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Advanced Abrasion Resistant Coatings for Vacuum Systems
Hégr, Eduard ; Kudláček,, Petr (referee) ; Hrubý, Vojtěch (referee) ; Švejcar, Jiří (advisor)
The thesis is focused on research of advanced surface resistant coatings which have a direct effect on increasing of functional properties of vacuum systems (eg reducing wear of individual pump components, surface inertia to aggressive gases/molecules). But they can also secondarily affect other important pump properties (eg reducing pump temperature). The studied layers/coatings are divided into three areas (i) hard anodic layer, (ii) hard anodic layer with PTFE coating and (iii) DLC coating. The initial material (substrate) is an aluminum-based alloy, which was used for this purpose. In presented thesis, the influence on increase of material and physical properties was demonstrated, such as the increase of hardness and abrasion resistance of the surface after the application of the anodic layer with PTFE coating. The theoretical part of thesis describes the basic principles of preparation of abrasion-resistant layers/coatings and also introduces the vacuum physics. It shows the basic principles of obtaining vacuum, which give a comprehensive picture of the importance of working with advanced coatings. The experimental part is divided into the evaluation of the microstructure of the sample material and the second part is focused on the experiments needed to obtain/measure the required properties, which can be further used to predict damage of the layers/coatings.
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Surface treatment of roll bearings
Kubelka, Milan ; Klakurková, Lenka (referee) ; Švejcar, Jiří (advisor)
The bearings are one of the most widely used construction components enabling mutual movement of parts and at the same time transmission of interacting load. The basic requirements placed on components of roll bearings are particulary increase of contact fatigue resistance, decrease of the friction coefficient between the rolling bodies and bearing rings, increase of hardness and abrasion resistance of functional surfaces, the wear resistance, corrosion protection and finally the electrical and optical properties too. As production of bearings from materials with these attributes would be quite expensive, surface modifications are used for improving the mechanical properties. The main task of this bachelor thesis is description and evaluation of technologies suitable for surface treatment of roll bearings with increased attention to those types of surface treatment which, in cooperation with SVÚM will be studied in more detail in the experimental part of this work (especially polymer coatings, phosphate films and DLC - type coatings). The wear evaluation of different types of coatings was performed with the aid of scanning electron microscopy after the tribological testing.
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Concept and Development of Single-purpose Scanning Electron Microscope
Foret, Zdeněk ; Vašina, Radovan (referee) ; Starý,, Vladimír (referee) ; Svoboda, Milan (referee) ; Švejcar, Jiří (advisor)
Electron microscopy has become an essential component in many scientific fields, in which it contributes to new discoveries. The microscopy itself is continually being developed and the limits, which seemed to be insurmountable, have been overcome. The instruments have become user friendlier and their mobility enables flexible practical use in the field. The subject of this work is the design of a scanning electron microscope, the calculation of a magnetic curcuit of an immersion objective combined with standard lens, the theoretical calculation of a microscope resolution and the design solution of the mechanical parts of the microscope with a sample manipulator. The thesis includes a description of the electron microscopy development summarizing it briefly from the very beginning up to now. It also deals with electron sources, especially the Shottky cathode, which is to be the main object observed by the proposed device. The work also contains a description of the calculation of the microscope resolution as a function of the current density distribution. Another interesting issue included in the theoretical part is the signal detection, a description of several types of detectors and possible signal processing. The solution of the thesis includes a description of the concept of the scanning electron microscope with an explanation of the distribution of combined lens functions. The optical diagram shows the arrangement of the electron optics system and the distibution of pressure in the chamber of the microscope. The theoretical calculation is devoted to the magnetic curcuit design of the objective and to the resolution of the microscope for a given extent of working distances. Two modifications of the lens were designed – a standard simple objective and a combination of the standard objective with the immersion magnetic one. The results of both modifications are given for the parameters to be compared. The combined objective was designed with the possibility of use in two modes, as a standard and immersion lens. The deflection system is also divided into two modes, as a single deflection for the standard lens and as a two-dimension deflection for the immersion lens. Detectors for secondary electrons (SE) and detectors for back scattered electrons (BSE) will be used for the signal detection. The design of the microscope is another large part, which gives details on the most significant components of the microscope. The content of the technical solution is a three-dimensional computer model, created in Autodesk Inventor, which also includes a sample manipulator driven by piezoelectric actuators.
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Evaluation of the machined surface and subsurface properties using Barkhausen noise analysis
Blažíček, Dominik ; Malec, Jiří (referee) ; Švejcar, Jiří (advisor)
Master thesis deals with the influence of milling to resulting surface integrity of gear tested by Barkhausen Noise Analysis technique. Two sets of gears milled by different machines by comparable parameters were used to solve the task. The testing of surface integrity was carried out after heat treatment and final grinding. It was experimentaly approved the effected surface/subsurface damage caused by milling remains in the material through the heat treatment. Based on these results, it can be assumed that different milling affects the resulting surface integrity after HT.
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Development of Nanofabrication Methodology for Study of Mechanical Properties of Thin Films using Focused Ion Beams
Kuběna, Ivo ; Švejcar, Jiří (referee) ; Kruml, Tomáš (advisor)
The main goal of this work is to find a methodology of the fabrication of microcompressive specimens (pillars) from thin metallic film prepared by means of PVD. The studied film was prepared by the ON Semiconductor company, Roznov pod Radhostem. Its chemical composition was Al-1.5 wt.% Cu; such films are used for electric connections on integrated circuits. At first, a thin intermediate layer of W-10 wt.% Ti was deposited on the Si single crystalline substrate with the purpose of improving adhesion properties of the studied film. The geometry of the microcompressive specimen should be as close to the cylindrical shape as possible. The height of the cylinder is given by the film thickness, its diameter is approximately 1 m. Such specimens were prepared in Quanta 3D FEG Dual BeamTM facility using focused ion beams technology. Experiments were done at FEI Company in Brno. In total, 39 microcompressive specimens were prepared at various ion milling conditions. The required geometry was finally attained by the optimization of processing parameters, in particular the parallelism of lateral faces was improved, the bottom of the removed zone in the vicinity of the pillar was almost flat and the transition pillar – flat bottom was regular. The prepared pillars are suitable for the microcompression tests; the first of them have been already performed within the cooperation with the Institut of Physics, Academy of Sciences of the Czech Republic, Praha.
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Application of Homogenization Annealing to Suppress Silicon and Nickel Segregation in Ductile Iron
Pavloušková, Zina ; Zemčík, Ladislav (referee) ; Vřešťál, Jan (referee) ; Švejcar, Jiří (advisor)
This doctoral thesis deals with the comparison of different methods of alloying elements’ concentration measurement based on energy dispersive spectroscopy and also with the suitability of particular methods of quantitative assessment of heterogeneity of the spheroidal graphite cast iron matrix. The segregation curves construction, distribution coefficient and heterogeneity index formulation is also discussed. The notion “normalized distribution coefficient” is introduced newly. The goal of the thesis, which is to be achieved by means of evaluation of large experimental data sets, is the evaluation of applicability of homogenization annealing of spheroidal graphite cast iron with the aim to eliminate segregation of silicon, and mainly nickel, as pearlite- and carbide-forming agent at the border of an eutectic cell. The result is an optimized homogenization annealing schedule maximizing the suppression of silicon and nickel segregation while taking into account the minimization of financial expenses and risk of grain coarsening.
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Processing and Structural Stability of Nanocrystalline Thermal Barrier Coatings
Jech, David ; Ctibor, Pavel (referee) ; Ziegelheim, Jindřich (referee) ; Švejcar, Jiří (advisor)
Complex thermal barrier coating systems are one the most efficient high-temperature surface treatments which open up practical applications in land-based turbines and air jet engines. In the case of most exposed rotor and stator jet engine components, the combination of thermal barrier coatings together with the inner cooling system made it possible to increase working temperature by several tens of degrees of Celsius. Nevertheless, it is very difficult to achieve any further increase in working temperature by using the conventional thermal barrier coatings based on the ZrO2-Y2O3 ceramic top coat and the MCrAlY metallic bond coat, which currently work at their material limits. The working temperature inside the combustion chamber of the jet engine is proportional to engine’s efficiency and inversely proportional to fuel consumption and production of undesirable CO2 emission. Therefore, a considerable effort has recently been devoted to research and development of new types of ceramic coatings that can withstand long term extreme working conditions. New design approaches of multi-layer composite thermal barrier coating systems can sustain the required trend of increasing working temperature of jet engines mainly because of possibility of optimization of high-temperature durability and long lifetime. The theoretical part of thesis provides a fundamental overview of thermal barrier coatings, their properties, deposition technologies and testing methods. The experimental part is focused on optimization of deposition parameters of conventional ZrO2-Y2O3 / MCrAlY thermal barrier coatings prepared by means of atmospheric plasma spraying. Furthermore, a novel multi-layer thermal barrier coating system based on ZrO2-Y2O3-Al2O3-SiO2 / ZrO2-Y2O3 / MCrAlY, which contains amorphous and/or nanocrystalline regions, is developed, tested and characterized as well. Structural stability, phase transformations and growth of the thermally grown oxide in both conventional and experimental systems after high-temperature isothermal oxidation, cyclic oxidation and burner-rig tests were evaluated by means light microscopy, scanning electron microscopy with energy-dispersive microanalysis and X-ray diffraction. In comparison with the conventional thermal barrier coatings, the novel multi-layered systems have lower thermal conductivity, slower thermally grown oxide kinetic, better structural stability, and generally higher lifetime in all high-temperature tests.
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Application of Electron Backscatter Diffraction in Materials Engineering
Man, Ondřej ; Vodárek, Vlastimil (referee) ; Svoboda, Milan (referee) ; Švejcar, Jiří (advisor)
The thesis deals with principles and common applications of the electron backscatter diffraction (EBSD) method. Some practical experience in application of the method to a study of highly deformed structure of copper and its thermal stability is described on one hand, and, on the other hand, to a study of phase composition of TRIP steel on various levels of imposed strain. The limitations of EBSD method are discussed along with its resolution in comparison with other complimentary techniques.
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Advanced Abrasion Resistant Coatings for Vacuum Systems
Hégr, Eduard ; Kudláček,, Petr (referee) ; Hrubý, Vojtěch (referee) ; Švejcar, Jiří (advisor)
The thesis is focused on research of advanced surface resistant coatings which have a direct effect on increasing of functional properties of vacuum systems (eg reducing wear of individual pump components, surface inertia to aggressive gases/molecules). But they can also secondarily affect other important pump properties (eg reducing pump temperature). The studied layers/coatings are divided into three areas (i) hard anodic layer, (ii) hard anodic layer with PTFE coating and (iii) DLC coating. The initial material (substrate) is an aluminum-based alloy, which was used for this purpose. In presented thesis, the influence on increase of material and physical properties was demonstrated, such as the increase of hardness and abrasion resistance of the surface after the application of the anodic layer with PTFE coating. The theoretical part of thesis describes the basic principles of preparation of abrasion-resistant layers/coatings and also introduces the vacuum physics. It shows the basic principles of obtaining vacuum, which give a comprehensive picture of the importance of working with advanced coatings. The experimental part is divided into the evaluation of the microstructure of the sample material and the second part is focused on the experiments needed to obtain/measure the required properties, which can be further used to predict damage of the layers/coatings.
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