Materials science and engineering a-structural materials properties microstructure and processing vol:413-414 pages:514-520
During casting, unconstrained solidification occurs most frequently. The objectives of the present study were to describe the different stages of a ternary eutectic solidification path, its unconstrained solidification and to assess gravity dependent phenomena as a preparation for a MAXUS sounding rocket microgravity experiment. Two alloys within the Al-Cu-Ag system were selected. They form a different primary phase alpha(Al) or theta-Al2Cu that however share the further solidification path. Nucleation of primary non-faceted alpha(Al) was enhanced by the addition of TiB2. The same addition did not influence the nucleation of faceted theta-Al2Cu. Gravity driven flotation of primary alpha(Al) was observed. Nucleation of the univariant eutectic alpha(Al) + theta-Al2Cu is triggered by theta-Al2Cu, whereas growth occurs with a lamellar, rod-like or irregular morphology. Growth of the invariant eutectic alpha(Al) + theta-Al2Cu + xi-Ag2Al occurs either with an irregular, semi-regular brick type or regular double-rod type morphology, however, always with a strong association between theta-Al2Cu and xi-Ag2Al. (c) 2005 Elsevier B.V. All rights reserved.