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Mechanical properties of pre-compressed Mg-Zn-Ca alloy
Hegedüs, Marius ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
In wrought Mg alloys, their hexagonal closed packed structure together with a pronounced basal texture lead to anisotropy of mechanical properties. This bachelor thesis is focused on understanding the influence of previous deformation with further relaxation and/or additional heat treatment on deformation behaviour of the extruded Mg-Zn-Ca alloy. The significant influence of twins formed after pre-compression on mechanical properties was investigated. Evolution of microstructure, especially a formation of twins, is observed by light and scanning electron microscopy. The acoustic emission technique is used to determine active deformation mechanisms: dislocation slip and twinning. The results can be used for developing Mg alloys with enhanced properties.
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Electron microscopy studies of materials thermal stability.
Králík, Rostislav ; Cieslar, Miroslav (advisor) ; Lukáč, Pavel (referee)
Thermal stability of Al-Fe-Mn-Si alloys prepared by twin roll casting accom- panied by intensive cooling and plastic deformation was studied. The goal of the study is to map processes occurring during a model homogenizaton annealing of individual alloys which differ by the ratio of alloying elements. Model in-situ an- nealing in the transmission electron microscope and resistometry measurements with linear heating were used for identification of occurring processes. Another goal is to determine the crystalographic structures of primary and secondary pha- ses present in the alloys. Results show that the concentration of alloying elements has a significant influence on transformation temperatures of primary phases as well as the structure of primary and secondary phases. 1
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Study of mechanical and thermal properties of nanoparticle-reinforced composites
Németh, Gergely ; Mathis, Kristián (advisor) ; Lukáč, Pavel (referee)
Title: Study of mechanical and thermal properties of composites reinforced by nanoparticles Author: Gergely Németh Department: Department of Physics of Materials Supervisor: RNDr. Kristián Máthis, Ph.D. Abstract: In the present work the deformation behavior of magnesium-based alloy AZ31 reinforced by SiC nanoparticles which was produced by horizontal continual casting is studied. Tension tests in the room temperature, compression tests in the temperature range of 20řC-300řC have been preformed. Samples was with two different orientation. Deformation strain rate was 10-3 s-1 . Simultaneously, the acoustic emission is recorded and studied. The mechanisms of plastic deformation of material are discussed mainly in term of mechanical twinning. Dependence of deformation behavior in compression on temperature is analyzed. The microstructure of original and deformed material is also studied. Keywords: magnesium alloys, composit material, mechanical twinning, metals with hexagonal structures.
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Studium nestabilní plastické deformace metodou akustické emise
Molnárová, Orsolya ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
The influence of the strain rate and heat treatment on the occurrence of plastic instabilities in extruded AlSi1MgMn (6082) and cold rolled AlMg4.5Mn0.4 (5182) alloys was studied. The samples were uniaxially loaded at various strain rates and at room temperature (RT). The results are discussed using concurrent acoustic emission (AE) monitoring during mechanical testing and the AE parameters are correlated to the microstructure and to the stress-time curves. All samples exhibited the Portevin-Le Châtelier (PLC) effect of different types, dependently on the heat treatment and the applied strain rate. The occurrence of the PLC effect is manifested by burst AE signals with high amplitudes. Statistical analysis of the AE signals has shown the power-law probability distribution.
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Vliv příměsových prvků a textury na plastickou deformaci protlačovaných hořčíkových slitin
Horváth, Klaudia ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
This work is focused on the study of the relationship between microstructure, texture and deformation mechanisms in aluminum-free magnesium (Mg) alloys. Extruded alloys containing zirconium, zinc, manganese and neodymium (ZK10, MN11, ZN11) in a form of rectangular profiles were deformed at room temperature. Uniaxial tensile and compression tests were performed in the extrusion (ED), transversal (TD) and normal direction (ND). The concurrent acoustic emission (AE) measurement was used in order to study the collective dislocation dynamic and the nucleation of twins. The deformation texture was studied by X-ray diffraction on samples deformed in compression up to different stress levels. Keywords: Mg alloys, deformation tests, acoustic emission, texture
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An Acoustic Emission Study of Deformation Mechanisms in Novel Magnesium Alloys at Uniaxial and Low Cyclic Loading
Horváth, Klaudia ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
This work is focused on the study of the relationship between microstructure and deformation mechanisms in magnesium (Mg) alloys during uniaxial (tension, compression) and low cyclic loading by the acoustic emission (AE) technique. The main attention is paid to the study of tension-compression yield asymmetry and twinning-detwinning process during changes in deformation mode in novel aluminium-free Mg alloys, where the deformation texture influences the activation of various deformation mechanisms. The results contribute to the understanding of dislocation processes and twin activation (especially of twinning-detwinning process) during cyclic loading. These processes are of great importance because they influence significantly the fatigue life of Mg alloys.
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Investigation of collective behaviour of lattice defects by the acoustic emission technique
Molnárová, Orsolya ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
The Portevin-Le Chatelier effect is a macroscopic, spatio-temporal instability of plastic deformation. This phenomenon appears in some industrially important metallic alloys, e.g. based on iron, aluminum or magnesium if these materials are deformed at suitable temperature and strain rate. The effect is manifested as stress fluctuations (serrations) on deformation curves, which corresponds to macroscopic and localized events of plastic deformation in the material. It demonstrates a nonlinear cooperative motion of dislocations (line defects of the microstructure) during plastic deformation. Study of nonlinear aspects of dislocation dynamics is of great importance for understanding the patterns of plastic deformation. It also brings a considerable application potential for the design of novel structural materials. By the collective motion of dislocations the stress fields of the structural defects interact and release mechanical energy in form of elastic waves. These waves can easily be detected by the acoustic emission technique.
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Dependence of mechanical properties of polycrystalline magnesium on microstructural parameters
Čapek, Jan ; Mathis, Kristián (advisor) ; Lukáč, Pavel (referee)
The deformation of commercially pure magnesium with various grain size in different temperatures is investigated in the present work. Compression and tensile test were done on three different samples in temperature range of 20řC-300řC. Samples are deformed at strain rate of 1,8 mm/min. Simultaneously, the acoustic emission is recorded. The microstructure of the deformed material is also studied by means of optical microscopy. We focus on twinning activity at various temperatures and asymmetry between tensile and compression deformation.
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