基于熔体微观结构不均匀变化的准晶/镁基复合材料中I相形成与演变机制研究

Formation and the controlling of the icosahedral quasicrystal phase (I phase) from the melt is a key science issue for fabricating quasicrystal phase reinforced magnesium matrix composites. Based on the microstructural inhomogeneity of alloy, the changes of structure of Mg-Zn-Y melt will be firstly investigated by electrical resistivity measurement. Meanwhile, the solidification pathways and reactions of Mg-Zn-Y melts should be studied in detail by thermal analysis with cooling curve. The influence of constituent, melting temperature, holding time and cooling rate on the formation and transition of I phase will be investigated deeply. The microstructure and isothermal crystallization behavior of as-quenched Mg-Zn-Y amorphous alloys should be studied to reveal the internal relation of structure between liquid and solid alloy. At the same time, the order clusters in the melt will be modeled. The formation and growth mechanism of quasicrystal phase should be discovered from the viewpoint of atom radius and valence electron. The research of this project is to solve the fundamental problems from source, which has the great significance of theory and application for designing, predicting and controlling the quasicrystal phase formation, transition, morphology, distribution as well as the mechanical properties of the magnesium-matrix composite.

从熔体微观结构变化的角度控制二十面体准晶相（I相）的形成是制备准晶增强镁基复合材料首要的关键科学问题。基于合金液-固微观组织之间的遗传规律，本项目提出从合金熔体结构微观不均匀变化出发，通过对合金熔体微结构变化敏感的电阻率和熔体凝固行为的研究，探讨合金成分配比、温度、保温时间、冷却速度等对镁基复合材料中I相形成、演变的影响规律；通过对快凝Mg-Zn-Y准晶增强镁基复合材料微观不均匀结构和等温晶化过程转变的研究，揭示镁基复合材料熔体微观结构与固相显微组织之间的内在联系，从原子半径和原子配位角度构建合金熔体中近程有序原子团模型，并从原子尺寸、价电子角度探究复合材料中准晶I相的形成和演变机制。本项目将从液固组织遗传角度认识问题，对设计、预测和控制镁基复合材料中准晶相的形成、转变及力学性能具有重要的理论意义和实际应用价值。

项目从合金熔体微观结构信息遗传角度出发，基于结构的微观不均匀变化，利用高温熔体电阻率、凝固冷却曲线和高温熔体DSC，结合固相微观组织分析，研究了Mg-Zn-Y（Gd、Nd）等系列准晶合金熔体中二十面体短程序（ISRO）变化与凝固微观组织中二十面体准晶（I）相之间的遗传关系，深入分析了不同体系合金熔体的凝固行为，探讨了I相在液相中形成与演变机制，制备了含准晶I相的镁基复合材料，并对材料的力学性能进行了分析研究。对多个系列的准晶合金研究表明，ISRO结构的演变导致合金熔体电阻率的异常变化；熔体中存在的ISRO团簇为准晶的形核质点，快速凝固过程中形成的较大过冷度会增大ISRO的形成几率。随着冷却速率的提高，准晶的生长方式由小平面生长和共生生长转变为快速凝固时的非小平面生长。在含准晶相的镁基复合材料中，准晶相以（I-phase+α-Mg）共晶组织的形式存在。本项目的研究对从液固组织遗传角度认识问题，为设计、预测和控制镁基复合材料中准晶相的形成、转变及力学性能具有重要的理论指导意义和一定的实际应用价值。