极端非平衡条件下Ti基包晶型合金的快速凝固机制研究

极端非平衡条件下初生相和包晶相的亚稳耦合生长现象比较独特，关于耦合生长的直接实验证据、形成机制、动力学特征以及其与典型包晶凝固模式的关系等仍需探索。本项目采用电磁悬浮和熔体急冷两种超常凝固技术，实现液态Ti-Ni/Fe包晶型合金的快速凝固，研究其凝固路径选择和亚稳凝固动力学。系统分析深过冷和急冷条件下凝固组织演变、组成相的晶体取向关系以及溶质再分配规律，探索凝固模式的转变机理。对深过冷液态合金的典型包晶凝固过程进行原位高速摄影和同步辐射研究，鉴别过冷熔体的液态结构，测定初生枝晶生长速度和包晶凝固特征参数随过冷度的变化关系，揭示典型包晶凝固动力学。利用高速摄影和同步辐射技术，实时侦测悬浮液态合金中初生相和包晶相的亚稳耦合生长过程，建立耦合生长速度对过冷度的依赖关系，明晰过冷度与合金体系特征参数对耦合生长形貌的影响，阐明亚稳耦合生长动力学。

The metastable coupled growth phenomenon of primary phase and peritectic phase under the extreme non-equilibrium condition is relatively unique. The directly experimental evidences, formation mechanisms, kinetics characteristics of the coupled growth and its relationship with typical peritectic solidification modes still need a deep exploration. In this project, the solidification path selection and metastable solidification kinetics of liquid Ti-Ni/Fe peritectic-type alloys are systematically investigated by the electromagnetic levitation and melt quenching methods. The solidification microstructure evolution, crystal orientation relationship of constituent phases and solute redistribution under the conditions of high undercooling and rapid cooling are systematically analyzed to explore the transition mechanism of solidification modes. The in-situ high-speed photography and synchrotron radiation studies are performed on the typical peritectic solidification process of undercooled liquid alloys. Special attentions are paid to identify the liquid structure of the undercooled melt, determine the undercooling dependences of primary dendrite growth velocity and peritectic solidification characteristic parameters, and finally reveal the typical peritectic solidification kinetics. Using the high-speed photography and synchrotron radiation techniques, the metastable coupled growth process of the primary phase and the peritectic phase in the levitated liquid alloy is directly detected in real time. The relationship between its growth velocity and the undercooling is established, the effects of bulk undercooling and alloy system parameters on the coupled growth morphology are clarified and the metastable coupled growth kinetics is elucidated.