Degree of short-to-medium-range order in metallic glasses

金属玻璃中短程至中程有序度

• 批准号: 1505621
• 负责人: En (Evan) Ma
• 金额: $ 37.22万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1505621&HistoricalAwards=false
• 关键词: Degree; short; medium; range; order; Degree; short; medium; range; order

Nontechnical abstractMost metals and alloys in use are crystals, with an internal structure characterized by long-range order. Their structures have been well studied over the past century, providing concrete basis of their properties. Such a structure-property paradigm is well established in the field of materials science. In contrast, metallic glasses (MGs) obtained by fast cooling of their parent liquids have a liquid-like amorphous structure with no discernable microstructure inside. Though lacking long-range periodicity, MGs do have structure, at the level of nearest-neighbor atomic coordination and positional correlations on the length scale of a couple of nanometers. This structural organization is difficult to characterize and remains poorly understood. As a result, the understanding of the links between the atomic structure and properties in MGs lags far behind that achieved for conventional metals. This project aims to resolve the short-to-medium range order in MGs, using computer simulation approaches. The detailed structural information is expected to shed light on the macroscopic behavior of these glasses, enabling better judgement in designing their applications. In terms of education, this research has significance in enriching key materials science subjects, in particular the core subject of Structure of Materials. Many of the computer molecular dynamics simulations are amenable to the participation of undergraduate students in Senior Design/Research Experience courses, providing interesting case studies to compare with the familiar crystal symmetry learnt previously in the classroom. Technical abstractThe goal of this project is to 1) quantify the degree and extent of short-range order (SRO) realizable in metallic glasses (MGs), and 2) reliably identify the characteristic patterns of medium-range order (MRO) in different types of MGs. This basic understanding of the ordering in amorphous solids is a fundamental materials science issue, but has been difficult to achieve so far because the MG configurations constructed to date, either by fitting to scattering data or by liquid quenching in molecular dynamics (MD) simulations, are inherently far less ordered than experimental glasses. The project aims to develop efficient MD simulation routes that are capable of producing MG structures having potential energy, atomic density, elastic constants, and therefore degree of order all similar to real-world MGs. A focus is algorithm development to accelerate MD in the search of deeper energy basins. The plan is to use 1) prolonged aging, 2) cyclic-stress-assisted aging, and 3) a new deletion-addition protocol, building upon amorphous structures obtained from simulated collapse of crystals or vapor deposition. Preliminary results suggest that these approaches (and their combination) can access low-energy glassy states along the way towards eventual crystallization. The configurations captured provide an unprecedented opportunity to uncover the SRO/MRO at a level of make-up and saturation that resembles those in laboratory glasses, to allow connections with atomistic mechanisms underlying shear transformations, relaxation and other glass properties. The results are expected to be a major step-forward towards establishing concrete structure-property relations in MGs.

非技术抽象的金属和使用的合金是晶体，其内部结构的特征是远程顺序。在过去的一个世纪中，他们的结构进行了很好的研究，为其性质提供了具体的基础。这种结构范式范式在材料科学领域已建立。相比之下，通过快速冷却母体液体获得的金属玻璃（MGS）具有内部没有可辨别的微观结构的液体状无定形结构。尽管缺乏远距离周期性，但MG确实在最近的邻居原子协调和位置相关性的水平上具有结构。这个结构性组织很难表征，并且仍然了解得很糟糕。结果，对MGS原子结构与特性之间的联系的理解落后于传统金属所获得的联系。该项目旨在使用计算机模拟方法来解决MGS中短期范围顺序。预计详细的结构信息可以阐明这些眼镜的宏观行为，从而在设计其应用时更好地判断。在教育方面，这项研究在丰富关键材料科学主题方面具有重要意义，尤其是材料结构的核心主题。许多计算机分子动力学模拟都可以适应本科生参加高级设计/研究经验课程的参与，从而提供有趣的案例研究，以与先前在课堂上学到的熟悉的水晶对称性进行比较。技术摘要该项目的目标是1）量化金属眼镜（MGS）可实现的短程顺序（SRO）的程度和程度，以及2）可靠地确定不同类型的MGS中中等顺序（MRO）的特征模式。对无定形固体中排序的基本理解是一个基本的材料科学问题，但是到目前为止很难实现，因为迄今为止构建的MG配置是通过拟合散射数据或通过分子动力学（MD）模拟中的液体淬灭来构建的，其本质上比实验镜的有序差得多。该项目旨在开发能够生产具有势能，原子密度，弹性常数以及因此与现实世界中MG相似的MG结构的有效MD模拟途径。重点是算法开发以加速MD，以寻求更深的能源盆地。该计划是使用1）长时间的老化，2）循环压力辅助衰老，3）建立在从晶体或蒸气沉积的模拟崩溃中获得的无定形结构建立的新的缺失 - 添加方案。初步结果表明，这些方法（及其组合）可以在最终结晶的过程中访问低能玻璃状态。捕获的配置提供了一个前所未有的机会，可以在类似于实验室眼镜的化妆和饱和水平的水平上发现SRO/MRO，以允许与剪切转换，放松和其他玻璃特性的原子机制的连接。 预计该结果将是建立MGS中混凝土结构特性关系的主要步骤。