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Influence of heat treatment on deformation behaviour of wrought Mg-Zn-based alloys
Olejňák, Juraj ; Drozdenko, Daria (advisor) ; Mathis, Kristián (referee)
Title: Influence of heat treatment on deformation behaviour of wrought Mg-Zn alloys Author: Juraj Olejňák Department: Department of Physics of Materials Supervisor: RNDr. Mgr. Daria Drozdenko, Ph.D. Abstract: The aim of the present thesis is to understand an influence of heat treatment on microstructure and mechanical properties of extruded Mg-Zn based alloys containing an addition of Ca and Nd. Microstructural analysis provided by electron microscopy gave us information about homogeneity and distribution of precipitates in investigated Mg alloys after extrusion and a subsequent heat treatment. Microhardness and compression test along the extrusion direction have been performed to determine optimal aging conditions for achieving better mechanical properties, such as hardness and strength. The acoustic emmision technique was used to follow active deformation mechanisms during plastic deformation. Application of the acquired knowledge in material research can contribute to design novel Mg alloys with enhanced mechanical properties for specific applications. Keywords: magnesium alloys, isothermal aging, precipitation, mechanical properties
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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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Investigation of deformation mechanisms of advanced light-weight alloys
Németh, Gergely ; Mathis, Kristián (advisor) ; Drozd, Zdeněk (referee)
The objective of this thesis is to investigate the mechanical and damping properties in AZ91 alloys with different boron concentrations and in two experimental alloys based on commercial pure magnesium. Further aim is to identify the influence of heat treatment of alloys AZ91+B on the properties mentioned above. Micro-structural observations were achieved by optical and scanning electron microscope. Mechanical tests were performed in a wide range of temperatures from 23řC to 300řC and, simultaneously, the acoustic emission was recorded at room temperature. The temperature spectrum of internal friction was determined in the temperature range from 23řC to 400řC. Moreover, the amplitude dependence of damping properties of materials were studied. Phenomena leading to dissipation of mechanical energy in the temperature spectrum were determined by micro-structural observation.
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Phase transformation in bio-compatible Mg-based alloys
Hornát, Bohumil ; Vlach, Martin (advisor) ; Mathis, Kristián (referee)
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Study of ultrafine-grained materials prepared with different methods of severe plastic deformation
Krajňák, Tomáš ; Mathis, Kristián (advisor) ; Hadzima, Branislav (referee) ; Kalvoda, Ladislav (referee)
Title: Study of ultrafine-grained materials prepared with different methods of severe plastic deformation Author: RNDr. Tomáš Krajňák Department: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Supervisor: Doc. RNDr. Kristián Máthis, PhD., Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Abstract: Interstitial free steel with ultrafine-grained (UFG) structure was prepared by high-pressure torsion (HPT). The development of the microstructure as a function of the number of HPT turns was studied at the centre, half-radius and periphery of the HPT-processed disks by X-ray line profile analysis (XLPA), positron annihilation spectroscopy (PAS) and electron microscopy. The dislocation densities and the dislocation cell sizes determined by XLPA were found to be in good agreement with those obtained by PAS. The evolution of the dislocation density, the dislocation cell and grain sizes, the vacancy cluster size, as well as the high-angle grain boundary (HAGB) fraction was determined as a function of the equivalent strain. It was found that first the dislocation density saturated, then the dislocation cell size reached its minimum value and finally the grain size got saturated. For very high strains after the...
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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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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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