|
|
Advanced high-temperature resistant metal-ceramic composites based on TiB2 for cutting tools
Halmazňa, Jiří ; Drdlík, Daniel (referee) ; Chlup, Zdeněk (advisor)
This diploma thesis deals with the preparation of new high-temperature resistant cermets based on TiB2. The hard ceramic phase is bonded by NiW metallic alloy, which was prepared by mechanical alloying using a planetary ball mill. The first part of the thesis is targeted to the optimization of mixing of both powders in the planetary ball mill. The procedure of preparation of powders mixture with homogenous particles distribution of the NiW alloy was designed and verified with simultaneous particle size refinement. The second part is focused on the microstructure characterisation and mechanical properties evaluation of sintered materials. In this case both powders, TiB2 and NiW, were mixed in a tubular mill and consequently compacted by a rapid hot pressing method at four different sintering temperatures. The influence of the sintering temperature on the microstructure development characterized by the density, porosity and grain size was monitored. The elastic modulus, fracture toughness, flexural strength and hardness were measured on prepared test specimens. The results of conducted experiments show a significant dependence of the microstructure and mechanical properties on applied sintering temperatures. The higher sintering temperatures are used the better mechanical properties are observed. However, the sintering temperature of 1375°C seems to be an optimal one. The sintering temperature of 1400°C leads to the significant losses of the metal phase due to sublimation of nickel resulting in increased porosity in the metal phase regions.
|
|
|
Ceramic dental restoration milling from stock based on ZrO2
Ščasnovič, Erik ; Spusta, Tomáš (referee) ; Kaštyl, Jaroslav (advisor)
In this bachelor thesis, the theoretical overview about the milling of the dental zirconia blanks was performed. The tests of biaxial flexural strength were evaluated in the experimental part, as well as the roughness and the grain size in sintered state and the linear shrinkage was determined. These tests were done for gel cast blanks from zirconia dioxide prepared in laboratories and also for two types of commercially available zirconia oxide blanks fabricated by cold isostatic pressing. The relationship between strength and grain size was shown. The samples prepared from gel cast blanks had statistically significantly higher strength than samples from commercial blanks. At the end of the thesis, the milling of dental crown was carried out based on real tooth model from gel cast zirconia blank studied in this thesis.
|
|
|
Lining of the induction furnaces
Kopečný, Vendelín ; Pernica, Vítězslav (referee) ; Myška, Martin (advisor)
This work deals with lining of electric induction furnaces. The first part describes the preparation of lining, its function during the running of furnace and also its tearing down at the end of work process. In the thesis is also discussed the use of rammed crucibles. The materials used for lining and rammed crucibles are described also in the sense of their chemical properties in connection with the possibilities of their use under different conditions. The practical part of the thesis describes the process of lining the electric induction furnace, which was realized by the author under the supervision of the supervisor.
|
|
|
Synthesis and sintering of zirconia based ceramics for biomedical applications
Jahodová, Daniela ; Novotná, Lenka (referee) ; Částková, Klára (advisor)
The present thesis focuses on the preparation of tetragonal zirconia doped with yttria oxide, ceric dioxide, and magnesium oxide. In its theoretical part the thesis covers the characteristics of doped ceramics, the possible methods of powders preparation and of their further processing. The experimental part describes the precipitation synthesis of zirconia in base environment and further processing for ceramics. Also studied were the influences of dopant and of the processing technique used on the phase composition and microstructure of the resulting ceramics. To describe the powder structure, the thermal, dilatometric, surface area, and x-ray analyses were performed; as well as both the scanning and transmission electron microscopy employed. Dry processed ceramics showed the average grain size of 87–94 nm and the relative density in the range of 84,0–99,3 %. In comparison, the ceramics produced of hydrothermally synthesised powders proved the average grain size of 75–85 nm and the relative density between 92,7-99,9 %. As the next step, samples were subjected to low-temperature degradation for the time of 5 and 15 hours. Samples consisting of pure tetragonal ZrO2 were resistant to 5 and 15 hours of low-temperature degradation at 180 °C.
|
|
|
Kinetics of Heterogeneous Processes in Silicate Technologies -Dehydroxylation and Disolution of Clay Minerals
Křečková, Magdaléna ; Kutzendörfer, Jaroslav (referee) ; Kuřitka, Ivo (referee) ; Havlica, Jaromír (advisor)
The first part of the thesis discuss general characterization of heterogeneous processes in silicates. This part is focused on kinetics of heterogeneous processes and mathematical description of reactions time behavior. The other part describes important technologies in silicate industry such as sintering, solid matter decomposition, transition modification, etc. Another chapter deals mineralogy, structure and properties of eminent silicate raw materials. Emphases is given to characterization of clay minerals and their utilising. The experimental part handle the analytic techniques used for investigation of thermal decompostion, dehydroxylation, crystalization of Al-Si spinel phase and sintering process of washed kaolin Sedlec Ia from the region Carlsbad (Czech Republic). Concluding chapter reports on results of experimental work.
|
|
|
Preparation and properties of porous zinc material
Ryšťák, Jaroslav ; Fintová, Stanislava (referee) ; Doležal, Pavel (advisor)
Bachelor thesis is focused on preparation of bulk material prepared from zinc powder by cold pressing followed by sintering. Topic of the work includes characterization of prepared material depending on the choice of the compaction process conditions. Bulk material is characterized by physical-mechanical tests, structure and porosity. Thesis solving and focuses on study and control of processes during bulk material preparation and description of the processes from physically-chemical point of view of the structure creation and final material properties.
|
|
|
Powder metalurgically prepared materials based on Zn and Ca
Morcinek, Tomáš ; Hasoňová, Michaela (referee) ; Doležal, Pavel (advisor)
The topic of this bachelor thesis is a process of preparation and characterization of bulk material from zinc and calcium powder mixture by hot pressing. Materials thus prepared were evaluated in terms of their microstructure and physical-mechanical properties. The influence of calcium content in the material on physical-mechanical properties of the resulting structure was observed. The solution is focused on exploration of the influence of material composition in the process of preparation of bulk material, and description of these processes from the physical-chemical point of view on the structure formation and the resulting properties of the material.
|
|
|
Preparation processes and properties of porous zinc material
Moleková, Kristína ; Březina, Matěj (referee) ; Hasoňová, Michaela (advisor)
Bachelor thesis occupy with preparation of porous material from zinc powder by cold pressing, cold pressing followed by sintering and hot pressing. This thesis contain both preparation of bulk material, and charakterization of materials based on the compaction process conditions. Impact of pressing process on subsequent progress of sintering and final attributes of materials is evaluated. Bulk material is characterized considering to structure, porosity, and physical-mechanical properties. Properties of final metarial will serve to optimize conditions for process of pressing and sintering.
|
|
|
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.
|
|
|
Study of microstructure evolution during intermediate stage of sintering of advanced ceramic materials
Jemelka, Marek ; Pouchlý, Václav (referee) ; Maca, Karel (advisor)
Hlavním cílem této diplomové práce byl popis závislosti kritické hustoty (tj. hustota, při které se tubulární póry zcela přemění na póry izolované a uzavřené) a průměrné velikosti zrn při této hustotě na rozdílných rychlostech ohřevu během druhého stádia slinovacího procesu. Dosažené výsledky jsou velice důležité, např. pro produkci transparentních balistických pancířů, vysoce výkonných řezných nástrojů či kostních a kloubních implantátů, jelikož poskytují informace pro výběr nejvhodnější slinovací metody, jejímž výsledkem jsou vzorky v předslinutém stavu s minimální velikostí zrn pro následnou metodu izostatického lisování za tepla (post –HIP). Bylo zjištěno, že kritická hustota všech studovaných oxidových materiálů (Al2O3, tetragonální ZrO2 a kubické ZrO2) není významně závislá na rychlosti ohřevu v rozmezí od 2°C/min do 200°C/min a průměrné hodnoty kritických hustot jsou 96.3 %; 92,4 % a 93,0 % pro Al2O3, t- ZrO2 a c-ZrO2. Výsledky z dosavadní literatury prokázali, že kritická hustota není taktéž závislá na mikrostruktuře keramického polotovaru, a tedy je možné usuzovat, že kritická hustota je materiálovou konstantou závislou na dihedrálním úhlu materiálu. Slinovací trajektorie (tj. závislost průměrné velikosti zrn na relativní hustotě) byly vyhodnoceny jak pro všechny tři způsoby slinování lišící se rychlostí ohřevu (2, 10 a 200 °C/min s dobou výdrže 5 min), tak pro takzvaný způsob slinování- long-dwell (nízké slinovací teploty s dobou výdrže 5 – 10 h). Výsledky nepotvrdily, že by některá z alternativních metod slinování vedla ke snížení průměrné velikosti zrn při kritické hustotě materiálu, a tudíž v současnosti nejvyužívanější metoda pro přípravu materiálů v předslinutém stavu, tzv. metoda konvenčního slinování (rychlost ohřevu 10 °C/min, doba výdrže 5 min), zůstává i nadále vhodnou metodou pro přípravu vzorků s optimální mikrostrukturou pro následný post-HIP proces.
|
guest ::
