Verification of a scaling relation for dendritic solidification with interdendritic convection; simulation and experiment. Part I: Simulation

合金在陆地条件下的凝固不可避免地受到浮力流动的影响，这是由于熔体中的高密度梯度造成的偏析。大多数预测铸件微观组织的现有模型都忽略了这种影响，这种影响显著地影响了物种的迁移，并且已知会导致单晶凝固中的有害缺陷，如雀斑。在二维近似相场研究的基础上，提出了与合金、工艺条件和重力矢量有关的定向凝固初生枝晶最小间距和平均间距的标度关系。使用今天的计算设备，这些预测将使用3D模拟进行验证。由于不可能通过实验定量评价树突间流动，因此计划在第二个项目期间进行能够间接验证模拟的关键实验。合金凝固的相场模拟将与流体流动的晶格-玻尔兹曼模拟相结合。仿真将在大规模并行架构上使用自适应多网格策略进行。该项目预计将提供在陆地条件下决定枝晶凝固结构的复杂机制的完整画面。结垢理论将指出一条改进微观结构模型的路线，用于优化铸造工艺。

Alloy solidification under terrestrial conditions is inevitably influenced by buoyancy flow due to high density gradients in the melt caused by segregation. Most available models to predict casting microstructures neglect this effect which significantly affects transport of species and is known to cause detrimental defects like freckles in single crystal solidification. Based on recent phase-field studies in 2D approximation a scaling relation was proposed which predicts the minimum and average spacing of primary dendrites in directional solidification in dependence of the alloy, the process conditions and the vector of gravity. Using today’s computational facilities these predictions shall be verified using 3D simulations. Since it is impossible to quantitatively evaluate the interdendritic flow by experiments, critical experiments which allow an indirect verification of the simulations are planed for a second project period. Phase-field simulation of alloy solidification will be coupled to Lattice-Boltzmann simulation of fluid flow. The simulation will be performed using adaptive multi grid strategies on massive parallel architectures. The project is expected to give a complete picture of the complex mechanisms determining dendritic solidification structures under terrestrial conditions. The scaling theory will pinpoint a route to improved microstructure models to be used in optimization of casting processes.