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Beta-Ti alloys for medical applications
Preisler, Dalibor ; Stráský, Josef (advisor) ; Karlík, Miroslav (referee) ; Caram jr., Rubens (referee)
1 Title: Beta-Ti alloys for medical applications Author: Dalibor Preisler Department / Institute: Department of Physics of Materials Supervisor of the doctoral thesis: doc. PhDr. RNDr. Josef Stráský, Ph.D., Department of Physics of Materials Abstract: Interstitial strengthening by a high amount of oxygen can be used in metastable beta-Ti alloys, for achieving very high strength without compromising ductility. The content of oxygen however influences the phase stability and consequently increases the Young's modulus. Several alloys with various content of beta-stabilizing elements were prepared by common metallurgical route. On top of that, dozens of compositions were prepared by a high-throughput powder metallurgy method and thoroughly studied. Lattice softening due to proximity to a martensitic transformation was utilized to minimize the Young's modulus. Effect of omega phase was thoroughly studied; it was found that the embrittlement by the athermal omega phase is most probably connected with the high oxygen content and its room-temperature diffusion into omega particles. Fundamental difference between elastic behaviour of alloys containing a significant fraction of omega and those with only a limited amount of omega was demonstrated. Regarding the plastic deformation mechanisms, it was found that...
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Microstructure of non-equiblirium Al-Mn based solid solutions
Poková, Michaela ; Cieslar, Miroslav (advisor) ; Karlík, Miroslav (referee)
Heat exchangers in automotive industry are often manufactured from aluminum-based alloy AW 3003. In recent time, the aim to reduce the weight of the cars leads to thickening of the foils, which are used for manufacturing of the heat exchangers. In order to fulfill all requirements on mechanical properties of the exchanger, new materials and thermo-mechanical treatments have to be found. Modified alloy AW 3003 with addition of zirconium seems to be perspective. Zirconium forms metastable precipitates Al3Zr, which pin moving grain boundaries and shift recrystallization to higher temperatures. The most effective heat treatment, which leads to precipitation of these particles, seems to be a two-step annealing at temperatures 250 řC and 450 řC with slow heating rate. The precipitates formed were of diameter 10 nm.
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Complex investigation of fine-grained polycrystals of Cu and CuZr alloy processed by equal channel angular pressing a high pressure torsion
Srba, Ondřej ; Janeček, Miloš (advisor) ; Hadzima, Branislav (referee) ; Karlík, Miroslav (referee)
Title: Complex investigation of fine-grained polycrystals of Cu and CuZr alloy processed by equal channel angular pressing and high pressure torsion Author: RNDr.Ondřej Srba Department: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University Prague Supervisor: Doc. RNDr. Miloš Janeček, CSc. Abstract: In the thesis the microstructure development, mechanical, elastic and corrosion properties of deformed specimens of pure Cu and binary alloy CuZr processed by equal channel angular pressing (ECAP) are investigated. Several properties of pure Cu processed by ECAP are compared with properties of the same material processed by high pressure torsion (HPT). The microstructure development is characterized in detail by several experimental techniques (light and electron microscopy, electron back scatter diffraction, positron annihilation spectroscopy, etc.). The microstructure development in specimens processed by ECAP is characterized by the continuous fragmentation of the initial coarse grain structure and the formation of new grains having the sizes in the submicrocrystalline range (of 460 nm and 260 nm in Cu and CuZr alloy, respectively). During the deformation by ECAP the fraction of high-angle grain boundaries, the dislocation density and the concentration of vacancies are...
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Study of deformation processes in hexagonal materials
Čapek, Jan ; Mathis, Kristián (advisor) ; Karlík, Miroslav (referee)
The deformation mechanisms of commercially pure magnesium using advanced in-situ methods were investigated in the present work. Compression and tensile test were done at room temperature. Simultaneously, the neutron diffraction was measured and the acoustic emission was recorded. The microstructure of the deformed material was also studied by means of optical microscopy and electron back-scattered diffraction. These measurements provided information about twin nucleation and growth, microstructure changes and the influence of the orientation of grains on the number of twins and their shape. The values obtained were compared to the Elasto-Plastic Self-Consistent model, which provides information about the activity of deformation mechanisms. We focused on clarifying the influence of twinning activity on asymmetry between tensile and compression deformation.
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Analysis of twin-roll cast aluminium-steel clad strips
Křivská, Barbora ; Šlapáková, Michaela (advisor) ; Karlík, Miroslav (referee)
The microstructure, diffusion and phase transformations in aluminum-steel clad sheet were studied within the thesis by means of light optical microscopy, electron microscopy, resistometry and positron annihilation spectroscopy. Results of experimental methods were supplemented by finite element method employed for evaluation of electrical resistivity and simulation of diffusion between steel and aluminum. Several annealing experiments were carried out. The effective interdiffusion coefficient was evaluated by Boltzmann-Matano method from measured concentration profiles through the interface. Formation of an interfacial intermetallic phase was studied and orthorhombic phases Al13Fe4 and Al5Fe2 were identified present in the layer. Surprising results were obtained from the in-situ annealing in TEM (SEM) which go against the results found in a recent literature - the interfacial layer grows towards steel layer.
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Optimization of properties of Ti based alloys for biomedical and structural applications
Stráský, Josef ; Janeček, Miloš (advisor) ; Hadzima, Branislav (referee) ; Karlík, Miroslav (referee)
Title: Optimization of properties of Ti based alloys for biomedical and structural applications Author: Josef Stráský Department / Institute: Department of Physics of Materials Supervisor of the doctoral thesis: Assoc. Prof. Miloš Janeček, Ph.D. Abstract: Titanium alloys belong to the mostly used biomaterials for orthopaedic implants. Advanced surface treatments of Ti alloys for orthopaedic use and newly developed biomedical beta-Ti alloys are investigated in this thesis. Wide spectrum of experimental techniques was employed in order to correlate material processing, microstructure and mechanical properties. Electric discharge machining was used as a biocompatibility enhancing surface treatment of Ti-6Al-4V alloy, but the treated material suffered from the poor fatigue performance. Two subsequent surface treatments - chemical etching and shot- peening - were proposed and it was shown that their combination significantly improves the fatigue performance of the material making it applicable in orthopaedics. This process was patented in the Czech Republic. The thesis further reviews complex problematic of biocompatible beta-Ti alloys. Several new biocompatible beta-Ti alloys were designed on the basis of Ti-Nb-Zr-Ta quaternary alloy. The effect of Fe, Si and O additions on microstructure, elastic modulus and...
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Microstructure and properties of enhanced twin-roll cast aluminium alloys.
Poková, Michaela ; Cieslar, Miroslav (advisor) ; Karlík, Miroslav (referee) ; Kruml, Tomáš (referee)
Three aluminium alloys from AA3003 series modified by zirconium were pre- pared by twin-roll casting. The role of composition, heat treatment and deforma- tion by cold-rolling or equal channel angular pressing on evolution of microstruc- ture and mechanical properties were studied. High density of α-Al(Mn,Fe)Si pre- cipitates formed during annealing between 300 ◦ C and 500 ◦ C. Coherent Al3Zr particles precipitated during annealing at 450 ◦ C with slow heating rate. Recrys- tallization resistance of deformed alloys was enhanced by either Al3Zr precipitates formed before deformation or by α-Al(Mn,Fe)Si particles nucleating simultane- ously with recrystallization. 1
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Influence of Solid Solution Elements and Precipitate Formation on the Mechanical Behaviour of Magnesium Alloys
Illková, Kseniya ; Chmelík, František (advisor) ; Karlík, Miroslav (referee) ; Landa, Michal (referee)
Title: Influence of Solid Solution Elements and Precipitate Formation on the Mechanical Behaviour of Magnesium Alloys Author: Mgr. Kseniya ILLKOVÁ Department / Institute: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Supervisor of the doctoral thesis: Doc.RNDr.František Chmelík, CSc. Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Abstract: Mg-1 wt. % Mn alloys containing about 1 wt.% of calcium (MX10), aluminium (AM11), cerium(ME11), yttrium (MW11), neodymium (MN11) and 8 wt.% of aluminium (AM81) were indirectly extruded with two different speeds. The partially recrystallised microstructures obtained in MX10, AM11, ME11 and MW11 after slow extrusion exhibited bimodal grain size distributions. Only in the case of AM81 and MN11 a fully recrystallised microstructure was found, indicating differences in the grain nucleation rate during recrystallisation. In these alloys, the weakest texture and, correspondingly, the lowest asymmetry in mechanical properties were also observed. The acoustic emission technique was used to reveal dislocation or twin controlled deformation in differently textured fractions of the microstructure during tensile and compression testing. A direct correlation between the acoustic...
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