Microstructure evolution in undercooled Al-8 wt%Fe melts: comparison between terrestrial and parabolic flight conditions

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DOIResolve DOI: http://doi.org/10.1016/j.jallcom.2012.11.182
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Journal titleJournal of Alloys and Compounds
Pages243251; # of pages: 9
SubjectAcicular morphology; Cooling rates; Electromagnetic levitation; Eutectic growth; Hypereutectic alloy; Intermetallic phase; Micro-structure evolutions; Neutron diffraction technique; Non-equilibrium solidification; Nucleation and growth; Parabolic flight; Reduced gravity; Scanning electrons; Solidification condition; Solidification paths; Solidification process; Star-like; Electromagnetic propulsion; Eutectics; Intermetallics; Iron alloys; Levitation melting; Morphology; Neutron diffraction; Scanning electron microscopy; Solidification; Transmission electron microscopy; Undercooling; X ray diffraction; Aluminum
AbstractAl-8 wt%Fe, a hypereutectic alloy, was studied under electromagnetic levitation (EML) solidification conditions in both terrestrial and reduced gravity conditions. The latter was carried out on the A300 aircraft using the TEMPUS facility. The solidified samples were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction and neutron diffraction techniques. The results are interpreted in the light of the temperature-time measurements taken in situ during the solidification process in the EML. It is shown that both samples experienced some undercooling for the solidification of the primary Al-Fe intermetallic phase, which is likely Al mFe. The solidification path continues with the nucleation and growth of Al13Fe4 followed by primary α-Al. These last two phases do not seem to show any measureable undercooling and recalescence events. Finally, the metastable AlxFe (where x = 5) nucleates starting with the formation of eutectic. This metastable intermetallic continues the eutectic growth as Al13Fe4. The morphology differences of the intermetallics growing under terrestrial and reduced gravity conditions are clear with acicular morphology for the former and a star like morphology for the latter. The primary α-Al has a clear strong textured structure in the reduced gravity sample, while a weak one is observed in the terrestrially processed sample. The difference in texture is attributed to the weaker fluid flow occurring in the droplet under reduced gravity conditions while the difference in the morphology of the primary intermetallic is attributed to the higher cooling rate experienced by the reduced gravity sample compared to that for the terrestrially processed sample. © 2012 Elsevier B.V. All rights reserved.
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NPARC number21271801
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Record identifier518fc7a7-1208-44c0-9892-da756ce3cb9f
Record created2014-04-22
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