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Study of novel magnesium alloys with controlled microstructure and texture
Drozdenko, Daria ; Dobroň, Patrik (advisor)
Title: Study of novel magnesium alloys with controlled microstructure and texture Author: Daria Drozdenko Department / Institute: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Supervisor of the doctoral thesis: Ing. Patrik Dobroň, Ph.D., Department of Physics of Materials. Abstract: The work elucidates the role of dislocation slip and twinning during plastic deformation in selected magnesium (Mg) alloys with controlled microstructure and texture. The acoustic emission (AE) technique was concurrently applied during deformation to determine the activity of particular deformation mechanisms. A detailed insight into microstructure was provided by electron microscopy. In order to obtain a comprehensive set of AE data for particular deformation mechanisms, Mg single crystals with various crystallographic orientations were channel-die and uniaxially compressed. The obtained results were applied on deformation mechanisms in polycrystalline textured Mg alloys. Particularly, the twinning - detwinning processes, in the sense of twin boundary mobility, during one cycle loading (pre-compression followed by tension) were described. Clear correlations between changes in the AE response and the inflection points on the deformation curve were found. An analysis of twin...
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Investigation of basic deformation mechanisms of magnesium alloys by means of advanced in-situ methods and theoretical modeling
Čapek, Jan ; Mathis, Kristián (advisor) ; Landa, Michal (referee) ; Šiška, Filip (referee)
The work is focused on developing testing methods for investigating of the deformation mechanisms of magnesium alloys. The work involves the measurement of in-situ acoustic emission and neutron diffraction and comparison to the theoretical models. Mg + 1wt.% Zr alloy was selected for investigation of the compression - tension asymmetry. Advanced analysis of acoustic emission and neutron diffraction data revealed activation of different slip systems during deformation. Moreover, the different evolution of twinning was explained. The same methods were used to investigate the aluminum influence on deformation mechanisms. The hardening of basal slip and twinning and increasing importance of prismatic slip was observed.
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Microstructure and thermal stability of ultra fine grained Mg-Zn-Y alloys
Vlasák, Tomáš ; Čížek, Jakub (advisor) ; Procházka, Ivan (referee)
The aim of this diploma thesis is to investigate microstructure and thermal stability of ultra fine grained magnesium alloys. The thesis first summarises methods using plastic deformation in order to achieve ultra fine grained structure that are used to process metals. Then experimental methods employed in the experimental part including microhardness testing, scanning electron microscopy and positron annihilation spectroscopy are described. Brief summary of previous research on MgZnY alloys strengthened by quasicrystalline phases and Mg22Gd alloys is given. Finally, results of experimental investigation of MgZnY alloys with various Zn/Y ratios and Mg22Gd alloy are discussed. These results suggest that presence of phases in MgZnY alloys depend on Zn/Y ratio, hardness of these alloys depends on Zn content and that rapid cooling of MgZnY alloys annealed at 500 řC lead to significant increase in volume fraction of quasicrystalline icosahedral phase. In the second section of the experimental part thermal behaviour of Mg22Gd alloy is investigated. Furthermore, formation of GdH2 particles in Mg22Gd is examined and attributed to reaction of hydrogen decomposed from water vapour with gadolinium in areas rich in gadolinium. Finally, significant hardening of Mg22Gd alloy processed by high pressure torsion has been...
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Advanced Magnesium Alloys Surface Modification by Ni-P Based Coatings
Kosár, Petr ; Pacal, Bohumil (referee) ; Nový,, František (referee) ; Havlica, Jaromír (advisor)
The dissertation thesis deals with the modification of the surface of advanced magnesium alloys with Ni-P based coatings. At the beginning of the theoretical part, the structures of the used magnesium alloys and the influence of individual alloying elements on their properties are characterized. In the following part of the thesis the current knowledge in the field of electroless deposition on metal substrates is summarized. The theoretical part of the thesis is closed with contemporary research study in the field of clarification and determination of possible mechanism of electroless deposition. For the subsequent investigation of the mechanism of electroless deposition on magnesium alloys, it was necessary to characterize the microstructure and composition of individual magnesium alloys in the first phase of the experimental part. The exact composition of elements was determined using glow discharge optical emission spectroscopy and scanning electron microscopy with EDS was used for composition of phases of magnesium alloys. Using scanning electron microscopy and detailed elemental analysis of the coated magnesium substrate, it was found that for optimal Ni-P coating deposition on magnesium alloys, acid pickling prior coating is required in a mixture of acetic acid and sodium nitrate. Using the XPS method, it was found that the phosphorus atom in the sodium dihydride-diphosphate reducing agent has a + V charge. 4 At the end of the experimental part scanning electron microscopy and detailed elemental analyses were used for monitoring of the Ni-P particles nucleation and growth in the first 120 seconds of the coating process.
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Study of deformation mechanisms in extruded magnesium alloys containing neodymium and yttrium
Hojnoš, Peter ; Minárik, Peter (advisor) ; Chmelík, František (referee)
Submitted work shows results of the investigation of ternary (WN43) and two binary magnesium alloys containing neodymium (2Nd) and yttrium (4Y) extruded at two different extrusion rates (2 and 5 mm/s). Microstructure of the investigated samples was analysed by light microscope. Additionally, texture of all samples was measured by X-ray diffraction. Mechanical properties were studied by compression deformation tests with two different deformation directions with respect to the processing direction. Acoustic emission was recorded during the deformation tests in order to correlate deformation behaviour with the micros- tructure. Analysis of the acoustic emission helps to identify deformation micro- mechanisms acting during the mechanical straining. Additionally, effect of sample size and deformation rate on the deformation mechanisms was investigated. 1
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Superplastic deformation of ultrafine-grained magnesium alloys with potential for use in medicine
Vávra, Tomáš ; Minárik, Peter (advisor) ; Málek, Přemysl (referee)
Mechanical properties of ultra-fine grain magnesium alloys AE42 and LAE442 prepared by ECAP were investigated. The study was focused on finding suitable conditions for the superplastic deformation. In the first place, the thermal stability of the microstructure was investigated. Afterwards, the strain rate sensitivity was measured in the temperature range 180-240 řC and the strain rate of =5·10-5 -2·10-3 s-1 . Conditions for tensile tests of =10-4 s-1 at 180 ř C and =10-3 s-1 at 240 řC ware selected. Finally, the microstructure change as a result of deformation was observed by AFM and EBSD. The results were discussed with mechanical tests. The best superplastic properties were observed in LAE442 alloy deformed at 180 ř C and =10-4 s-1 . Under these conditions, the achieved tensile strain was 395%.
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Study of novel magnesium alloys with controlled microstructure and texture
Drozdenko, Daria ; Dobroň, Patrik (advisor) ; Sklenička, Václav (referee) ; Vinogradov, Alexei (referee)
Title: Study of novel magnesium alloys with controlled microstructure and texture Author: Daria Drozdenko Department / Institute: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Supervisor of the doctoral thesis: Ing. Patrik Dobroň, Ph.D., Department of Physics of Materials. Abstract: The work elucidates the role of dislocation slip and twinning during plastic deformation in selected magnesium (Mg) alloys with controlled microstructure and texture. The acoustic emission (AE) technique was concurrently applied during deformation to determine the activity of particular deformation mechanisms. A detailed insight into microstructure was provided by electron microscopy. In order to obtain a comprehensive set of AE data for particular deformation mechanisms, Mg single crystals with various crystallographic orientations were channel-die and uniaxially compressed. The obtained results were applied on deformation mechanisms in polycrystalline textured Mg alloys. Particularly, the twinning - detwinning processes, in the sense of twin boundary mobility, during one cycle loading (pre-compression followed by tension) were described. Clear correlations between changes in the AE response and the inflection points on the deformation curve were found. An analysis of twin...
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Investigation of deformation mechanisms of advanced light-weight alloys
Németh, Gergely ; Mathis, Kristián (advisor) ; Drozd, Zdeněk (referee)
The objective of this thesis is to investigate the mechanical and damping properties in AZ91 alloys with different boron concentrations and in two experimental alloys based on commercial pure magnesium. Further aim is to identify the influence of heat treatment of alloys AZ91+B on the properties mentioned above. Micro-structural observations were achieved by optical and scanning electron microscope. Mechanical tests were performed in a wide range of temperatures from 23řC to 300řC and, simultaneously, the acoustic emission was recorded at room temperature. The temperature spectrum of internal friction was determined in the temperature range from 23řC to 400řC. Moreover, the amplitude dependence of damping properties of materials were studied. Phenomena leading to dissipation of mechanical energy in the temperature spectrum were determined by micro-structural observation.
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Physical properties of ultrafine-grained magnesium based alloys prepared by various severe plastic deformation techniques
Stráská, Jitka ; Janeček, Miloš (advisor) ; Dlouhý, Antonín (referee) ; Kalvoda, Ladislav (referee)
Title: Physical properties of ultrafine-grained magnesium based alloys prepared by various severe plastic deformation techniques Author: Jitka Stráská Department / Institute: Department of Physics of Materials Supervisor of the doctoral thesis: Doc. RNDr. Miloš Janeček, CSc. Abstract: The objective of the doctoral thesis is the complex investigation of ultrafine-grained magnesium alloy AZ31 prepared by two different severe plastic deformation techniques, in particular the hot extrusion followed by equal-channel angular pressing (EX-ECAP) and high pressure torsion (HPT). These severe plastic deformation methods, and as well as many others, are described in detail in the introductory theoretical section. Experimental results are summarized in the following experimental part of the thesis. Mechanical properties, lattice defect structure and especially microstructure were investigated using various experimental techniques. Thermal stability of ultrafine-grained microstructure of AZ31 after EX-ECAP was investigated and the activation energies for grain growth in different temperature ranges were calculated using kinetic equation for grain growth and Arrhenius equation. Results from the dislocation density measurements proved temperature ranges of the recovery and the following grain growth. Results from the...
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