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Inverse-Heusler Mn2FeSi alloy prepared by powder metallurgy route
Životský, O. ; Skotnicová, K. ; Čegan, T. ; Juřica, J. ; Gembalová, L. ; Zažímal, František ; Jirásková, Yvonna ; Szurman, I.
The Mn2FeSi inverse-Heusler alloy was prepared by solid-state reactions using ball milling for 168 h in n hexane. Two milling procedures varying in the ball-to-powder ratio, namely 4:1 and 10:1, were used to follow \ntheir influence on alloy formation and its physical properties. In both cases no Heusler structure was obtained \ndirectly and therefore the subsequent annealing at 1223 K for 1.5 h in pure Ar was applied. The energy dispersive X-ray analysis resulted in the chemical composition about 49.0-49.9 at% Mn, 25.3-25.6 at% Fe, and \n24.8-25.4 at% Si, in a good agreement with nominal one. X-ray diffraction of both powders confirmed inverse Heusler XA structure of lattice parameters 0.5675 nm (4:1) and 0.5677 nm (10:1), only slightly higher as \ntheoretically obtained 0.560 nm. The presence of minor oxidation phases was also observed in the particle \nstructure of powders. Magnetic properties were analysed at low and room temperatures. Both alloys exhibit \nparamagnetic behaviour at room temperature confirmed by transmission Mössbauer spectroscopy \nmeasurements. Different magnetic behaviour of alloys is observed below 65 K.
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Structural and magnetic properties of Fe-oxide layers prepared by inkjet printing on Si-substrate
Zažímal, František ; Svoboda, T. ; Dzik, P. ; Homola, T. ; Jirásková, Yvonna
Magnetic films with two, four, six, and eight layers were prepared using 2D inkjet printing on the 333 K heated Si-substrates at ambient conditions. The microstructure, phase composition of layers, and magnetic studies were investigated using wide spectrum of experimental methods with the aim to find the optimal conditions for producing magnetic sensors by digital printing technology in the near future. As the magnetic compound, the hematite powder was chosen and its milling with Si-binder dissolved in dowanol using glass balls and vial to prevent contamination was done to prepared suspension appropriate for printing. It is shown that hematite transformed markedly into maghemite, thus the layers consisted of small amount hematite and dominant maghemite phases determining the magnetic properties. From the viewpoint of magnetic behavior, the highest saturation magnetization and the lowest coercivity was obtained at the sample with 8 layers.
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Theory-guided design of novel Fe-Al-based superalloys
Friák, Martin ; Holec, D. ; Jirásková, Yvonna ; Palm, M. ; Stein, F. ; Janičkovič, D. ; Pizúrová, Naděžda ; Dymáček, Petr ; Dobeš, Ferdinand ; Šesták, Pavel ; Fikar, Jan ; Šremr, Jiří ; Nechvátal, Luděk ; Oweisová, S. ; Homola, V. ; Titov, Andrii ; Slávik, Ondrej ; Miháliková, Ivana ; Pavlů, Jana ; Buršíková, V. ; Neugebauer, J. ; Boutur, D. ; Lapusta, Y. ; Šob, Mojmír
Our modern industrialized society increasingly requires new structural materials\nfor high-temperature applications in automotive and energy-producing industrial\nsectors. Iron-aluminides are known to possess excellent oxidation and sulfidation\nresistance as well as sufficient strength at elevated temperatures. New Fe-Al-based\nmaterials will have to meet multiple casting, processing and operational criteria\nincluding high-temperature creep strength, oxidation resistance and room-temperature\nductility. Such desirable combination of materials properties can be achieved in multi-phase\nmulti-component superalloys with a specific type of microstructure (the matrix contains\ncoherent particles of a secondary phase - a superalloy microstructure). In order to design\nnew Fe-Al-based superalloys, we employ a state-ofthe-art theory-guided materials design\nconcept to identify suitable combinations of solutes.
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Vliv tepelného zpracování na mechanické vlastnosti slitiny FeNiB
Zábranský, Karel ; Jirásková, Yvonna
Byl studován vliv tepelného zpracování v rozsahu 150 - 350 °C na strukturní a mechanické vlastnosti amorfní slitiny na bázi FeNiB. Byla zjištěna vysoká mez pevnosti 2200 Mpa v původním stavu, která se vzrůstající teplotou přibližně do 200 °C klesala, oproti stoupajícím hodnotám mikrotvrdosti. Nad 200°C se obě charakteristiky významně zhoršují, což odráží výrazné zkřehnutí amorfní struktury. Nebyly pozorovány žádné známky krystalizace.
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Vliv tepelného namáhání na mechanické vlastnosti FeNiB amorfní slitiny
Zábranský, Karel ; Jirásková, Yvonna
Vliv tepelného namáhání v teplotním intervalu 150 - 350 °C na změny struktury a mechanických vlastností je studován na vzorcích FeNiB s amorfní strukturou. Vysoká pevnost v tahu, 2200 MPa, naměřená u vzorku v původním amorfním stavu mírně klesá s rostoucí teplotou žíhání vzorků do přibližně 200 °C na rozdíl od mikrotvrdosti, u níž je pozorován růst. Nad touto teplotou však dochází k výraznému zhoršení obou vlastností vlivem křehnutí amorfní struktury bez jakýchkoliv známek krystalizace.
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Preparation and properties of MgO-Ni(Fe) nanocrystalline composite
Schneeweiss, Oldřich ; Pizúrová, Naděžda ; Jirásková, Yvonna ; Žák, Tomáš ; Bezdička, Petr ; Večerníková, Eva
We have prepared MgO-Ni(Fe) nanocrystalline composites by controlled heat treatment of compacted spark synthesized nanocrystalline powders. Besides particle sizes and their chemical compositions, influence of interaction with surrounding atmosphere and adsorbed gases on phase composition and magnetic properties were investigated. Mössbauer spectroscopy, x-ray diffraction and TEM were used for phase analysis. Thermomagnetic curves and DTA/TG measurements were applied for detection of changes in structure and phase composition during heat treatments. The simultaneous gas analysis using mass spectroscopy by heating yielded information on adsorbed and dissolved gases and their reactions with the nanoparticles.
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