In situ observations of dendritic fragmentation due to local solute-enrichment during directional solidification of an aluminum alloy
✍ Scribed by D. Ruvalcaba; R.H. Mathiesen; D.G. Eskin; L. Arnberg; L. Katgerman
- Publisher
- Elsevier Science
- Year
- 2007
- Tongue
- English
- Weight
- 795 KB
- Volume
- 55
- Category
- Article
- ISSN
- 1359-6454
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✦ Synopsis
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 Al-20 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.