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Study of the effect of metallurgical and technological parameters on mechanical properties of aluminium alloys
Pešek, Jakub ; Krahula, Karel (referee) ; Zemčík, Ladislav (advisor)
Sugested thesis has been made with the intent to observe and describe the length of the modifying effect of three different types of modifiers and their effect on the mechanical properties of aluminium alloy. Next step was to process and evaluate links between mechanical properties and chemical composition. Chemical analysis and mechanical properties of cast samples were obtained. For this purpose and a method of metallographic processing was applied afterwards. The grain size was evaluated before and after the heat treatment. Measurements of the secondary dendrite branches and evaluation of the eutectic morphology were made. The hardness was measured on selected samples.
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Analysis of the Structure and Properties of Al-Si Alloy during Holding Time of the Melt
Krahula, Karel ; Lichý, Petr (referee) ; Kaňa, Václav (referee) ; Zemčík, Ladislav (advisor)
This thesis is dedicated to the production of aluminum casting alloys. It maps the course of changes in the morphology of eutectic and its influence on mechanical properties during the long-term meltdown. In particular, the use of image analysis methods contributes to describing these processes. The presented results show that the eutectic shape does not change even during the meltdown for 110 minutes. There is only a roughing and an increase in grain size. There was also no influence on the mechanical properties that fit the practical application of the alloy examined
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Analysis of the Structure and Properties of Al-Si Alloy during Holding Time of the Melt
Krahula, Karel ; Lichý, Petr (referee) ; Kaňa, Václav (referee) ; Zemčík, Ladislav (advisor)
This thesis is dedicated to the production of aluminum casting alloys. It maps the course of changes in the morphology of eutectic and its influence on mechanical properties during the long-term meltdown. In particular, the use of image analysis methods contributes to describing these processes. The presented results show that the eutectic shape does not change even during the meltdown for 110 minutes. There is only a roughing and an increase in grain size. There was also no influence on the mechanical properties that fit the practical application of the alloy examined
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Study of the effect of metallurgical and technological parameters on mechanical properties of aluminium alloys
Pešek, Jakub ; Krahula, Karel (referee) ; Zemčík, Ladislav (advisor)
Sugested thesis has been made with the intent to observe and describe the length of the modifying effect of three different types of modifiers and their effect on the mechanical properties of aluminium alloy. Next step was to process and evaluate links between mechanical properties and chemical composition. Chemical analysis and mechanical properties of cast samples were obtained. For this purpose and a method of metallographic processing was applied afterwards. The grain size was evaluated before and after the heat treatment. Measurements of the secondary dendrite branches and evaluation of the eutectic morphology were made. The hardness was measured on selected samples.
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ELASTIC-PLASTIC BEHAVIOUR OF ADVANCED ADI STUDIED BY IN-SITU SEM TENSILE TEST
Petrenec, M. ; Tesařová, H. ; Krahula, Karel ; Polák, Jaroslav
In-situ SEM tensile tests at room temperature have been performed on flat specimen of advanced austempered ductile cast iron (ADI) alloyed with nickel with the aim to study elastic-plastic behavior together with the nucleation and growth of cracks. During tensile loading the systematic observation of selected locations was studied. The in-situ observation was used to elucidate the tensile curves in agreement with the deformation mechanisms. In the early stage of loading the stress-strain response is elastic. After exceeding elastic limit decohesion of graphite nodules from the matrix was observed. It can be related to the departure of the tensile curve from the elastic behavior. The cracks initiated preferably from interface of graphite nodule and the ausferrite matrix. Elastic-plastic region is connected with the plastic deformation of the matrix and growth and linking of short cracks.
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Effect of heat treatments with a pointed cooling on the mechanical compression properties of TiAl intermetalic
Petrenec, Martin ; Kruml, Tomáš ; Zemanová, Adéla ; Krahula, Karel
The influence of the graded cooling heat treatments on a change in the structure and the room temperature mechanical compression properties of cast Ti-44Al-8Nb intermetallic were studied. The coolings were the air cooling and the graded cooling which was composed of combination of furnace cooling and air cooling for selected two temperatures 1315 °C and 1200 °C. These selected temperatures were used from the measuring of the differential thermal analysis (DTA). All heat treatments used remold the cast nearly lamellar structure ?/?2 to the fully lamellar uniform structure and decreased the average grain size to the half. The air cooling and the graded cooling with temperature 1315 °C were produced in higher yield stress and lower plasticity due the very thin lamellar thickness and planar grain boundary. While higher plasticity and lower yield stress are obtained using the graded cooling with temperature 1200 °C. It is caused by the very thick lamellar spacing and locked grain boundaries.
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The role of microstructure in racture behaviour of TiAl based intermetalics
Krahula, Karel ; Prokešová, Zdenka ; Dlouhý, Ivo
The contribution is focused on the analysis of the role of microstructural parameters in fracture behaviour of TiAl intermetalics at room and increased temperatures. Flexural strength and fracture toughness have been evaluated for alloys Ti-40Al-2Cr-2Nb-1B and Ti-46Al-0,7Cr-0,1Si-7Nb-0,2Ni. Positive effect of Nb on fracture resistance has been found; fracture toughness of the high Nb alloy increased at contemporary increase of flexural strength. Fracture surfaces have been evaluated using scanning electron microscopy showing the key role of mechanical twinning in deformation of both alloys followed. As a governing mechanism of crack nucleation microcrack formation at boundaries between mechanical twins and gama grains has been confirmed.
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The structural and the fundamental mechanical properties of intermatallics on the base of TiAl
Krahula, Karel ; Dlouhý, Ivo
Gamma TiAl alloys are emerging as a pervasive structural material. Remarkable progresses have been made through refining lamellar microstructure and grains, microalloying, chemistry modification, process development and/or their combination. The main thrust was to enhance resistance to creep deformation, oxidation and high cycle fatigue deformation/failure. Less or even no knowledge have been obtained in the field of the intermetalics fracture at uniaxial or bending loading, there are missing data about their behaviour at the presence of cracks and other defects. The reason is simply in the other properties that are key from application point of view. Due to their brittleness at temperature close to room temperature the investigation of the intermetalics fracture is complicated but promissible provided it bring ideas for the further development of the alloying and microstructure. The paper is focused on the first steps in this field.
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