|
|
Highly porous ceramic materials prepared by Spark Plasma Sintering
Barančíková, Miriama ; Spusta, Tomáš (referee) ; Salamon, David (advisor)
Porous ceramic materials are an interesting group of materials due to a wide range of physical properties, low density, and good permeability. Production of a monolith with a shape stability that would also have a high specific surface area and high porosity is a common problem with porous ceramics. The goal of this work was to maintain the high specific surface area and to produce a monolith with a shape stability. Two forms of porous silica nanofibers (as prepared and milled) were used and partially sintered using the Spark Plasma Sintering method (SPS). Different sintering times and temperatures for SPS were tested. The findings revealed that the best SPS conditions were as follows: temperature: 600 °C, sintering time: 5 minutes, pressure: 3 MPa, and the heating rate: 144 °C/min. These sintering conditions resulted in a stable silica based machinable monolith made from fibers or milled fibers. The monoliths have the specific surface area of up to 470 m^2/g and porosity of 72 %, or the specific surface area of up to 422 m^2/g and porosity of 69 % for as prepared fibers and milled fibers, respectively.
|
|
|
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.
|
|
|
Microstructure and microhardness evaluation for NiCrAlY materials manufactured by spark plasma sintering and plasma spraying
Hulka, Iosif ; Mušálek, Radek ; Lukáč, František ; Klečka, Jakub ; Chráska, Tomáš
NiCrAlY deposited by different thermal spraying methods is commonly used as the bond coat material in thermal barrier coatings (TBCs). In the present study, two experimental coatings were deposited by hybrid water stabilized plasma (WSP-H) and radio frequency inductively coupled plasma (RF-ICP) using the same feedstock powder. Spark plasma sintering (SPS) was used to manufacture a compact NiCrAlY from the same feedstock powder as a reference material. Microstructure, internal oxidation, phase characterization and quantification of the mechanical behaviour in terms of microhardness were studied. The investigations clearly showed microstructural and mechanical differences between the NiCrAlY samples manufactured by different plasma technologies. The results confirmed that SPS and RF-ICP provide dense structures with no oxides due to the fabrication under protective atmosphere and similar mechanical properties. Thus, RF-ICP may be used for deposition of very dense coatings with microstructure and hardness comparable to compacted materials prepared by SPS.
|
|
|
Properties of quasicrystal-reinforced high entropy alloys
Adami, Martin ; Tesař,, Tomáš (referee) ; Čížek, Jan (advisor)
This diploma thesis deals with the processing of the high-entropy alloys with the addition of quasicrystals by the spark plasma sintering method. The aim of this thesis is to evaluate the influence of quasicrystals content on the microstructure and wear resistance. The literature review part is divided into several section. The first part is an overview of high-entropy alloys and quasicrystals, including their properties and production methods. The next part pertains to spark plasma sintering and the wear phenomenon. In the experimental part, spark plasma sintering compacts were produced at 1100 °C and an analysis was performed using scanning electron microscope as well as X-ray diffraction and their tribological properties were measured by the pin-on-disc method. It was found that increasing the content of quasicrystals triggered an improvement in the compacts’ wear resistance.
|
|
|
Advanced aluminium alloys prepared by powder metallurgy and spark plasma sintering
Molnárová, Orsolya ; Málek, Přemysl (advisor) ; Haušild, Petr (referee) ; Vojtěch, Dalibor (referee)
Mechanical properties of aluminium alloys highly depend on their phase composition and microstructure. High strength can be achieved among others by introduction of a high volume fraction of fine, homogeneously distributed second phase particles and by a refinement of the grain size. Powder metallurgy allows to prepare fine grained materials with increased solid solubility which are favourable precursors for further precipitation strengthening. Gas atomization was used for the preparation of powders of the commercial Al7075 alloy and its modification containing 1 wt% Zr. A part of gas atomized powders was mechanically milled at different conditions. Mechanical milling reduced the grain size down to the nano-size range and the corresponding microhardness exceeded the value of 300 HV. Powders were consolidated by the spark plasma sintering method to nearly fully dense compacts. Due to a short time and relatively low temperature of sintering the favourable microstructure can be preserved in the bulk material. The grain size of compacts prepared from milled powder was retained in the submicrocrystalline range and the microhardness close to 200 HV exceeded that of the specially heat treated ingot metallurgical counterparts. The prepared compacts retained their fine grained structure and high...
|
|
|
Tailoring of microstructure of advanced ceramic materials by conventional and non-conventional sintering approaches
Prajzler, Vladimír ; Bermejo, Raúl (referee) ; Bača,, Ľuboš (referee) ; Maca, Karel (advisor)
Tato doktorská práce se zabývala mikrostrukturálním vývojem vybraných oxidových keramických materiálů během konvenčního slinování (CS), rychlého slinování (RRS), flash slinování (FS) a slinování pomocí plazmatu (SPS). S ohledem na keramiku pro strukturální aplikace byly pomocí RRS připraveny relativně velké (1 cm3), bez defektní a téměř hutné pelety oxidu hlinitého a yttriem stabilizovaného oxidu zirkoničitého (YSZ) s homogenní mikrostrukturou. RRS bylo také shledáno jako optimální metoda pro přípravu vysoce hutné bezolovnaté piezoelektrické keramiky s podobnými vlastnostmi, jako byly získány po časově a energeticky náročnějším CS. Metoda SPS dále zlepšila vlastnosti bezolovnaté piezoelektrické keramiky a produkovala plně hutné vzorky, což je dobrým předpokladem pro translucenci a z níž vyplývajícím optoelektrickým vlastnostem. Nejoptimálnějších výsledků – plné hustoty a vysokých piezoelektrických vlastností – bylo dosaženo kombinací SPS a RRS. Analýzy provedené v této studii také poukázaly na důležitost eliminace těkavých nečistot před rychlým ohřevem. Jinak totiž dochází k zachycení těchto látek ve slinuté keramice, což ve výsledku limituje její konečnou hustotu. Ukázalo se, že nízké konečné hustoty RRS YSZ jsou spojeny se zachycením zbytkového chloru pocházejícího ze syntézy prášku. Pokud byl zbytkový chlor odstraněn vysokoteplotním žíháním keramických kompaktů před zahájením RRS, byly touto metodou získány téměř plně hutné YZS vzorky. Negativní vliv zbytkového chloru na zhutnění byl viditelný také u flash slinovaných YSZ vzorků. Navíc FS YSZ často vede ke zrychlení růstu zrn v jádře vzorku, v důsledku vyšší teploty a elektrochemické redukce. Ve spektru procesních parametrů použitých v rámci této práce dokonce došlo k abnormálnímu růstu zrna (AGG). Silně bimodální distribuce velikosti zrn ukázaná v této práci nebyla dříve nalezena u flash slinutého YSZ. AGG byl vysvětlen dvěma přispívajícími faktory – relativně velkou velikostí vzorku, která vedla k lokalizaci elektrického proudu a vzniku horkých míst (z angl. hot-spots), a celkově akcelerovanou kinetikou růstu zrn v jádře vzorku způsobenou elektrochemickou redukcí.
|
|
|
Structure and mechanical properties of magnesium materials prepared by SPS
Pleskalová, Kateřina ; Hutařová, Simona (referee) ; Doležal, Pavel (advisor)
This diploma thesis deals with the processing of the magnesium-based powder materials with the addition of zinc by the spark plasma sintering. The aim of this thesis is to evaluate influence of sintering parameters and zinc content on the microstructure and mechanical properties of the material. First part of the thesis is literary research which is divided into two main chapters. The first chapter describes magnesium-based materials and mentions their use as biomaterials. The second chapter discusses powder metallurgy, specifically magnesium powders and spark plasma sintering. In the experimental part the powders were sintered at temperatures 300 °C and 400 °C and an analysis was performed using optical microscope, scanning electron microscope, then also EDS analysis and hardness, microhardness and three-point bending tests were performed. An increase in hardness was observed with increasing zinc content and with increasing sintering temperature. The flexural strength was higher for materials sintered at a temperature of 400 ° C.
|
|
|
Preparation of the lead-free piezoceramic by non-conventional sintering methods
Sršeň, Maroš ; Prajzler, Vladimír (referee) ; Pouchlý, Václav (advisor)
Ceramic materials that exhibit piezoelectric properties currently have a variety of uses in various industries, such as the automotive industry or information technology. Leading materials are currently the best ceramic piezoelectrics, but these materials show considerable toxicity. This has led to the need to find health-safe and environmentally friendly materials based on lead-free piezoelectric materials. Among these materials, KNN-based materials prove to be good candidates. However, their preparation has its own specifications, and therefore the use of conventional sintering methods may not lead to the desired results. It is for this reason that research into the preparation of these materials using unconventional sintering methods that use electric current for sintering has come to the fore in recent years. One of these methods is the Spark Plasma Sintering method, which has therefore been intensively researched in recent years. Within the experimental part of the work, ceramic bodies based on KNN were prepared. Sintering was performed by a conventional method using a laboratory oven, as well as by an unconventional Spark Plasma Sintering method, and the results were compared. Compacting ceramic bodies with high relative density were obtained by sintering by both methods. It has been shown that the Spark Plasma Sintering method can be used to prepare lead-free piezoelectric materials with a high relative density in a relatively short time. It has also been confirmed that the Spark Plasma sintering method has several advantages over conventional sintering methods, and that the ceramic bodies obtained have a higher relative density when sintered by this method.
|
|
|
Highly porous ceramic materials prepared by Spark Plasma Sintering
Barančíková, Miriama ; Spusta, Tomáš (referee) ; Salamon, David (advisor)
Porous ceramic materials are an interesting group of materials due to a wide range of physical properties, low density, and good permeability. Production of a monolith with a shape stability that would also have a high specific surface area and high porosity is a common problem with porous ceramics. The goal of this work was to maintain the high specific surface area and to produce a monolith with a shape stability. Two forms of porous silica nanofibers (as prepared and milled) were used and partially sintered using the Spark Plasma Sintering method (SPS). Different sintering times and temperatures for SPS were tested. The findings revealed that the best SPS conditions were as follows: temperature: 600 °C, sintering time: 5 minutes, pressure: 3 MPa, and the heating rate: 144 °C/min. These sintering conditions resulted in a stable silica based machinable monolith made from fibers or milled fibers. The monoliths have the specific surface area of up to 470 m^2/g and porosity of 72 %, or the specific surface area of up to 422 m^2/g and porosity of 69 % for as prepared fibers and milled fibers, respectively.
|
|
| |
guest ::
