An experimental investigation into the effects of grain transport on columnar to equiaxed transition during dendritic alloy solidification
- Pennsylvania State Univ., University Park, PA (United States). Dept. of Mechanical Engineering
An experimental study has been conducted to investigate the effects of grain transport on the columnar to equiaxed transition (CET) in dendritic alloy solidification. Using the aqueous ammonium chloride solution as a transparent model alloy, experiments were performed in a vertical test cell with cooling from the top, resulting in unidirectional columnar crystals growing downwards. Ahead of the columnar front, equiaxed nuclei were observed to originate mostly by fragmentation of the columnar dendrites in the presence of a thermally driven flow in the melt beneath the columnar mushy zone. Being heavier than the liquid, these fragments fall into the bulk melt where they may grow or remelt. The survival equiaxed crystals finally settle towards the floor and pile up to form an equiaxed bed. The CET occurs when the bottom equiaxed packed bed rises and eventually obstructs the columnar mushy zone growing from the upper surface. Therefore, the CET in the present configuration was predominantly controlled by the sedimentation of equiaxed crystals. A parametric study by varying initial concentration, cooling rate, and superheat was performed.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 361758
- Journal Information:
- Journal of Heat Transfer, Journal Name: Journal of Heat Transfer Journal Issue: 2 Vol. 121; ISSN 0022-1481; ISSN JHTRAO
- Country of Publication:
- United States
- Language:
- English
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