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Microstructure Characterization and Faigue Behavior of Beta Phase Containing Gama-TiAl Alloy
Petrenec, Martin ; Beran, Přemysl ; Šmíd, Miroslav ; Chlupová, Alice ; Kuběnová, Monika
The microstructure and fatigue properties of Ti–44Al–7.8Nb – 0.2Ni (at.%) alloy after graded cooling heat treatment were investigated. Different techniques as SEM, TEM and FIB were used for characterization of microstructure. Quantification of phase volume fraction was measured by neutron diffraction method. After graded cooling heat treatment the structure consists of fully lamellar uniform grains which contain lamellar phases /2 and cubic phases (ordered B2 and disordered phases) at grain boundary and interlamellar spaces. The foils for TEM were prepared using FIB technique and observed in TEM in order to identify B2 phase by selected electron diffraction. Low cycle fatigue behaviour at 750 °C shows stable fatigue crack propagation due the presence of plastic beta and B2 phases.
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Experimentální studium elektronových vlastností systému RT1- xT, xAl
Prchal, Jiří
Sloučeniny RNiAl a RCuAl patří ke skupině sloučenin typu RTX (R ~ vzácná zemina, T ~ tranzitivní kov, X ~ p-prvek), které krystalizují v hexagonální struktuře typu ZrNiAl (prostorová grupa P-62m). Zajímavé vlastnosti byly pozorovány u série TbNi1-xCuxAl vzhledem k změně mechanismu zodpovědného za magnetické uspořádání. Přechod od ErNiAl k ErCuAl navíc zahrnuje změnu krystalové anizotropie. ErNiAl je antiferomagnet (AF) s momenty uspořádanými v bazální rovině, ErCuAl je feromagnet (F) s momenty podél osy c. ErNi1-xCuxAl vykazuje ,skok' mřížových parametrů mezi x = 0.5 a 0.6 v teplotách do 5 K. Podle měření magnetizace a měrné tepelné kapacity se uspořádání z AF do F děje mezi x = 0.2 a x = 0.4. V oblasti 0.05 x 0.20 je možná koexistence F a AF složek, vzorky v tomto oboru vykazují dva fázové přechody, což pro x = 0.05 potvrdila i měření tepelné kapacity. Vzorky s x 0.4 vykazují ferromagnetické chování. Konečné rozhodnutí o uspořádání erbiových momentů vyžaduje změření neutronové difrakce.
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Blaze Gratings with a Ribbed Back Slope
Krátký, Stanislav ; Meluzín, Petr ; Horáček, Miroslav ; Kolařík, Vladimír ; Matějka, Milan ; Chlumská, Jana ; Král, Stanislav
Binary relief phase-modulated gratings provide symmetrical diffraction of the incoming light beam. Asymmetrical gratings, e.g. asymmetrical triangular blazed gratings, are characteristic by an asymmetrical diffraction behavior, where one of the first diffraction orders is more important than the other one. Electron beam lithography is a suitable and flexible tool for patterning of such kind of gratings. High quality results can be readily obtained when the period of the grating is relatively large and the relief depth is relatively low, this is the case of gratings with a small blaze angle. As the blaze angle increases, the quality of result suffers from several patterning-related issues. One of the problems is a reflection of the incoming light beam from the back slope (anti-blaze facet) of the blaze grating. We propose a novel configuration, with a ribbed modulation of the back slope. This modulation is perpendicular to the direction of the grating grooves. This paper presents an analysis of the proposed blazed grating configuration. E-beam pattern generators were used to prepare a few\nsamples of blaze gratings with a ribbed back slope. One part of the experiment was performed with a Gaussianshaped beam and another one with the variable-shaped beam. Results of the experiment are presented.\nFinally, we discuss the optical performance of two blaze gratings with similar parameters, one of them is with the flat back slope and another one is with the ribbed back slope.
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THE INVESTIGATION OF AN Al7075 ALLOY PREPARED BY SPARK PLASMA SINTERING OF MILLED POWDERS
Molnárová, O. ; Málek, P. ; Nemeth, G. ; Kozlík, J. ; Lukáč, František ; Chráska, Tomáš ; Cinert, Jakub
Atomized powder of an Al7075 alloy was high energy ball milled at room and cryogenic temperatures and compacted by spark plasma sintering (SPS) method. The influence of processing parameters on phase composition and microstructure was studied by X-ray diffraction, light and scanning electron microscopy. The mechanical properties were characterized by microhardness measurements. The atomized powder contained a large volume fraction of intermetallic phases located predominantly in continuous layers separating cells or dendrites in the interior of individual powder particles. Consolidation by SPS destroyed partially this morphology and replaced it by individual particles located at boundaries of original powder particles, at cell boundaries or arranged in chains in previous dendritic regions. High energy milling destroyed most intermetallic particles and enriched the matrix by solute atoms. The high deformation energy introduced into the powder during milling enhanced microhardness up to 220 HV. Consolidation of milled powders by SPS led to the formation of very fine-grained structure with the grain size even below 1 μm and with the fraction of high-angle boundaries about 0.9. Two main types of heterogeneously distributed precipitates were found. The irregularly shaped precipitates with a size about 1 μm seemed to encompass areas with rod like nano-precipitates in most samples. A drop in microhardness to 118HV was observed after SPS, predominantly due to a release of introduced deformation energy.
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The effect of σ-phase formation on long-term durability of SUPER 304H steel
Horváth, J. ; Král, Petr ; Janovec, J. ; Sklenička, Václav
This work presents results of the analysis of phases formed in a SUPER 304H steel during a medium-term static isothermal ageing (675 degrees C/15000 h). The investigations of the precipitates were especially focused on the occurrence of sigma-phase because its formation leads to the serious embrittlement. \nThe evaluation and distribution of brittle sigma-phase were determined on macroscopic level by using light microscopy/colour etching. The microstructure was also investigated on microscopic level by scanning electron microscopes Tescan Lyra 3 and JEOL JSM 5410 equipped by electron backscatter diffraction unit and by transmission electron microscope Jeol 2100F. This work also investigates the effect of sigma-phase formation on the impact strength of an aged state of SUPER 304H steel. For comparison reasons the microstructure and the mechanical properties of the initial as-received) state were also investigated. It was found that the formation of brittle sigma-phase in the aged and therefore degraded microstructure led to the significant decrease of the impact strength. The influence of brittle sigma-phase on long-term durability of the degraded steel regarding its insufficient impact strength is discussed.
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Souhrnný report výsledků smluvního výzkumu mezi FZU AV ČR, v.v. i. a HVM Plasma s.r.o. za rok 2016
Mates, Tomáš ; Fejfar, Antonín ; Ledinský, Martin ; Vetushka, Aliaksi ; Pikna, Peter ; Bauerová, Pavla
Několika diagnostickými metodami byly zkoumány vzorky ochranných vrstev na bázi DLC (Diamond-like-Carbon) na různých substrátech (testovací tělíska i reálné součástky). Pomocí Ramanovské spektroskopie byly vyhodnocovány vazby ve vzorcích pro bližší určení strukturních variací a povrchových modifikací, a to jak pro čerstvě připravené vzorky, tak zejména pro vzorky které prošly různými zátěžovými testy.\nSkenovacím elektronovým mikroskopem (SEM) byla zkoumána povrchová struktura vrstev v různých místech vzorků a vyhledávána vhodná testovací místa pro následnou analýzu pomocí Mikroskopu atomárních sil (AFM). Mikroskopem AFM ve speciálních režimech byly měřeny mapy lokálních mechanických vlastností (tření, adheze hrotu, disipace energie, atd.). Na vybraném vzorku byla metodou Focussed Ion Beam (FIB) analyzována struktura průřezu vzorku a dále bylo zdokumentováno prvkové složení v různých tloušťkách vrstvy metodou Energy-dispersive X-ray Spectroscopy (EDS).\n
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Vlastnosti a in vitro degradace kovových biodegradabilních materiálů
Ročňáková, Ivana ; Trojanová, Zuzanka (oponent) ; Vojtěch,, Dalibor (oponent) ; Podrábský, Tomáš (vedoucí práce)
Biodegradabilní kovové materiály pro medicínské aplikace si v posledních letech získaly značnou pozornost. Hlavním důvodem je, že nabízí vysoký potenciál pro výrobu dočasných ortopedických implantátů, jako například kostní fixační zařízení. Hořčík je vynikajícím kandidátem pro výrobu biodegradabilních implantátů díky své biokompatibilitě, mechanickým vlastnostem podobným vlastnostem lidské kosti a významností pro biologické funkce v těle. Vysoká rychlost degradace hořčíku a jeho slitin ve fyziologickém prostředí brání jejich klinické aplikaci. Dalším atraktivním materiálem v oblasti biodegradabilních materiálů je zinek, který se řadí mezi nepostradatelné prvky pro lidské tělo. Zinek vykazuje vynikající korozní odolnost, ale horší biokompatibilitu v porovnání s hořčíkem. Z tohoto důvodu se v případě Mg a Zn biomateriálů stává zajímavým tématem tvrdá, hustá/porézní biokompatibilní povrchová úprava odolná vůči korozi. Vzhledem k tomu, že hydroxyapatit vykazuje dobrou snášenlivost s živými organismy a navíc zlepšuje růst kosti, jeví se jako výborný kandidát pro výrobu povlaků na povrchu biodegradabilních materiálů. Tato dizertační práce je zaměřena na porovnání korozního chování čistých neželezných kovů (Mg a Zn) a těchto kovů s hydroxyapatitovým povlakem v roztocích simulujících tělní tekutiny. K produkci hydroxyapatitové vrstvy na povrchu materiálu byla použita modifikovaná technologie atmosférického plazmového nástřiku – nanášení pomocí suspenze. Složení a struktura povlaku a korozní produkty byly zkoumány pomocí světelné mikroskopie, rastrovací elektronové mikroskopie s energiově disperzním mikroanalyzérem a rentgenové difrakce. Koroze Mg a Zn vzorků byla sledována měřením hmotnostního úbytku a rentgenové mikrotomografie. Aplikací povrchové úpravy na bázi HA bylo dosaženo zpomalení korozní rychlosti čistého Mg. Koroze Mg s povlakem HA vykazovala o 27,3 % nižší korozní rychlost v porovnání s korozní rychlostí čistého nepovlakovaného Mg. Korozní degradace nepovlakovaného i povlakovaného Zn probíhala v minimálním rozsahu. Použití HA na povrch neželezných materiálů se zdá být velice slibnou metodou ke zlepšení korozních a biologických vlastností těchto biodegradabilních materiálů.
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Preparation of Magnesium Silicide from Recycled Materials for Energy Storage.
Bumba, Jakub ; Dytrych, Pavel ; Šolcová, Olga ; Koštejn, Martin ; Fajgar, Radek ; Maléterová, Ywetta ; Kaštánek, František
Recycling technologies help to save energy, materials and environment. This is the main reason of their popularity. The recovery of semiconductors and metals depends on recycling treatment. A new multi-step technology, which enables to obtain pure silicon and hydrogen from waste materials,is reported in this study. The only by-product is magnesium phosphate, which is a desired fertilizer. Magnesium silicide was successfully prepared from milled silicon photovoltaic (PV) panels and milled Mg obtained from the scrap. The formed magnesium silicide was then hydrolysed by phosphoric acid to form a mixture of silanes. Gaseous products (silanes) were separated by cooling below their boiling temperature by liquid nitrogen and then thermally decomposed by a hot wire, e.g. Pt.This treatment leads to pure silicon and hydrogen release. In this study a deep-in characterization by various methods spectroscopy, Scanning Electron Microscopy (SEM) with Energy Dispersive X- Ray spectroscopy (EDX), etc.) of prepared samples was also done to explain the individual influences, e.g. reaction temperature and atmosphere.
Plný tet: SKMBT_C22016111814301 -  PDF
Plný text: content.csg - PDF
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Processing and Properties of 1D and 2D Boron Nitride Nanomaterials Reinforced Glass Composites
Saggar, Richa ; Cihlář, Jaroslav (oponent) ; Tatarko, Peter (oponent) ; Dlouhý, Ivo (vedoucí práce)
Glasses and ceramics offer several unique characteristics over polymers or metals. However, they suffer from a shortcoming due to their brittle nature, falling short in terms of fracture toughness and mechanical strength. The aim of this work is to reinforce borosilicate glass matrix with reinforcements to increase the fracture toughness and strength of the glass. Boron nitride nanomaterials, i.e. nanotubes and nanosheets have been used as possible reinforcements for the borosilicate glass matrix. The tasks of the thesis are many fold which include: 1. Reinforcement of commercially derived and morphologically different (bamboo like and cylinder like) boron nitride nanotubes in borosilicate glass with the concentration of 0 wt%, 2.5 wt% and 5 wt% by ball milling process. Same process was repeated with reinforcing cleaned boron nitride nanotubes (after acid purification) into the borosilicate glass with similar concentrations. 2. Production of boron nitride nanosheets using liquid exfoliation technique to produce high quality and high aspect ratio nanosheets. These boron nitride nanosheets were reinforced in the borosilicate glass matrix with concentrations of 0 wt%, 2.5 wt% and 5 wt% by ball milling process. The samples were consolidated using spark plasma sintering. These composites were studied in details in terms of material analysis like thermo-gravimetric analysis, detailed scanning electron microscopy and transmission electron microscopy for the quality of reinforcements etc.; microstructure analysis which include the detailed study of the composite powder samples, the densities of bulk composite samples etc; mechanical properties which include fracture toughness, flexural strength, micro-hardness, Young’s modulus etc. and; tribological properties like scratch resistance and wear resistance. Cleaning process of boron nitride nanotubes lead to reduction in the Fe content (present in boron nitride nanotubes during their production as a catalyst) by ~54%. This leads to an improvement of ~30% of fracture toughness measured by chevron notch technique for 5 wt% boron nitride nanotubes reinforced borosilicate glass. It also contributed to the improvement of scratch resistance by ~26% for the 5 wt% boron nitride nanotubes reinforced borosilicate glass matrix. On the other hand, boron nitride nanosheets were successfully produced using liquid exfoliation technique with average length was ~0.5 µm and thickness of the nanosheets was between 4-30 layers. It accounted to an improvement of ~45% for both fracture toughness and flexural strength by reinforcing 5 wt% of boron nitride nanosheets. The wear rates reduced by ~3 times while the coefficient of friction was reduced by ~23% for 5 wt% boron nitride nanosheets reinforcements. Resulting improvements in fracture toughness and flexural strength in the composite materials were observed due to high interfacial bonding between the boron nitride nanomaterials and borosilicate glass matrix resulting in efficient load transfer. Several toughening and strengthening mechanisms like crack bridging, crack deflection and significant pull-out were observed in the matrix. It was also observed that the 2D reinforcement served as more promising candidate for reinforcements compared to 1D reinforcements. It was due to several geometrical advantages like high surface area, rougher surface morphology, and better hindrance in two dimensions rather than just one dimension in nanotubes.
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Fatigue crack growth in 316L under uniaxial and torsional loading
Karol, Michal ; Chlupová, Alice ; Mazánová, Veronika ; Kruml, Tomáš
A study of fatigue crack initiation and growth in 316L austenitic stainless steel is reported. Fatigue experiments were performed at room temperature on full cylindrical specimens cycled axially (tension-compression) and on hollow cylindrical specimens tested in reversed torsion. Microstructure and damage evolution (crack initiation and growth) on the surface of mechanically and electrolytically polished specimens were observed using light and electron microscopy. An analysis of the orientation of microcracks and macrocracks which led to failure was made. Axially loaded specimens exhibited presence of several microcracks which resulted in macrocrack propagating perpendicularly to specimen axis. In the case of torsional loading, orientation of macrocrack propagation was dependent on applied load and presence of notches. High amount of short cracks initiated parallel to specimen axis. Long cracks exhibited a tendency to bifurcate with crack branches oriented at approximately 45° to the specimen axis.
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