|
|
Preparation of transparent advanced ceramic base on Al2O3.MgO
Chvíla, Martin ; Maca, Karel (referee) ; Pouchlý, Václav (advisor)
Ceramic materials are in general characterized by high hardness, high modulus of elasticity, excellent abrasion resistance, etc. These properties make ceramics among others useful in optically transparent applications. An ideal form of optically transparent ceramic material is monocrystalline. However, the monocrystalline fabrication is expensive and/or time consuming. From this point of view polycrystalline ceramics is preferred. But the polycrystalline transparent ceramics fabrication is fraught with complications such as porosity, inappropriate grain size and insufficient purity. These circumstances could be solved by using sintering additives. This master’s thesis compiles literature research summarizing modern technologies of advanced ceramics sintering and ceramic polycrystalline microstructure dependence on its optical properties. The experimental part of this thesis focuses on the fabrication parameters of polycrystalline advanced ceramics based on Al2O3MgO and evaluation of their optical properties. Polycrystalline magnesium-aluminate spinel with sintering additive contents 0; 0.3 and 0.6 weight % LiOH was fabricated by optimalisation of Spark Plasma Sintering cycle. Fully dense ceramic samples of polycrystalline magnesium-aluminate spinel with favourable optical properties in visible spectrum radiation were achieved. Real In-line Transmission RIT and Total Forward Transmittance TFT were analysed. RIT exceeded 84 % at wavelength of 633 nm and TFT exceeded 83 % at wavelength above 860 nm. The decisive factors in terms of the optical properties of ceramics sintered with sintering additives were the amount of time-spending at high temperatures and the purity of ceramic powders.
|
|
|
Mechanical properties of WN43 magnesium alloy prepared by spark plasma sintering
Knapek, Michal ; Minárik, P. ; Greš, A. ; Zemková, M. ; Cinert, Jakub ; Král, R.
The spark plasma sintering (SPS) method was used to prepare bulk materials form WN43 magnesium alloy atomized powder. Compression tests were carried out in order to investigate the effect of different sintering regimes (10 min at 400, 450, or 500 degrees C) on the mechanical properties of the material. Furthermore, complementary in-situ acoustic emission (AE) recording was employed to reveal the dynamics of deformation processes during compression. It was shown that by increasing the sintering temperature, the ultimate compressive strength and ductility were significantly improved. The AE data and microstructure observations suggest that pronounced twin nucleation takes place around the yield point whereas twin growth and dislocation activity are the dominant deformation mechanisms in the later stages of deformation.
|
|
|
Preparation and characterisation of selected d and p elements carbides
Nižňanský, Matěj ; Tyrpekl, Václav (advisor) ; Vilémová, Monika (referee)
This thesis is focused on carbide ceramics synthesis, more specifically on the synthesis of a Ti2AlC MAX Phase carbide using solution chemistry rather than powder metallurgy. Chloride and nitrate precursors have been used as a source of metals and citric acid as a source of carbon for carbothermal reduction and as a complexing agent. A new route of precursor synthesis has been developed based on peroxo-titanic acid, which helps retain aluminium. The syntheses were performed using the SPS facility to ensure high heating rates. Al4C3 and TiC carbides and their mixtures were prepared successfully. However, the Ti2AlC phase was not synthesized under used conditions. The phase composition, structure and grain sizes of the samples were investigated by powder X-ray diffraction, X-ray fluorescence and electron microscopy. The contents of carbon in the precursors were determined by thermogravimetric analysis.
|
|
|
Preparation of Mg-Al-Ti bulk materials via powder metallurgy
Brescher, Roman ; Doskočil, Leoš (referee) ; Březina, Matěj (advisor)
This diploma thesis deals with research and preparation of bulk materials based on the Mg–Al–Ti system. The theoretical part summarizes the basic knowledge about magnesium alloys, focusing mainly on Mg–Al and Mg–Ti systems. Furthermore, basic information on powder metallurgy methods was included here, from the production of powder materials, through their compaction, to heat treatment and spark plasma sintering (SPS). The theoretical part ends with literature review on the current research of the Mg–Al–Ti system. In the experimental part, bulk materials based on the Mg–Al–Ti system was prepared using traditional methods of powder metallurgy, as well as using the SPS method. The microstructure of the material, elemental and phase composition was examined in this thesis. Subsequently, Vickers hardness and flexural strength were measured, and fractographic observation of the fracture surface was performed. It was found that the aluminum was completely dissolved during the heat treatment, but the titanium particles remained almost intact in the material and worked as a particulate reinforcement. Materials prepared by methods of conventional powder metallurgy showed increased porosity compared to materials prepared by the SPS, resulting in lower hardness and flexural strength. The hardness increased with increasing the amount of aluminum and titanium and with the amount of magnesium phase . Fractographic observation of the fracture surface suggests that a diffuse connection between the reinforcement and the matrix may have occurred after the sintering process.
|
|
|
The influence of mechanical alloying on contamination of powder mixtures and bulk materials
Kubíček, Antonín ; Hadraba, Hynek (referee) ; Moravčík, Igor (advisor)
This thesis deals with the influence of process parameters on the contamination level of powder materials produced by mechanical alloying (MA) technology. For this purpose austenitic stainless steel 316 L and equiatomic CoCrFeNi high-entropy alloy (HEA) were prepared by high-energy ball milling. Both materials were milled in argon and nitrogen atmospheres from 5 to 30 hours. Spark plasma sintering method (SPS) was then used for consolidation of chosen powder samples. Chemical analysis of contamination within MA was carried out using combustion analysers for determination of carbon, oxygen, and nitrogen contents after different lengths of milling. Also differences in chemical composition of powder and corresponding bulk samples were measured. The microstructure analysis using scanning electron microscopy (SEM) of both powder and bulk materials was executed with focus on oxide and carbide presence and dispersion. Increasing content of carbon with increasing milling time was observed across all measured samples. This contamination is attributed to using milling vial made of tool steel AISI D2 (containing 1,55 wt. % of carbon). Increase of carbon content within consolidation using SPS was also observed. Milling of specimens using N2 as milling atmosphere caused higher contamination level in both AISI 316 L and HEA compared to milling in argon.
|
|
|
Experimental manufacturing of multiphase Ni-Si based layers
Rončák, Ján ; Moravčík, Igor (referee) ; Jan, Vít (advisor)
The diploma thesis deals with the preparation of the composite material based on the NiSi system using powder metallurgy supplemented by the sintering with the usage of SPS method (spark plasma sintering). Theoretical part contains general information about the mechanical-chemical process and sintering, while materials and methods used for experimental observation are explained in a separate chapter. Experimental part explains the procedure of the experiment and selected parameters of individual processes. In the experiment, two powder mixtures were created in order to form the NiSi phase in the maximum possible amount of powder material. After successfully reaching presence of the NiSi phase in the range of 87 to 89 wt. %, both mixtures were used to produce sintered samples at temperatures from 700 to 900 °C. Experiments showed the best results for sample number 2, which was sintered at 900 °C for 4 minutes. Resulting porosity was 0.9 % and hardness reached a maximum value of 718 HV 1. However, all sintered samples show cracks at room temperature associated with increased brittleness of the material.
|
|
|
Preparation of Mg-Ti based bulk materials via powder metallurgy
Žilinský, Martin ; Wasserbauer, Jaromír (referee) ; Březina, Matěj (advisor)
The aim of this thesis is preparation and characterization of bulk Mg–Ti based materials. In the first theoretical part properties of base materials and the complexity of preparation alloy from these metals is discussed. Second part is focused on powder metallurgy and its applicability on Mg–Ti system. In another part particle composites are described. In chapter current research another possible methods of alloy preparation from magnesium and titanium are mentioned. The experimental part of this thesis was the preparation of bulk Mg–Ti materials from metal powders. For sample preparation conventional methods of powder metallurgy and spark plasma sintering was employed. Furthermore a characterisation of these materials was done. Microstructure was observed. Present phases were found using X-ray diffraction analysis. Amounts of these phases were determined using a scanning electron microscope with energy–dispersive spectrometry and using X-ray fluorescence. Furthermore hardness was measured and bending test with evaluation was done. Significant difference in results of sample preparation using conventional methods of powder metallurgy and spark plasma sintering was observed.
|
|
|
Extremely fast sintering of advanced ceramic materials
Tan, Hua ; Chlup,, Zdeněk (referee) ; Sedláček,, Jaroslav (referee) ; Salamon, David (advisor)
Techniky rychlého slinování jako „Spark Plasma Sintering (SPS)“, „Flash Sintering“ (FS), „Selective Laser Sintering“ (SLS), „Induction Sintering“ (IS) a „Microwave Sintering“ (MS) jsou navrženy tak, aby účinně a předvídatelně kontrolovaly mikrostrukturu během slinovací proces. Spark Plasma Sintering jako jedna z nejmodernějších technik rychlého slinování a byla studována po celá desetiletí. V SPS má tři hlavní rysy: přímý ohřev elektrickým proudem, pulzní stejnosměrný elektrický proud a mechanický tlak. Mechanismy působení faktorů během SPS procesu však nejsou zatím jasně objasněny. Tato práce byla inspirována zvýšeným zájmem o techniky rychlého slinování a snahou o objasnění působení hlavních faktorů. Tato studie je rozdělena do čtyř částí: efekt elektromagnetického pole, efekt pulzního vzoru, tlakový efekt a přímý Joulův ohřev. Výsledky ukázaly, že elektromagnetické pole v SPS může být ignorováno, jak ukázaly simulace, a rovněž během experimentů nebyl nalezen žádný „efekt pole“. Na druhou stranu účinek pulzního vzoru byl významný, prášek TiO2 byl slinován pulzními vzory 12:2 a 10:9 s konstantním příkonem. Po aplikaci pulzního vzoru 10:9 došlo ke zvýšení velikosti zrna o jeden řád a ke zvýšení hustoty o 8%, zatímco množství spotřebované energie zůstalo konstantní. Při zahřátí s různými vzory pulzů se mění účinný výkon a kontaktní odpor indukovaný mechanickým pulsem, což jsou dva hlavní důvody, které vysvětlují měnící se energetickou účinnost. Vliv tlaku byl také významný, výsledky ukázaly, že použití tlaku při 900 ° C přineslo vysokou hustotu a malou velikost zrn, což vedlo k nejvyšší tvrdosti měřenou podle Vickerse. Interakce mezi tlakem a parami, vedoucí k rozdílné rychlosti přenosu páry v prvním slinovacím stupni, je považována za důvod pro rozdíly v mikrostruktuře, jako jsou mikropóry. Načasování mechanického tlaku může také podporovat difúzní mechanismy zhutňování během druhého slinovacího stupně, jako je difúze na hranicích zrn a mřížková difúze. Přímý ohřev, kdy se vede elektrický proud přímo skrz vzorek, vede k nízké měřené teplotě při slinování karbidu boru a jeho kompozitů, avšak teplota uvnitř vzorku je podstatně vyšší. Přidání slitiny titanu a křemíku do B4C významně zvýšilo finální hustotu, což byl hlavní důvod ovlivnění mechanických vlastností. Vzorek B4C + 1.0Ti (1 obj. % Ti slitiny) dosáhl nejvyšší tvrdosti 3628.5 ± 452.6 HV1 (16.2% vyšší než čistý B4C) s lomovou houževnatostí 2.11 ± 0.25 MPa m0.5. Zatímco při dopování křemíkem dosáhl vzorek B4C + 0.5Si (0.5 obj. % křemíku) nejvyšší tvrdosti 3524.6 ± 207.8 HV1 (o 13.0% vyšší než čistý B4C), vzorek B4C + 1.0Si dosáhl nejvyšší lomové houževnatosti 2.97 ± 0.03 MPa m0.5 (o 15.6% vyšší než čistý B4C). Velikost zrn kompozitů dotovaných titanem se oproti čistému karbidu boru byla o něco větší a mikrostruktura více nehomogenní. Naproti tomu se velikost zrn vzorků dotovaných křemíkem příliš nezměnila ve srovnání s velikostí zrn čistého karbidu boru. Sekundární fáze karbid křemíku byla dobře spojena s matricí karbidu boru a vykazovala pozitivní účinek jak na tvrdost, tak na lomovou houževnatost. Tato práce zkoumala vliv různých kontroverzních a nepopsaných aspektů na slinování keramických materiálů metodou Spark Plasma Sintering, což vedlo k lepšímu pochopení této techniky slinování.
|
|
|
Effect of sintering temperature on microstructure and mechanical properties of AE42 magnesium alloy prepared by spark plasma sintering
Minárik, P. ; Lukáč, František ; Cinert, Jakub ; Šašek, S. ; Král, R.
Magnesium alloy AE42 was prepared by powder metallurgy technique of spark plasma sintering. The effect of sintering parameters, particularly sintering temperature, on the microstructure and mechanical strength was investigated. The gas-atomized powder was sintered at four temperatures in the temperature range of 400-550 °C. It was found that mechanical strength of the sintered samples was significantly affected by several microstructural features. Application of relatively high load during sintering caused deformation of the individual particles and consequent recrystallization depending on the processing temperature resulted in the release of internal strain and in grain growth. As a result, the evolution of the mechanical strength as a function of the sintering temperature was significantly affected by residual stress, grain size and coarsening of secondary phase particles.
|
|
|
High-speed sintering of ceramic materials
Chvíla, Martin ; Spusta, Tomáš (referee) ; Pouchlý, Václav (advisor)
Modern ceramic materials are of a key function in a number of applications in all industrial sectors. The process of preparation of the modern ceramic materials includes an important technological step – sintering. Recently methods operating also with sintering by an electric field have been used. These methods are called non-conventional sintering methods (Spark Plasma Sintering, Flash Sintering etc.) and they represent a promising progress in the manufacturing of advanced ceramic materials. These methods provides time and energy saving, and materials produced by these technologies can achieve better specific properties. The sintering in Spark Plasma Sintering have been in the past few years subject of intensive research. Nevertheless, all the sintering conditions (for example the sintering mechanism) in Spark Plasma Sintering are not completely clarified. The aim of this thesis is to summarize the findings about the preparation of advanced ceramic materials using the non-conventional methods of sintering. During experimental work, the effect of the heating rate while sintering by the Spark Plasma Sintering method on the amount of activation energy of sintering that is needed for sintering of the material ZrO2 + 3 mol. % Y2O3 with regard to the microstructure has been investigated. During the thesis was proved that the time and energetic efficiency is increased using the Spark Plasma Sintering method with higher rating rate (50 °C/min compared to 750 °C/min). The relative densities of samples manufactured by using different heating rate with constant pressure stayed almost unchanged. By using higher heating rates, it was possible to achieve a high relative density and shrinkage already at lower temperature. The method of Master Sintering Curve proved that the activation energy of sintering decreases when higher heating rates of sintering were used.
|
guest ::
