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Recrystallization study of free-cutting steel by in-situ SEM/EBSD technique
Babinský, Tomáš ; Němec, Karel (referee) ; Petrenec, Martin (advisor)
Placing recrystallization annealing in a manufacturing proces is often necessary in order to restore plasticity of worked blanks right before working products to its final shape. For better understanding of processes which are taking place in a material during annealing the use of in-situ techniques is favorable. Such observations enable us to watch changes in the materiál in real time at the original spot. Observations at grain-level are ideally made with scanning electron microscope – SEM by electron back-scattered diffraction – EBSD. The technique makes watching nucleation, growth and potential coarsening of recrystallized grains possible. Special construction of a tensile stage allows us to watch changes of a sample during tensile tests which can be used in observing influence of MnS inclusions on plasticity of free-cutting steels. Materials studied in this work are commonly used free-cutting steel 11SMnPb30 and its lead-free alternative 11SMnBi30.
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New analytical techniques for the study of amber inclusions
Škorpíková, Šárka ; Prokop, Jakub (advisor) ; Sakala, Jakub (referee)
Amber is an amorphous organic material, a fossil plant resin, mostly produced by Mesozoic and Cenozoic wetland trees. It was often used in jewelry in the past. However, together with the development of paleobiology it has begun to be used as an object of scientific studies, due to its unique abilities to conserve various inclusions in their three-dimensional matter and unusual preservation of their structures. These facts show its important role in the reconstruction of past ecosystems and organism interactions. Various groups of insects and chelicerates groups are typical inclusions that can be found in fossil resins. But the spectrum of these fossil organisms is much wider - from unicellular to vertebrates. For menaningful research of fossil material, precise analytic observations methods are necessary. Their development made a huge progress in last few years. This thesis summarizes the overview of some of these methods and also of inclusions described in several past years from various amber deposits (review of major deposits is included). Powered by TCPDF (www.tcpdf.org)
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Dynamics of structural defects in CdTe-based semiconductors
Bugár, Marek ; Belas, Eduard (advisor) ; Holý, Václav (referee) ; Fochuk, Petro (referee)
Title: Dynamics of structural defects in CdTe-based semiconductors Author: RNDr. Marek Bugár Institute: Institute of Physics, Charles University in Prague Supervisor of the doctoral thesis: Doc. Ing. Eduard Belas CSc.; Institute of Physics, Charles University in Prague Abstract: The work was aimed at investigation of the effect of annealing on structural, electrical and optical properties of CdZnTe epitaxial substrates and CdTe-based and CdZnTe-based X-ray and gamma-ray detectors. The first part of the work is focused on investigation of structural properties of one type of second phase defects - inclusions - present in the material, which degrade the material quality. Consequent annealing experiments were aimed at reduction of these defects. In case of CdZnTe substrates, an annealing treatment leading to increase of the infrared transmittance was investigated. On the other hand, annealing experiments on the detectors of high-energetic radiation were focused on preservation of the high-resistive state. Moreover, the work contains detailed measurements of transport properties of CdTe taken directly at high temperatures. Key words: CdTe, annealing, inclusions, detectors, defects
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Influence of using the secondary metallurgy on steel properties
Navrátil, Horymír ; Fila, Pavel (referee) ; Záděra, Antonín (advisor)
This bachelor thesis describes metallurgical processes of production of steel in electric arc furnaces. It also describes oxidation and reduction phases of melting. Furthermore, it describes the main elements of secondary metallurgy used in steel foundries and their applications. The thesis also concerns with impurities in the steel, namely non-metallic inclusions, gases and trace elements, which is also connected with final utility properties of the steel. This thesis also describes in detail the technological properties of steel. The influence of several selected elements on steel properties is also described. Finally, the thesis evaluates the effect of secondary metallurgy on the volume of defects in steel castings, on mechanical properties and the resulting chemical composition.
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Metallurgy and properties of heavy steel castings
Kubík, Jiří ; Čech, Jan (referee) ; Záděra, Antonín (advisor)
The work deals with the determination of the chemical composition and morphology of inclusions in experimental casting foundry in operating conditions as ŽĎAS in compliance with the optimum content appropriate deoxidation depending on the conditions of solidification. The introductory part is devoted to theoretical analysis of possible defects in castings. We also describe the experimental casting, sampling sites and their markings. Subsequently evaluated morphology microanalysis inclusions and the effect of inclusions on the mechanical properties and the formation of defects in the casting. The conclusion summarizes the results and proposal for further direction in the production of heavy steel castings.
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Reoxidation in steel
Kotásek, Petr ; Veselý, Pavel (referee) ; Šenberger, Jaroslav (advisor)
This work is about development and methodology verification of data collection which will be used in the research of the reoxidation in steel castings. To examine reoxidation rate will be measured oxygen activity in the furnace, in the ladle and in the mould. Next it will be evaluated the chemical structure of mould slag, the chemical changes of steel and measured the volume and the area of the casting defects. Each technique is briefly described by the principle of measurement and each method has the results which are analysed. In the conclusion the experiment is summarized and there are mentioned the observations from this experiment.
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Influence of filters on running of metal flow
Makalouš, Jakub ; Veverka, Aleš (referee) ; Roučka, Jaromír (advisor)
This study deals with influence of filters on running of aluminum metal flow. The main objective was to describe hydraulic resistances of assorted filters and running of silting filters by inclusions. Theoretical part generally describes filtration process and also filtration from the point of view of aluminum alloys and the most important characteristics of each type of alumina inclusions. Experimental part deals with flow rate tests, influence of filters on gassiness of melt and metallographic analysis. It was find out, that filter GEPHAL made minimal hydraulic resistance, on the other hand ceramic foam filters type LD made the maximal hydraulic resistance. It is necessary to reduce filtration surface for study running of silting filters by inclusions. Metallographic analysis showed amorphous alumina film inclusions, spinell Al2O3.2MgO, sludge and carbide of silicon.
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Filtration of foundry alloys
Šíma, Jakub ; Láník, Boris (referee) ; Tomek, Ladislav (advisor)
Presented bachelor work deals with filtering of casting alloys. This issue is described with focus on the importance of filtration, the requirements placed on filters, a description of the filtering mechanisms, the influence of using filters on the melt flow, types of filters and options include filters in the gating system of casting. The second part contains case studies of the use of ceramic foam filters in foundry and analysis of samples taken from a particular casting.
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