Journal
ACTA MATERIALIA
Volume 55, Issue 13, Pages 4287-4292Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2007.03.030
Keywords
fragmentation; directional solidification; x-ray microscopy; constitutional undercooling
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High-brilliance synchrotron X-radiation microscopy and further image processing allowed in situ observations of local solute-enrichment during fragmentation of dendrite arms under normal non-forced-convection conditions during directional solidification of an Al20 wt.% Cu alloy. An open dendritic network is exposed to solute-rich liquid which arrives from the solidification front. At grain boundaries such openness is even more pronounced, leaving higher-order branches highly exposed to the incoming solute-rich liquid stream. It was found that streaming of solute-enriched liquid at the tip of high-order branches promotes growth by local undercooling. Further solute advection and local solute rejection due to the local growth causes solute pile-up at the roots of the branches. This solute pileup alters the local compositional balance at the solid-liquid interface at the root, causing the root to remelt, which in turn results in further branch detachment. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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