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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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Powder Metallurgy of Hybrid Materials for Advanced Applications
Kozlík, Jiří ; Stráský, Josef (advisor) ; Kim, Hyoung Seop (referee) ; Novák, Pavel (referee)
Powder Metallurgy of Hybrid Materials for Advanced Applications The field-assisted sintering technology (FAST) is a versatile powder consolidation method, which uses electrical current for rapid heating of the sintered material. It is routinely used for sintering of various metallic materials, but mostly with preal- loyed powders as a feedstock. The aim of the thesis is to explore the capabilities of FAST for sintering of composite materials and for using blended elemental powders as a raw material in following areas: 1. Manufacturing of architectured composites 2. Consolidation and ageing in a single processing run (in-situ ageing) 3. Rapid alloy prototyping using blended elemental powders 4. High-throughput experimental investigations of multicomponent phase dia- grams Al6061 + Ti-6Al-4V architectured composite was produced, but issues with the pow- der penetration into the lattice have arisen due to the small lattice dimensions. Me- chanical properties could have been assessed by a three-point bending only. The composite has shown improved strength over the plain, unannealed Al6061 matrix, but a premature fracture when the Al matrix was aged properly. Using FAST was found to be inconvenient for architectured composite manufacturing. A long, fully dense rod was manufactured from the Ti-5Al-5V-5Mo-3Cr...
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Zeemanův jev v polovodičových kvantových strukturách
Stráský, Josef ; Grill, Roman (advisor) ; Výborný, Karel (referee)
This theoretical thesis presents detailed study of negatively charged excitons - trions - confined in single quantum well in presence of perpendicular magnetic field. Complex valence band of GaAs/GaAlAs compound is described within Luttinger Hamiltonian framework. Singlet and triplet states of negative trion are introduced. Advanced theoretical analysis of Zeeman effect for different states of trion is performed. Landau gauge of magnetic field and unusual wavefunctions basis is chosen and its accuracy is tested. Evolution of ground state energy and photoluminescence spectra with magnetic field is evaluated for different values of Landé g-factors. Probability of occurrence of electrons with respect to the hole position and their spatial correlation function are investigated.
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Effect of molybdenum content on phase transformations in binary Ti-Mo alloys
Valešová, Veronika ; Stráský, Josef (advisor) ; Janeček, Miloš (referee)
Title: Effect of molybdenum content on phase transformations in binary Ti-Mo alloys Author: Veronika Valešová Department: Department of Physics of Materials Supervisor: PhDr. RNDr. Josef Stráský, Ph.D., Department of Physics of Mate- rials Abstract: β titanium alloys are highly appreciated group of structural materials. They provide an extraordinary combination of strength, toughness and fatigue resistance. These alloys are used predominantly in aerospace sector, chemical industry and medical engineering. We have studied three binary titanium alloys: Ti-12Mo, Ti-15Mo and Ti-18Mo (wt %). Apart from low temperature hexagonal close packed α phase and high temperature base centered cubic β phase, a metastable ω phase can be also found in this type of alloys. The ω phase is created in a diffusionless process by shifting the planes in the β phase and affects both mechanical properties and the α phase precipitation. We have examined the phase transformations occurring in the studied alloys using both in-situ and ex-situ methods. Resistometry, dilatometry and differential scanning calorimetry were used as the indirect in-situ methods. For the ex-situ methods, scanning electron microscopy and microhardness measurement were used. Complex characterization of β metastable titanium alloys showed the formation of the...
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Housing financing support
Marková, Diana ; Hlaváček, Michal (advisor) ; Stráský, Josef (referee)
This thesis presents the system of housing financing support generally in the context of European countries and concretly in the Czech Republic. First, the housing market and the specificity of housing as a good are presented. Next, the thesis describes taxation in relation to housing and the influence of taxation on affordability of housing. The main part of the thesis is devoted to general concept of housing policy and overview of the instruments of housing financing support, which is followed by concrete example of the Czech Republic. The overview of the instruments in the Czech Republic is followed by an attempt to estimate their impact to the state and public budgets. The situation in the Czech Republic was wery interesting because of the started application of the new concept from 2011, which changed the direction of the housing policy and the portfolio of instruments. Almost at the end of the thesis, there is briefly presented the model of real estate market by DiPasquale and Wheaton. According to this model it is possible to make a statistic comparative analysis of the impacts of some instuments of housing financing support on the real estate market. The knowledge, acquired during the work on the thesis, is used in the last chapter to prepare the SWOT analysis and evaluation of the current portfolio...
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Can Bayesian econometric methods outperform traditional econometrics in inflation forecasting?
Stráský, Josef ; Baxa, Jaromír (advisor) ; Netuka, Martin (referee)
Forecasting of inflation has become crucial for both policy makers and private agents who try to understand and react to Central Bank decisions because many Central Banks implemented inflation targeting rules instead of control of monetary aggregates. Inflation forecasting is considered to be very complicated issue because univariate regression models and structural macroeconomic models are usually outperformed by naive random walk model. This work is intended for forecasting inflation in the Czech Republic by employing Bayesian econometric method (namely Bayesian vector autoregression - BVAR). Bayesian methods proved to be useful in inflation forecasting in developed countries (Fabio Canova: G-7 Inflation Forecasts: Random Walk, Phillips Curve or What Else?, 2007). Bayesian econometrics is one of the fast developing fields of econometrics for past two decades. In the centre of the approach is Bayesian probabilistic theory based on conditional probabilities. This probabilistic approach is, however, computationally demanding. Fast computer evolution enables wide applications of Bayesian models. Model estimations are based on combining information from some prior beliefs and from the data. Many different sorts of models have their Bayesian variants (e.g. OLS) but the emphasis in this work is on Bayesian...
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Phase transformations in ultra-fine grained titanium alloys
Bartha, Kristina ; Stráský, Josef (advisor) ; Kalvoda, Ladislav (referee) ; Vojtěch, Dalibor (referee)
Title: Phase transformations in ultra-fine grained titanium alloys Author: Kristína Bartha Department: Department of Physics of Materials Supervisor of the doctoral thesis: PhDr. RNDr. Josef Stráský, Ph.D., Department of Physics of Materials Abstract: Ti15Mo alloy in a metastable β solution treated condition was processed by high pressure torsion (HPT) and equal channel angular pressing (ECAP). The microstructure after HPT is severely deformed and ultra-fine grained, while ECAP deformation results in rather coarse-grained structure with shear bands containing high density of lattice defects. Two types of thermal treatments - isothermal annealing and linear heating - were carried out for the solution treated condition and both deformed materials. Wide spectrum of experimental techniques was employed to elucidate the differences in phase transformations, especially in α phase precipitation, occurring in deformed and non-deformed material upon thermal treatment. It was shown that the α phase precipitation is accelerated in the deformed materials due to a high density of lattice defects, which provide a dense net of preferred sites for nucleation and also fast diffusion paths necessary for accelerated growth. The enhanced precipitation of the α phase in deformed materials also affects the stability of the ω...
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Metastable beta titanium alloys for biomedical use
Preisler, Dalibor ; Stráský, Josef (advisor) ; Janeček, Miloš (referee)
In this work the effect of die-forging and annealing on the mechanical properties and microstructure of biocompatible metastable alloy Ti-35.3Nb-7.3Zr -5.7Ta-0.7O (wt. %) was studied. Light and scanning electron microscopy, microhardness tests and tensile tests were used to study all prepared conditions. As-cast and as-annealed conditions showed chemical inhomogeneities exhibited as dendritic structure, grains with size of hundreds of micrometers and numerous pores having size of units of micrometers. Precipitation of alpha phase particles was negligible in as-annelaed conditions and only grain boundary alpha paticles formed. Die-forged condition showed grain sizes in the wide range of hundreds of micrometers down to micrometers. Both as-annealed and die-forged conditions showed increased microhardness compared to as-cast condition, but there were no significant differences between different annealing conditions. Yield stress of 870 MPa was found for as-cast condition while as-forged condition exhibited even higher yield stress of 1120 MPa. In both conditions, good room-temperature ductility was demonstrated. Due to its high strength, this alloy is perspective for manufacturing of joint implants.
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Plan curved structures supported by arches
Trenz, Jan ; Zich, Miloš (referee) ; Vítek,, Jan (referee) ; Stráský, Jiří (advisor)
The aim of this doctoral thesis is the research of the plan curved footbridges with the deck supported by arch. The research is preceded by the survey of present findings about arch structures with upper deck. The summary of reasons and difficulties of design of plan curved structures follows. The appropriate approach for design of plan curved structure is searched on the basis of methods for design of straight structure. The design of arch which is subjected to minimal bending moments is emphasised. At first, the structure is designed in the same way as straight structure and the limit plan curvature (for which the method is not suitable anymore) is sought. Then the approach based on method of inversion of suspended cable is examined and adapted for designing of plan curved arch geometry. The approach is thoroughly analysed through calculation model and experimentally verified on physical model in scale 1:10. The process of design, construction and testing of the physical model is described in detail. Measured deformations and stresses are compared with expected behaviour based on numerical analysis. The comparison proves good correlation between calculation and measurement, as well as high load bearing capacity of the structure.
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