Rapid Solidification of Supercooling Binary Molten Metal Droplets

提出了一个描述金属液滴撞击基片变形和凝固行为的数学模型。使用有限元法对数学模型进行数值求解。在实验中，熔融锡液滴（直径2.2-4.3 mm）以各种冲击速度（1.4-4.0 m/s）冲击铜、不锈钢和玻璃基板。在液滴/基板界面处的传热系数的值进行评估，通过比较计算的飞溅直径的实验。估计值在先前报告的范围内。该模型几乎预测的实验飞溅直径的韦伯数依赖。数值计算的飞溅直径随时间的变化也与实验结果一致。模拟结果表明，在飞溅的边缘，而不是在中心区域的冻结层，影响液滴扩散的减速。从凝固速度的角度解释了凝固过程对溅射直径的影响，并通过数值求解一维传热传质问题预测了合金快速凝固过程中的微观组织发展。该模型考虑了非平衡凝固。枝晶尖端半径估计使用界面稳定性分析。模型预测与Sn-5 wt.%的微观结构进行了比较。通过在Sn衬底上沉积单一尺寸的液滴产生Pb溅射。通过调节到衬底的飞行距离来控制冲击时的液滴温度。存款微观结构主要匹配那些预测的数值模拟，虽然不是完美的。模型预测和实验观测之间的差异进行了讨论。

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.