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Martensite microstructures in thin films and monocrystals of Heusler alloys Ni-Mn-Ga
Onderková, Kristýna ; Heczko, Oleg (advisor) ; Kopeček, Jaromír (referee)
Title: Martensite microstructures in thin films and monocrystals of Heusler alloys Ni-Mn-Ga Author: Kristýna Onderková Department: Department of Surface and Plasma Science Supervisor: Mgr. Ing. Oleg Heczko, Dr., Institute of Physics of the Czech Academy of Sciences Abstract: The submitted thesis examines mainly the first thin films from Ni-Mn-Ga Heusler alloy prepared by magnetron sputtering on the new equipment at Institute of Physics of Charles University. However, the work also analysed the thin films prepared in IFW Dresden and bulk material. The main focus of the work is primarily on the martensitic microstructures, because of the significant effect that their twin boundaries have on the magnetic shape memory phenomena. Microscopic techniques used for the research were mainly Scanning Electron Microscopy (SEM), but also Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). As the Ni-Mn-Ga properties are stronly dependent on chemical composition, the composition was evaluated by two different methods (Electron Dispersive X-ray Spectroscopy and X-ray Fluorescence) and observed differences discussed. Finally the results were compared with X-ray diffraction (XRD) measurements and the films were further characterised by magnetic measurements using Vibrating Sample Magnetometer (VSM)....
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Properties of thin films studied by in-situ TEM
Bajtošová, Lucia ; Cieslar, Miroslav (advisor) ; Kopeček, Jaromír (referee)
Mechanical properties of widely applicable thin nanocrystalline films have been a sub- ject of interest for some time due to deviation of their properties from the properties of bulk and micro sized grain materials. The deformation mechanisms in these materials are altered by restricted size of the material and high ratio of surface and grain boundary areas. Recent advances in transmission electron microscopy (TEM) allow direct obser- vations of the deformation mechanisms during nanoindentation or tensile deformation of the specimen. Thin Al films prepared by DC magnetron sputtering were deformed in situ in TEM and bright field TEM. High resolution TEM and automated crystallographic orientation mapping (ASTAR) were implemented to observe the ongoing deformation mechanisms. Molecular dynamic simulation designed to approach the conditions of per- formed experiment were used to visualize the deformation mechanisms on atomic scale and the reliability of both methods was discussed. 1
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Martensite microstructures in thin films and monocrystals of Heusler alloys Ni-Mn-Ga
Onderková, Kristýna ; Heczko, Oleg (advisor) ; Kopeček, Jaromír (referee)
Title: Martensite microstructures in thin films and monocrystals of Heusler alloys Ni-Mn-Ga Author: Kristýna Onderková Department: Department of Surface and Plasma Science Supervisor: Mgr. Ing. Oleg Heczko, Dr., Institute of Physics of the Czech Academy of Sciences Abstract: The submitted thesis examines mainly the first thin films from Ni-Mn-Ga Heusler alloy prepared by magnetron sputtering on the new equipment at Institute of Physics of Charles University. However, the work also analysed the thin films prepared in IFW Dresden and bulk material. The main focus of the work is primarily on the martensitic microstructures, because of the significant effect that their twin boundaries have on the magnetic shape memory phenomena. Microscopic techniques used for the research were mainly Scanning Electron Microscopy (SEM), but also Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). As the Ni-Mn-Ga properties are stronly dependent on chemical composition, the composition was evaluated by two different methods (Electron Dispersive X-ray Spectroscopy and X-ray Fluorescence) and observed differences discussed. Finally the results were compared with X-ray diffraction (XRD) measurements and the films were further characterised by magnetic measurements using Vibrating Sample Magnetometer (VSM)....
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Model of static recrystallization in the coarse-grained B2 iron aluminide
Schindler, I. ; Šumšal, V. ; Kopeček, Jaromír ; Kawulok, P. ; Jozwik, P. ; Rusz, S. ; Kawulok, R. ; Opěla, P.
Microstructure of the laboratory castings made from Fe-40at.%Al-Zr-B alloy was homogenized by the multipass hot rolling in protective capsules and subsequent lannealing. Based on the isothermal hot compression tests and EBSD analysis, the sufficiently accurate model describing the static recrystalization kinetics of the such prepared coarse-grained B2 iron aluminide after strain 0.2 was developed. The independent variables in this model are temperature of deformation as well as annealing time equal to the deformation temperature. Unexpected effect of the previous strain value on the static softening was observed. Static recrystallization begins relatively easy in the studied alloy in the whole range of testing temperatures (900-1100 °C), but a very long-term annealing is quite necessary for the complete course of recrystallization.\n
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PHASE EVOLUTION IN Ni-48 at.% TI SHAPE MEMORY ALLOY PREPARED BY SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS
Karlík, M. ; Haušild, P. ; Beran, Přemysl ; Novák, P. ; Čapek, J. ; Kučera, V. ; Kopeček, Jaromír
In Ni rich Ni–Ti alloys, various phases such as hexagonal Ni3Ti, cubic NiTi2 and rhombohedral Ni4Ti3 appear during heat treatment. The presence of these precipitates affects the shape memory effect and superelasticity in an important manner. In this paper we present a study of the phase evolution during annealing of the Ni–48at.%Ti shape memory alloy elaborated by self-propagating high-temperature synthesis (SHS). Morphology and crystallography of the phases were examined by means of light metallography, scanning electron microscopy (SEM), neutron and X-ray diffraction, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Besides the phases mentioned in the\nliterature, a Ni-rich phase with the composition near Ni3Ti2 stoichiometry and having a cubic symmetry was found. This phase develops from Ni4Ti3 particles during slow (furnace) cooling from the temperature of 1000 °C. Its particles have the form of thin platelets coherent with the (B2) NiTi matrix. The orientation relation is either cube-to-cube, [111]P || [115]B2 and (1-10)P || (1-10)B2 or [011]P || [011]B2 and (1-10)P || (1-41)B2.\n
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Thermocouples
Kopeček, Jaromír
Analsis of different samples of thermocouples before and after laser marking what is used to produce barcode close to spike of the probes. The aim is to investigate the influence of laser marking by detailed analysis of the material structure of the samples.
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