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

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.

大多数使用的金属和合金都是晶体，其内部结构以长程有序为特征。在过去的一个世纪里，人们对它们的结构进行了很好的研究，为它们的性质提供了具体的基础。这种结构-性能范式在材料科学领域已经很好地建立起来。相比之下，通过母体液体快速冷却获得的金属玻璃（mg）具有类似液体的非晶结构，内部没有可识别的微观结构。虽然缺乏长程周期性，但mg确实具有结构，在最近邻原子配位和几纳米长度尺度上的位置相关水平上。这种结构组织很难表征，并且仍然知之甚少。因此，对mg原子结构和性质之间联系的理解远远落后于传统金属。本项目旨在利用计算机模拟方法解决mg中的中短程顺序问题。详细的结构信息有望阐明这些玻璃的宏观行为，从而更好地判断设计它们的应用。在教育方面，本研究对丰富材料科学重点学科，特别是材料结构核心学科具有重要意义。许多计算机分子动力学模拟适合本科生参加高级设计/研究经验课程，提供有趣的案例研究，与之前在课堂上熟悉的晶体对称进行比较。技术摘要本课题的目标是1)量化金属玻璃（mg）可实现的短程订单（SRO）的程度和范围，2)可靠地识别不同类型金属玻璃（mg）的中程订单（MRO）的特征模式。这种对非晶固体有序的基本理解是一个基本的材料科学问题，但迄今为止很难实现，因为迄今为止构建的MG结构，无论是通过拟合散射数据还是通过分子动力学（MD）模拟中的液体淬火，本质上都远不如实验玻璃有序。该项目旨在开发有效的磁流变模拟路线，能够产生具有势能、原子密度、弹性常数和有序度的磁流变结构，这些都与现实世界的磁流变相似。一个重点是算法开发，以加速MD在寻找更深的能量盆地。计划是使用1)延长时效，2)循环应力辅助时效，3)一个新的删除-添加协议，建立在模拟晶体崩溃或气相沉积获得的非晶结构上。初步结果表明，这些方法（以及它们的组合）可以在最终结晶的过程中进入低能玻璃态。捕获的结构提供了一个前所未有的机会，可以在类似于实验室玻璃的构成和饱和度水平上揭示SRO/MRO，从而允许与剪切转换、弛豫和其他玻璃性质的原子机制联系起来。研究结果有望成为在MGs中建立具体结构-性质关系的重要一步。