1,721,064 research outputs found
Complex investigation of fine-grained polycrystals of Cu and CuZr alloy processed by equal channel angular pressing a high pressure torsion
Get PDFTitle: 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..
Optimization of properties of Ti based alloys for biomedical and structural applications
No full textTitle: 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..
Evaluation of electrochemical characteristics of AZ61 magnesium alloy processed by squeeze casting
No full textBachelor thesis deals with the characterization of electrochemical corrosion properties of AZ61 magnesium alloy prepared by squeeze casting method. The theoretical part of the work focuses on properties of AZ61 alloy, influence of alloying elements on magnesium alloys and corrosion. The practical part of the work deals with electrochemical characteristics of AZ61 alloy with different surface condition in of 0.1 M NaCl solution. Corrosion potential (Ekor) and corrosion current density (ikor) were determined by potentiodynamic test. Polarisation resistance was determined by electrochemical impedance spectroscopy. Based on the measured results was discussed the influence of production, chemical composition, structure and surface treatment (grinding and polishing) on corrosion characteristics of the alloy
Effect of microstructure on mechanisms of plastic deformation in fine-grained magnesium alloys
No full textIn this work were studied effects of the grain refinement on the mechanical properties and the corrosion resistance of magnesium alloys potential for medical applications - AE21 and AE42. Mechanical properties changed after ECAP pressing in consistency with literature data. Enhanced corrosion resistance in AE42 alloy was achieved by the grain refinement. Corrosion layer created on the surface was observed by light and electron microscopy. Effect of the grain size on the character of the corrosion layer was investigated. AE42 alloy is suitable for further investigation as potential biodegradable material. AE21 alloy was excluded from further investigation due to low corrosion resistance even after ECAP treatment
Electrochemical corrosion characteristics of Mg-Zn systems prepared by powder metallurgy
No full textThe diploma thesis deals with evaluation of electrochemical corrosion characteristics of Mg-Zn systems prepared by powder metallurgy in SBF solution. The main aim of the thesis is to analyze the influence of chemical composition, achieved structure and parameters of the process of production of Mg-Zn systems on their electrochemical corrosion characteristics. The basic electrochemical properties of the prepared materials will be evaluated by electrochemical impedance spectroscopy. In order to clarify the mechanism of corrosion of materials, the immersion tests will be used, accompanied by metallographic observations
Evaluation of electrochemical characteristics of AZ61 magnesium alloy processed by squeeze casting
No full textBachelor thesis deals with the characterization of electrochemical corrosion properties of AZ61 magnesium alloy prepared by squeeze casting method. The theoretical part of the work focuses on properties of AZ61 alloy, influence of alloying elements on magnesium alloys and corrosion. The practical part of the work deals with electrochemical characteristics of AZ61 alloy with different surface condition in of 0.1 M NaCl solution. Corrosion potential (Ekor) and corrosion current density (ikor) were determined by potentiodynamic test. Polarisation resistance was determined by electrochemical impedance spectroscopy. Based on the measured results was discussed the influence of production, chemical composition, structure and surface treatment (grinding and polishing) on corrosion characteristics of the alloy
Study of mechanical properties and microstructure development of fine-grained Cu and Cu alloy polycrystals
No full textThe 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
Optimalizace vlastností Ti slitin pro biomedicínské a strukturní aplikace
Get PDFTitle: 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...Název práce: Optimalizace vlastností Ti slitin pro biomedicínské a strukturní aplikace Autor: Josef Stráský Katedra / Ústav: Katedra fyziky materiálů Vedoucí doktorské práce: Doc. RNDr. Miloš Janeček, CSc. Abstrakt: Slitiny titanu patří mezi nejpoužívanější materiály pro výrobu tělních implantátů. Předkládaná dizertace se věnuje experimentálnímu studiu pokročilých technologií povrchových úprav titanových implantátů a vývoji nových beta-titanových slitin pro využití v ortopedii. Široké spektrum experimentálních technik bylo využito pro studium souvislostí mezi přípravou materiálu, mikrostrukturou a mechanickými vlastnostmi. Elektroerozivní obrábění bylo využito netradičně jako povrchová úprava pro zvýšení biokompatibility slitiny Ti-6Al-4V. Nevýhodou povrchové úpravy je snížená únavová odolnost. Dvě následné úpravy povrchu - chemické leptání a kuličkování - byly navrženy pro zvýšení únavové odolnosti. Dosažená únavová odolnost je dostatečná pro využití takto upraveného materiálu v ortopedii. Tento proces byl patentován českým úřadem průmyslového vlastnictví. Dizertace dále shrnuje dosažené poznatky v oblasti biokompatibilních beta-slitin Ti. Na základě výchozí slitiny Ti- Nb-Zr-Ta bylo navrženo několik nových slitin s příměsemi železa, křemíku a kyslíku. Vliv příměsí na mikrostrukturu, modul pružnosti a...Katedra fyziky materiálůDepartment of Physics of MaterialsFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult
Evaluation of electrochemical properties of wrought Mg-Al-Zn type magnesium alloys
No full textThe aim of this master’s thesis is electrochemical characteristics evaluation of magnesium alloys. The theoretical part describes the properties of magnesium and its alloys and their corrosion characteristics. In the experimental part are presented results of corrosion resistance measurement of two types of wrought magnesium alloys. It was AZ31 and AZ61 magnesium alloys, which were measured in Hank’s solutions with addition of ions Ca2+ and Mg2+ (SBF+) and without addition of the ions (SBF). The solution temperature during the measurement was 37 ± 1 °C. The experiments were used electrochemical impedance spectroscopy (EIS) and potentiodynamic tests using linear polarization (LP). EIS measurements were done in times of 5 minutes, 1, 2, 4, 8, 12, 24, 48, 72, 96 and 168 hours. Potentiodynamic tests were only short-term and they started after 5 minutes of stabilization. Both methods were used for measuring the electrochemical characteristics of polished and ground surface of the samples. The most important measurement results were polarization resistance, corrosion potential and corrosion current density. The electrochemical measurements are used to estimate the chemical composition influence and alloy’s structure of the corrosion resistance
Microstructure and mechanical properties study of the finegrained magnesium alloys processed by severe plastic deformation
No full textTwo magnesium alloys (Mg-4Y-4Gd-2Ca and Mg-2Y-2Gd-1Ca) with high ignition tem- perature were successfully processed by extrusion. Mg-2Y-2Gd-1Ca alloy was addition- ally processed by equal channel angular pressing (ECAP) to achieve ultrafine-grained microstructure. The effect of extrusion parameters on fraction of recrystallized grains, grain size, and texture was revealed by EBSD analysis. The presence of Mg2Ca, REH2 and Mg5RE secondary phases was proven by SEM and TEM. Microstructural condition including distribution and morphology of secondary phase par- ticles directly affected the mechanical properties. Yield tensile stress exceeding 200 MPa was achieved in each condition. Large non-recrystallized grains with strong {10̄10} tex- ture resulted in a significant anisotropy in mechanical properties. Processing by ECAP led to a homogeneous microstructure with a mean grain size below 1 µm. ECAP condition showed superior mechanical properties with a low anisotropy. The developed and analysed microstructural condition resulted in favourable mechanical properties. The studied alloys are therefore promising for the application in aerospace industry.
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