Rapid Solidification of Supercooling Binary Molten Metal Droplets

提出了一种描述金属熔滴撞击基体时变形和凝固行为的数学模型。采用有限元法对数学模型进行了数值求解。实验中，熔化的锡液滴（直径2.2-4.3 mm）以不同的冲击速度（1.4-4.0 m/s）冲击铜、不锈钢和玻璃基底。通过将计算的飞溅直径与实验值进行比较，计算了液滴/基体界面处的换热系数。估计值在以前报告的范围内。该模型几乎预测了实验片径与韦伯数的关系。数值计算结果与实验结果吻合。模拟结果表明，影响液滴扩散减速的主要是飞溅边缘的冻结层，而不是中心区域的冻结层。从板条边缘的冻结速率解释了凝固对板条直径的影响。通过对一维传热传质问题的数值求解，预测了合金片材在快速凝固过程中的组织发展。该模型考虑了非平衡凝固。利用界面稳定性分析估计了枝晶尖端半径。将模型预测结果与Sn-5wt的微观结构进行了比较。在锡衬底上沉积单一尺寸的液滴而产生的铅片。液滴在撞击时的温度是通过调整到基材的飞行距离来控制的。矿床微观结构与数值模拟预测结果基本吻合，但并不完全吻合。讨论了模型预测与实验观测之间的差异。

A mathematical model describing the deformation and solidification behavior of molten metal droplets impinging on substrates is presented. The mathematical model is numerically solved using a finite element method. In the experiment, a molten tin droplet (2.2-4.3 mm diameter) impacts copper, stainless steel and glass substrates at various impact velocities (1.4-4.0 m/s). The values of the heat transfer coefficient at the droplet/substrate interface are evaluated by comparing the calculated splat diameters to the experimental ones. The estimated values are within the previously reported ranges. The model almost predicts the Weber number dependence of the experimental splat diameters. The time variations of the numerical splat diameters also agree with the experimental results. The simulation reveals that the frozen layer at the splat edge, rather than at the center region, affects the deceleration of the droplet spreading. The effect of the solidification on the splat diameter is explained from the freezing rate at the splat edge.One-dimensional heat and mass transfer problems are numerically solved to predict microstructure development in alloy splats in rapid solidification. The model accounts for nonequilibrium solidification. The dendrite tip radius is estimated using an interface stability analysis. Model predictions are compared with microstructures of Sn-5wt.%Pb splats produced by depositing mono-size droplets on a Sn substrate. The droplet temperature at impact is controlled by adjusting the flight distance to the substrate. The deposit microstructures primarily match those predicted by the numerical simulation, although not perfectly. The discrepancies between the model predictions and the experimental observation are discussed.