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Study of ultrafine-grained materials prepared with different methods of severe plastic deformation
Krajňák, Tomáš ; Mathis, Kristián (advisor) ; Hadzima, Branislav (referee) ; Kalvoda, Ladislav (referee)
Title: Study of ultrafine-grained materials prepared with different methods of severe plastic deformation Author: RNDr. Tomáš Krajňák Department: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Supervisor: Doc. RNDr. Kristián Máthis, PhD., Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Abstract: Interstitial free steel with ultrafine-grained (UFG) structure was prepared by high-pressure torsion (HPT). The development of the microstructure as a function of the number of HPT turns was studied at the centre, half-radius and periphery of the HPT-processed disks by X-ray line profile analysis (XLPA), positron annihilation spectroscopy (PAS) and electron microscopy. The dislocation densities and the dislocation cell sizes determined by XLPA were found to be in good agreement with those obtained by PAS. The evolution of the dislocation density, the dislocation cell and grain sizes, the vacancy cluster size, as well as the high-angle grain boundary (HAGB) fraction was determined as a function of the equivalent strain. It was found that first the dislocation density saturated, then the dislocation cell size reached its minimum value and finally the grain size got saturated. For very high strains after the...
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Microstructure and mechanical properties of aluminium alloys prepared by severe plastic deformation
Bajer, Jan ; Cieslar, Miroslav (advisor) ; Král, Robert (referee)
New technologies of components assembling in car and aircraft industries and requests on improved mechanical and corrosion properties of metallic materials in the packing industry activate the utilization of highly innovative and unconventional manufacturing processes. There are only a limited number of processing, that retain the original material thickness and in an appropriate manner modify material properties. These are different types of annealing, severe plastic deformation methods or combination of both. In recent years constrained groove pressing (CGP) was devoloped with this method the grain size can be reduced from tens of micrometers to sub-micrometers. The present work is focused on a study of evolution of microstructure and mechanical properties of two alloys based on EN AW 3003 after CGP deformation and subsequent annealing.
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Studium mikrostruktury ultrajemnozrnných kovových materiálů metodou pozitronové anihilace
Barnovská, Zuzana ; Čížek, Jakub (advisor) ; Procházka, Ivan (referee)
In the presented thesis we study the changes in distribution of the size of vacancy clusters in metals processed by severe plastic deformation, so called ul- tra fine grained materials. We use a modern non-destructive method of positron annihilation spectroscopy, which is one of the few methods that allow us to inves- tigate point defects like vacancies with sizes of a few ˚A. The obtained spectra of positrons annihilating in the samples enable us to determine changes of vacancy cluster sizes depending on temperature or severity of the deformation applied on the samples. 1
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Microstructure and mechanical properties of lightweight structural AZ31 alloy prepared by twin-roll casting method.
Zimina, Mariia ; Cieslar, Miroslav (advisor)
Title: Microstructure and mechanical properties of lightweight structural AZ31 alloy prepared by twin-roll casting method Author: Mariia Zimina Abstract: Microstructure of AZ31 twin-roll cast magnesium alloy was studied using light optical, electron and atomic force microscopy. The effect of annealing temperature on the microstructure was tested. Mechanical properties of a thin magnesium strip were investigated by means of microhardness tests and tensile tests at a relatively low strain rate 10-3 s-1 . Results show that the ductility of the twin roll cast strip increases with increasing deformation temperature, however, a remarkable decrease was observed at about 200 řC. This effect appears also in a conventionally cast ingot of a master alloy and is caused by a change of a deformation mode occurring at this temperature. Moreover, the effect of severe plastic deformation on the microstructure and mechanical properties was studied. Equal channel angular pressing was applied on magnesium strip samples and lead to a significant grain refinement accompanied by an unfavorable strengthening of the initial basal texture, which is effectively suppressed by a subsequent annealing. A constrained groove pressing was for the first time successfully applied on AZ31 twin-roll cast strip leading to an increase of...
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Mechanical properties of magnesium alloy AZ91E prepared by ECAP method
Darida, Jiří ; Válka, Libor (referee) ; Pantělejev, Libor (advisor)
This thesis deals with mechanical and fatigue properties of magnesium alloy AZ91 processed by EX-ECAP method. This method involves the application of extrusion followed by equal-channel angular pressing. To obtain basic mechanical characteristics, the tensile test were carried out at room and elevated temperatures. Further the fatigue tests were performed and obtained data were used to compile S-N curve. The work also includes metallographics analysis of microstructure and fractographic analysis of fracture surfaces of tensile and fatigue test specimens.
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TEM and SEM study of precipitation hardened Cu-Co alloys after severe plastic deformation
Buršík, Jiří ; Svoboda, Milan ; Král, Petr ; Dvořák, Jiří ; Sklenička, Václav
The paper reports on preliminary results of microstructural study of Cu-2wt.%Co alloy processed by ECAP. The experimental alloy was cast and annealed at 1273 K for 10 hours followed by water cooling, resulting in the solid solution (the initial state). Further heat treatment was then applied to produce two-phase material with fine distribution of precipitates. ECAP was then conducted at room temperature on both the initial and the precipitation hardened states. Resulting microstructures were studied and characterized by microhardness testing, TEM observations and texture analysis by means of electron backscatter diffraction (EBSD) technique in SEM.
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