Atomic Scale Deformation Mechanisms in New Ductile Cu-Based Bulk Metallic Glasses with High Manufacturability

非技术性块状金属玻璃(BMG)是一种具有非晶态(玻璃)内部结构的新型先进材料。它们不像金属中常见的那样含有与晶体有关的缺陷。这种特殊的结构赋予了BMG许多性能(例如，强度、硬度、弹性、耐磨性和耐腐蚀性)，这些性能可能优于许多金属。这种不同创造了极大地改善在几个工程应用中广泛使用的许多金属的性能的潜力。然而，宝马面临的一个重大挑战是它们弯曲和拉伸的能力有限。即使当它们断裂时，BMG在失败之前也不会显示出显著的伸展或弯曲的证据。一些BMG表现出了良好的延展性，但它们往往很难制造成大尺寸，或者需要昂贵、有毒和/或难以找到的元素。设计具有良好延展性、可规模化生产、不使用有毒或难获得元素的BMG是该领域的一个突出问题。这个项目通过研究首席研究员最近发现的铜基BMG中的原子尺度变形机制来解决这一挑战。这些铜基BMG具有高强度、良好的延展性、卓越的可制造性和工程友好的组成的特殊组合。了解这些BMG的弯曲、拉伸和最终失效的方式，将有助于未来发现其他同样或更出色的BMG，它们将比我们目前使用的材料更好地满足社会对高性能材料的需求。该项目吸引了多名研究生和本科生参与直接研究，并为他们未来在学术界或工业中从事与材料相关的职业做好准备。通过一个成熟的暑期计划，该项目还吸引了K-12年级的学生，特别是来自服务不足地区和群体的学生，培养他们对材料科学的好奇心和兴趣，同时促进STEM教育的多样性、公平性和包容性。研究成果被用来丰富在俄勒冈州立大学教授的本科生材料科学导论课程。该项目还有助于美国成为宝马研究的领先者，宝马是一种具有重要战略意义的材料，也是未来国防和航空航天应用中潜在的游戏规则改变者。技术总和(或可塑性)经常与各种材料的强度发生冲突。此外，组合物的可制造性和工程友好性是工程材料的另一个常见权衡。块体金属玻璃(BMG)受到了这两方面的挑战。在不牺牲强度、可制造性和工程友好性的情况下，通过合金设计实现BMG良好的延展性是该领域的核心问题。这些挑战的一个重大障碍是缺乏对BMG中原子尺度特征(键、元素)如何控制其宏观变形以及如何通过设计其元素组成来控制这些影响的了解。本项目结合实验和计算方法来研究最近发现的一系列铜基BMG的原子销售变形机制，这些BMG具有高强度、良好的延展性、出色的可制造性和工程友好的组成。通过同步光束线的协调原位应变和扫描电子显微镜来跟踪新的BMG中原子键和剪切带在不同应力和应变水平下的行为，以探索成分变化对其变形行为的影响(通过原子键和剪切带)。然后利用分子动力学模拟和有限元模拟对实验数据进行了分析和解释。预计该项目将确定主要负责弹性变形的原子键，并确定主要负责塑性变形和延展性的原子键的强度。通过这种方式，研究人员正在阐明这种新类型的BMG中强度和塑性的不寻常组合的根本原因，并揭示合金成分如何影响应力驱动的原子键行为和宏观变形。这些知识对于设计未来的具有良好延展性和附加性能的理想组合的BMG是必要的。该项目还在极端应力下的材料塑性领域推动了基础材料科学的发展，这是普通金属、陶瓷或聚合物材料无法探索的。由该项目资助的研究生体验了一个独特的机会，学习材料的宏观变形和原子尺度行为，掌握重要的实验和计算技术，并为未来在材料相关领域的职业生涯做准备。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYBulk metallic glasses (BMGs) are a fairly new class of advanced material that has a non-crystalline (glassy) inner structure. They do not contain crystal-related defects as are common in metals. This special structure gives BMGs a host of properties (e.g., strength, hardness, resilience, wear- and cor-rosion-resistance) that can be superior to many metals. This difference creates the potential to dras-tically improve upon the performance of many metals widely used in several engineering applica-tions. However, one significant challenge facing BMGs is their limited ability to bend and stretch. Even when they break, BMGs do not show evidence of significant stretching or bending before failure. A few BMGs have demonstrated good ductility but they are often very difficult to make in large sizes or require elements that are either expensive, toxic and/or hard to find. Designing BMGs with good ductility, that can be manufactured at scale and which do not use toxic or hard to acquire elements is an outstanding question in the field. This project addresses this challenge by investigating the atomic-scale deformation mechanisms in Copper-based BMGs that were recently discovered by the principal investigator. These Cu-based BMGs possess an exceptional combination of high strength, good ductility, excellent manufacturability, and engineering-friendly compositions. Understanding the way these BMGs bend, stretch and ultimately fail, will help future discovery of other equally or more remarkable BMGs that will better serve the societal needs of high performance materials than the materials we currently use. This project engages multiple graduate and undergraduate students in direct research and prepares them for future materials-related careers in academia or industry. Through a well-established summer program, the project also involves K-12 students, particularly from underserved areas and groups, to cultivate curiosity and interest in materials science while promoting diversity, equity and inclusion in STEM education for all. Research findings are used to enrich an undergraduate Introduction to Materials Science course taught at Oregon State University. This project also aids the U.S. in being a place for leading research for BMGs which are a strategically important class of materials and a potential game changer in future defense and aerospace applications.TECHNICAL SUMMARYDuctility (or plasticity) often conflicts with strength in various types of materials. In addition, manufacturability and engineering-friendliness of composition is an additional common trade-off for engineering materials. Bulk metallic glasses (BMG) are challenged by both. Achieving good ductility in BMGs by alloy design without sacrificing strength, manufacturability and engineering-friendliness of composition are central issues in the field. A significant barrier to these challenges is the lack of understanding relative to how atomic-scale features (bonds, elements) in a BMG govern their macroscopic deformation and how to control these effects by design of their elemental compositions. This project combines experimental and computational methods to investigate atomic-sale deformation mechanisms in a recently discovered family of Cu-based BMGs which possess exceptional combinations of high strength, good ductility, excellent manufacturability and engineering-friendly compositions. Coordinated in-situ straining via a synchrotron beamline and a scanning electron microscope are used to track the behavior of the atomic bonds and shear bands in the new BMGs at different levels of stress and strain to probe the effects of changing composition on their deformation behavior (through atomic bonds and shear bands). Molecular dynamics simulations and finite element modeling are then used to analyze and interpret the experimental data. The project is expected to identify the atomic bonds primarily responsible for elastic deformation and determine the strength of those bonds chiefly responsible for plastic deformation and ductility. In this way, investigators are elucidating the fundamental origin of the unusual combination of strength and ductility in this new class of BMGs as well as revealing how alloy composition influences stress-driven atomic bond behavior and macroscopic deformation. Such knowledge is needed for the design of future BMGs with good ductility and ideal combinations of additional properties. This project also advances fundamental materials science in the area of materials plasticity at extreme stresses which cannot be explored with common metallic, ceramic or polymeric materials. Graduate students supported by the project experience a unique opportunity to learn about materials macroscopic deformatiion and atomic-scale behavior, master important experimental and computational techniques, and prepare for future careers in materials-related fields.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.