National Repository of Grey Literature 37 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
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.
RF-ICP deposition of tungsten coatings
Zlatník, Rostislav ; Houdková, Šárka (referee) ; Čížek, Jan (advisor)
The main object of this work is the technology of radio frequency controlled inductively coupled plasma, abbreviated RF-ICP. The specific goal of the work was the application of surface layers of tungsten and analysis of the influence of changes in process conditions on the resulting microstructure and chemical composition of deposited coatings. The monitored conditions were torch power, choice of carrier gas, powder feedrate.
Characterization of suspension plasma sprayed coatings deposited using different organic carriers
Dukovský, Daniel ; Toma, Filofteia-Laura (referee) ; Čížek, Jan (advisor)
Cí­lem této bakalářské práce bylo charakterizovat a porovnat povlaky nanesené plazmovým žárovým nanášení­m ze suspenze s použití­m různých organických nosičů. Teoretická část obsahuje stručný popis běžně použí­vaných metod žárového nanášení­ a blí­že se věnuje technologii hybridní­ho vodou stabilizovaného plazmatu (hořák s touto technologií­ byl využit pro nanesení­ povlaků v tomto výzkumu). Druhá polovina teoretické části se zabývá věcným popisem povlaků a metodami nanášení­ prášku o velikosti částic v řádu nanometrů, kde hraje důležitou roli právě použití­ suspenze. Experimentální­ část je zaměřena na vliv použitého solventu v suspenzi na charakteristiky výsledného povlaku. V závěrečné části jsou prezentována a diskutována naměřená data a vyhodnoceny výsledky.
Cold spray deposition of reduced thermal expansion multiphase materials
Kašuba, Matúš ; Andrew, Ang Siao Ming (referee) ; Čížek, Jan (advisor)
Cieľom predkladanej diplomovej práce je skúmať a analyzovať možnosti prispôsobovania koeficientu tepelnej rozťažnosti nástrekov z kompozitných materiálov deponovaných na substráty pomocou technológie cold spray. Kompozitné materiály sú v tomto prípade reprezentované zmiešanými práškami, ktoré sú pripravené pridávaním fázy s negatívnou tepelnou rozťažnosťou do základného materiálu s kladným koeficientom tepelnej rozťažnosti. Takto pripravené nástreky môžu byť užitočné pri opravovaní a renovácii strojárenských súčiastok. V prvej časti je priblížená samotná technológia cold spray spolu s jej využitím pri opravách a renováciách v strojárenskom priemysle. Ďalej sa práca zaoberá tepelnou rozťažnosťou materiálov, kde je predstavený jav negatívnej tepelnej rozťažnosti. V experimentálnej časti práce je vyhodnotený potenciálny efekt negatívnej tepelnej rozťažnosti pri deponovaní nástrekov pomocou technológie cold spray.
Looking for Weak States of RC4 by Means of Waiting Tables
Čížek, Jan ; Drápal, Aleš (advisor) ; Boháček, Milan (referee)
AbstractEN.txt 07/23/2018 09:51:19 AM Page 1 of 1 Waiting Tables were introduced by Drápal and Hojsík in 2006 to study weak states of the stream cipher RC4. This thesis revisits Waiting Tables and some of their most important properties. An equivalent model from graph theory, called Waiting Paths, is established in this work and the equivalence of the two models is proved. Afterwards, Waiting Matrices are defined and used for the analysis of a subclass of Waiting Paths.
Powder feeding analysis in RF-ICP
Zlatník, Rostislav ; Veverka, Jakub (referee) ; Čížek, Jan (advisor)
The work is focused on the problematics of inductively coupled plasma, which is used for deposition of layers. We focused on two goals in the work. The first one focused on powder feeder, which is working on the vibration principle and is used in an apparatus that is using inductively coupled plasma. The aim is to determine its properties, dependence on different input parameters and working conditions. Is important to verify the suitability of its use for this kind of application. The assumption was to find the ideal configuration of the feeder for the given powder. After an overall assessment of the feeder properties, it was recognized as inappropriate for this application. The second goal is to spray tungsten layers with three different tungsten powders. Layers made with an inductively coupled plasma technology delivers promising results, but this issue needs to be intensively addressed in the future.
Modification of SPS quasicrystalline compacts via electron beam treatment
Poczklán, Ladislav ; Lukáč,, František (referee) ; Čížek, Jan (advisor)
The quasicrystals are characterized by unusual rotational symmetries that are not observed in the crystalline materials, which is the cause of their interesting material properties. Because of that a particular attention was paid to quasicrystalline structures in the literature research. The research also contains a description of electron beam technology, spark plasma sintering method and introduction to the problematics of wear. As the default materials for the experimental part were selected Titanium Grade 2 powder and Cristome A5 powder which was partially composed of quasicrystalline phase. The first series of samples was sintered only from powder Cristome A5. The second series was sintered from the mixture of 80 % Titanium Grade 2 powder and 20 % Cristome A5 powder. For the compaction of samples spark plasma sintering technology was selected. Samples were then systematically modified by electron beam and subjected to pin on disc tests. Samples modified at 750 °C had the best wear resistance. Samples modified at 1150 °C contained increased amount of quasicrystalline phase.
High entropy alloys fabricated via SPS compaction of high energy milled feedstock powders
Gubán, Ivan ; Hadraba, Hynek (referee) ; Čížek, Jan (advisor)
The subject of this thesis is preparation of CoCrFeMnNiNx high entropy mixtures via the methods of mechanical alloying and spark plasma sintering (SPS). Three series of specimens were fabricated in this thesis: samples milled in argon (benchmark materials), samples milled in nitrogen atmosphere (to observe their ability of nitrogen absorption) and samples microalloyed with CrN, FeN nitrides (to observe their dissociation into the solid solution potential). The fabricated powders and SPS compacts were subsequently observed by electron microscopy and their phase content by X-Ray diffraction (XRD) and elemental composition by EDS analysis were carried out. A method of reduction melting in inert atmosphere was used to determine the exact oxygen and nitrogen content in powders, while the respective particle size distribution measured by laser diffraction method. The influence of nitrogen content on the hardness of the samples was studied via the microhardness measured. After completing the process of mechanical alloying under the Nitrogen atmosphere was the maximal concentration of nitrogen in the structure 0,208% after 24 hours of milling (dependency on time was linear), which means, the method of milling under the Nitrogen atmosphere was successful. XRD of milled samples showed the existence of the only FCC single solid solution phase, while samples milled under the Nitrogen atmosphere showed the trend of the growth of the lattice parameter with the increasing nitrogen content. There was observed the presence of the chromium nitrides precipitates on the grain boundaries of the FCC phase in microalloyed samples. All specimen were contaminated by a mixture of metallic oxides and manganeese sulphides, which were present in the default manganeese powder. The greatest value of microhardness showed the duplex sample. The increase in values of microhardness (344 HV 0,3) in comparison with the standard sample (262,9 HV 0,3) was recorded on the samples milled under the nitrogen atmosphere, which conforms the positive influence of the nitrogen content on strength characteristics of this alloy.
Fabrication and characterization of solution precursor hydroxyapatite coatings deposited via hybrid water-stabilized plasma gun
Antoš, Zdeněk ; Tkachenko, Serhii (referee) ; Čížek, Jan (advisor)
Hydroxyapatite coatings have been used as a barrier between a metal core of replacement and living tissue for long time in medicine. Plasma spray is a typical technology for preparation these coatings. This thesis concerns a new plasma spray technology with hybrid system of arc stabilization (WSP-H). Simultaneously it uses an innovative method of feeding the initial material in a form of water suspension (SPPS). The aim of this thesis was to produce water solutions of hydroxyapatite and make coatings with WSP-H. These coatings were characterized in terms of their morfology, chemical and phase composition. Their biocompatibility was tested by a cultivation and an analysis of RAW 264.7 and MG-63 cells. The coatings made by SPPS have a very rough surface which is suitable for biological application. The biocompatibility testing discovered that the coatings will by tolerated in a human body very well. This method of production of hydroxyapatite coatings could be a good replacement of older methods after a better optimalisation of the processing parameters and after reaching purity of coating.
Modification of Elektron 21 magnesium alloy microstructure via electron beam treatment
Hanáček, Josef ; Šiška, Filip (referee) ; Čížek, Jan (advisor)
This work presents a basic research on the influence of electron beam technology modification on chemical, structural and phases changes of Elektron 21 magnesium alloy. The samples were systematically modified under various parameters of the electron beam and coatings on their respective surfaces were deposited via controlled plasma electrolytic oxidation (PEO) subsequently. The influence of the EB modification on the PEO coating formation was observed. Several samples with remelted fine-grained surface layer were obtained. Having a thickness of 10^1 to 10^3 µm, the average grain sizes in this layer were quantitatively evaluated. The performed EDS analysis revealed in identical chemical composition of the remelted surface layer and the original alloy material, despite the detected sample weight loss upon the EB treatment. XRD analysis revealed an increased content of Mg3(Nd,Gd) intermetallic phase in the remelted area. The PEO coatings were more compact and less porous as compared with their counterpart coatings on the original, unmodified alloy material.The results of the presented work showed, among others, a suitable microstructure and chemical composition of some of the modified samples that could potentially exhibit enhanced corrosion resistance as opposed to the unmodified material. The corrosion testing will be part of a follow-up study. More compact PEO coatings formed on some of the modified surface layers likely represent, too, a more durable variant as compared to the original material.

National Repository of Grey Literature : 37 records found   1 - 10nextend  jump to record:
See also: similar author names
2 ČÍŽEK, Josef
5 Čížek, Jakub
1 Čížek, Jiří
2 Čížek, Josef
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