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Titanium and titanium alloys prepared by cryogenic milling
Kozlík, Jiří ; Stráský, Josef (advisor) ; Janeček, Miloš (referee)
Ultra-fine grained materials are presently thoroughly investigated due to their enhanced mechanical properties. Cryogenic milling is one of the severe plastic deformation methods, which allow production of these materials. Titanium powder was processed by cryogenic milling in liquid nitrogen and argon and consequently consolidated via spark plasma sintering method. In this work, the influence of milling conditions (liquid nitrogen vs. liquid argon, material of balls, duration and speed of milling, usage of stearic acid) on size and shape of powder particles, contamination and mechanical properties was investigated. Particle size reduction was generally not observed, while their morphology changed significantly. Using liquid nitrogen as a cooling medium leads to strong contamination of prepared material and consequently to its hardening and embrittlement. Stearic acid supresses cold welding of particles during milling and enhances its efficiency. It is possible to eliminate stearic acid from powder by cleaning in acetone before sintering, to prevent contamination of processed material. Microhardness increased, depending on milling efficiency (in liquid argon), from original 178 HV to 200-300 HV range. Increase of yield and ultimate stength was observed in compression tests while maintaining ductility....
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Materiály pro fúzní aplikace a jejich interakce s tokamakovým plazmatem
Klevarová, Veronika ; Janeček, Miloš (advisor) ; Šíma, Vladimír (referee)
Title: Materials for fusion applications and their interaction with tokamak plasma Author: Veronika Klevarová Department: Department of Physics of Materials Supervisor: doc. RNDr. Miloš Janeček, CSc., Department of Physics of Materials Abstract: Tungsten represents a perspective option in the context of fusion devices first-wall materials. In the first part of this work, set of tungsten samples with variable grain size was prepared by spark plasma sintering. Specimens were exposed to steady state deuterium plasma beam and high energy heat pulses, simulating thus the normal operation in the tokamak. As a consequence of the exposure, samples surfaces were roughened, as-prepared grains were recovered and in some cases cracks were formed. Moreover, post-irradiation analysis of the damaged samples revealed activation of in-grain slip systems within the loaded surfaces. Threshold grain diameter for this mechanism was determined to be between 5.5 - 6.6 μm at the particular loading conditions. However, damaged features showed to depend more on the fabrication parameters than on the grain diameter. Synergistic effects of simultaneous loading were proven to be important since those reduced the heat propagation within the volume of the tested samples. In the second part of this thesis, introduction to plasma-surface...
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Optimization of properties of Ti based alloys for biomedical and structural applications
Stráský, Josef ; Janeček, Miloš (advisor) ; Hadzima, Branislav (referee) ; Karlík, Miroslav (referee)
Title: Optimization of properties of Ti based alloys for biomedical and structural applications Author: Josef Stráský Department / Institute: Department of Physics of Materials Supervisor of the doctoral thesis: Assoc. Prof. Miloš Janeček, Ph.D. Abstract: Titanium alloys belong to the mostly used biomaterials for orthopaedic implants. Advanced surface treatments of Ti alloys for orthopaedic use and newly developed biomedical beta-Ti alloys are investigated in this thesis. Wide spectrum of experimental techniques was employed in order to correlate material processing, microstructure and mechanical properties. Electric discharge machining was used as a biocompatibility enhancing surface treatment of Ti-6Al-4V alloy, but the treated material suffered from the poor fatigue performance. Two subsequent surface treatments - chemical etching and shot- peening - were proposed and it was shown that their combination significantly improves the fatigue performance of the material making it applicable in orthopaedics. This process was patented in the Czech Republic. The thesis further reviews complex problematic of biocompatible beta-Ti alloys. Several new biocompatible beta-Ti alloys were designed on the basis of Ti-Nb-Zr-Ta quaternary alloy. The effect of Fe, Si and O additions on microstructure, elastic modulus and...
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Physical properties of ultrafine-grained magnesium based alloys prepared by various severe plastic deformation techniques
Stráská, Jitka ; Janeček, Miloš (advisor) ; Dlouhý, Antonín (referee) ; Kalvoda, Ladislav (referee)
Title: Physical properties of ultrafine-grained magnesium based alloys prepared by various severe plastic deformation techniques Author: Jitka Stráská Department / Institute: Department of Physics of Materials Supervisor of the doctoral thesis: Doc. RNDr. Miloš Janeček, CSc. Abstract: The objective of the doctoral thesis is the complex investigation of ultrafine-grained magnesium alloy AZ31 prepared by two different severe plastic deformation techniques, in particular the hot extrusion followed by equal-channel angular pressing (EX-ECAP) and high pressure torsion (HPT). These severe plastic deformation methods, and as well as many others, are described in detail in the introductory theoretical section. Experimental results are summarized in the following experimental part of the thesis. Mechanical properties, lattice defect structure and especially microstructure were investigated using various experimental techniques. Thermal stability of ultrafine-grained microstructure of AZ31 after EX-ECAP was investigated and the activation energies for grain growth in different temperature ranges were calculated using kinetic equation for grain growth and Arrhenius equation. Results from the dislocation density measurements proved temperature ranges of the recovery and the following grain growth. Results from the...
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Money Laundering
Janeček, Miroslav ; Kohajda, Michael (advisor) ; Kotáb, Petr (referee)
Money laundering can be defined as a process of converting the proceeds of illegal activities to legitimate money or other assets, or as a process whose aim is to conceal the origin and ownership of proceeds that come from illegal activities. Its main phases are placement, layering and integration. The main sources of dirty money are drug trafficking, procuring, arms trafficking, extortion, robbery and property crimes. The aim of this thesis is the analysis of the fight against money laundering in terms of financial law and from institutional point of view, evaluation of its success and the formulation of my own opinions on the possible improvement of the system components. The first part of thesis deals with the term of money laundering, its phases and characteristics and history. The second part analyses the legislation at international, EU and national level. Attention is paid to the AML Directives and to the AML Act. Main obligations prescribed by Directives and AML Act to obliged persons are identification obligation, due diligence, preservation of information, reporting of suspicious transactions, postponement of client's order, creation of internal policies and staff training. Then follows characterization of individual authorities and institutions involved in combating money laundering....
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Complex investigation of fine-grained polycrystals of Cu and CuZr alloy processed by equal channel angular pressing a high pressure torsion
Srba, Ondřej ; Janeček, Miloš (advisor) ; Hadzima, Branislav (referee) ; Karlík, Miroslav (referee)
Title: Complex investigation of fine-grained polycrystals of Cu and CuZr alloy processed by equal channel angular pressing and high pressure torsion Author: RNDr.Ondřej Srba Department: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University Prague Supervisor: Doc. RNDr. Miloš Janeček, CSc. Abstract: In the thesis the microstructure development, mechanical, elastic and corrosion properties of deformed specimens of pure Cu and binary alloy CuZr processed by equal channel angular pressing (ECAP) are investigated. Several properties of pure Cu processed by ECAP are compared with properties of the same material processed by high pressure torsion (HPT). The microstructure development is characterized in detail by several experimental techniques (light and electron microscopy, electron back scatter diffraction, positron annihilation spectroscopy, etc.). The microstructure development in specimens processed by ECAP is characterized by the continuous fragmentation of the initial coarse grain structure and the formation of new grains having the sizes in the submicrocrystalline range (of 460 nm and 260 nm in Cu and CuZr alloy, respectively). During the deformation by ECAP the fraction of high-angle grain boundaries, the dislocation density and the concentration of vacancies are...
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Fázové transformace a mikrostrukturní změny ve slitině TIMET LCB
Šmilauerová, Jana ; Janeček, Miloš (advisor) ; Šíma, Vladimír (referee)
In the present work, phase transformations in TIMETAL LCB tita- nium alloy and their influence on mechanical properties were studied. Different initial conditions were prepared by solution treating above β-transus immedi- ately followed by heat treatment in α/β temperature regime. These resulted in different grain boundary α thicknesses and contiguities at a fixed α vol- ume fraction. The subsequent ageing response of this material was studied by low temperature ageing at 400 ◦ C, 450 ◦ C and 500 ◦ C. Phase transformations were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and resistivity measurements. Mechan- ical properties were investigated using microhardness measurements and tensile tests. It has been proved that metastable ω phase is formed during annealing at 400 ◦ C and 450 ◦ C. ω particles further transform to very fine precipitates of α phase when exposed to annealing for longer time periods. These fine precip- itates significantly contribute to increase of microhardness and achieving high value of yield stress. Keywords: Metastable beta Ti alloys, phase transformations, microstructure changes, ω phase 1
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Interaction of tokamak plasma with selected fusion materials
Klevarová, Veronika ; Janeček, Miloš (advisor) ; Horáček, Jan (referee)
Title: Interaction of tokamak plasma with selected fusion materials Author: Veronika Klevarová Department: Department of Physics of Materials Supervisor: Doc. RNDr. Miloš Janeček, CSc. Supervisor's e-mail address: Milos.Janecek@mff.cuni.cz Abstract: The following work is devoted to structural analysis and study of relevant physical properties of materials with perspective use for the first wall and as construction materials of the tokamak device, prior to their interaction with the high-temperature plasma in Compass-D tokamak. The theoretical part contains an introduction to the interaction of tokamak plasma with fusion materials, including a description of the processes taking place during the plasma discharge (such as implantation, erosion, particles traveling in the tokamak vacuum vessel, redeposition, co-deposition with tritium etc.) and selection of appropriate fusion materials. The experimental part consists of structural analysis of selected materials by optical and scanning electron microscopy. Analysis of the structure revealed the presence of oxide layers in some samples prepared by the technology of plasma spraying; which was probably caused by sample preparation in the ambient air. Qualitative elemental analysis of the samples was performed by electron dispersive X-ray spectroscopy (EDS) in SEM....
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