Národní úložiště šedé literatury Nalezeno 22 záznamů.  1 - 10dalšíkonec  přejít na záznam: Hledání trvalo 0.00 vteřin. 
STRUCTURAL, THERMODYNAMICS AND PHYSICAL PROPERTIES OF Zn Sn Al ALLOYS
Drápala, J. ; Musiol, J. ; Petlák, D. ; Vodárek, V. ; Smetana, B. ; Zlá, S. ; Kostiuková, G. ; Kroupa, Aleš ; Sidorov, V.E.
Some results of thermodynamic, structural and physical properties of Al-Sn-Zn alloys are presented in our paper. The ternary Al-Sn-Zn alloys were prepared in a resistance furnace in evacuated ampoules. The alloys were studied metallographically, their micro-hardness and X-ray micro-analysis (EDX, SEM) of individual phases were measured. Temperatures of phase transitions (liquidus, solidus, invariant reactions, etc.) were obtained using the DTA method (Setaram SETSYS 18 (TM)). The long time annealing (250, 300, 350 degrees C; 3, 7, 14 or 28 days) was used in order to achieve the thermodynamic equilibrium. The results were confronted with thermodynamic modelling of the ternary Al Sn Zn system in the Institute of Physics of Materials AS of the Czech Republic in Brno. We have studied density (by gamma-absorption method), electrical resistivity (by contactless method in rotating magnetic field) and magnetic susceptibility (by Faraday's method) of some Al-Sn-Zn alloys containing up to 10 at.% of aluminum and up to 65 at.% of zinc. The increasing of zinc content resulted in the decrease of the density and susceptibility values, except for one sample. The resistivity values practically didn't depend on the zinc content in the crystalline state, whereas a maximum was found for one of the samples in the liquid state. This work has been made in the frame of COST Action MP0602 project "Advanced Solder Materials for High-Temperature Application".
Processing and Martensitic Transformations of NiTi-based Alloys
Kuběnová, Monika ; Kroupa, Aleš (oponent) ; Zemčík, Ladislav (oponent) ; Dlouhý, Antonín (vedoucí práce)
The thesis aims at: (i) an assessment of alloy contamination which may result from vacuum induction melting of Ni-rich NiTi-based shape memory alloys in conventional porous Y2O3 crucibles. (ii) an optimization of NiTi melting conditions with respect to the alloy purity and cost efficiency. (iii) an obtaining new differential scanning calorimetry (DSC) and 3D atom probe (AP) data on martensitic transformations and related hydrogen distributions in the Ni-rich NiTi shape memory alloys subjected to heat treatments under controlled environments with systematic variation of the hydrogen partial pressure. The following experiments were carried out: – Five different melting routes were designed and carried out in order to decrease melting temperature. – Five re-melting experiments were performed at 1500 °C with holding time 2, 10 and 20 min, and at 1550 °C and 1450 °C with 20 min holding time to examine the effect of temperature and holding time on oxygen content. – Ni-rich NiTi alloys were heat treated in Regime I (annealing) and in Regime II (annealing and aging) in either hydrogen or hydrogen-helium mixture (H2 partial pressure 20, 100, 500 and 700 mbar). Reference experiment were also performed in a pure helium atmosphere. It was found that designed melting routes lead to the lowering of maximum temperature during the induction melting cycles from 1800 to 1400 °C. Despite this significant maximum temperature drop, oxygen content of the final solidified alloy does not markedly reduce. During re-melting at 1500 °C with 2 min of holding time, the content of oxygen becomes triple the initial oxygen level and does not too differ from the re-melting experiments carried out at the same melting temperature but with 10 min of holding time. Furthermore, the oxygen content increases about fourfold with respect to the initial oxygen level during re-melting for 20 min at 1450 °C. This contamination level does not vary markedly with further rise of the melting temperature by 100 °C. Heat treatments in the controlled gaseous environments revealed that the one-step B2-B19’ martensitic transformation ceases with the increasing partial pressure of hydrogen. A pronounced drop in the DSC peak heights occurs at the hydrogen partial pressure exceeding 100 mbar. 3D AP measurements showed that there are no local variations in the Ni and Ti compositions in the sample after the Regime I heat treatment in hydrogen. Hydrogen was found to form stable interstitial solid solution in B2 NiTi. The distribution of hydrogen atoms is inhomogeneous; they organize into nano-domains with the hydrogen content exceeding locally a level of 10 at%.
Z-phase in Cr-Nb-N system studied by analytical electron microscopy
Buršík, Jiří ; Kroupa, Aleš
In this work we study the Z-phase in model Cr-Nb-N alloys by means of analytical electron microscopy (SEM and TEM).
CALPHAD type modelling of phase diagrams of nanomaterials
Kroupa, Aleš ; Káňa, Tomáš ; Zemanová, Adéla
The method was described for the calculation of phase diagrams of nanoalloys, combining the semiempirical CALPHAD method and ab-initio calculation of surface tension.
New types of lead-free solders and their properties
Drápala, J. ; Petlák, D. ; Malcharcziková, J. ; Vodárek, V. ; Konečná, K. ; Smetana, B. ; Zlá, S. ; Kostiuková, G. ; Seidlerová, J. ; Lasek, S. ; Madaj, M. ; Kroupa, Aleš ; Urbánek, J. ; Dušek, K. ; Sedláček, J. ; Sidorov, V.E.
Ternary and binary alloys with different ratios of Ag, Al, Bi, Cu, In, Mg, Sb, Sn and Zn were prepared experimentally. The following characteristics were studied: temperatures and enthalpies of phase transformations (DTA, TG, DSC), macro-and micro-structural analysis, micro-hardness, chemical analysis, X-ray and density measurements and electrical resistivity of selected solders, test of wettability with or without use of fluxes, measurement of corrosion properties.
Study of Zn-Sn-Al alloys for high-temperature solders
Drápala, J. ; Kroupa, Aleš ; Smetana, B. ; Burkovič, R. ; Lasek, S. ; Musiol, L.
The specimens were studied metallographically including the micro-hardness measurements, complete chemical analysis (ICP-AES, OES), X-ray micro-analysis of alloys by EDAX or WDX including SEM (BSE) in order to determine the composition and identification of individual phases.
Fázové rovnováhy v soustavách pro pájky bez olova
Vřešťál, J. ; Kroupa, Aleš ; Zemanová, Adéla ; Houserová, J. ; Pinkas, J.
V roce 2006 byla dokončena optimalizace parametrů soustav Bi-Pd a AG-In-Pd,zveřejněním v příslušných publikacích a zařazením parametrů do databáze COST 531.Dále byla provedena optimalizace parametrů pro výpočet fázového diagramu Bi-Sb-Sn a In-Sb-Sn,která byla rovněž dovedena do publikace v Journal of Alloys and Compounds a parametry zařazeny do databáze COST 531 a byla rozpracována optimalizace parametrů v soustavě Cu-In-Sn.
Termodynamické re-modelování systému Cu-Ni-Sn
Zemanová, Adéla ; Kroupa, Aleš
Cu-Ni-Sn systém je důležitý systém v bezolovnatém pájení. V rámci projektu COST 531 data pro binární systém Ni-Sn vyžadovala modifikaci. V termodynamické databázi, vysoko teplotní forma Ni3Sn fáze s D03 strukturou, byla modelována jako BCC_A2 fáze pro kompatibilitu s Cu-Sn systémem. Re-modelování této fáze bylo provedeno pomocí modulu Parrot v programu ThermoCalc a bylo dosaženo velice dobré shody mezi novým modelem této fáze a předchozími daty. Nicméně, bylo nezbytné také re-modelovat termodynamický popis ternárního systému Cu-Ni-Sn. Nová optimalizace byla založena na práci Miettinena, který se původně zaměřil na oblast bohatou mědí, a dále na experimentálních datech pro nižší teplotu.
Využití výsledků výpočtů elektronové struktury z prvních principů pro výpočet fázových diagramů
Vřešťál, J. ; Kroupa, Aleš ; Šob, Mojmír
Jsou ukázány aplikace výsledků výpočtů elektronové struktury z prvních principů na konstrukci fázových diagramů v kovových systémech.

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