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Nickel coatings on magnesium alloys
Kosár, Petr ; Richtera, Lukáš (referee) ; Zmrzlý, Martin (advisor)
This diploma thesis is focused to nickel coatings on magnesium alloys. At the introduction of this work is briefly commented phase composition of AZ91 alloy, which is followed by detailed description of five very different theories of Ni-P coatings formation. Theoretical part is ended by review aimed to current states of development in areas of chemical nickel coating, influence of AZ91 alloy microstructure to current less deposition and possibility of surfactants influence to decrease of surface roughness. In experimental part of this thesis was the morphology and composition of Ni-P coatings including interlayers dependence on chemical composition of nickel-plating bath and magnesium alloy surface pre-treatment investigated using scanning electron microscopy and inverted optical microscopy. Average phosphorus content was obtained using energy dispersive analysis. Closing part of experimental part was dedicated for mechanical properties of coatings by micro-indentation analysis.
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Adhezion wear mechanisms of moving engine parts
Cahová, Kristýna ; Válka, Libor (referee) ; Jan, Vít (advisor)
The thesis describes adhesion wear on a contact area between Common rail and the component and deals with various effects on this kind of wear. The aim of the thesis is to gain information about adhesion wear phenomena and to understands its physical principals. Theoretical part deals with description of Common rail and then it is focused on research of adhesion wear. Experimental part firstly summarizes available data from tests that have been already done and then continues with analysis of microstructure of materials which are in contact during assembling process and the formation of adhesion wear is increased there.
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High-performance concretes based on the secondary raw materials
Sáček, Josef ; Brandštetr, Jiří (referee) ; Šoukal, František (advisor)
This work is devoted to study of physical-mechanical properties and structure of high performance concretes (HPC) based on portland cement. The attention is focused on possibility of substitution of economic high-cost components of concrete with utilization of secondary raw materials or cheaper components. Properties of raw materials and their influence on whole quality of concrete were tracked by various methods. Mechanical properties of prepared HPC samples were tested especially (compression and flexural strength) with further microscopic study of structure. Isoperibolic calorimetry and X-ray powder diffraction method were also used for concrete characterisation. These methods allowed to determine the influence of raw materials on prepared HPC and to carry out a certain optimization among price and quality of this material.
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Metal Matrix Composites Prepared by Powder Metallurgy Route
Moravčíková de Almeida Gouvea, Larissa ; Novák, Pavel (referee) ; Hadraba, Hynek (referee) ; Dlouhý, Ivo (advisor)
Vývoj nových materiálů pro součásti v moderních technologiích vystavené extrémním podmínkám má v současné době rostoucí význam. Děje se tak v důsledku neustále se zvyšujících požadavků průmyslových odvětví na lepší konstrukční vlastnosti nosných materiálů. Ve světle těchto faktů si tato studie klade za cíl posoudit nové složení slitin s vysokou entropií, které se vyznačují vysokým aplikačním potenciálem pro kritické aplikace. Slitiny jsou připravovány práškovou metalurgií, t.j. kombinací mechanického legování a slinování v pevné fázi. Pro účely srovnávaní vlastností jsou vybrané kompozice vyrobeny také tradičními metalurgickými metodami v roztaveném stavu, jako je vakuové indukční tavení a následné lití nebo vakuové obloukové tavení. Prášková metalurgie umožňuje postupný vývoj kompozitů s kovovou matricí (MMC) prostřednictvím přípravy oxidicky zpevněných HEA slitin. To je možné díky inherentním in-situ reakcím během procesu výroby. Když se naopak zvolí výrobní postup z taveniny, připravený kovový materiál vykazuje velké rozdíly v mikrostrukturách a souvisejících vlastnostech, v porovnání se stejným materiálem vyrobeným práškovou cestou (PM). Vyrobené práškové a tavené materiály jsou detailně charakterizovány s ohledem na komplexní vyhodnocení vlivu různých metod zpracování. Práce se zejména orientuje na mikrostrukturní charakteristiky materiálů a jejich mechanické vlastnosti, včetně vlivu tepelného zpracování na fázové transformaci a mikrostrukturní stabilitu připravených materiálů.
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Testing of Surge Arresters
Jeřábek, Lukáš ; Paar, Martin (referee) ; Krbal, Michal (advisor)
This bachelor's thesis is devoted to metal oxide surge arresters. After historical and theoretical introduction, which explains their principles and describes their characteristical properties, analysis of the standard IEC 60099-4 and testing according to the standard with focus on the type tests follows. This chapter is also amended with review of the standard's imperfections and with its most probable future development. The work concludes with a market survey, a review of the largest manufacturers and a comparison of their products.
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Study of the properties of fillers to the composites requiring high temperature resistance
Vovesný, Václav ; Gross,, Tomáš (referee) ; Bydžovský, Jiří (advisor)
The diploma thesis is focused on the behaviour of natural and synthetic aggregates and their behaviour in polymer – cement composites, while being exposed to high temperature. The processes, happening in aggregates and mortar under the thermal load, were described in the theoretical part of the thesis same as the testing of heat effects on the aggregates and mortar. Further, the influence of high temperature on each component of concrete was described, followed by the suggestion of the appropriate components for concrete exposed to high temperature. Various aggregates were tested in the experimental part of the thesis. The basic physical and mechanical properties of aggregates were examined same as their mineralogical composition with using XRD, DTA and SEM methods. At the mortar, the influence of high temperature on the concrete density, compressive strength and tensile strength was defined. The gained knowledge was evaluated in the final part of the thesis
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Properties of quasicrystal-reinforced high entropy alloys
Adami, Martin ; Tesař,, Tomáš (referee) ; Čížek, Jan (advisor)
This diploma thesis deals with the processing of the high-entropy alloys with the addition of quasicrystals by the spark plasma sintering method. The aim of this thesis is to evaluate the influence of quasicrystals content on the microstructure and wear resistance. The literature review part is divided into several section. The first part is an overview of high-entropy alloys and quasicrystals, including their properties and production methods. The next part pertains to spark plasma sintering and the wear phenomenon. In the experimental part, spark plasma sintering compacts were produced at 1100 °C and an analysis was performed using scanning electron microscope as well as X-ray diffraction and their tribological properties were measured by the pin-on-disc method. It was found that increasing the content of quasicrystals triggered an improvement in the compacts’ wear resistance.
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Structure and properties of welded joints of steam turbine rotor
Machala, Jan ; Hutařová, Simona (referee) ; Juliš, Martin (advisor)
This thesis deals with the assessment of the structural-mechanical properties of welded joints of steam turbine rotor. Experimental weld material is low alloy steel 30CrMoNiV5-11 in the state after the artificial degradation. The theoretical part of the literary researches the issue, focusing on the weldability of different types of steel used in the energy industry, the metallurgical processes in welding and provides an overview of the most important methods of welding. Great attention is paid to the evaluation of weld quality in accordance with relevant standards and destructive and non-destructive testing of welded joints. In the experimental part of this work was carried out measurements of hardness and microhardness of the weldment by Vickers and evaluation of the microstructure by light microscopy. The obtained values and information about the properties of the material after artificial degradation were compared with previously obtained experimental results in the default state (after annealing).
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Study of intermetallic phases in cast duplex steel
Ponížil, Ondřej ; Foret, Rudolf (referee) ; Pacal, Bohumil (advisor)
This thesis deals with the study of intermetallic phases in cast duplex stainless steel ASTM A890 Grade 4A considering degradation of mechanical properties in the result of isothermal aging in the temperature of 700 °C and 595 °C. The period of aging in the temperature of 700 °C was ranging from 1 to 160 hours and in the temperature of 595 °C it was ranging from 24 to 245 hours. The study of microstructure after aging in the temperature of 700 °C has proved that the -phases, Laves phases, chromium carbides and chromium nitrides were excluded. The phase was observed after four hours of aging in the temperature of 700 °C in / interface for the first time. The transformation was performed by eutectoid mechanism according to the equation + 2. The Laves phase has been observed after 10 hours of aging in / interphase and later in the ferrite grain as well. Chromium carbides and nitrides have created a continuous contour along to the / and /2 interface. After the temperature of 595°C there have been observed a large amount of small precipitates in the structure. The precipitates have been extracted from some selected samples to carbon replica. Following analysis has confirmed the presence of chromium carbides, -phases and Laves phases. The deterioration of mechanical properties, caused by the influence of secondary phase exclusion, has been confirmed by the Vickers hardness test and impact test including fractography analysis of the fracture surface. The hardness has an increasing tendency while the impact strength has been significantly reduced.
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