviour of pure polycrystalline cobalt in compressive deformation is influenced by the presence of high temperature fcc phase. To investigate this influence samples are prepared using annealing at different temperatures (600 řC- 1100 řC) with ≈ 6-10% of residual fcc phase. Additional sets of samples are also subjected to thermal cycling around the phase transformation temperature for ten or twenty cycles with the goal of stabilising the microstructure and creating material with no fcc fraction. Samples are tested in compression and a decrease in ductility and strength is observed after the the fcc phase is removed using thermal cycling. The interrupted deformation experiment shows that the transformation is rather sluggish and the main contribution of fcc grains to deformation is their ability to accommodate shape change. The presence of 71ř boundaries also sug- gests that the transformation is not fully stabilised and further thermal cycling could lead to further evolution of microstructure. Additionally the slow transfor- mation does not seem to produce detectable acoustic emission (AE) signal. The energies of AE events (recorded mostly around the yield point) follow a power law distribution. This is in line with recent investigations of the collective nature of dislocation motion and the...
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Study of deformation processes of perspective magnesium-based composites
Farkas, Gergely ; Mathis, Kristián (advisor) ; Száraz, Zoltán (referee)
The goal of the present work is investigation of deformation mechanisms in magnesium-based metal matrix composites and examination of the influence of morphology of strengthening phase on the mechanical properties. The microstructure of the specimen was studied by means of light optical and electron microscopy (SEM). Compression tests in the temperature range of 20řC-300řC were preformed. Acoustic emission measurements were performed during compression test at room temperature, whose help us elucidate the ongoing micromechanisms during the straining. Furthermore residual stress in the magnesium matrix at different strain levels was measured by neutron diffraction.
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Phase transformation in magnesium MgZnAl-based alloys
Kodetová, Veronika ; Vlach, Martin (advisor) ; Mathis, Kristián (referee)
In the present work, there was analyzed thermal evolution of the phase transformation in the MgZnAl and MgZnAlCa alloys with different concentration of the Zn and Ca. The grains were occupied by the phase with quasicrystaline icosaedral structure in the as-cast alloys and after isochronal annealing up to 240 řC. The thermal measurements revealed two exothermic effects in the MgZnAl alloy and three exothermic effects in the MgZnAlCa alloy during linear heat treatment in the temperature range of 100 - 250 řC. In agreement to the thermal response, two and three stages of electrical resistivity decrease were observed in the same temperature range. The lower thermal changes, absolute resistivity changes and microhardness were observed in the alloy with Ca-addition and lower concentration of Zn.
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Phase transformation in bio-compatible Mg-based alloys
Hornát, Bohumil ; Vlach, Martin (advisor) ; Mathis, Kristián (referee)
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Investigation of basic deformation mechanisms of magnesium alloys by means of advanced in-situ methods and theoretical modeling
Čapek, Jan ; Mathis, Kristián (advisor) ; Landa, Michal (referee) ; Šiška, Filip (referee)
The work is focused on developing testing methods for investigating of the deformation mechanisms of magnesium alloys. The work involves the measurement of in-situ acoustic emission and neutron diffraction and comparison to the theoretical models. Mg + 1wt.% Zr alloy was selected for investigation of the compression - tension asymmetry. Advanced analysis of acoustic emission and neutron diffraction data revealed activation of different slip systems during deformation. Moreover, the different evolution of twinning was explained. The same methods were used to investigate the aluminum influence on deformation mechanisms. The hardening of basal slip and twinning and increasing importance of prismatic slip was observed.
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Study of mechanical and thermal properties of nanoparticle-reinforced composites
Németh, Gergely ; Mathis, Kristián (advisor) ; Lukáč, Pavel (referee)
Title: Study of mechanical and thermal properties of composites reinforced by nanoparticles Author: Gergely Németh Department: Department of Physics of Materials Supervisor: RNDr. Kristián Máthis, Ph.D. Abstract: In the present work the deformation behavior of magnesium-based alloy AZ31 reinforced by SiC nanoparticles which was produced by horizontal continual casting is studied. Tension tests in the room temperature, compression tests in the temperature range of 20řC-300řC have been preformed. Samples was with two different orientation. Deformation strain rate was 10-3 s-1 . Simultaneously, the acoustic emission is recorded and studied. The mechanisms of plastic deformation of material are discussed mainly in term of mechanical twinning. Dependence of deformation behavior in compression on temperature is analyzed. The microstructure of original and deformed material is also studied. Keywords: magnesium alloys, composit material, mechanical twinning, metals with hexagonal structures.
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Investigation of deformation mechanisms in Mg-Gd alloys
Szabóová, Andrea ; Mathis, Kristián (advisor) ; Drozdenko, Daria (referee)
Title: Investigation of deformation mechanisms in Mg-Gd alloys Author: Andrea Szabóová Department: Department of Physics of Materials Supervisor: doc. RNDr. Kristián Mathis, DrSc. Abstract: In the present work, the deformation behavior of magnesium-gadolinium binary alloys was investigated. Dependence on the concentration of Gd and deformation temperatures was studied. Extruded samples had relatively strong initial texture. Compression tests were done at room temperature and 200řC. Simultaneously with deformation acoustic emission was recorded. Data from acoustic emission was analyzed with advanced statistical methods. Results of the combination of these two experimental methods indicated that at the beginning of the deformation twinning is the dominant mechanism. In the following stage of plastic deformation non-basal slip systems became the governing deformation mechanism. With higher content of Gd the size of twins decreases as a result of the decreased mobility of twin boundaries caused by solute atoms. At higher temperatures twinning activity was increasing. In addition, results were confirmed by optical light and scanning electron microscopy. Keywords: magnesium alloy, deformation tests, acoustic emission, microscopy
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Study of mechanical properties of magnesium-based composites
Farkas, Gergely ; Mathis, Kristián (advisor) ; Drozd, Zdeněk (referee)
In the present work, the mechanical properties of AJ51 magnesium alloy and composite is studied. Compression tests in the temperature range of 20řC-300řC have been preformed. The microstructure of the specimen was studied by means of light optical microscopy. The work is focused on the elucidation of the micromechanisms acting during plastic deformation of the composite specimens. Further a comparison between the mechanical properties of alloy and the composite is presented.
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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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