Interactive Effects of Interfacial Energy Anisotropy and Solute Transport on Solidification Patterns of Al-Cu Alloys
Interactive Effects of Interfacial Energy Anisotropy and Solute Transport on Solidification Patterns of Al-Cu Alloys
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DOI：
10.1016/j.actamat.2022.117859
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发表时间：
2022-03
期刊：
影响因子：
9.4
通讯作者：
G. Azizi;Sepideh Kavousi;M. A. Zaeem
中科院分区：
文献类型：
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作者：
G. Azizi;Sepideh Kavousi;M. A. Zaeem
采用分子动力学和相场模拟相结合的方法研究了冷却速率、合金成分和晶体-熔体界面各向异性对Al-Cu合金凝固过程的综合影响。采用分子动力学模拟方法，对Cu含量为3 ~ 11at%的合金，用毛细管涨落法测定了CM界面能性质。虽然平均CM界面能随Cu含量的增加而降低，但其各向异性并不随组成的变化而呈现明显的趋势。通过相场模拟计算了一次和二次枝晶臂间距以及θ相分数，并在1 ~ 1250 K/s的冷却速率范围内与实验测量值和解析解进行了对比验证。结果表明，随着冷却速度的增加，θ相含量减少，Cu含量越高，θ相含量减少越明显。此外，显微组织特征受到生长动力学的影响，其中海藻结构的形成导致θ相的更均匀分布和更精细的显微组织。温度梯度，铜浓度梯度，和界面能特性对Al-Cu合金的枝晶生长形态的影响总结了一个地图的过冷度与CM界面各向异性预测图案的形成。结果表明，无论Cu含量和冷却速率如何，当CM界面各向异性大于0.005时，海藻结构的形成停止。随着各向异性的降低，不同的海藻结构可以形成关于组成过冷。在低各向异性（Al-3和Al-8.4at%Cu）和低过冷度（Al-3at%Cu）下，分形或简并海藻占主导地位，而在高过冷度（Al-8.4at%Cu）下，致密海藻形成。这种过冷的差异源于不同的溶质原子输运速率。
Combined effects of the cooling rate, alloy composition, and crystal-melt (CM) interfacial anisotropy on solidification of Al-Cu alloys are studied by integrating molecular dynamics and phase-field simulations. Capillary fluctuation method is used to determine the CM interfacial energy properties by molecular dynamics simulations for alloys ranging from 3 to 11 at% Cu. While the average CM interfacial energy decreases with increasing Cu content, its anisotropy does not present a clear trend with composition change. Primary and secondary dendrite arm spacings as well as θ-phase fraction are calculated by phase-field simulations, and validated against experimental measurements and analytical solutions at cooling rates ranging from 1 to 1250 K/s. Results show that the θ-phase fraction decreases with increasing the cooling rate, and this reduction is more drastic in alloys with a higher Cu content. Also, the microstructure features are influenced by the growth dynamics, where seaweed structure formation results in a more homogenous distribution of θ-phase and a finer microstructure. The effects of temperature gradient, Cu concentration gradient, and interfacial energy properties on the dendritic growth morphology of Al-Cu alloys are summarized by a map of supercooling versus the CM interfacial anisotropy to predict pattern formation. The results show that, irrespective of Cu content and cooling rate, the seaweed structure formation is halted at CM interfacial anisotropies larger than 0.005. As the anisotropy decreases, different seaweed structures can form regarding the constitutional supercooling. At low anisotropies (Al-3 and Al-8.4 at% Cu) and low supercooling (Al-3 at% Cu) fractal or degenerate seaweed is dominant while at high supercooling (Al-8.4 at% Cu) compact seaweed forms. This difference in supercooling stems from different solute atom transport rates.