Microstructural Simulations of the Influence of Solidification Velocity on Freckle Initiation during Directional Solidification
Microstructural Simulations of the Influence of Solidification Velocity on Freckle Initiation during Directional Solidification
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DOI：
10.2355/isijinternational.50.1814
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发表时间：
2010-12
影响因子：
1.8
通讯作者：
L. Yuan;P. Lee
中科院分区：
文献类型：
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作者：
L. Yuan;P. Lee
在微观组织水平上对Pb-Sn合金定向凝固过程中热溶质对流引起的斑点形成进行了数值模拟研究。该模型预测了详细的枝晶组织，显微偏析和枝晶间对流的三维。溶质通道（雀斑）的发生和持续增长被模拟为铸造速度的函数。通过引入瑞利数的预测与实验测量进行了比较。取得了良好的一致性，这表明随着进一步的发展，此类模型可用于预测更复杂合金系统的临界Rayleigh数。结果表明，Pb-Sn合金较大的密度变化引起了分离液的强烈向上对流，促进了溶质通道的形成。然而，向上溶质运输和树枝状生长之间的竞争决定了这些通道的起始和持续生长。这些开放的溶质通道在最终凝固时变成称为雀斑的缺陷结构。
The initiation of freckles by thermosolutal convection during the directional solidification of Pb–Sn alloys was studied numerically at the microstructural level. The model predicts the detailed dendritic structures, microsegregation and interdendritic convection in three dimensions. The onset and sustained growth of solutal channel (freckles) was simulated as a function of casting speed. The predictions were compared with experimental measurements via the introduction of a Rayleigh number. Good agreement was achieved, suggesting that such models might be used to predict the critical Rayleigh number for more complex alloy systems with further development. It was found that the large density variation of Pb–Sn alloys induces strong upward convection of segregated liquid and promotes the formation of solutal channels. However, the competition between upward solute transport and dendritic growth determines both the initiation and sustained growth of these channels. These open solute channels become the defect structure known as a freckle upon final solidification.