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Advanced metallographic techniques for aluminum and its alloys
Rychlý, David ; Gejdoš, Pavel (referee) ; Mikmeková, Šárka (advisor)
Hlavním cílem této práce je optimalizovat metalografickou přípravu hliníku pro specifické potřeby rastrovací elektronové mikroskopie. Rastrovací elektronová mikroskopie je velice citlivá na kvalitu připraveného povrchu a základní metody přípravy užívané pro světelnou mikroskopii jsou nedostatečné. Práce se zaměřuje na optimalizaci a hledání nových metalografických metod, které splňují vysoké požadavky rastrovací elektronové mikroskopie. Povrch musí být připraven co nejkvalitněji, bez defektů a artefaktů z přípravy. Jako testovací materiál pro experimenty byl vybrán čistý hliník. Základní a pokročilé metody přípravy byly experimentálně testovány a nejvíce slibné postupy poté optimalizovány. Několik různých variant přípravy povrchu bylo vyzkoušeno v rámci metod koloidních silik a elektrolytického leštění. Připravený povrch byl následně zkoumán pomocí světelné mikroskopie, rastrovací elektronové mikroskopie s nízkými urychlovacími napětími a konfokální mikroskopie. Závěrem byl stanoven optimální metalografický postup vyhovující vysokým požadavkům elektronové mikroskopie a zajišťující připravený povrch s minimem defektů.
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Microstructural classification of multiphase steels by advanced microscopy and image analysis techniques
Jozefovič, Patrik ; Materna, Jiří (referee) ; Mikmeková, Šárka (advisor)
Austenitické nerezové ocele si vďaka svojim charakteristickým vlastnostiam našli uplatnenie naprieč rôznymi sektormi. Metastabilný charakter niektorých z nich, ktorý umožňuje martenzitickú tranformáciu so sebou však prináša určité riziká spojené s poklesom húževnatosti. Na odhalenie martenzitickej fázy v mikroštruktúre oceli sa v dnešnej dobe využívajú techniky ako je napríklad difrakcia spätne odrazených elektrónov v rastrovacom elektrónovom mikroskope. Difrakcia spätne odrazených elektrónov je však veľmi časovo náročná a takisto kladie vysoké nároky na kvalitu metalografickej prípravy vzoriek. Cieľom tejto práce je nájdenie iných techník, umožňujúcich separáciu fáz v metastabilnej austenitickej oceli v rastrovom elektrónovom mikroskope, ako aj optimalizácia metalografickej prípravy tejto oceli pre potreby elektrónovej mikroskopie. Po naplnení týchto cieľov sa táto práca zameriava na možnosť využitia takzvaného hlbokého učenia za účelom automatizovanej separácie fáz v mikrosnímkach z rastrovacieho elektrónového mikroskopu. Pre tieto účely boli natrénované 4 neurónové siete založené na rôznych architektúrach a ich výsledky boli následne porovnané.
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Characterization of Automotive High-Strength Steels Using an Electron Microscope
Báborský, Tomáš ; Jánský, Pavel (referee) ; Mikmeková, Šárka (advisor)
The diploma thesis deals with the determination of the structure of AHSS steels and offers solutions in the form of new observation methods with the aid of a scanning electron microscope using filtration of slow secondary electrons. The thesis describes electron filtration in order to display secondary electrons in a certain energy range which carry a surface information that is not normally visible. The advantages and benefits of such observation are clearly demonstrated.
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Study of beta phase in Al-Mg-Si alloys by means of unconventional methods of electron microscopy
Ligas, Aleš ; Julišová, Martina (referee) ; Mikmeková, Šárka (advisor)
Aluminium Al-Mg-Si alloys are the most commonly used in automotive and construction industry. Hexagonal ’-phase is one of the metastable phases occured in this type of alloys. Unlike classic square -phase, this ’-phase is characterized by different crystalographic orientation to the matrix and shape. Standard method used for identification of aluminium alloys is scanning electron microscopy (SEM), because of its quickness and efficiency, but in case of very thin or damaged structures (as a result of metallographic process) it’s insufficient. Scanning low energy electron microscopy (SLEEM) can be appropriate for identification of mentioned precipitates due to its physical principles resulting in many advantages compared to SEM. So the most important benefits are interaction volume reduction (which leads to improvement of surface sensitivity), increase of material contrast (ability to change matrix / precipitates contrast) as well as crystalographic contrast.
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Design of automated electro-polishing apparatus for electron microscopy specimens preparation
Čermák, Jan ; Szabari, Mikuláš (referee) ; Mikmeková, Šárka (advisor)
This diploma thesis deals with the automation of the electropolishing process, which is per-former as the last step in the preparation of metallographic samples intended for observation in an electron microscope. A complete hardware design of a single-purpose machine has been developed, which provides the automatic preperation of up to six samples per insertion. There was the design of a manipulator for sample handling together with chemically re-sistant sample holder suitable for automatic operation as a part of solution. The design of the whole machine was developed with regard to the safety of the operator. The thesis includes detailed 3D model of the device and the desing of an application for measurement in the LabVIEW. It describes the future working process of the machine, including a description of a software for controlling the machine and sending process data of each sample to the to the database in accordance with the principles of industry 4.0. In the conclusion, the achieved results and the proposal of further steps necessary for the realization of the machine are for-mulated.
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Study of metals by low voltage SEM
Ligas, Aleš ; Jánský, Pavel (referee) ; Mikmeková, Šárka (advisor)
The aim of this thesis is to demonstrate the advantages of the scanning low energy electron microscopy (SLEEM) in the field of materials science. The SLEEM can be very effectively used for investigation of wide range of materials, such as steels, alloys, ceramics and thin films. Experimental part of this work was performed on the scanning electron microscope TESCAN VEGA TS 5310 equipped with cathode lens mode at Institute of Scientific Instruments of the ASCR, v.v.i..
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Microstructure modifications of Al-Si-coated press-hardened steel 22MnB5 by laser welding
Šebestová, Hana ; Horník, Petr ; Mika, Filip ; Mikmeková, Šárka ; Ambrož, Ondřej ; Mrňa, Libor
Weld microstructure depends on the characteristics of welded materials and parameters of welding technology, especially on the heat input that determines the peak temperature and the cooling rate. When the coated sheets are welded, the effect of the chemical composition of the coating must be also considered even though its thickness is only a few tens of microns. During 22MnB5+AlSi laser welding experiments, the ferrite-stabilizing elements of coating modified the weld metal microstructure. Ferrite appeared in a quenched weld metal. The rapid cooling rate accompanying welding with a focused beam limited the homogenization of the weld metal which resulted in the formation of ferritic bands in the regions rich in Si and especially in Al. On the other hand, a high level of homogenization was reached when welding with the defocused beam. The ferritic islands uniformly distributed in the weld metal were formed at 0.4 wt% and 1.6 wt% of Si and Al, respectively. The doubled heat input reduced the Al content to 0.7 wt% insufficient for the ferrite formation at still relatively high cooling rates. Predicting the distribution of ferrite in the weld metal is challenging due to its dependence on various factors, such as cooling rate and the volume of dissolved coating, which may vary with any modifications made to the welding parameters.
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Automation of metallographic sample cleaning process
Čermák, Jan ; Ambrož, Ondřej ; Jozefovič, Patrik ; Mikmeková, Šárka
Specimen cleaning and drying are critical processes following any metallographic preparation steps. The paper focuses on automation by reason of absence of the process repeatability during manual sample handling. An etchant or electrolyte results in inhomogeneous surface quality because the solution runs off the specimen surface during its removal from the beaker. High-quality specimen cleaning is absolutely crucial for the acquisition of the specimen suitable for characterization by a scanning electron microscope operated at very low landing energies of the primary electrons (SLEEM). The SLEEM technique is a powerful tool for the characterization of advanced steels, as described by many scientific papers. The SLEEM requires the specimen absolutely free of water and any organic residues on the surface. This work presents a novel unique apparatus enabling automatic specimen cleaning and drying after the etching or electropolishing processes. Automation reduces the influence of dependent variables that would be introduced into the process by the metallographer. These variables include cleaning time, kinematics, and motion dynamics, but the process can also be affected by variables that are not obvious. Performed experiments clearly demonstrate our in-house designed apparatus as a useful tool improving efficiency and consistency of the sample cleaning process. The high quality of the specimen surface is verified using a light optical microscope, an electron scanning microscope, and above mentioned SLEEM technique.
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Welding of Al-Si coated high-strength steel 22MnB5
Šebestová, Hana ; Horník, Petr ; Mikmeková, Šárka ; Novotný, Jan ; Mrňa, Libor
Al-Si-based coatings are widely used as surface protection of steel sheets against high-temperature oxidation during the hot stamping process. Laser welding is a suitable technology for hardened components joining because it does not produce a wide heat-affected zone with a degraded microstructure. The highly concentrated energy of the laser beam is responsible for rapid heating and subsequent rapid cooling of material which results in insufficient homogenization of the weld metal. In Al-rich areas (Al originates from the coating), ferritic bands are formed in the dominantly martensitic matrix. These bands decrease the strength of laser weld by more than one third compared to the base metal. The low-power electric arc placed immediately behind the laser beam can help to achieve a slower cooling of the weld metal, reduce the ferritic bands and increase the strength of weld joints up to 90 % of base metal tensile strength.
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