Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, Liaoning, 110016, P. R. China.
Sci Rep. 2017 Mar 31;7:45770. doi: 10.1038/srep45770.
Motion of growing dendrites is a common phenomenon during solidification but often neglected in numerical simulations because of the complicate underlying multiphysics. Here a phase-field model incorporating dendrite-melt two-phase flow is proposed for simulating the dynamically interacted process. The proposed model circumvents complexity to resolve dendritic growth, natural convection and solid motion simultaneously. Simulations are performed for single and multiple dendritic growth of an Al-based alloy in a gravity environment. Computing results of an isolated dendrite settling down in the convective supersaturated melt shows that solid motion is able to overwhelm solutal convection and causes a rather different growth morphology from the stationary dendrite that considers natural convection alone. The simulated tip growth dynamics are correlated with a modified boundary layer model in the presence of melt flow, which well accounts for the variation of tip velocity with flow direction. Polycrystalline simulations reveal that the motion of dendrites accelerates the occurrence of growth impingement which causes the behaviors of multiple dendrites are distinct from that of single dendrite, including growth dynamics, morphology evolution and movement path. These polycrystalline simulations provide a primary understanding of the sedimentation of crystals and resulting chemical homogeneity in industrial ingots.
枝晶生长的运动是凝固过程中的常见现象，但由于复杂的多物理过程，在数值模拟中常常被忽略。本文提出了一个包含枝晶-熔体两相流的相场模型，用于模拟动态相互作用过程。该模型避免了复杂性，可以同时解决枝晶生长、自然对流和固体运动的问题。针对在重力环境下的单相和多相 Al 基合金的枝晶生长进行了模拟。对孤立的枝晶在对流过饱和度熔体中沉降的计算结果表明，固体运动能够克服溶质对流并导致与仅考虑自然对流的固定枝晶不同的生长形态。在存在熔体流动的情况下，模拟的尖端生长动力学与改进的边界层模型相关联，很好地解释了尖端速度随流动方向的变化。多晶体模拟表明，枝晶的运动加速了生长碰撞的发生，导致多枝晶的行为与单枝晶明显不同，包括生长动力学、形态演化和运动路径。这些多晶体模拟为工业铸锭中晶体的沉降和由此产生的化学均匀性提供了初步的理解。
