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Obloukové svařování korozivzdorných ocelí pro náročné pracovní podmínky
Matějíček, Josef ; Hála, Michal (oponent) ; Kubíček, Jaroslav (vedoucí práce)
Předložená bakalářská práce se zabývá obloukovým svařováním korozivzdorných ocelí. Pomocí svařovací technologie u státního podniku DIAMO jsou spojovány trubky, příruby a plechy k vedení roztoku síranu sodného, který je získáván jako doprovodný produkt při výrobě uranu. Vlivem chemické reakce dochází ke koroznímu napadání a praskání svaru již v krátké době. Na základě informací o materiálech, použitých přídavných materiálech a svařovacích technologií jsem zhodnotil použité materiály s ohledem na náchylnost ke korozi a vzniku horkých trhlin. Pomocí zkoušek a výpočtů jsem posoudil náchylnost k mezikrystalové korozi u austenitických korozivzdorných ocelí. Pro větší spektrum materiálů byla teoreticky řešena i austeniticko-feritická korozivzdorná ocel. Po výpočtech a zhodnocení zkoušky jsem provedl diskuzi a doporučení pro praxi.
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Výpočet atributů pro předpověď důsledku mutace na funkci proteinu
Matějíček, Jiří ; Burgetová, Ivana (oponent) ; Jaša, Petr (vedoucí práce)
Tato bakalářská práce se pohybuje v oblasti bioinformatiky a zabývá se problematikou získávání atributů proteinů užitečných pro předpověď vlivu mutace na jejich funkci. Práce má především za cíl vytvořit uživatelsky přívětivou aplikaci, která pomocí specializovaných algoritmů jako je FoldX umožní snadno získat atributy mutací ze sekvence a struktury proteinů. Vyvinutá aplikace poskytuje standardizované rozhraní, které umožňuje rozšiřovat sadu výpočetních metod a získat tak rozmanité sady atributů z různých zdrojů. Tyto sady pak mohou být vstupem predikčních metod a mohou tak přispět ke zlepšení predikce škodlivosti mutace.
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Preparation of W-Cu composites by infiltration of w skeletons review
Matějíček, Jiří
Tungsten-copper composites feature high corrosion and erosion resistance, very good thermal and electrical conductivity, low thermal expansion and good mechanical properties. They are used in a variety of demanding applications, such as arc-resistant electrodes, high voltage electrical contacts, heat sinks for integrated circuits, etc. They are also foreseen for use in plasma-facing components of fusion reactors, e.g. as a transition layer between the (refractory) plasma-facing tungsten and the (highly conductive) copper-based cooling structure. In general, high density and good bonding of the tungsten and copper phases is desired. Molten copper infiltration into tungsten preforms is among the prospective fabrication technologies - the structure and properties of the resultant composites are dependent on the specific technological parameters. In this paper, the preparation of W-Cu composites by infiltration of W skeletons is reviewed and attention is paid to the influence of these particular parameters: infiltration temperature, time and atmosphere, tungsten preform porosity, orientation and chemistry (presence or absence of other elements). Optimum parameter combinations for achieving high density and proper bonding of copper and tungsten are identified.
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Tungsten-steel and tungsten-chromium composites prepared by RF plasma spraying
Matějíček, Jiří ; Klečka, Jakub ; Čížek, Jan ; Veverka, Jakub ; Vilémová, Monika ; Chráska, Tomáš ; Ganesh, V.
For future fusion reactors, materials able to withstand harsh environments are needed. In particular, this concerns the plasma-facing components which are foreseen to consist of tungsten based plasma-facing armor and structural and cooling part made of steel. Currently, joining of these materials presents a significant challenge. The stress concentration at their interface, which arises due to thermal exposure and the difference in thermal and mechanical properties, can be reduced by composite/graded interlayers. Plasma spraying is among the prospective technologies for their preparation. In this work, tungsten-steel and tungsten-chromium composites were prepared by radio-frequency inductively coupled plasma (RF-ICP) spraying. Initial optimization of the spraying process for pure materials as well as their mixtures was carried out. Basic characterization of the layers for their structure, porosity and composition is presented.
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Thin nitride layers as permeation barriers
Veverka, Jakub ; Matějíček, Jiří ; Lukáč, František ; Pospíšil, D. ; Cvrček, L. ; Nemanič, V.
Permeation barriers represent one of the crucial fields in materials development for thermonuclear fusion. Primary objective of the barriers is to suppress the permeation of hydrogen isotopes (mainly tritium) from future thermonuclear fusion facilities. Secondary objective is to reduce their retention in structural materials. Expected reactor conditions put high demands on the material, as well as on the final barrier quality. Key properties are tritium permeation reduction, absence of defects (especially cracks), high-temperature stability and corrossion resistance, and compatibility with structural materials (mostly ferritic-martensitic steels). Thin nitride layers, identified as promising permeation barriers, were prepared by diffusion-based nitridation and physical vapour deposition (PVD), and characterized.
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Alternative Methods of Permeation Barriers Preparation
Veverka, Jakub ; Matějíček, Jiří
Permeation barriers represent one of the crucial fields in materials development for thermonuclear fusion. Primary objective of the barriers is to suppress the permeation of hydrogen isotopes (mainly tritium) from future thermonuclear fusion facilities. Secondary objective is to reduce their retention in structural materials. Expected reactor conditions put high demands on the material, as well as on the final barrier quality. Key properties are tritium permeation reduction, absence of defects (especially cracks), high-temperature stability and corrossion resistance, and compatibility with structural materials (mostly ferritic-martensitic steels). Thin nitride layers, identified as promising permeation barriers, were prepared by diffusion-based nitridation and physical vapour deposition (PVD), and characterized.
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ELECTRON BEAM REMELTING OF PLASMA SPRAYED ALUMINA COATINGS
Matějíček, Jiří ; Veverka, J. ; Čížek, J. ; Kouřil, J.
Plasma sprayed alumina coatings find numerous applications in various fields, where they enhance the properties of the base material. Examples include thermal barriers, wear resistance, electrical insulation, and diffusion and corrosion barriers. A typical structure of plasma sprayed coatings, containing a multitude of voids and imperfectly bonded interfaces, gives them unique properties - particularly low thermal conductivity, high strain tolerance, etc. However, for certain applications such as permeation barriers or wear resistance, these voids may be detrimental.\nThis paper reports on the first experiments with remelting of plasma sprayed alumina coatings by electron beam technology, with the purpose of densifying the coatings and thereby eliminating the voids. Throughout the study, several parameters of the e-beam device were varied - beam current, traverse velocity and number of passes. The treated coatings were observed by light and electron microscopy and the thickness, structure and surface morphology of the remelted layer were determined and correlated with the process parameters. Based on the first series of experiments, the e-beam settings leading to dense and smooth remelted layer of sufficient thickness were obtained. In this layer, a change of phase composition and a marked increase in hardness were observed.\n
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