液态多元Ti-Ni基合金的深过冷与快速枝晶生长研究

The rapid solidification of multicomponent alloys under electromagnetic levitation condition may show a series of new phenomena. Multicomponent Ti-Ni-based alloys are chosen as the research objectives. A systematic study is accomplished on the rapid solidification within substantial undercooled alloy melts, based on the determination of thermodynamic properties of the undercooled liquid alloys. Substantial undercooling (∆T=200~350 K) of liquid multicomponent alloys is obtained by the electromagnetic levitation technique. The oscillating drop method and drop calorimeter are applied to determine the surface tension and specific heat of undercooled liquid alloys, and other related thermodynamic properties are further analyzed by molecular dynamics simulation. It provides base data support for the research of rapid solidification. By electromagnetic levitation technology, experimental explorations are performed to reveal the common rules in the rapid solidification of multicomponent Ti-Ni-based alloys. Nucleation mechanism and the phase selection are explored under high undercooling condition. The growth velocity (V=1~50 m/s) is measured to study the rapid dendritic growth kinetics mechanism in multicomponent alloy melts, with special attention to the critical condition of microstructure morphology evolution, multicomponent solute trapping effect, crystal orientation characteristics. Additionally, the mechanism for high frequency electromagnetic field on crystal nucleus formation and dendrite growth is also discussed. On the basis of fundamental research, the final attempt is directed toward to the influence of rapid solidification in high undercooling states on shape memory properties.

在电磁悬浮无容器处理过程中，深过冷液态多元合金的快速凝固将呈现出一系列新规律。本项目选取三~五元Ti-Ni基合金为研究对象，从亚稳态合金熔体的热物理性质测定入手，开展深过冷快速凝固研究。采用电磁悬浮技术实现液态多元Ti-Ni基合金的深过冷(∆T=200~350 K)，实验测定其比热和表面张力随过冷度和成分的变化关系，并通过分子动力学方法进一步计算其它相关热物理性质，为快速凝固定量研究提供必需的基础数据。研究在电磁悬浮无容器状态下，液态多元Ti-Ni基合金的过冷水平与形核机制和相选择的相关规律，测定枝晶生长速度(V=1~50 m/s)随过冷度的变化特性，揭示多元溶质扩散作用下的快速枝晶生长动力学规律。分析发生微观组织形态转变的临界条件，阐明电磁搅拌引起的强制对流效应对溶质截留和晶体取向的影响，研究高频电磁场对晶体形核和枝晶生长的作用机理，并探索深过冷快速凝固条件对合金形状记忆性能的影响规律。

采用电磁悬浮、静电悬浮和自由落体等无容器处理技术研究了二~四元Ti基合金熔体的深过冷与快速凝固规律，悬浮实验中获得的过冷度高达315 K（0.19TL）。研究了深过冷Ti基合金的焓变和比热等热物理性质随温度和成分的变化规律，分析了熔体过冷水平对竞争形核、相选择行为、晶体生长动力学的作用机制。发现了初生相和包晶相在深过冷条件下协同耦合生长的现象，阐明了深过冷包晶合金熔体中亚稳耦合生长的动力学机制。揭示了深过冷液态Ti基合金的凝固组织演变规律和溶质分布特征，探索了高频电磁场中深过冷合金熔体的液相流动规律。上述研究结果的部分内容已发表SCI期刊论文6篇，会议论文1篇。