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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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Investigation of deformation mechanisms in textured magnesium alloy by advanced in-situ methods
Dittrich, Jan ; Minárik, Peter (advisor) ; Janeček, Miloš (referee)
Title: Investigation of deformation mechanisms in textured magnesium alloy by advanced in-situ methods Author: Bc. Jan Dittrich Department: Department of Physics of Materials Supervisor: RNDr. Peter Minárik, PhD., Department of Physics of Materials Abstract: This thesis aims to investigate the correlation between texture and the activation of particular deformation mechanisms during the deformation of a rolled magnesium alloy AZ31. A combination of advanced in-situ techniques, providing complementary information about the processes within the material during its deformation, was employed to achieve this goal. The combination of neutron diraction and acoustic emission measurements allowed to investigate both rapid and continuous processes related to changes of the material microstructure resulting from its deformation. The in-situ loading of the sample inside the chamber of a scanning electron microscope, coupled with the electron backscatter diraction analysis, provided more direct observations of the microstructural evolution. Furthermore, the high-speed camera imaging of the deformed sample surface enabled a direct, real-time view of the occurring rapid processes. The results of the experiments conrmed the anisotropy of the mechanical behaviour of samples oriented diversely with respect to the...
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Study of mechanical properties and microstructure development of fine-grained Cu and Cu alloy polycrystals
Srba, Ondřej ; Janeček, Miloš (advisor)
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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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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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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