Solidification and Gravity V

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Authors: Erik G. Fuchs
Abstract: The Hungarian research group which dealt with some solidification problems have obtained a possibility to work out an space metallurgy project in 1980 during the Hungarian-Soviet joint space mission. The goals of the experiment were to control the developed simulation method and the demonstration of some fundamental effects. The experiments were performed on the SALYUT 6 space station in the SPLAV and KRISTAL furnaces. The materials were Al-4%Cu alloy and pure aluminum rod covered by copper mantle. In case of the Al-4%Cu alloy the details of the solidification (microsegregation, dendritic structure) while in case of copper covered aluminum rod the diffusion in the melt were investigated. The results of the space experiments have confirmed the usability of the developed simulation and have established the further work. The experiences of this work have contributed to the developing of the so called Hungarian Space Furnace (Universal Multizone Crystallizator, UMC).
Authors: J. Gyulai, I. Gyúró
Abstract: A brief historical overview of one of Hungary's space projects on Soviet spacecrafts, the so-called "Eötvös" Project on semiconductor crystal growth, is given. Three experiments were proposed and performed: i) epitaxial growth of GaAs under flux, ii) seedless growth of GaSb, and as a control, iii) seeded growth of an InSb crystal. Because of thermal control problems of the furnace, only the growth of a structurally perfect GaSb bicrystal was a successful novelty. Results of structural and electrical analyses are briefly summarized. Finally, a list of related publications is given.
Authors: Fabienne Lemoisson, S. Mc Fadden, Marek Rebow, David J. Browne, Ludo Froyen, D. Voss, David John Jarvis, A.V. Kartavykh, S. Rex, W. Herfs, D. Groethe, Juraj Lapin, Olga Budenkova, J. Etay, Yves Fautrelle
Abstract: The authors are members of the integrated project Intermetallic Materials Processing in Relation to Earth and Space Solidification (IMPRESS), funded within the European Framework (FP6). One of the aims of IMPRESS is to develop new alloys and processes for the casting of TiAl-based turbine blades for the next generation of aero and industrial gas turbine engines. Within IMPRESS, two related issues have been identified during the primary solidification stage, namely, segregation and the columnar-to-equiaxed transition (CET). The authors have set out to isolate the effects of thermo-solutal convection, by designing a microgravity experiment to be performed on a European Space Agency platform. This experiment will investigate the CET formation during solidification. It is planned to use a sounding rocket providing a microgravity time of approximately twelve minutes. The results of this microgravity solidification experiment will be used as unique benchmark data for development and validation of new computational models of TiAl solidification. This in turn will produce accurate models and ultimately new robust industrial processes by project partners in the aerospace industry. The evolution of the design of the microgravity experiment is discussed and the results of preliminary ground reference experiments are presented. Future plans and objectives for the project are also highlighted.
Authors: Viktor Bánhidi, Tamas J. Szabo
Abstract: In the frame of an international cooperation a 4 year long project was executed to determine thermal conductivity in metallic melts. During the project, the University of Miskolc designed and developed unique apparatus which was capable to perform measurements under microgravity conditions. The experiments were carried out at the Drop Tower „Bremen” where the conditions of reduced gravity could be provided for 4.7 s and a gravity level of 10-5g was achieved. The registered temperature distribution data of the examined melts always show a clear difference between the experiments measured in the normal and in the low gravity environment. During the evaluation of the datasets it was proven, that the well known canonical evaluations could not be used with high reliability for all the measurements, for all the materials and for all the geometry used. Besides of the understanding of the underlying physics and evaluating the measured data, the Crank-Nicolson method and error function analysis were used at the beginning, some numerical analyses were also initiated to simulate the system in FEM (Marc). The results showed acceptable results, but also pointed out a need for further study, so a detailed numerical analysis on a specialized FVM (Fluent) system was started. The code used for the numerical simulation (Fluent) was able to handle the heat conductivity, the liquid flow, the complex material parameters changes and the used geometries as well. With this technique, from the data of the drop experiments, the pure - free from the effect of the liquid flow - thermal conductivity could be separated. The results show that after these simulations, using different conditions (temperature, gravity level, etc.) for one material the same thermal conductivity value could be determined, within acceptable tolerance.
Authors: A.V. Kartavykh, V.P. Ginkin
Abstract: A brief review is given of the results obtained and published in 2003–2007 by IChPM and IPPE during their joint study and modeling of Ge:Ga, Ge:Sb, GaSb:Te, InP:S single crystal growth from stoichiometric and non-stoichiometric melts on board the Photon satellite series. The use of microgravity is shown to be justified and holding promise for research into the structural self-organization processes (cluster forming) taking place within the transient layer of the melt during the solidification. The mathematical model of convective heat and mass transfer taking into account the dual-phase character of matter in the boundary layers near the interface has been created and used as an independent tool for the study of such processes. Prospects are discussed for this new area of space material science.
Authors: R.V.S. Prasad, G. Phanikumar
Abstract: Microstructure of rapidly solidified Ni2MnGa ferromagnetic shape memory alloy has been investigated experimentally by melt-spinning technique. At a constant ribbon width of 3 mm, two speeds of melt spinning 17m/sec and 30m/sec at the extrema of conditions for a good quality of ribbon resulted in two thicknesses of the ribbon, viz., 62 μm and 44 μm, respectively. TEM and AFM analysis reveals the formation of very fine clusters of Ni2MnGa at lower wheel speeds. However at higher wheel speeds nanocrystalline Ni2MnGa particles of size about 10-20 nm and martensitic phases were confirmed.
Authors: Livio Battezzati, Erik Johnson, Nini Pryds, Andrea Penna, Stefano Curiotto
Abstract: Alloys displaying positive enthalpy of mixing demix below a critical temperature. In Co-Cu and related ternaries the miscibility gap is metastable, i.e. it occurs at temperatures lower than the liquidus. In order to study the liquid phase separation high melt undercooling is necessary. This was obtained via rapid solidification techniques using melt spinning and casting in moulding devices, as well as high temperature DSC experiments with samples embedded in a flux. Results are given for Co-Cu, Co-Cu-Fe and Co-Cu-Ni systems. Phase diagrams were optimised using the DSC data. The mechanism of phase separation was investigated by comparing samples produced under different cooling conditions. The hierarchy of microstructures obtained was interpreted accounting for the processing technique and the phase diagram. They constitute a database useful for the interpretation of the thermal history of samples processed in microgravity.

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