Collaborative Research: Probing Atomic Structure Changes in Deformation of Metallic Glasses: An Experimental and Computational Study

金属玻璃或非晶态合金是结构无序的固体，没有晶体中常见的长程平移顺序。结构无序在原子尺度上起源于彼此邻近的随机堆积的原子。这种无序导致了一些最显着的机械性能，他们的晶体同行只能羡慕：高强度接近理论值，大弹性应变，高韧性。金属玻璃涵盖了广泛的系统，包括过渡金属，难熔金属，稀土金属及其合金。这些独特而卓越的性能使其成为许多应用的理想选择，包括结构部件、耐用和高性能设备、涂层以及承受大载荷、磨损和腐蚀保护以及精密成型的微型设备。在过去的十年中，人们对金属玻璃的利用进行了广泛的研究和开发，特别是其机械性能。这项合作研究的重点是探测原子尺度的变形过程和原子结构。它结合了使用同步加速器X射线散射和中子散射的实验方法，以及使用分子动力学和第一原理计算的原子模拟。具体而言，它涉及以下问题：（1）原子结构，包括短程和中程有序及其变形引起的变化;（2）具有不同原子结构的系统的力学响应及其差异;（3）结构-力学响应的原子尺度表征，如自由体积、局部剪切变换、和局部原子键的变化，不能很容易地捕捉到直接通过实验测量。非技术摘要：本研究的最终目标是建立本构关系的应力，应变，应变速率，温度和各种物理，结构性能和成分的变化。由于金属玻璃中结构无序所带来的困难，可靠的本构关系必须建立在对原子尺度过程和机制的详细而准确的理解之上。这一努力极大地促进了这一领域知识的进步。我们也期望这一努力有助于扩大这种奇妙材料的应用，从而在竞争激烈的世界市场上为美国工业赢得优势。这项拟议工作的另一个组成部分是教育和外联方案。该项目在这方面遵循两条轨道：（1）通过演示、研讨会和实践学习经验，参与当地少数民族工程本科生的外展教育计划和对工程职业感兴趣的学生的K-12计划，（2）为格鲁吉亚理工学院和田纳西大学的研究生建立实验和计算工作之间的密切合作和交流计划，为本科生和研究生提供丰富的教育经验。

TECHNICAL SUMMARY:Metallic glasses, or amorphous alloys, are structurally disordered solids without the long-range translational order commonly seen in crystals. The structural disorder originates at the atomic scale from randomly packed atoms in proximity to each other. This disorder leads to some of the most remarkable mechanical properties that their crystalline counterparts can only envy: high strength close to the theoretical value, large elastic strain, and high toughness. Metallic glass covers a wide range of systems including transition metals, refractory metals, rare earth metals, and their alloys. These unique and superb properties make them the perfect candidates for many applications including structural components, durable and high performance equipment, coatings, and miniature devices subject to large loading, wear and corrosive protection, and precision shaping. In the past decade, extensive research and development have been done to utilize metallic glasses, especially their mechanical properties. This collaborative research is focused on probing atomic scale deformation processes and atomic structures. It combines experimental approaches using synchrotron X-ray scattering and neutron scattering, and atomistic simulations using molecular dynamics and first-principle calculations. Specifically, it addresses the following issues: (1) Atomic structures, including short- and medium-range order and their changes caused by deformation; (2) Mechanical responses and their differences for systems with different atomic structures; (3) Atomic scale characterizations of structure-mechanical responses such as free volume, local shear transformation, and local atomic bond changes that cannot be easily captured directly by experimental measurements.NON-TECHNICAL SUMMARY:The ultimate goal of this research is to establish the constitutive relations among stress, strain, strain rate, temperature and various physical, structural properties and compositional changes. Due to the difficulties posed by the structural disorder in metallic glasses, reliable constitutive relations must be built on detailed and accurate understanding of atomic scale processes and mechanisms. This effort contributes critically to the advancement of knowledge in this area. We also expect this effort to contribute a positive step in widening the applications of this marvelous material, thus gaining an edge for US industries in the highly competitive world market. Another integral part of this proposed work is the education and outreach program. The project follows two tracks in this regard: (1) participation in outreach education program for local minority engineering undergraduates and K-12 program for students interested in engineering careers through demonstrations, workshops, and hands-on learning experiences, (2) establishment of a close collaboration and exchange program between experimental and computational work for graduate students in Georgia Tech and University of Tennessee, contributing to a rich education experience for both undergraduates and graduate students.