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EFFECT OF OXIDE DISPERSION ON ELECTRIC CONDUCTIVITY OF ROTARY SWAGED POWDER-BASED COPPER COMPOSITES
Kunčická, Lenka ; Benč, Marek ; Kačor, P. ; Marek, M.
Copper is a very popular electro-conductive material, however, the mechanical properties of pure Cu are low. They can be typically improved by (micro)alloying, or via structure modifications introduced by optimized deformation and thermomechanical treatments. Designing a Cu-based composite, possibly strengthened by a dispersion of fine oxides, is another way how to favourably improve the strength properties of Cu. In this study, we performed mechanical alloying of a Cu powder with a powder of Al2O3 oxide, which is known to have strengthening effects on metallic materials. After mixing, we sealed the powder mixture into evacuated tubular Cu containers (i.e. cans). As for the consolidation procedure, we applied direct consolidation of the canned powders via the intensive plastic deformation method of rotary swaging, performed under warm conditions. Subsequently, we subjected the swaged conductors to measurements of electric conductivity and detailed structure observations. The results revealed that the applied swaging ratio was sufficient to fully consolidate the canned powders as the final conductor was unrecognizable from a cast alloy from the viewpoints of visual and structure assessment. In other words, the structure did not exhibit any voids or remnants of unconsolidated powder particles. The observed fine grains with homogeneous dispersion of Al2O3 oxide particles provided improvement of the mechanical properties, as proven by microhardness measurements. Moreover, the electric properties remained favourable.
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Ceramic materials and composites for advanced applications
Mařák, Vojtěch ; Částková, Klára (referee) ; Michálková,, Monika (referee) ; Drdlík, Daniel (advisor)
Tato dizertační práce se zaměřuje na pokročilou oxidovou keramiku a částicové a vrstevnaté kompozity. Studované materiály zahrnují biokeramický hydroxyapatit, termomiotický wolframan hlinitý a bezolovnaté piezoelektrické materiály na bázi titaničitanu barnatého. Příprava těchto keramik má několik omezení ovlivňující finální vlastnosti, zahrnující použití toxických stabilizátorů, nízké zhutnění, náchylnost k praskání, vznik nežádoucích chemických reakcí, nízké mechanické a elektrické vlastnosti. Tato práce řeší tyto problémy přizpůsobením jednotlivých kroků zpracování a použitím progresivních výrobních metod pro optimalizaci požadovaných funkčních vlastností materiálů. Úprava hydroxyapatitového prášku studenou plazmou umožnila elektroforetickou depozici bez toxických stabilizátorů, což vedlo k hutnějším povlakům bez trhlin. Praktický benefit tohoto přístupu byl demonstrován v případě bezdefektních hydroxyapatitových povlaků ortopedických šroubů. Termomiotický wolframan hlinitý, vyznačující se svým téměř nulovým koeficientem tepelné roztažnosti, byl syntetizován optimalizovanou koprecipitací za účelem zlepšení slinovatelnosti prášku. Rychlé beztlaké slinování a slinování plazmovou jiskrou byly použity ke zhutnění materiálu, přičemž bylo dosaženo dosud nejvyšších publikovaných hodnot hustot při nejnižší slinovací teplotě. Vývoj mikrostruktury piezokeramiky titaničitanu barnatého byl studován pomocí rychlého beztlakého slinování a slinování s pomocí radiace. Získané poznatky byly využity pro slinování částicových kompozitů na bázi titaničitanu barnatého vyztuženého oxidovými keramikami. Vysoká reaktivita mezi zvolenými materiály měla negativní vliv na vlastnosti kompozitů a jeden z reakčních produktů byl podrobněji charakterizován. Byly připraveny vrstvené kompozity střídáním vrstev na bázi titaničitanu barnatého a dielektrického oxidu zirkoničitého. Vysoká reaktivita piezoelektrických materiálů byla potlačena volbou slinovací strategie. Souhrnným cílem této disertační práce je posunout vědění v oblasti vlastností a zpracování keramických materiálů, poskytnout náhled na optimalizaci funkčnosti a řešit kritická omezení v různých aplikacích.
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Transparent YAG ceramics
Nowak, Ondřej ; Šťastný, Přemysl (referee) ; Trunec, Martin (advisor)
In this bachelor thesis was done basic theoretical analysis of problems regarding transparent ceramics, their preparation and aplications. Transparent YAG ceramics was prepared with 2 methods, cold isostatic pressing (CIP) and gelcasting (GC). Green bodies were prepared with CIP at pressure 700 MPa and 1000 MPa from 2 different slurries with 2 different Al2O3 powders and 1 prepared with gelcasting method. After that green bodies were annealed to remove binderes and vacuum sintered (10-3 Pa). Sintered samples were compared based on optical properties and microstructure. Because of better optical properties, microstructure analysis was done only on sampled pressed to 1000MPa and gelcasted. In both pressed samples high level of porosity was reported, one was almost completely non-transparent, the other was ranslucent. Sample prepared by gelcasting was almost clearly transparent, but due to presence of unreacted phase Y2O3, minor scattering of light passing through the sample was observed.
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Effect of material thickness on the width and properties of the heat-affected zone
Horák, Tomáš ; Slováček, Marek (referee) ; Kubíček, Jaroslav (advisor)
Thess deals with the welding of high-strength steel by the MAG method and the evaluation of structural and dimensional changes depending on the thickness of the material. CREUSABRO 4800 steel was chosen using MEGAFILL 742 M additive material. A weld was created with welding parameters of 130 A, 20.7 V and a feed speed of 35 cm/min with a swing of 7 m, on steel with a thickness of 3, 6, 10 mm. Subsequently, a weld was made on samples with a thickness of 10 mm with welding parameters of 300 A, 28.8 V, 35 cm/min with a swing of 7 mm, while one of the samples was preheated to the recommended temperature. The resulting macro structure, micro images and the thermally affected area were evaluated.
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Modification of the crystallographic texture of austenitic steel by 3D printing
Fábry, Adam ; Dočekalová, Kateřina (referee) ; Koutný, Daniel (advisor)
The microstructure, and therefore the mechanical properties of the material, depend on the cooling rate and the direction of the temperature gradient during cooling, which can be easily influenced in additively manufactured metal parts. In previous research, this change has been achieved by altering the scanning strategy during production. This work focuses on modifying the crystallographic structure of material X30Mn22 by varying the laser speed and power while maintaining a constant meander scanning strategy without rotation. To determine the applicable production parameters, a test of simple welds was conducted, providing a basis for future production and testing of bulk samples. The suitability of the production parameters and the microstructure achieved in the sample cross-section were evaluated using porosity on the fabricated bulk samples, and the microstructure was depicted using EBSD maps, showing significant changes in microstructure solely by altering the laser production parameters. Tensile samples were further fabricated for selected microstructure samples, and their mechanical properties were tested. The results of tensile tests showed differences between individual microstructures of 18% for yield strength and up to 10% for ultimate tensile strength. However, the most significant difference was in the achieved tensile modulus, which differed by up to 27%. The work provides fundamental insights into modifying and adjusting the structure of manganese-rich material by changing laser power and speed settings.
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Friction of Titanium Surfaces in Implantology
Heto, Matyáš ; Odehnal, Lukáš (referee) ; Ranuša, Matúš (advisor)
This bachelor thesis focuses on the frictional properties and wear resistance of Ti6Al4V alloy. This alloy is suitable for use in orthopaedic implants such as the first metatarsophalangeal (MTP) joint in the big toe. The aim is to investigate different surface treatment methods that can reduce friction and wear of this material. The effect of applying DLC coatings and creating microtextures or microstructures on the surface is described. Metal on metal pair tests have been carried out using profilometer and tribometer in pin on plate configuration. The results show a noticeably higher coefficient of friction for the Ti6Al4V alloy than for the compared CoCrMo alloy. DLC coating significantly helped in reducing the friction and wear of Ti6Al4V. This cannot be said for the two microstructures tested, which did not have a significant effect on the observed tribological properties. The results indicate the importance of surface treatment of Ti6Al4V alloy for use in implants.
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Inverse-Heusler Mn2FeSi alloy prepared by powder metallurgy route
Životský, O. ; Skotnicová, K. ; Čegan, T. ; Juřica, J. ; Gembalová, L. ; Zažímal, František ; Jirásková, Yvonna ; Szurman, I.
The Mn2FeSi inverse-Heusler alloy was prepared by solid-state reactions using ball milling for 168 h in n hexane. Two milling procedures varying in the ball-to-powder ratio, namely 4:1 and 10:1, were used to follow \ntheir influence on alloy formation and its physical properties. In both cases no Heusler structure was obtained \ndirectly and therefore the subsequent annealing at 1223 K for 1.5 h in pure Ar was applied. The energy dispersive X-ray analysis resulted in the chemical composition about 49.0-49.9 at% Mn, 25.3-25.6 at% Fe, and \n24.8-25.4 at% Si, in a good agreement with nominal one. X-ray diffraction of both powders confirmed inverse Heusler XA structure of lattice parameters 0.5675 nm (4:1) and 0.5677 nm (10:1), only slightly higher as \ntheoretically obtained 0.560 nm. The presence of minor oxidation phases was also observed in the particle \nstructure of powders. Magnetic properties were analysed at low and room temperatures. Both alloys exhibit \nparamagnetic behaviour at room temperature confirmed by transmission Mössbauer spectroscopy \nmeasurements. Different magnetic behaviour of alloys is observed below 65 K.
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3D microstructure evaluation of developed Si3N4 material for alloyed wire rolling applications
Lövy, Vít ; Salamon, David (referee) ; Chlup, Zdeněk (advisor)
This diploma thesis is devoted to the use of 3D reconstruction using EBSD method for microstructural analysis of silicon nitride ceramic material predetermined for the rolling-mill used in the wire production. Application of this method can be used for the grain structure reconstruction and basic microstructural parameters can be than extracted. The development of a suitable method for 3D reconstruction of the structure of the materials the main aim of this work. There are described the different steps begun by sample preparation from the investigated material trough the optimisation of analysis parameters up to the visualization of the grain structure. New type of sample geometry has been designed which leads to the better and faster observation of the microstructure of ceramic materials. This thesis also describes optimal reconstruction parameters such as the geometry of the assembly used in the microscope without mechanical movement of the sample or the influence of conductive coating prepared via in-situ sputtering of suitable metal, or adjustment of the electron and ion beams. Further are described two options of software which can be used for the final generation of 3D structure information and are assessed their advantages and disadvantages. The effect of the filter setting and other parameters and their influence on the resulting structural parameters are also evaluated.
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Using simulation to predict defects in and cast Al-alloy castings
Šolc, Petr ; Bařinová, Dagmar (referee) ; Čech, Jaroslav (advisor)
The aim of this work is comparing three casting process simulation programs for porosity and microstructure prediction capabilities for die-casting. After confronting these results with experimentally measured data taken from real castings it could be said that simulation is pretty accurate for DAS microstructure prediction and hot-spot areas. Amount of measured porosity could not be compared with predicted values because specimens were not taken from the exact hot-spot areas.
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Structural analysis of austenitic weld joints
Procházka, Robert ; Foret, Rudolf (referee) ; Havlík, Petr (advisor)
The bachelor thesis deals with structural analysis of austenitic weld joints by using methods of material science. The theoretical part of the thesis summarizes the problematics of welding of high-alloy steels. After the general definition of welding and weldability of high-alloy steels, the thesis focuses on structural adjustments including welding defects during the welding process. Selected methods of fusion welding that were used to create these welds are mentioned in the second half of the theoretical part. The experimental part covers the structural analysis of the welds, which consists of microstructure evaluation, chemical composition analysis, and microhardness test.
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