静电悬浮条件下液态合金的热物理性质与快速凝固研究

The containerless processing of liquid ternary Ni and Ti based alloys is accomplished by electrostatic levitation technique. This ensures the realization of high undercooling and rapid solidification. An experimental study will be conducted about the surface polarization process of both solid and liquid alloys. The influences of electrostatic induction on droplet oscillation, heat and mass transfer as well as crystal nucleation are to be explored during containerless processing. By taking full advantage of the electrostatically levitated state, systematic measurements are carried out about the thermophysical properties of substantially undercooled liquid alloys such as surface tension,viscosity, density and solute diffusivity. These physical parameters provide the indispensable original data for the further quantitative research of rapid solidification kinetics. The keynote of this project is focused upon the experimental investigations of rapid dendritic, eutectic and peritectic growth processes with the coupled effects of electrostatic field and intense laser. The undercooling thresholds for microstructural transitions are determined for both single phase and composite alloys, whereas the correlations of solid/liquid interface advancement with temperature and concentration fields as well as solute trapping are examined through detailed experiments. Meanwhile, both molecular dynamics and phase field theory methods are employed to perform numerical simulation investigations on the atomic scale microstructure, thermophysical property and crystallization process of highly undercooled liquid alloys. On the basis of these experimental studies and theoretical analyses, the kinetic characteristics of rapid solidification are to be modelled for ternary single phase and composite alloys.

采用静电悬浮实验技术模拟空间环境条件，实现三元Ni基和Ti基合金熔体的深过冷与快速凝固。研究高压静电场中固态和液态合金的表面极化过程，探索静电感应对悬浮液滴运动形态、传热传质和晶体形核的作用机制。在静电悬浮状态下，系统地测定液态合金的表面张力、粘度、密度和扩散系数等热物理性质随过冷度变化规律，为定量研究快速凝固动力学获取必需的原始数据。重点研究静电场和强激光的耦合作用下深过冷三元合金中枝晶、共晶和包晶生长特征，实验确定单相和复相凝固组织发生形态演变的临界过冷度，揭示固/液界面高速运动与传热传质和溶质截留的本征关系。同时采用分子动力学和相场理论方法，对深过冷合金熔体的微观原子组态、宏观热物理性质和晶体形核与生长进行深入的数值模拟研究。在实验研究和理论分析的基础上，阐明三元单相和复相合金的快速凝固共性规律，并建立相应的组织形成理论模型。

本项目自行设计并研制成功国内第一台超高真空静电悬浮金属材料无容器熔凝处理实验装置。采用强激光辐照加热技术，实现了三元Ni基和Ti基合金熔体的深过冷与快速凝固。同时，结合电磁悬浮、自由落体和熔体浸浮等空间模拟实验技术，并借助分子动力学和相场模拟计算方法，开展了五方面实验和理论研究：一是系统探索了不同物质在高压静电场中的感应极化及带电过程；二是实验测定了深过冷液态合金的密度和比热；三是深入研究了静电悬浮条件下晶体形核与组织形成；四是理论分析了液相分离和壳核组织的动力学机制；五是对亚稳合金熔体的原子组态和热物理性质进行了分子动力学模拟研究。发表SCI收录论文44篇，培养博士生10人。