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Preparation and Characterization of Porous Magnesium Based Materials
Březina, Matěj ; Pacal, Bohumil (referee) ; Vojtěch, Dalibor (referee) ; Ptáček, Petr (advisor)
Bulk magnesium materials produced nowadays via powder metallurgy are based on a vastly extensive technological spectrum, which makes it possible to create a wide range of materials. This work focuses on the preparation of bulk materials from magnesium powder by cold pressing and hot pressing, sintering and field assisted sintering. The bulk materials were prepared in a series of compacting pressures from 100 MPa to 500 MPa and the sintering temperatures were selected in the range of 300 ° C to 600 ° C in order to characterize the influence of the manufacturing conditions and technology on the final properties of bulk materials. Prepared materials were evaluated in terms of microstructure, hardness, microhardness, three-point bend test, and fractography. From the hot pressed materials, the samples prepared at 400 and 500 MPa and 400 °C had the highest strength and hardness. The classic sintering of magnesium in the furnace with argon atmosphere proved to be ineffective due to the oxide layer on the surface and the presence of oxygen in technical argon. The SPS sintering (Spark Plasma Sintering) was the more effective with the lower applying pressure used to make the preforms and with the higher applied pressure during the SPS process itself. Highest strength and hardness were achieved in this case of materials sintered at 600 ° C prepared from free powder and the most porous preform (100 MPa). The bulk materials were prepared using all methods used, but the properties of these materials varied considerably depending on the technology used.
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Duplex microstructures preparation by mechanical alloying and spark plasma sintering
Neboha, Oksana ; Štěpánek, Roman (referee) ; Moravčík, Igor (advisor)
This master´s thesis focuses on duplex microstructures preparation by powder metallurgy. A hybrid material can be created by combining two or more existing materials in different geometries, and thus the newly formed composite can provide a superposition of the properties of the starting materials (powders). This means that it will have an improved combination of the required properties. The theoretical part describes in detail the hybrid materials and the architectured materials that contain highly controlled structures. Structure control allows to change the variety of possible geometries and opens up a number of other useful properties. Therefore, this thesis also deals with the mechanical alloying and SPS. The experimental part describes procedures of preparation of four samples of composites with a duplex structure from a powder of a significantly tough alloy (austenitic steel 316L) in combination with a powder of a significantly strong alloy (titanium carbonitride). A crucial part of this thesis is characterization of these four samples by electron microscopy methods (SEM, TEM, EDS) and supported by hardness measuring.
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New compositions of advanced oxide dispersion steels based on rare earth elements
Pech, Filip ; Kuběna, Ivo (referee) ; Hadraba, Hynek (advisor)
The main objective of present diploma thesis is to prepare three different classes of steels, differing by their content of chromium: 9Cr, 14Cr, 17Cr steels and their oxide dispersion strengthened variants. Steels were prepared from atomic and pre-alloyed powders by the mechanical alloying and compacted by the spark plasma sintering method. Used strengthening elements were yttrium, which is most commonly used, and aluminium. Preparation of oxide dispersion was done in two ways: direct adding of yttria and alumina and inner oxidation of aluminium and yttrium. In the experimental part has been found, that it is possible to make oxide dispersion by both ways, but aluminium strengthened steel has to be prepared by inner oxidation to ensure fine oxide dispersion.
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Mechanical Reinforcement of Bioglass®-Based Scaffolds
Bertolla, Luca ; Prof. Dr.-Ing. habil. Aldo R. Boccaccini (referee) ; Kotoul, Michal (referee) ; Pabst, Willi (referee) ; Dlouhý, Ivo (advisor)
Bioactive glasses exhibit unique characteristics as a material for bone tissue engineering. Unfortunately, their extensive application for the repair of load-bearing bone defects is still limited by low mechanical strength and fracture toughness. The main aim of this work was two-fold: the reinforcement of brittle Bioglass®-based porous scaffolds and the production of bulk Bioglass® samples exhibiting enhanced mechanical properties. For the first task, scaffolds were coated by composite coating constituted by polyvinyl alcohol (PVA) and microfibrillated cellulose (MFC). The addition of PVA/MFC coating led to a 10 fold increase of compressive strength and a 20 fold increase of tensile strength in comparison with non-coated scaffolds. SEM observations of broken struts surfaces proved the reinforcing and toughening mechanism of the composite coating which was ascribed to crack bridging and fracture of cellulose fibrils. The mechanical properties of the coating material were investigated by tensile testing of PVA/MFC stand–alone specimens. The stirring time of the PVA/MFC solution came out as a crucial parameter in order to achieve a more homogeneous dispersion of the fibres and consequently enhanced strength and stiffness. Numerical simulation of a PVA coated Bioglass® strut revealed the infiltration depth of the coating until the crack tip as the most effective criterion for the struts strengthening. Contact angle and linear viscosity measurements of PVA/MFC solutions showed that MFC causes a reduction in contact angle and a drastic increase in viscosity, indicating that a balance between these opposing effects must be achieved. Concerning the production of bulk samples, conventional furnace and spark plasma sintering technique was used. Spark plasma sintering performed without the assistance of mechanical pressure and at heating rates ranging from 100 to 300°C /min led to a material having density close to theoretical one and fracture toughness nearly 4 times higher in comparison with conventional sintering. Fractographic analysis revealed the crack deflection as the main toughening mechanisms acting in the bulk Bioglass®. Time–dependent crack healing process was also observed. The further investigation on the non-equilibrium phases crystallized is required. All obtained results are discussed in detail and general recommendations for scaffolds with enhanced mechanical resistance are served.
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Transparent ceramic materials
Krupa, Filip ; Drdlík, Daniel (referee) ; Maca, Karel (advisor)
This Bachelor thesis deals with processing of transparent cubic ZrO2 ceramic doped by 8 mol% Y2O3. Technology used in this Bachelor thesis are uniaxial pressing, cold isosatic pressing, SPS and hot isostatic pressing. Microstructure, real in-line transparency and hardness were evaluated for sintered transparent materials.
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Study of microstructure evolution during final stage of sintering of advanced ceramic materials
Hrubý, Jan ; Salamon, David (referee) ; Maca, Karel (advisor)
This diploma thesis deals with the study of microstructure development during the final stage of sintering of two zirconia based ceramic materials (tetragonal ZrO2 doped with 3 mol% of Y2O3 and cubic ZrO2 doped with 8 mol% of Y2O3). Conventional, microwave and SPS sintering methods were used. Achieved relative densities and mean grain sizes were evaluated for sintered materials. It was found that the non-conventional sintering methods are capable of rapid processing of ceramics with improved microstructure compared to conventional sintering.
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High entropy alloy preparation by means of mechanical alloying
Gamanov, Štěpán ; Krajňáková, Petra (referee) ; Moravčík, Igor (advisor)
This thesis deals with topic of high entropy alloys. The teoretical part explains what are high entropy alloys, how are they different from conventional alloys, how is their chemical composition proposed and what potencial these alloys have. The experimental part describes procedures of preparation of three high entropy alloys witch consists of Co, Cr, Fe, Ni and Ti, where the concentration of all elements except Ti remains the same. These alloys were prepared via mechanical alloying and sintered by SPS process. Crucial part of this thesis is characterization of these three alloys with EDS and XRD supported by hardness measuring and tensile tests.
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Preparation of Mg-Al based bulk materials via powder metallurgy
Jakůbek, Zdeněk ; Fintová, Stanislava (referee) ; Březina, Matěj (advisor)
This diploma thesis is focused on preparation of Mg-Al based bulk materials via powder metallurgy. The bulk materials were prepared by cold pressing, cold pressing followed by sintering, cold pressing followed by sintering and artificial aging, SPS (spark plasma sintering), SPS followed by solution annealing, SPS followed by solution annealing and artificial aging. The prepared materials were characterized in terms of microstructure and physical and mechanical properties. The properties of the prepared materials differed depending on the method of preparation and Al content. All materials after heat treatment were consisted of solid solution (Mg), intermetallic phase Mg17Al12 and MgO. The composition of the materials depended on Al content. Sintering by the SPS method resulted in material with better mechanical properties compared to materials whose first step of preparation was cold pressing.
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Binary eutectoid alloys
Skopalová, Simona ; Pouchlý, Václav (referee) ; Jan, Vít (advisor)
The bachelor thesis deals with the search for suitable binary systems consisting of technically important metals in which eutectoid decay occurs. The work aims to describe and document this disintegration of the emerging structure. The introductory theoretical part describes a general apparatus for describing the phase composition of binary systems which is followed by a description of selected technically important metals which include iron, titanium and manganese. The experimental part dealing with the production of alloys, preparation of metallographic samples and description of the resulting microstructure follows.
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