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Measurement of mechanical properties of thin films using the bulge test technique
Holzer, Jakub ; Cieslar, Miroslav (referee) ; Kruml, Tomáš (advisor)
Main objective of this diploma thesis is to finish a construction of the Bulge test apparatus for measurement of thin films, perform first tests on commercially available Si3N4 membranes and bilayer membrane with aluminium. First part of the thesis is focused mainly on literature review of current knowledge regarding this topic and other methods of thin films testing. Experimental part deals with construction of apparatus, methodology of data evaluation and results of the measurement. The thin films of interest are fabricated as amorphous silicon nitride or bilayer of mentioned nitride and either aluminium, titanium or Ta-B-C layer. The apparatus has been built in house in collaboration with Institute of Scientific Instruments of CAS. Both reliability and repeatability of this method has been tested on over 160 measurements of commercially available membrane. The results of measurements are compared with literature and nanoindentation test. More detailed data analysis is currently under development with colleagues at Institute of Physics of Materials. It has been proven beyond doubt that Bulge test method and constructed apparatus are suitable for the measurement of several mechanical properties of thin films.
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Stability of dispersoids in aluminium alloys at elevated temperatures.
Králík, Rostislav ; Cieslar, Miroslav (advisor)
The AA8079 aluminum alloy prepared by twin-roll casting is commonly used as foil stock for manufacturing of thin packaging foil. Due to the nature of the casting method and material composition microstructure of the material is not homogenous and contains a fraction of intermetallic particles clustered in eutectic colonies. As such, the material requires heat treatment before further processing. Different temperatures of homogenization annealing affect the microstrucutre of the material in different ways. The homogenized material then undergoes a series of rolling passes which causes work hardening. A recrystallization annealing is required at an intermediate gauge before rolling to final thickness to restore ductility of the material. Recrystallization behavior is affected by the present intermetallic particles, their size and distribution. The influence of different homogenized microstructures on control of the recrystallization process through was studied, recrystallization kinetics were evaluated and two main influencing mechanisms - particle stimulated nucleation and Zener drag were identified.
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Microstructure of non-equiblirium Al-Mn based solid solutions
Poková, Michaela ; Cieslar, Miroslav (advisor) ; Karlík, Miroslav (referee)
Heat exchangers in automotive industry are often manufactured from aluminum-based alloy AW 3003. In recent time, the aim to reduce the weight of the cars leads to thickening of the foils, which are used for manufacturing of the heat exchangers. In order to fulfill all requirements on mechanical properties of the exchanger, new materials and thermo-mechanical treatments have to be found. Modified alloy AW 3003 with addition of zirconium seems to be perspective. Zirconium forms metastable precipitates Al3Zr, which pin moving grain boundaries and shift recrystallization to higher temperatures. The most effective heat treatment, which leads to precipitation of these particles, seems to be a two-step annealing at temperatures 250 řC and 450 řC with slow heating rate. The precipitates formed were of diameter 10 nm.
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Stability of dispersoids in aluminium alloys at elevated temperatures.
Králík, Rostislav ; Cieslar, Miroslav (advisor) ; Michalcová, Alena (referee)
Hliníková slitina AA8079 připravena plynulým odléváním mezi válce je běžně používána pro výrobu tenké potravinářské fólie. Vzhledem k použité metodě odlévání a složení slitiny je struktura litého materiálu značně nehomogenní a obsahuje intermetalické fáze, které se shlukují v eutektických koloniích. Litý materiál tak vyžaduje tepelné zpracování před dalšími kroky výroby. Mikrostruktura materiálu po homogenizačních žíháních na různých teplotách je rozdílná, což ovlivňuje další zpracování. Po homogenizaci je materiál válcován což způsobuje snížení tažnosti. Rekrystalizační žíhání je vyžadováno po zválcování na střední tloušťku před finálním válcování, aby byla tažnost obnovena. Chování materiálu během rekrystalizačního žíhání je ovlivněno přítomnými fázemi, jejich velikostí a rozdělením. Byl studován vliv mikrostruktury po homogenizaci na rozdílných teplotách na rekrystalizaci, byla vyhodnocena kinetika rekrystalizace a byly identifikovány dva hlavní mechanismy ovlivňující rekrystalizaci - částicemi stimulovaná nukleace a Zenerův tlak.
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Influence of deformation on precipitation processes in commercial Al-based alloys with Sc,Zr-addition
Leibner, Michal ; Vlach, Martin (advisor) ; Cieslar, Miroslav (referee)
1 Abstract: Mechanical and thermal properties of Al-5.4wt.%Zn-3.1wt.%Mg-1.5wt.%Cu (AA- 7075), Al-5.2wt.%Zn-3.0wt.%Mg-1.4wt.%Cu-0.2wt.%Sc-0.1wt.%Zr (AA-7075-ScZr) and Al-2.93wt.%Mg-0.34wt.%Mn-0.33wt.%Si-0.22wt.%Fe-0.19wt.%Cr-0.24wt.%Sc-0.06wt.%Zr (AA-5754-ScZr) alloys in as-cast and cold-rolled states were studied by differential scanning calorimetry and microhardness measurements. The initial values of microhardness reflect an effect of cold-rolling. The Sc,Zr-addition caused a pronounced hardening during annealing above ~ 300 řC. An easier diffusion of Zn, Mg, Cu and Mn atoms along dislocations led to a precipitation of Zn,Mg,Cu-containing and Mn-containing particles at lower temperatures in comparison with the AA-7075(-ScZr) and AA-5754-ScZr alloy in the as-cast state, respectively. The Sc,Zr-addition does not significantly influence precipitation of the particles form the Al-Zn-Mg-Cu system.
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Properties of thin films studied by in-situ TEM
Bajtošová, Lucia ; Cieslar, Miroslav (advisor) ; Kopeček, Jaromír (referee)
Mechanical properties of widely applicable thin nanocrystalline films have been a sub- ject of interest for some time due to deviation of their properties from the properties of bulk and micro sized grain materials. The deformation mechanisms in these materials are altered by restricted size of the material and high ratio of surface and grain boundary areas. Recent advances in transmission electron microscopy (TEM) allow direct obser- vations of the deformation mechanisms during nanoindentation or tensile deformation of the specimen. Thin Al films prepared by DC magnetron sputtering were deformed in situ in TEM and bright field TEM. High resolution TEM and automated crystallographic orientation mapping (ASTAR) were implemented to observe the ongoing deformation mechanisms. Molecular dynamic simulation designed to approach the conditions of per- formed experiment were used to visualize the deformation mechanisms on atomic scale and the reliability of both methods was discussed. 1
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Microstructure and properties of Al-Li based alloys
Belejová, Sára ; Cieslar, Miroslav (advisor) ; Málek, Přemysl (referee)
This bachelor thesis is devoted to a study of rapidly solidified metallic strips prepared from two Al-Li-based alloys of the third generation. The aim of the thesis is to provide initial information about this new class of materials that could find application in aerospace industry. Al-Li third-generation alloys differ from previous generations by a lower Li content and thus by a type of main reinforcing phases. However, since conven- tional processings have already exhausted their possibilities that would significantly im- prove mechanical properties of these alloys, less traditional methods are tested, including rapid solidification processing by a melt-spinning method. These materials can achieve exceptional properties after milling and compactization thanks to finer microstructure and higher supersaturation of the solid solution. LOM, TEM (STEM) observations, and EDX analyses were used for the examination of the microstructure. In-situ resistometric measurements and in-situ TEM heating were performed to investigate the phase transi- tions. The structure of the alloys changes during heating. Grains of both alloys do not contain large particles after annealing. Only newly-formed coarse particles were observed on grain boundaries. The added scandium and zirconium resulted in a formation of a fine...
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