凝固亚稳液相分离合金制备新型纳米金属玻璃的组织调控及变形机理

Liquid-liquid phase-separation alloy systems are typically characterized by a liquid miscibility gap. Phase-separating metallic materials with different microstructure and phases can be obtained through skillfully controlling the solidification process of these liquid-liquid phase-separation alloys. Liquid-phase-separating metallic glasses are vitrified solids consisting of two glassy phases induced by the liquid-liquid phase separation in the miscibility gap and the subsequent liquid-to-glass transitions in the two separated coexistent liquids. Recently, much attention was focused on this kind of metallic glasses due to their fascinating two-glassy-phase structure. Various two-glassy-phase alloy systems were discovered. It was indicated that the liquid-phase-separation metallic glasses exhibit unique mechanical, magnetic and thermal properties. Such metallic glasses have potential applications as structural and/or functional materials. However, the control of solidification microstructure and the integrative structure-property design is still missing, resulting in shortcomings and limitations in the mechanical properties and deformability of liquid-phase-separation metallic glasses. To these key issues, in this project, utilizing the metastable liquid-liquid phase separation phenomenon of Fe/Co-Cu system, through rapid solidification we develop a new-type bulk metallic nanoglasses with unique superplasticity and consisting of a high-population density of glassy spherical grains in nano-meter scale. The new Fe/Co-Cu-Al-Zr alloy system is designed. The effects of the processing parameters and the cooling condition on the formation of the phase-separating metallic nanoglass are investigated. A model describing the kinetics of the metastable liquid-liquid phase separation of multi-component alloys is developed to clarify the formation of the solidification microstructure. The competition between the metastable liquid-liquid phase separation and the liquid-to-glass transition has been discussed. In order to build a valid route to adjust and control the microstructure of the phase-separating nanoglasses, the effects of the micro-alloying and the mechanism of liquid-liquid phase separation on the solidification microstructure have been clarified. In addition, the local microstructure evolution during shearing deformation of the phase-separating nanoglasses is studied, and the relationship between microstructure and mechanical properties and the deformation mechanism are investigated. The investigation via this project not only provides opportunities for deeply understanding non-equilibrium solidification behavior of multi-component metastable immiscible/monotectic alloys but also opens new perspectives for developing new-type high-performance phase-separating metallic nanoglasses to break through the brittleness problem of metallic glasses at room temperature.

调控液-液相分离合金凝固过程，使两分离液相发生玻璃转变，可获得具有特殊组织和性能的双非晶相合金。但由于双非晶态结构与组织均匀性之间相互制约，其机械性能较差，易发生脆性断裂。针对双非晶相合金存在的问题，本项目提出利用Fe/Co与Cu亚稳液-液分离反应并结合快速凝固技术，研制由高数量密度纳米非晶粒子组成的和具有超塑性的新型相分离纳米金属玻璃。以Fe/Co-Cu-Al-Zr合金为研究对象，探索工艺参数和冷却条件以及液-液相分离与玻璃转变之间的竞争行为，对相分离纳米金属玻璃凝固组织形成的影响。建立描述合金液-液分离过程的理论模型，考察熔体过冷行为与组织结构之间的关联。阐明微合金和液-液分离机制对组织的影响规律，建立调控组织结构的有效方法。分析形变过程中组织结构演变，揭示组织与机械性能间的关系以及变形机理。这既是亚稳相分离合金凝固行为的研究，也是发展新型纳米金属玻璃和解决金属玻璃室温脆性难题的探索。

调控相分离合金凝固路径，使两分离液相均发生玻璃转变，可获得具有特殊组织和性能的相分离金属玻璃材料。本项目基于Cu-Fe合金亚稳液-液相分离并结合快速凝固技术，研究了由高数量密度纳米非晶粒子组成的新型相分离纳米金属玻璃。以Cu-Fe-Zr-(Al)合金为研究对象，考察了合金成分与冷却条件等对相分离纳米金属玻璃凝固组织的影响规律，探索了液-液相分离与玻璃转变之间的竞争行为对相分离纳米金属玻璃凝固组织形成的影响；阐明了微合金元素和液-液分离机制对组织的影响规律，建立了调控组织结构的有效方法；探索了变形过程中微观组织结构的演化规律以及组织结构与机械性能之间的关系，揭示了相分离纳米金属玻璃的变形机理及其与微观组织结构演变之间的关联。取得如下主要研究结果：1）通过液-液相分离过程的理论分析，揭示了Cu-Fe-Zr合金组织演变规律及相竞争形成机制，快冷下(Cu0.5Fe0.5)40Zr60合金液-液分离形成富Cu和富Fe两液相，随后两液相分别发生玻璃转变，形成数量密度~10^24/m^3、尺寸2~8 nm纳米的富Cu非晶粒子，并阐明了该相分离纳米金属玻璃晶化过程中电阻的变化行为；2）揭示了微合金元素对(Cu0.5Fe0.5)40Zr60合金组织与相结构的影响规律。研究了不同微合金化元素调控的相分离纳米金属玻璃的非均匀结构及其变形行为，发现剪切带约50 nm范围内富Fe纳米非晶粒子通过Ostwald机制粗化，剪切带内部非晶粒子因剧烈机械混合而消失，富Fe纳米非晶粒子“原位”记录了剪切带内部及其相邻基体微观组织结构演变特征；3）设计了系列Cu-Fe-Zr-Al相分离纳米金属玻璃，研究了Al含量和Cu/Fe原子比对非晶形成能力、热稳定性及组织结构的影响，探明了非均匀结构与合金样品塑性及锯齿流变之间的关系，当Cu与Fe原子比在5:5到8:2之间时，(CuxFey)33Zr59Al8合金具有较好的非晶形成能力和热稳定性，发现塑性较好的(Cu0.6Fe0.4)33Zr59Al8合金剪切带动力学上处于更稳定的自组织临界状态；4）通过本项目研究，发表论文20篇，其中SCI收录16篇，申报3项国家发明专利，培养研究生4名，达到了研究成果预期目标。