由难混溶合金制备相分离块体金属玻璃的凝固过程与性能研究

Liquid-phase-separation 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 liquids. 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. Although extensive efforts have been devoted to investigate the synthesis and structural characterization of the liquid-phase-separation metallic glasses, the dynamic formation mechanism of such metallic glasses is still not clarified. The reasonable design method is still missing, and the critical thickness of such metallic glasses is limited within a few tens of microns. Essentially, the formation mechanism of the liquid-phase-separation metallic glasses is an issue in the field of alloy solidification. Herein, in this project, starting from the study of the solidification behavior of immiscible/monotectic alloys, we develop the liquid-phase-separation bulk metallic glasses. The phase separation into two liquids in the miscibility gap of the ZrLnCoCuAl or Fe(Co)NbCuAlZr alloy is investigated experimentally and by simulation modeling. The mechanism of the liquid-liquid phase decomposition and the microstructural evolution during cooling the melt through the liquid miscibility gap have been clarified. The solidification behavior, including the glassy phase formation and control method etc., of the two coexistent liquids has been investigated in detail. Accordingly, a method, based on the immiscible/monotectic alloys, has been proposed to design the liquid-phase-separation bulk metallic glasses. In addition, the effects of the morphology feature, the characteristic size, phase nature, spatial distribution of the secondary glassy phase in the glassy matrix on the mechanical and magnetic properties have been systematically investigated, attempting to explore the relationship between the structure and property. The investigation via this project not only provides opportunities for deeply understanding the solidification mechanism of multicomponent immiscible/monotectic alloys but also opens new perspectives for developing bulk metallic glasses and exploring new metal materials.

相分离金属玻璃是一种由液-液相分离导致形成双非晶相的金属玻璃，具有良好力学、磁学和热性能。在结构表征和制备研究方面已开展了大量工作，然而相分离金属玻璃的形成过程与控制尚不清楚，合金设计方法不合理，以致其尺寸偏小。从本质上来说，其形成过程应属于凝固领域内的问题。针对相分离金属玻璃研究不足，本项目从难混溶合金凝固特征研究入手，以ZrLnCoCuAl或Fe(Co)NbCuAlZr合金为研究对象，实验与模拟计算研究相结合，揭示由难混溶合金制备相分离块体金属玻璃的凝固过程，阐明合金液-液相分离机制和组织演变规律以及两液相冷却过程中相形成与控制；进而，提出在难混溶合金基础上发展相分离块体金属玻璃的方法；考察第二非晶相的形貌、尺寸、结构和空间分布等对力学和磁性能的影响，探索相分离块体金属玻璃材料结构与性能间的关系。这对加深多元难混溶合金凝固机理认识、拓展块体金属玻璃研究以及新材料的开发具有多重研究意义。

块体非晶合金是一种具有高性能的结构和功能材料。通常，不同合金系的块体非晶合金表现出不同性能。相分离非晶合金是一种由液-液相分离导致形成双非晶相合金。虽然在其结构表征和制备研究方面已开展了大量工作，然而相分离非晶合金的形成过程与控制尚不清楚，合金设计方法不合理，以致其尺寸偏小。本项目从难混溶合金入手，以ZrLnCoCuAl (Ln=Ce, La, Pr或Nd)合金为研究对象，实验研究与理论分析相结合，主要开展了四方面工作：①难混溶合金组元液态不混溶区域和合金凝固特征;②相分离金属玻璃合金液-液相分离机制与组织演变规律;③两液相冷却过程中的凝固行为、非晶相的形成与控制及其影响因素;④相分离块体金属玻璃制备、结构表征以及性能。取得的关键结果与数据有：1）揭示了二元Zr-Ce合金凝固特征，解析了二元合金组元液态不混溶区域的基本数据，阐明了两分离液相各自的凝固路径与行为及其影响因素；2）揭示了合金成分对分离两液相相形成的影响规律，系统研究了Zr-CL-Al-Co（CL为Ce33La67合金）合金中Zr:CL、Co:Al、Ce:La原子比对两分离液相发生玻璃转变的影响，阐明了样品中组织演变机理以及非晶相形成机制；3）揭示了难混溶合金液-液相分离机制以及组织演变规律，阐明了双相块体非晶合金组织结构形成过程，建立了由难混溶合金设计双相块体非晶合金的合金热力学设计准则；4）提出了增强双非晶形成能力的双共晶点准则和相似元素部分替代等策略，建立由难混溶合金设计双相块体非晶合金的动力学模型，研制了双相块体非晶合金，开展了力学性能研究，建立了双相块体非晶合金力学性能与合金系本身、第二相非晶粒子的体积分数及尺寸、第二相非晶粒子的相分布、以及两非晶相体系匹配之间的关联；5）在Acta Materialia(两篇)和Scientific Reports(两篇)等国际知名期刊上发表了9篇学术论文；授权发明专利2项；培养课题负责人亲自带的博士研究生1名（在读，2018年毕业）、硕士研究生2名（在读，其中1名2018年毕业）。本项目研究对提高了多元难混溶合金凝固机理认识、拓展块体非晶合金研究以及新材料的开发具有多重意义。