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New methods of sample preparation for modern scanning electron microscopy
Ambrož, Ondřej ; Čermák, Jan ; Mikmeková, Šárka
Modern scanning electron microscopes (SEM) are equipped with a very sophisticated detection system that allows the detection of signal electrons by several differently located detectors simultaneously. Signal electrons are filtered according to energy and angle. Effective signal filtering in SEM together with the possibility of using very low impact energies of the primary beam leads to the extreme sensitivity of this method to the quality of the sample surface. Current metallographic methods of sample preparation are becoming insufficient for advanced imaging in modern SEM instruments. Classical sample preparation proves to be completely unsuitable especially for low-voltage scanning electron microscopy. The work will present the first results of the influence of preparation methods on the surface condition and the possibility of differentiating the individual phases of TRIP steel using advanced electron microscopy techniques. The possibilities of new procedures using robotics will be shown.
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Artifacts and errors in EBSD mapping of retained austenite in TRIP steel
Mikmeková, Šárka ; Jozefovič, Patrik ; Ambrož, Ondřej
The present work aims to demonstrate artifacts and errors in visualization of retained austenite phase in TRIP steel by an electron back-scattered diffraction (EBSD) technique. Retained austenite phases size and shape obtained by the EBSD are directly compared with a real image of these phases acquired by means of an atomic force microscopy (AFM). The effect of the step size parameter used for the EBSD analysis on the retained austenite phase fraction and morphology is discussed in detail and quantified. Surface roughness as a barrier for the imaging of fine features situated on a specimen surface is demonstrated.
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Apparatus for automatic chemical etching of metallographic samples
Ambrož, Ondřej ; Čermák, Jan ; Mikmeková, Šárka
The microstructure of steels after mechanical polishing is revealed only by the application of a suitable etchant. To achieve adequate optical or electron microscope images, the specimen surface must be free of any artifacts. Chemical etching can be defined as a controlled corrosion process. The metal of the investigated material passes as cations into the etchant solution during the chemical etching reaction. Chemical etching is usually performed manually either by immersing the sample in the etchant with simultaneous stirring or by swabbing with a lint-free cloth soaked in the etchant. It is also extremely important to debug the process of removing the sample from the bath and subsequent cleaning. It is recommended to wash the sample after removal from the etchant with water (distilled or demineralized) or alcohol (ethanol, methanol, or isopropyl alcohol) and dry it properly (depending on the etchant and the etched material). The main problem with these processes is the human factor, which significantly contributes to the already limited repeatability. All operation steps must be performed by properly trained personnel in the field of occupational safety because hazardous substances are handled. A high manual dexterity is also needed. Training a new employee is a long-term process. Moreover, keeping the exact etching time can be a challenge and one second can decide success. These problems become more serious in the case of using surface sensitive analytical method, such as a low energy scanning electron microscopy, due to the high spatial resolution and extreme surface sensitivity. We have developed an apparatus for automatic etching of metallographic samples of purpose to overcome all above-mentioned difficulties. The apparatus and results of the first experiments will be presented.
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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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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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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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Study of secondary phases in trip steel by advanced sem and afm techniques
Mikmeková, Šárka ; Ambrož, Ondřej ; Hegrová, J. ; Aoyama, T.
The paper aims to demonstrate a modern scanning electron microscope (SEM) as a powerful tool for visualization of the secondary phases in TRIP steel. The TRIP steel specimens prepared by various metallographic techniques were imaged by the SEM and the secondary phases presence was confirmed by an electron back-scattered diffraction (EBSD) technique. The chemical polishing by 5 % HF in H2O2 for 10 seconds results in selective etching for each individual phase, as confirmed by an atomic force microscopy (AFM) and hybrid AFM-in-SEM techniques. The phases are easily distinguishable in the SEM micrographs created by the low energy high take-off angle signal electrons. The proposed sample preparation technique together with special SEM imaging conditions enables us accurate analysis of distribution of secondary phases within the TRIP steel matrix and moreover, the retained austenite is distinguishable from the martensite phase.
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Trip steel specimen preparation for advanced sem and EBSD
Ambrož, Ondřej ; Mikmeková, Šárka ; Hegrová, J. ; Aoyama, T.
Modern scanning electron microscopy (SEM) allows observations of specimens with high surface sensitivity. The surface sensitivity is significantly affected by the accelerating voltages. With the development of the scanning electron microscopy, the requirements for the surface quality of samples increase. Metallographic methods originally intended for light microscopy become insufficient. The problem occurs especially with multiphase materials having a fine-grained structure. The investigated TRIP steel consists of a ferritic-bainitic matrix, retained austenite and martensite phases. The sizes of the smallest phases are nanometer units. The volume of residual austenite was determined by X-ray diffraction. The basic preparation of all tested samples involved conventional metallographic grinding and very fine mechanical polishing. One sample was analysed in this state. Other samples were subsequently chemically polished, electropolished and chemical-mechanically polished. The specimens were observed in the SEM using a SE and a BSE detector at low energies immediately after the preparation. An EBSD was performed in the same areas to characterize the retained austenite. Topographical imaging by special AFM, integrated into the SEM, demonstrated that the mechanical polishing results in surface deformation and residual austenite is transformed. All other methods have their specifics and for modern sensitive SEM instruments it is necessary to optimize individual procedures.
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Advanced methods of TRIP steel sample preparation and imaging using modern scanning electron microscope techniques
Ambrož, Ondřej ; Mikmeková, Šárka
Multiphase steels, including TRIP steels, excel in their mechanical properties and find application in many sectors, such as the automotive industry. Studying the microstructure of such materials is very difficult, especially with regard to the differentiation of phases. Current TRIP steels are failing in conventional characterization techniques and there is a demand for the development of new techniques that will enable precise characterization of phases on a nanoscale. The aim of this paper is to use benefit of modern scanning electron microscopy to characterize of individual phases in selected TRIP steel.
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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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