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Precipitation processes in Mg-Nd alloy
Drábek, Stanislav ; Čížek, Jakub (advisor) ; Lukáč, František (referee)
The objective of this bachelor thesis was to determine, whether precipitation processes occur in the Mg-Nd with 3% by weight of Nd admixture and to measure the kinetics of this process and what effect it has on subsequent hardening of the alloy at higher temperatures. The progression of the mechanical properties of the alloy was monitored by the Vickers hardness measurement method. Concurrently, the characterization of the crystal lattice defects of turbid alloy samples was performed using positron annihilation spectroscopy. It was measured that at elevated temperature, significant hardening occurs in the examined system due to the formation of precipitates of GP zones and β ′ phase by Nd and Mg atoms. 1
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Impact of lattice distortions on physical properties of high entropy alloys
Starý, Dominik ; Čížek, Jakub (advisor) ; Hruška, Petr (referee)
This bachelor thesis is focused on a group of mostly high entropy alloys, composed of metals Cr, Cu, Hf, Fe, Mo, Nb, Ni, Ta, Ti, V, Zr, Co and Al, and their properties studied by scanning electron microscopy, Vickers hardness test and positron lifetime spectroscopy. One of the high entropy alloys' characteristic properties is a presence of local lattice distortion, the magnitude of which is commonly estimated by δr parameter. Based on Vickers hardness test, positive and statistically significant correlation between alloys' microhardness and δr parameter was evaluated. Estimated value of Pearson correlation coefficient is 0,5(1) and obtained p-value is of order 10−4 . That is below significance level 0,05. Based on positron lifetime spectroscopy, it was found out, that positron lifetime and δr parameter are not significantly correlated. 1
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Study of the structure and properties of black aluminium thin films prepared by magnetron sputtering
Prokop, Dejan ; Hruška, Petr (advisor) ; Čížek, Jakub (referee)
Black metallic thin films are characterized by their excessively rough fractal-like surface structure. Furthermore, black metal films have a much bigger surface- to-volume ratio compared to classic reflective metals. Therefore, they can be used e.g. as a basis for optical or chemical sensors. In the present bachelor thesis, we study and pro- vide a comparison between the properties of reflective and black thin films with thickness in the range of 50-700 nm prepared by pulsed DC magnetron sputtering. A small amount of nitrogen that is introduced during deposition to a chamber is responsible for a change in the structure and the growth of the black films. Different surface morphology is studied using a contact profilometer, atomic force microscope and scanning electron microscope. The measurements obtained by these instruments provide valuable information regarding the overall surface structure and means of growth. The surface roughness, as well as the mean crystallite size was observed to increase with the thickness of the films. The X-ray diffraction analysis shows that both types of film crystallize in the face-centered cubic crystal structure. Spectrophotometrical measurements of specular reflectance pro- vide quantitative information about the optical properties. The ultraviolet, visible and near-infrared...
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Study of the structural changes of thin films by in-situ spectrophotometry
Jakubik, Matej ; Hruška, Petr (advisor) ; Čížek, Jakub (referee)
The focus of this bachelor thesis was on modifying vacuum chamber to study two different physical topics. First was the absorption of hydrogen in metals. Hydrogen ab- sorption was studied on palladium thin films. Palladium was chosen thanks to its high kinetics of hydrogen absorption at room temperature, which leads palladium to be the model system to study hydrogen absorption. Using optical measurement one can study hydrogen absorption for thin films. From the results of optical transmittance measure- ment, it is possible to study the change of atomic ratio between hydrogen and palladium, i.e. phase transformation. The second topic will be the study of the dependence of vari- ous conditions (initial temperature of sample, pressure) on the energy of laser pulse on laser-induced dewetting, i.e. structural changes in thin films caused by laser annealing. Minimal energy needed to initiate dewetting was calculated from one-dimensional heat equation. Minimal energy needed to initiate dewetting was tested implementing various initial temperatures and energy densities. 1
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Investigations of lattice defects in metallic coatings prepared by cold spraying
Chmúrny, Daniel ; Čížek, Jakub (advisor) ; Stráský, Josef (referee)
Thermal stability of copper and nickel samples prepared by gas dynamic cold spraying and high pressure torsion were studied by means of positron lifetime spectroscopy and Vickers hardness test. These groups of the same materials prepared by fundamentally different methods were then compared in terms of Vickers hardness, mean positron life- time, separate positron lifetime components examination, volume of clusters of vacancies and their concentration, dislocation densities. This comparison revealed differences in thermal stability, inner defect behavior and homogeneity between the samples prepared by cold spraying and those by high pressure torsion. However, both methods manifested qualitative similarities as well. The spectra of the cold sprayed materials were calculated via simple positron trapping model while for calculations regarding those prepared by high pressure torsion the diffusion trapping model was needed due to strongly inhomoge- neous spatial distribution of defects. Annealing leads to a recrystallized state independent on the history of the concrete specimen. 1
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Investigation of defects in quasicrystals
Vlček, Marián ; Čížek, Jakub (advisor)
Název práce: Studium defekt· v kvazikrystalech Autor: Marián Vlček Katedra: Katedra fyziky nízkých teplot Vedoucí disertační práce: doc. Mgr. Jakub ížek, Ph.D., Katedra fyziky nízkých teplot Abstrakt: V predloženej práci boli pomocou spektroskopie doby života poz- itrónov a koincidenčnej spektroskopie Dopplerovského rozšírenia anihilačného píku študované zliatiny WE43 s prídavkom zinku a ternárne zliatiny Mg-Zn-Y. V týchto zliatinách bola nedávno zistená prítomnos' ikosahedrálnej fázy Mg3Zn6Y1 s kvázikryštalickou štruktúrou, čo pritiahlo pozornos' výskumníkov. Spektroskopia doby života pozitrónov preukázala prítomnos' unikátnych vakanciám podobných defektov na rozhraní ikosahedrálnej fázy a horčíkovej matrice, ktoré sú charakter- istické pre horčíkové zliatiny obsahujúce ikosahedrálnu fázu. Tepelné spracovanie skúmaných zliatin vedie k významným zmenám morfológie hraničných fáz. Ke¤že vakanciám podobné defekty spojené s ikosahedrálnou fázou sa vyskytujú na jej rozhraní s horčíkovou matricou, zmeny v morfológii ikosahedrálnej fázy vedú k výrazným zmenám koncentrácie týchto defektov. "alej boli skúmané vzorky pripravené uhlovým pretláčaním kanálom rovnakého prierezu. Typy defektov prítomné v týchto zliatinách a ich teplotná stabilita bola určená pomocou spektroskopie doby života pozitrónov a merania tvrdosti...
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Investigation of defects in thin metallic films
Hruška, Petr ; Čížek, Jakub (advisor)
In the present work Mg films prepared by RF magnetron sputtering were studied. Variable energy positron annihilation spectroscopy (VEPAS) was employed for investigation of defects in the Mg films. VEPAS characterization was combined with scanning electron microscopy and X-ray diffraction in order to determine grain size, phase composition and texture. The effect of different deposition rate and deposition temperature, annealing, various substrates and film thickness on the structure and amount of defects present in the Mg films was examined. Defect studies by VEPAS showed that positrons in studied Mg films are trapped at misfit dislocations and at vacancy-like defects in grain boundaries and their density can be reduced by the deposition at elevated temperature. 1
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Analysis and comparison of boxing styles of elite amateur boxers from Cuba and Kazakhstan
Čížek, Jakub ; Zdobinský, Adam (advisor) ; Pavelka, Radim (referee)
Title: Analysis and comparison of boxing styles of elite amateur boxers from Cuba and Kazakhstan Objectives: The main goal of this thesis was to find out whether the frequency of use of punching techniques and the distance from which these punching techniques are used are statistically significant for the style of two the most successful countries in amateur boxing. The countries were compared in the use and success of the strikes and compared to their preference for long or medium combat distance. Methods: The method of quantitative observation was used, in which data was obtained by watching video recordings. Part of the matches was evaluated by recording the results manually on paper, the other part in the BORIS program. All data was then transcribed into a Microsoft Excel spreadsheet, where it was also processed. The source for the data were publicly available video recordings from top competitions in 2010-2020. Results: Differences between countries in the monitored indicators are insignificant and boxing styles do not differ much. In the frequency of the use of striking techniques between the rounds, a significant difference was found only between the first and second round of the Kazakhs. In the case of determining the preference for long and medium distance combat between the rounds, there...
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Superplastic deformation of ultrafine-grained magnesium alloys containing rare earth metals and zinc
Vávra, Tomáš ; Minárik, Peter (advisor) ; Čížek, Jakub (referee)
Superplastic behavior of two ultrafine-grained (UFG) magnesium alloys was investigated in this thesis. Commercial Mg-4Y-3RE (wt.%) alloy was prepared by equal channel angular pressing (ECAP) and new experimental alloy Mg-23Zn-2Y (wt.%) was prepared by extrusion and ECAP. Eight passes of Mg-4Y-3RE through ECAP resulted in grain refinement down to ~340 nm and formation of a high volume fraction of fine secondary phase particles. UFG microstructure with an average grain size of 3.2 µm after extrusion and 1.6 µm after Ex-ECAP was achieved in Mg-23Zn-2Y alloy. The microstructure of Mg-23Zn- 2Y was observed by scanning and transmission electron microscopy. The thermal stability of both alloys was measured by microhardness tests. Superplastic behavior was investigated in the temperature range of 250-450 řC and strain rate range of 5x10-4 s-1 - 10-1 s-1 . The results revealed a high strain rate superplasticity in Mg-4Y-3RE alloy. Deformation to fracture exceeded 1000% for several deformation conditions, even at the strain rate of 10-1 s-1 . The highest elongation of 656 % in Mg-23Zn-2Y alloy was achieved in extruded state at the strain rate of 10-3 s-1 .
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Study of hydrogen interaction with defects in thin metallic films
Hruška, Petr ; Čížek, Jakub (advisor) ; Krsjak, Vladimír (referee) ; Mathis, Kristián (referee)
Thin metallic films are particularly interesting as potential hydrogen storage materials as well as hydrogen sensitive optical sensors. Thin films with various microstructure from nanocrystalline to epitaxial can be relatively easily prepared by varying the deposition parameters. Deposition of multi-layers enables preparation of thin films with arbitrary composition. Defects structure plays a key role in hydrogen absorption. Hydrogen atoms segregated at open volume defects reduce their formation energy leading to enhan- ced concentration of hydrogen-induced defects in the material. Moreover hydrogen diffusion along dislocations and grain boundaries facilitates hydrogen absorption in the metal lattice. Thin films clamped to the stiff substrate undergo anisotropic volume expansion during the hydrogen loading. As a consequence high stresses are induced in the film and can result in detachment of the film from the substrate. In this work hydrogen absorption in Gd and Pd films and Pd-Mg multi-layers was studied. Development of the defect structure of hydrogen-loaded films was investigated by means of variable energy positron annihilation spectroscopy com- bined with X-ray diffraction, atomic force microscopy and optical transmittance measurement. Complementary studies of interaction of hydrogen with defects in...
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