金属玻璃及其液相的微观结构和热力学的核磁共振表征

Deformation mechanism of metallic glasses is a fundamental problem of condensed matter physics. The existence of flow units and their characteristics in metallic glasses are currently one of the research focuses in the field of metallic glasses.Unlike dislocations in crystalline systems, flow units in metallic glasses lack obviously recognizable characters in microscopic structures. Therefore, it is very challenging to detect and recognize flow units in experiments. This project proposes to utilize anelastic deformation to activate the shear flow of flow units and freeze the flow units in an intermediate state which could assume recognizable unique microscopic structures. Such unique microscopic structures could be detected and characterized by nuclear magnetic resonance (NMR). By choosing metallic glass systems with different activation energies of flow units, different fragilities, the relationships between flow units, the characteristics of α and β relaxations, and microscopic structures could be established.In addition, the structures, thermodynamics，and dynamic properties of glass forming liquids will be studied. This could offer important information on the relationship between the characteristics of liquid properties and the structure, glass forming ability (GFA), and mechanical properties of the glassy state of metallic glass forming alloys. By exploring the influence of alloy compositions (including eutectic points) on the properties of metallic liquids, the relationship between the characteristics of metallic liquids and GFA could be established. In addition, it will also provide information on the correlation between the characteristics of metallic liquids and the nanometer structures of the glassy state and its mechanical and relaxation properties. Such information on the microscopic properties of the liquid state offers deep insight into the mechanism of mechanical deformation of metallic glasses, GFA, and the nature of glass transition.

非晶合金的形变机理是凝聚态物理的一大基本科学问题。基本流变单元的存在与特征是当前金属玻璃领域研究的焦点之一。如何从微观上认识流变单元的结构特征、从实验上直接捕捉到流变单元是本领域的一大挑战。本项目提出利用滞弹性变形的方法使流变单元处于剪切变形的过程中，利用核磁共振的结构测试方法捕捉到流变单元，识别流变单元剪切变形后的微观结构特征。通过选择不同激活能和脆度的体系，系统研究流变单元、弛豫和微观结构的关系，为从微观上认识非晶合金的形变机理提供关键的实验与理论依据。同时，用高温核磁共振对非晶合金液态结构、热力学及动力学的研究会从金属玻璃的源头认识金属玻璃的结构、形成能力、和力学性能。通过研究合金成份（包括共晶点成份）对液态特性的影响认识液态微观特征与玻璃形成能力的关系，与玻璃态纳米尺度结构及力学性能和弛豫的关系。这些有关液态微观性质的研究为认识非晶合金形变、形成能力、及玻璃转变提供了重要信息。

非晶合金的形变机理是凝聚态物理的一大基本科学问题。基本流变单元的存在与特征是当前金属玻璃领域研究的焦点之一。本项目利用高温核磁共振对非晶合金液态结构、热力学及动力学的研究会从金属玻璃的源头认识金属玻璃的结构、形成能力、和力学性能。通过研究合金成份（包括共晶点成份）对液态特性的影响认识液态微观特征与玻璃形成能力的关系，与玻璃态纳米尺度结构及力学性能和弛豫的关系。主要成果如下：(1) 利用高温 NMR 实验平台，在La-Al-Ni金属玻璃形成体系的平衡熔体中观察到一级液体-液体相变，并且随着Al含量降低，发生在不同组分合金平衡熔体中的液-液相变的相变温度向低温偏移。第一性原理计算表明其有效序参量并不是密度，而是与键方向序参量W6相关的局域结构序参量S。（2）在Zr58.5Cu15.6Al10.3Ni12.8Nb2.8的过冷液相区变形过程中，除了观察到应变速率软化现象之外，还看到了应力应变曲线发生震荡的现象。应力应变曲线震荡现象在温度高于713K时消失，而应变速率软化即是温度高于733K时仍旧存在。分析表明动态化和相关性是对金属玻璃在Tg附近的流变过程产生影响的两个重要因素。(3) 在Pd-Ni-P金属玻璃形成体系的平衡熔体中观察到液体-液体相分离，并且随着P含量增加，发生在不同组分合金平衡熔体中的相分离的相变温度向低温偏移。当P含量高于19 atm%时，液体-液体相分离消失。分析表明这一液体-液体相分离现象对玻璃形成能力有着重要的影响。.截止目前，截止目前，项目取得的相关研究成果已经在Nature Communications、The Journal of Chemical Physics等国际学术期刊上发表SCI收录论文6篇，毕业博士研究生2名。这些有关液态微观性质的研究为认识非晶合金形变、形成能力、及玻璃转变提供了重要信息。