电磁悬浮大体积镍基合金快速凝固机理与组织形成控制

Using electromagnetic levitation technique, rapid solidification of bulk Ni-based superalloy will be achieved in order to explore the rule how to control the solidified microstructure. The surface oscillation and the inner heat and mass transfer will be studied for the sake of modeling the convection process under the effect of electromagnetic field and high undercooling conditions. Exploring the underlying reason of heterogeneous nucleation passivation by the eddy current heating of electromagnetic levitation, four kinds of nucleation and crystal growth will be achieved: free nucleation, single point trigger, multi-point trigger, and levitation drop solidification. The relationship will be clarified how the crystal growth velocity depends on the thermal history and the trigger conditions. The atom redistribution resulting from the competition diffusion of different kinds of atoms will be investigated in order to elucidate the crystal growth orientation and phase selection of face centered cubic matrix and intermetallic compound phases. This will be helpful to set up the model of solute trapping of multi-component Ni-based superalloy. Both of the electronic effect and the component segregation effect will be researched by the first principle method so as to clarify the physical mechanism of intermetallic compound distribution and crystal boundary microstructure. Finally, the levitated solidification samples with the mass of 50-1000 g will be prepared when the undercooling exceeds 0.2Tm. By achieving quantificational characterization of solidified microstructure, the effect of containerless processing and high undercooling on rapid solidification will be discovered, which will promote the development of the theoretical model of rapidly solidified microstructure control of bulk Ni-based superalloy.

本项目拟采用电磁悬浮技术，实现无容器条件下大体积镍基高温合金的快速凝固，探求微观组织结构的形成机理与主动控制规律。研究悬浮镍基高温合金表面振荡运动和内部传热传质规律，建立电磁场与深过冷耦合作用下液态合金的对流物理模型；探索电磁悬浮涡流效应对异质晶核的钝化机理，实现自由形核、单点、多点触发、悬浮落滴凝固4种方式形核与晶体生长，揭示生长速度与热历史、触发条件的关系规律；探索多组元竞争配位在溶质再分配中的作用，阐明基体相与化合物强化相的生长取向和选择规律，建立多元镍基高温合金溶质截留理论模型；通过第一原理计算，获取金属间化合物与基体相的电子配位结构和组元偏聚的电子效应，阐明化合物分布、晶界微观结构的物理机制；在0.2Tm过冷度以上制备出50-1000 g镍基高温合金的悬浮凝固样品，定量表征微观组织结构，揭示悬浮无容器与深过冷对凝固组织结构的作用规律，建立快速凝固微观组织结构主动控制理论模型。

本项目以实验研究为主，辅以第一原理计算及有限元分析，深入探索了大体积金属的电磁悬浮实验技术，研究了镍基高温合金在电磁悬浮条件下的快速凝固机制和组织形成规律。取得的创新性工作为：(1)建立电磁场优化计算模型获得多种优化线圈构型提高悬浮性能，成功悬浮Ni、Al、Cu、Ti等百克级大体积金属，探索出多物理场下大体积金属熔体的悬浮行为；(2) 通过电磁悬浮和落管无容器处理技术，探究了Ni-Zr包晶合金的深过冷和急冷条件下初生相与包晶相的竞争生长、取向关系和共生现象，阐明包晶凝固模式的转变规律；(3) 基于第一原理和分子动力学方法，对多种镍基合金(Ni-Zr合金、Ni3Al、Inconel 718)的热物理性质与温度的依赖关系进行了理论模拟并分析了液态金属的结构特征，阐明了化学和拓扑分布、晶界微观结构的物理机制。