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The Role of Bi/Material Interface in Integrity of Layered Metal/Ceramic
Masini, Alessia ; Černý, Martin (oponent) ; Bermejo, Raul (oponent) ; Chlup, Zdeněk (vedoucí práce)
The present doctoral thesis summarises results of investigation focused on the characterisation of materials involved in Solid Oxide Cell technology. The main topic of investigation was the ceramic cell, also known as MEA. Particular attention was given to the role that bi-material interfaces, co-sintering effects and residual stresses play in the resulting mechanical response. The first main goal was to investigate the effects of the manufacturing process (i.e. layer by layer deposition) on the mechanical response; to enable this investigation, electrode layers were screen-printed one by one on the electrolyte support and experimental tests were performed after every layer deposition. The experimental activity started with the measurement of the elastic characteristics. Both elastic and shear moduli were measured via three different techniques at room and high temperature. Then, uniaxial and biaxial flexural strengths were determined via two loading configurations. The analysis of the elastic and fracture behaviours of the MEA revealed that the addition of layers to the electrolyte has a detrimental effect on the final mechanical response. Elastic characteristics and flexural strength of the electrolyte on the MEA level are sensibly reduced. The reasons behind the weakening effect can be ascribed to the presence and redistribution of residual stresses, changes in the crack initiation site, porosity of layers and pre-cracks formation in the electrode layers. Finally, the coefficients of thermal expansion were evaluated via dilatometry on bulk materials serving as inputs for finite elements analyses supporting experiments and results interpretation. The second most important goal was to assess the influence of operating conditions on the integrity of the MEA. Here interactions of ceramic–metal interfaces within the repetition unit operating at high temperatures and as well at both oxidative and reductive atmospheres were investigated. The elastic and fracture responses of MEA extracted from SOC stacks after several hours of service were analysed. Layer delamination and loss of mechanical strength were observed with increasing operational time. Moreover, SEM observations helped to detect significant microstructural changes of the electrodes (e.g. demixing, coarsening, elemental migration and depletion), which might be responsible for decreased electrochemical performances. All the materials presented in this work are part of SOC stacks produced and commercialised by Sunfire GmbH, which is one of the world leading companies in the field.
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The Role of Bi/Material Interface in Integrity of Layered Metal/Ceramic
Masini, Alessia ; Černý, Martin (oponent) ; Bermejo, Raul (oponent) ; Chlup, Zdeněk (vedoucí práce)
The present doctoral thesis summarises results of investigation focused on the characterisation of materials involved in Solid Oxide Cell technology. The main topic of investigation was the ceramic cell, also known as MEA. Particular attention was given to the role that bi-material interfaces, co-sintering effects and residual stresses play in the resulting mechanical response. The first main goal was to investigate the effects of the manufacturing process (i.e. layer by layer deposition) on the mechanical response; to enable this investigation, electrode layers were screen-printed one by one on the electrolyte support and experimental tests were performed after every layer deposition. The experimental activity started with the measurement of the elastic characteristics. Both elastic and shear moduli were measured via three different techniques at room and high temperature. Then, uniaxial and biaxial flexural strengths were determined via two loading configurations. The analysis of the elastic and fracture behaviours of the MEA revealed that the addition of layers to the electrolyte has a detrimental effect on the final mechanical response. Elastic characteristics and flexural strength of the electrolyte on the MEA level are sensibly reduced. The reasons behind the weakening effect can be ascribed to the presence and redistribution of residual stresses, changes in the crack initiation site, porosity of layers and pre-cracks formation in the electrode layers. Finally, the coefficients of thermal expansion were evaluated via dilatometry on bulk materials serving as inputs for finite elements analyses supporting experiments and results interpretation. The second most important goal was to assess the influence of operating conditions on the integrity of the MEA. Here interactions of ceramic–metal interfaces within the repetition unit operating at high temperatures and as well at both oxidative and reductive atmospheres were investigated. The elastic and fracture responses of MEA extracted from SOC stacks after several hours of service were analysed. Layer delamination and loss of mechanical strength were observed with increasing operational time. Moreover, SEM observations helped to detect significant microstructural changes of the electrodes (e.g. demixing, coarsening, elemental migration and depletion), which might be responsible for decreased electrochemical performances. All the materials presented in this work are part of SOC stacks produced and commercialised by Sunfire GmbH, which is one of the world leading companies in the field.
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Basic features of aggregate-matrix-interface fracture of concrete: pilot modelling
Vyhlídal, M. ; Šimonová, H. ; Veselý, V. ; Keršner, Z. ; Klusák, Jan ; Malíková, Lucie
In this paper, the attention is paid to investigation of the importance of the Interfacial Transition Zone (ITZ) in concrete for the global fracture behaviour. A simplified cracked geometry (consisting matrix, ITZ and aggregate) is modelled by means of the finite element method with a crack terminating at the matrix-ITZ interface. Numerical studies assuming two various ITZ thicknesses and several various ITZ elastic moduli are performed. Based on the values of the opening stress ahead of the crack tip (its average value and stress range) a few conclusions are discussed. The pilot analyses dealing with the effect of ITZ on the stress distribution should contribute to better description of toughening mechanisms in silicate-based composites.
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Lomové chování vysocechromových 9% a 14% Cr-Mo a Cr-W ODS ocelí
Hadraba, Hynek ; Stratil, Luděk ; Kazimierzak, B. ; Fournier, B. ; Dlouhý, Ivo
Práce popisuje vliv mikrostruktury (pocházející z chemického složení a tvaru polotovaru) 9% a 14%Cr-W(Mo)-Ti-Y2O3 ODS ocelí vyrobených mechanickým legováním a následně extrudováním za tepla na jejich lomové chování. Lomové chování ODS ocelí bylo výrazně ovlivněno jejich chemickým složením a mikrostrukturou. 9Cr-2W feritickomartenzitická ocel vykazovala nižší hodnoty horních prahových hodnot (7 J) a nižší tranzitní teplotu DBTT (-30°C) než 14Cr-1W feritická ocel. Tranzitní křivka nárazové práce nízkoaktivační feritické 14Cr-1W ODS oceli byla posunuta o 50°C k nižším teplotám a horní prahové hodnoty nárazové práce byly posunuty o 4 J k vyšším energiím. Výrazný vliv na lomové chování ODS ocelí měl také tvar polotovaru. Textura pocházející z tvarovacího procesu také výrazně ovlivnila lomové chování ODS ocelí. Oproti tyčovým polotovarům byla u plochých polotovarů ODS ocelí pozorována delaminace lomových ploch zkušebních těles.
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Vliv povlaku na lomové chování keramických pěn při tahovém zatěžování
Řehořek, Lukáš ; Dlouhý, Ivo ; Chlup, Zdeněk
Porézní struktury představují perspektivní typ struktury pro řadu materiálů kovových, keramických nebo polymerních. Cílové aplikace lze přitom předpokládat tam, kde hraje roli nízká hmotnost, tlumení a tuhost. Pěnové kompozity mohou v kombinaci s dalšími materiály poskytovat příznivé mechanické vlastnosti. V případě keramických pěn jejich hlavní nevýhoda, křehkost, může být touto cestou redukována. Znalosti mechanických vlastností jsou pro příští aplikace tohoto materiálu potřebné. V článku jsou prezentovány tahové vlastnosti keramických pěn s otevřenou porózitou založené na korundové keramice s různými povlaky.
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Vliv povrchového tvrzení na lomové chování ocelí
Dlouhý, Ivo ; Chlup, Zdeněk ; Hadraba, Hynek
Práce je zaměřena na fenomén spojený s lomem v povrchové vrstvě vytvořené třemi různými způsoby. Standardní cementování, nitridování a povrchové kalení byly aplikovány u šesti nízkolegovaných konstrukčních ocelí. Pro hodnocení lomového chování byla použita zkouška rázem v ohybu těles s U vrubem. Kzatěžování bylo využito instrumentované Charpyho kladivo. Výsledky byly sumarizovány a klasifikovány do několika skupin na základě chrakteru diagramu síla průhyb. Vše bylo doplněno fraktografickou analýzou.
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