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Nanoscale AFM and TEM observations of elementary dislocation mechanisms
Veselý, Jozef ; Cieslar, Miroslav (advisor) ; Dlouhý, Antonín (referee) ; Novák, Pavel (referee)
Single crystals of iron with 20, 28 and 40 at. % aluminium were deformed in compression at room temperature. The later two alloys were deformed also at temperatures in the range of yield stress anomaly. Room temperature deformation was carried under the atomic force microscope (AFM) and the evolution of surface was recorded in-situ. Samples deformed at elevated temperatures were investigated by AFM after the deformation. Dislocation structures in deformed samples were then investigated in transmission electron microscope (TEM). Observations of surface (AFM) and bulk (TEM) are compared. Results of both techniques mutually agree and support the interpretation of observed phenomena. Several original analysis methods were developed. Most notably the stereographic reconstruction, which was applied to dislocation structures and carbide particles present in investigated alloys. Model explaining the distribution of carbide particle axes is presented. Powered by TCPDF (www.tcpdf.org)
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Physical properties of ultrafine-grained magnesium based alloys prepared by various severe plastic deformation techniques
Stráská, Jitka ; Janeček, Miloš (advisor) ; Dlouhý, Antonín (referee) ; Kalvoda, Ladislav (referee)
Title: Physical properties of ultrafine-grained magnesium based alloys prepared by various severe plastic deformation techniques Author: Jitka Stráská Department / Institute: Department of Physics of Materials Supervisor of the doctoral thesis: Doc. RNDr. Miloš Janeček, CSc. Abstract: The objective of the doctoral thesis is the complex investigation of ultrafine-grained magnesium alloy AZ31 prepared by two different severe plastic deformation techniques, in particular the hot extrusion followed by equal-channel angular pressing (EX-ECAP) and high pressure torsion (HPT). These severe plastic deformation methods, and as well as many others, are described in detail in the introductory theoretical section. Experimental results are summarized in the following experimental part of the thesis. Mechanical properties, lattice defect structure and especially microstructure were investigated using various experimental techniques. Thermal stability of ultrafine-grained microstructure of AZ31 after EX-ECAP was investigated and the activation energies for grain growth in different temperature ranges were calculated using kinetic equation for grain growth and Arrhenius equation. Results from the dislocation density measurements proved temperature ranges of the recovery and the following grain growth. Results from the...
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Investigation of Functional Properties of Thin NiTi Filaments for Applications in Smart Structures and Hybrid Textiles
Pilch, Jan ; Dlouhý, Antonín (referee) ; Heczko,, Oleg (referee) ; Pokluda, Jaroslav (advisor)
PhD thesis focuses the field of textile application of modern functional materials, namely metallic shape memory alloys with unique thermomechanical properties deriving from martensitic transformation in solid state. Particularly, it deals with the development of a nonconventional thermomechanical treatment of thin NiTi filaments via Joule heating by electric current and related basic research involving thermomechanical testing and modeling of functional properties of the filaments, investigation of martensitic transformations and deformation processes in NiTi and investigation of the fast recovery and recrystallization processes in metals heated by short pulses of controlled electric power. The method was developed and called FTMT-EC. In contrast to conventional heat treatment of metallic filaments in environmental furnaces, this method allows for precise control of the raise of the filament temperature and filament stress during the fast heating (rate ~50 000 °C/s). As a consequence, it is possible to precisely control the progress of the fast recovery and recrystallization processes in heat treated filaments. In this way it is possible to prepare filaments with desired nanostructured microstructure and related functional properties. A prototype equipment for application of the method for heat treatment of continuous SMA filaments during respooling in textile processing was designed and built. Comparing to the conventional heat treatment of SMA filaments in tubular environmental furnaces, this approach is faster, saves energy and allows for preparation of filaments with special functional properties. International patent application was filed on the method. It is currently utilized in the research and development of smart textiles for medical applications.
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Processing of Nb-containing TiAl intermetallics and its Physical and Chemical Aspects
Barták, Tomáš ; Dlouhý, Ivo (referee) ; Zemčík, Ladislav (referee) ; Dlouhý, Antonín (advisor)
Prezentovaná práce se zabývá vakuovým indukčním tavením intermetalické slitiny Ti-46Al-7Nb (at. %) v žáruvzdorných kelímcích na bázi Y2O3. Byla provedena série taveb pro teploty přehřátí taveniny 1630, 1680 and 1730 C a při různých dobách výdrže na této teplotě v rozmezí 5 až 30 minut. Ze slitin ztuhlých v tavících kelímcích byly připraveny metalografické výbrusy, které sloužily k hodnocení mikrostruktury a vyhodnocení složení fází. Pro získání těchto dat byly použity metosy elektronové mirkoskopie SEM a EDS. Kvantitativní hodnocení mikrostruktury, zejména obsahu oxidické faze ve slitině, bylo provedeno pomocí software Adaptive Contrast Control (ACC). Analýza obsahu kyslíku ve ztuhlé slitině byla provedena metodou IGF (fúze v inertním plynu). V této práci jsou pochody na rozhraní slitina/oxidický kelímek posuzovány také z termodynamického hlediska a to s použitím aktivit jednotlivých složek v systému. Data prezentovaná v této práci mohou být použita pro nastavení a optimalizaci procesů tavení intermetalik TiAlNb.
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Processing and Martensitic Transformations of NiTi-based Alloys
Kuběnová, Monika ; Kroupa, Aleš (referee) ; Zemčík, Ladislav (referee) ; Dlouhý, Antonín (advisor)
Cíle této práce jsou: (i) vyhodnocení vlivu Y2O3 kelímku na kontaminaci indukčně tavené NiTi slitiny obohacené niklem, (ii) optimalizace podmínek, při kterých jsou tavby uskutečněny a (iii) získání nových DSC a 3D AP dat o vlivu vodíkové atmosféry na martenzitickou transformaci a na strukturu NiTi slitin obohacené niklem s tvarovou pamětí. Byly provedeny následující experimenty: – Pět taveb bylo navrženo a provedeno tak, aby byla snížena maximální tavící teplota. – Pět přetaveb bylo uskutečněno při teplotě 1500 C s dobou výdrže 2, 10 a 20 minut a při teplotách 1450 C a 1550 C s 20 minutovou dobou výdrže. Experiment byl navržen tak, aby byl vyšetřen vliv tavící teploty a doby výdrže na obsah kyslíku pocházejícího z kelímku Y2O3 v tavenině. – Tepelné zpracování NiTi slitiny obohacené niklem v režimu I (žíhání) a v režimu II (kombinace žíhání se stárnutím) pod atmosférou vodíku, směsi vodíku s héliem a pod referenční atmosférou čistého hélia. Získané výsledky jsou: – Navržené tavící postupy vedou ke snížení maximální tavící teploty a to z 1800 C na 1400 C. Přesto toto velké snížení maximální tavící teploty nevedlo k významnému poklesu obsahu kyslíku. – Během přetavby uskutečněné při teplotě 1500 C s dobou výdrže 2 minuty se obsah kyslíku navýšil o trojnásobek jeho počáteční hodnoty a příliš se nelišil od obsahu kyslíku naměřeného ve slitině, která byla přetavena při stejné teplotě s dobou výdrže 10 minut. K nárustu o čtyřnásobek počáteční hodnoty obsahu kyslíku došlo u přetavby vedené na teplotě 1450 C po dobu 20 minut a hodnota obsahu kyslíku se příliš nelišila od hodnoty naměřené ve slitině přetavené při teplotě 1550 C se stejnou dobou výdrže. – S rostoucím parciálním tlakem vodíku dochází k potlačení jednokrokové martenzitické transformace. Významný pokles výšky DSC píku nastává při parciálním tlaku 100 mbar. 3D AP analýza odhalila, že nedochází k žádné lokální změně koncentrace a nebo pozic niklových a titanových atomů ve vzorku, který byl žíhán v režimu I ve vodíku. Bylo objeveno, že vodík tvoří stabilní intersticiální tuhý roztok v NiTi B2 mřížce, kde vytváří systém nanodomén s obsahem vodíku vyšší než 10 at%.
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DSC evaluation of homogenity of Ni-Ti alloys ingots
Kuběnová, Monika ; Zemčík, Ladislav (referee) ; Dlouhý, Antonín (advisor)
Alloy NiTi with nearequiatomic composition of nickel and titan belongs to a group of metal materials with a shape memory effect (Shape memory alloys). NiTi alloys are a guite attractive materials not only as practical shape memory alloys with hight strenght and ductility but also as those exhibiting unique physical properties. The production of these matrerials is complying with chemical composition. Final charakteristics of alloy are influenced by these bounderies and also by mechanical-heat treatment. This work deal with DSC evaluation of homogenity of ingot structure of NiTi alloy containing 50,8 at.% Ni. The alloy was melted in Y2O3 cricible. In the end the results of DSC method are compared to the microstructure of alloy obtained by SEM and TEM methods.
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Book of Abstracts: 17th International Conference on the Strength of Materials
Dlouhý, Antonín ; Kunz, Ludvík
The Book of Abstracts covers twelve exciting scientific topics addressed by the International Conference on the Strength of Materials 17 (ICSMA 17). Eight excellent plenary speakers were selected based on the discussion and vote within the International Committee of ICSMA. The topics include not only traditional areas like cyclic or high temperature deformation and scale-bridging modeling but also still growing subjects of nano-micro scale experiments and the strength of biological systems. Moreover, the Local Organizing Committee, in cooperation with the Department of Materials Physics, Charles University in Prague, has decided to highlight the 80th anniversary of Prof. Pavel Lukáč, a brilliant international teacher and scientist. The thirteenth topic of the ICSMA 17 is thus dedicated to honour his contribution to materials research. Altogether, the Book presents 376 abstracts evenly distributed among the individual research areas that entered the scope of the conference.
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INFLUENCE OF MELTING TEMPERATURE AND TIME ON THE OXYGEN CONTENT IN TiAlNb ALLOYS
Barták, Tomáš ; Zemčík, L. ; Dlouhý, Antonín
The present study investigates a cost-effective melting of TiAlNb intermetallics in a stable yttrium oxide refractory. We identify mechanisms that mainly contribute to the oxygen pick-up during melting. Systematic microstructural and chemical analysis provided evidence that erosion and dissolution of crucible wall are key factors of the process. Experiments were performed using two Ti46Al7Nb alloys with a different initial content of oxygen. The alloys were re-melted in vacuum induction furnace inside U-shaped yttria crucibles. The experiments involved three different temperatures in combination with melting times spanning from 300 to 1800 s. The oxygen content of re-melted and solidified alloys was assessed by means of inert gas fusion technique. Results of the chemical analysis provided clear evidence that the stability of the refractory wall in contact with the molten alloy and its rate of dissolution depend mainly on melting temperature. These results are further supported by microstructural observations that confirmed ever growing content of ceramic phases in the solidified intermetallic with increasing temperature of the melt. The work also contributed to the improved experimental methodology, in particular to temperature measurements of reactive melts.
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METALLURGY AND PROPERTIES OF ADVANCED NiAl-Mo EUTECTICS
Barták, Tomáš ; Kuchařová, Květa ; Záležák, Tomáš ; Dlouhý, Antonín
A NiAl-Mo eutectic alloy was melt from 99,99% purity components and cast by the drop casting technique. The drop-cast ternary alloy (nominal composition of Ni-45Al-9Mo at. %), was re-melted and directionally solidified using a high temperature optical floating zone furnace. A resulting in-situ composite consists of Ni-45,2Al matrix and Mo-10Al-4Ni fibers, all in at. %. The volume fraction of 14% Mo-fibers stems from the eutectic composition. Backscatter diffraction shows that the NiAl-matrix and the Mo-fibers are both < 001 >-oriented with respect to the axis of the cylindrical rods. Preliminary creep experiments confirmed an immense improvement of high temperature strength due to the fine distribution of Mo-fibres. The amount of strengthening in terms of minimum creep rate can be as high as 7 orders of magnitude. Post-mortem transmission electron microscopy experiments provided evidence that creep in the temperature range of 800 - 900 degrees C results in an extensive formation of subgrain boundaries. The strengthening effect is very likely associated with the reactions between subgrain boundaries and fine Mo-fibres.
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