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PROGRESSIVE PRODUCTION PROCESSES AND SIMULATION OF STRUCTURES AND PROPERTIES OF SPHEROIDAL GRAPHITE CAST IRON
Musilová, Iveta ; Mores, Antonín (referee) ; Pacal, Bohumil (referee) ; Šenberger, Jaroslav (advisor)
The thesis is concerned with relationships between progressive technological processes of spheroidal graphite cast iron’s production and their structural properties. The aim of the work is to explain causal relationship between parameters of the proposed manufacturing technology of the iron type given (involving selected variants of modification and inoculation of melt and the parameters of melt crystallization, solidification and cooling down in a mould), their structure and even chemical heterogeneity of elements in this structure. For close specification of presented relationships three-dimensional model of spheroidal graphite growth was used, which was developed at the Brno University of Technology, Faculty of Mechanical Engineering. Its usability in praxis has been verified on the basisis of the application of this model on experimentally acquired data. The U GRAFIT 20 model of the authors Stránský and Million counting segregation in the frame of eutectic cell has not still been used for prediction of segregation in real condition in greater extent. On the basis of the above mentioned model microsegregation within “on average” of the cell has been discovered during experimental melts. Microsegregation has been described by segregation and heterogeneity indexes. Calculated values of segregation and heterogeneity indexes have been compared with experimentally verified values. On the basis of comparison of calculated and measured values the possibility of further usage of the mentioned model in praxis has been explored.
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FATIGUE CHARACTERISTICS OF MODIFIED MAGNESIUM ALLOYS AFTER CORROSION DEGRADATION
Němcová, Aneta ; Očenášek, Vladivoj (referee) ; Hadzima, Branislav (referee) ; Pacal, Bohumil (advisor)
This doctoral thesis deals with the determination of the influence of plasma electrolytic oxidation (PEO) on fatigue behaviour of extruded AZ61 magnesium alloy in air and in the 3.5% NaCl solution. The coatings were formed in the silicate-phosphate electrolyte under pulsed current conditions at a frequency of 50 Hz. The influence of current density on coating formation was examined under current densities of 70, 130 and 200 mA cm-2 for different durations up to a maximum of 1800 s. 8 g dm-3 of KF were added to the electrolyte to study the influence of fluoride ions in plasma electrolytic oxidation. It is shown that fluoride ions inhibit localised oxidation in the initial stage of the process, associated with the secondary particles based on Al–Mn. The presence of fluoride also modified the sparking characteristics, decreased the rate of coating growth and changed the morphologies of the coatings. The influence of fluoride on the coating hardness, and the corrosion resistance of the alloy during exposure to salt spray, was negligible. Based on previous optimised PEO conditions, coatings formed under a current density of 130 mA cm-2 for 300 s in the electrolyte containing KF were chosen for fatigue testing. The high-cycle fatigue tests were carried out on cylindrical samples under a force controlled sinusoidal tension-tension cycle with asymmetry parameter R=0. The experimental data were fitted with Kohout & Věchet function. The fatigue limit of uncoated alloy in air for 107 cycles was determined at 145.4 MPa and the combination of PEO coating with chloride ions caused a reduction of ~55 %. Attention was paid to the fatigue crack initiation in different conditions of cyclic loading. The fracture surfaces underwent detailed fractography analysis including secondary crack observation on the gauge length. The contribution of Al–Mn particles were confirmed on the uncoated alloy in air and the presence of chloride ions were observed as another influential contributor to local corrosion attack. The cyclic loading caused spalling of the outer layer, and the multiple initiation was observed on PEO coated alloy, caused by cracks in the coating and stress transferring to the alloy.
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Structure and Properties of Selected Magnesium Cast Alloys
Svozil, Libor ; Pacal, Bohumil (referee) ; Podrábský, Tomáš (advisor)
Microstructure and mechanical properties of AZ91 magnesium alloy after die cast (casting under pressure) and squeeze casting were comparated. The compare of incident phases, their microhardness, gas bubbles in the alloy, hardness and other mechanical properties of alloy are included in this work. For compare has been used a light microscopy, tensile test, hardness and microhardness measurements, image analysis and scaning electron microscopy.
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Evaluation of corrosion on selected aluminium alloys
Skýba, Pavel ; Tulka, Jaromír (referee) ; Pacal, Bohumil (advisor)
The thesis focuses on the corrosion research of AlCu4Mg1 aluminium alloys of square shape and sheet metal coated in 99.5% aluminium. The theoretical part deals with the characteristics of aluminium, the classification and naming of aluminium alloys and the impact of admixtures on aluminium alloys. In the following chapter a general introduction to metal corrosion, its differentiation according to the type of corrosion attack, mechanisms of corrosion, the impact of corrosive environment, according to the choice of anti-corrosion protection, etc. is given. The main part is devoted to the corrosion of aluminium with a special importance of the impact of admixtures on aluminium alloys, the types of corrosion attack, the impact of corrosive environment as well as of the anti-corrosion protection of aluminium alloys. The corrosion tests in controlled atmosphere are considered in the next chapter, while the last one deals with the evaluation methodology of the process of corrosion. At the beginning of the experimental part all the used samples and materials are introduced. The thesis continues then with an overview and a description of the methods used for experiments. The measurement procedure and the results of the experiments are presented in the following chapter that focuses on the metallographic analysis of the aluminium alloy samples before the experiment and after the corrosion attack. The main part of the chapter deals with the dependence of corrosion speed of the individual aluminium alloy samples on time after being exposed in the climate chamber and the salt fog chamber
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Structural-mechanical characteristics of the selected type of low-carbon steel after cold drawing and heat treatment
Stopka, Maroš ; Molliková, Eva (referee) ; Pacal, Bohumil (advisor)
This bachelor's thesis focuses on changes in the mechanical properties of low-carbon wire that has been cold-drawn and subsequently heat-treated. Mechanical tests, from which the values of elongation, yield strength and tensile strength were measured, were performed on all samples within 24 hours after they were collected. Two different production rates were established on the hot dip galvanizing line to achieve different time intervals of the annealing process. The experiment was performed at all stages of wire diameter reduction, including the input material. This work also includes metallographic analyzes of samples that have been both polished and etched. The most representative samples were selected for analysis. The results show that deformation caused changes in mechanical properties and an increase in strain hardening, which was subsequently removed by heat treatment.
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Phase Transformations during Heat Treatment of Fe - C Materials
Škvarka, Jakub ; Pacal, Bohumil (referee) ; Molliková, Eva (advisor)
The goal of this thesis is a study of heat treatment of iron-carbon alloys from a physical angle. Characteristics of main components from this system and their modifications are described there. There is also described what is going on during heat treatment especially from an angle of thermodynamics and kinetics, thanks to available information from literature. The knowledge is applied on specific types of heat treatment of material and processes which can follow it.
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Processing of Mg-based powder materials by SPS method
Moleková, Kristína ; Pacal, Bohumil (referee) ; Doležal, Pavel (advisor)
Diploma thesis occupy with preparation of porous material from magnesium powder with a HAp admixture by cold pressing followed by spark plasma sintering (SPS). This thesis contain both preparation of bulk material, diffusion plot and charakterization of materials based on the compaction process conditions. On the basis of physical mechanical characteristics, the impact of the pressing process on the subsequent sintering and the resulting material properties are evaluated. Bulk material is characterized considering to structure and physical–mechanical properties. Properties of final metarial will serve to optimize conditions for process of bulk material preparation.
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