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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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Interaction of tokamak plasma with selected fusion materials
Klevarová, Veronika ; Janeček, Miloš (advisor) ; Horáček, Jan (referee)
Title: Interaction of tokamak plasma with selected fusion materials Author: Veronika Klevarová Department: Department of Physics of Materials Supervisor: Doc. RNDr. Miloš Janeček, CSc. Supervisor's e-mail address: Milos.Janecek@mff.cuni.cz Abstract: The following work is devoted to structural analysis and study of relevant physical properties of materials with perspective use for the first wall and as construction materials of the tokamak device, prior to their interaction with the high-temperature plasma in Compass-D tokamak. The theoretical part contains an introduction to the interaction of tokamak plasma with fusion materials, including a description of the processes taking place during the plasma discharge (such as implantation, erosion, particles traveling in the tokamak vacuum vessel, redeposition, co-deposition with tritium etc.) and selection of appropriate fusion materials. The experimental part consists of structural analysis of selected materials by optical and scanning electron microscopy. Analysis of the structure revealed the presence of oxide layers in some samples prepared by the technology of plasma spraying; which was probably caused by sample preparation in the ambient air. Qualitative elemental analysis of the samples was performed by electron dispersive X-ray spectroscopy (EDS) in SEM....
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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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Effect of substantial grain refinement on microstructure and mechanical properties of precipitation hardenable magnesium alloys.
Hofman, Daniel ; Minárik, Peter (advisor) ; Janeček, Miloš (referee)
Properties of magnesium alloy WE43 and the effect of substantial grain refinement by ECAP were studied. The compressive strength test revealed a significant increase of yield strength after ECAP, resulting in yield strength of over 400 MPa after 8 ECAP passes. The material remained surprisingly ductile in both compression and tension. Thermal stability of the material was investigated via Vickers hardness test. The ultrafine-grained structure shows good thermal stability up to 300 řC, where the precipitates start to dissolve and grain size starts to increase, resulting in sharp fall of hardness. Annealing of the initial state showed best results for 210 řC where the precipitation hardening led to an increase in hardness up to ∼101 HV.
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Study of mechanical properties and microstructure development of fine-grained Cu and Cu alloy polycrystals
Srba, Ondřej ; Janeček, Miloš (advisor) ; Hadzima, Branislav (referee)
The objective of the thesis is the study of mechanical properties, microstructure development and corrosion resistance of technical purity copper and Cu-0.18 wt.% Zr polycrystals prepared by ECAP. The tensile tests showed that the characteristic stresses 0,2 and max increase with increasing strain imposed by ECAP. The improvement of mechanical properties is compensated by the drop of ductility in the deformed state. The microstructure after 8 passes of ECAP is almost homogeneous consisting of equiaxed grains of the average size of 200 nm. The severe plastic deformation resulted in the grain size reduction of the factor of 1000. The specimen after 8 passes contains almost 50% of high angle grain boundaries. From the thermodynamic viewpoint the deformation did not change significantly the corrosion properties. However, the corrosion in the deformed material is slower and much more homogeneous.
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Utilization of field-assisted sintering technique for fabrication of metastable beta titanium alloy in a rod shape
Majoros, Adrián ; Veverková, Anna (advisor) ; Janeček, Miloš (referee)
Title: Utilization of field-assisted sintering technique for fabrication of metastable beta titanium alloy in a rod shape Author: Adrián Majoros Department: Department of Physics of Materials Supervisor: RNDr. Anna Veverková, Department of Physics of Materials Abstract: We worked with a metastable β titanium alloy Ti-15Mo in the form of a rod produced by field-assisted sintering method (FAST) in this bachelor's thesis. The samples were subjected to classical methods of thermomechanical processing, namely forging and solution treatment. We have investigated the effect of the alloy processing on its microstructure and mechanical properties and compared them with an alloy produced commercially. The characterization was performed by scanning electron microscopy, Vickers microhardness measurement, Archimedes method of porosity measurement and tensile testing. Using Archimedes method, we obtained a quantitative description of porosity of produced rods, which was further qualitatively confirmed by microstructure analysis using scanning electron microscopy. We have found out that in order to achieve a microstructure similar to the microstructure of a commercially produced rod, it is necessary to subject the sintered rod to further processing particularly to forging. After solution treatment, the forged sintered rod...
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The hip fracture register, optimalization of hip hemiarthroplasty position
Skála - Rosenbaum, Jiří ; Bartoníček, Jan (advisor) ; Chomiak, Jiří (referee) ; Janeček, Miloš (referee)
The study examines the monocentric epidemiological data of patients with hip fractures from 1997-2007. Adult patients treated for hip fracture between the years 1997-2007 were included in the study. Retrospective statistical assessment of continually gathered data focused on epidemiology and demographics. The second part of the study was concerned on risk factors on protrusion of hemiarthroplasty into the acetabulum. The goal was to specify exact indication, proper operative technique and selection of the implant. The study involved 3 683 patients (2 678 women, 1 005 men). Patients older than 70 years accounted for 82 % of all cases. There was an increase in the number of hip fractures resulting in a significant increase in pertrochanteric fractures (AO-31A1+2) (p<0.001). The ratio of trochanteric to neck hip fractures increased from 0.99 to 1.53. Continual monitoring of patients with hip fracture offers data which allows comparisons between regions and countries. The importace of a continual increase in the number of hip fractures has its importance in macroeconomical planning in traumatology. Hemiarthroplasty was conversed to total hip arthroplasty in 12 patients in our department. The indication, time period to conversion and hemiarthroplasty position were retrospectively assessed. The direction of...
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Low-modulus titanium alloys for biomedical use
Šalata, Kristián ; Preisler, Dalibor (advisor) ; Janeček, Miloš (referee)
Titanium alloys belong to a group of perspective biomaterials used for production of joint endoprotheses. In order to develop a biocompatible material with better mechanical properties, twelve alloys with 0.7 wt% of oxygen and different contents of Nb, Ta, Zr, Fe were fabricated. Microstructure and phase composition were studied by means of scanning electron microscopy, mechanical properties were determined by microhardness measurements and tensile testing. As follows from the microstructure analysis, only single alloy with composition Ti-20Nb-7Zr-0,7O (wt%) contained also the martensitic phase apart from the metastable phase. In case of other alloys we observed only phase. We found out that the microhardness of alloys gradually decreases with increasing content of -stabilizing elements until the solid solution is saturated. The high value of microhardness in case of alloys with low content of -stabilizing elements is thus considered as indirect proof of the presence of the brittle phase . Tensile tests showed that none of the alloys with increased hardness has undergone strain hardening. The interstitial oxygen atoms led to yield strengths of more than 1000 MPa for all investigated alloys. In some cases, the ultimate tensile strength was more than 1200 MPa. The most promising alloy for the...
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