Investigating the Shear Localization Mechanisms in Bulk Metallic Glasses via Novel Energy Landscape Exploration Techniques

本基金的研究目标是开发新的原子模型方法来探索势能景观，以便在实验相关的时间尺度上阐明大块金属玻璃（bmg）的基本原子剪切变形和局部化机制。由于其弹性模量与许多金属相同，bmg提供了一种诱人的可能性，即在室温下表现出高强度和中等韧性的材料，在燃料电池，航空航天，汽车零部件，体育用品和医疗设备方面具有一系列潜在的应用。bmg尚未解决的一个关键问题是，尚未确定控制剪切转变区（STZ）形成的原子细节，这是单位塑性变形机制。缺乏对BMG塑性的机械的、基于原子的理解，极大地抑制了BMG的进一步发展和应用。研究目标的实现将通过一种新的数值技术的发展成为可能，称为自主盆地爬升（ABC）方法，该方法将从任何亚稳初始状态在3n维势能表面上产生自主逃逸轨迹。具体来说，PI将(1)开发一种耦合ABC/动力学蒙特卡罗算法，使实验相关应变率下的剪切局部化研究成为可能；(2)开发新的非局部不稳定性标准，以识别相互作用的stz的大小、形状和动力学；(3)开发统一的自学习方案，以大幅降低计算成本，使ABC方法在应用于bmg或任何其他原子系统时，可以访问与经典分子动力学相当的长度尺度（即几十纳米），同时也能够访问远远超出经典分子动力学的时间尺度。如果成功，这项研究将对理解导致局部剪切变形和灾难性破坏的基本非弹性变形机制做出原创性贡献，特别是在bmg中，以及一般的非晶态固体。此外，了解这些原子变形机制及其与非晶固体结构的关系将导致新的、原子信息的非晶固体连续变形和塑性理论。教育和推广目标将集中在(1)招募妇女和代表性不足的少数民族参与令人兴奋和迅速发展的纳米材料研究领域；(2)向高中生推广，鼓励他们未来从事科学和工程方面的职业；(3)通过跨学科建模努力开发的新课程材料和软件界面的网络传播，将研究、教育和更广泛的影响联系起来。(4)本科阶段的课程开发，鼓励新生攻读理工科专业。

The research objective of this grant is to develop novel atomistic modeling approaches to explore the potential energy landscape in order to elucidate the fundamental atomistic shear deformation and localization mechanisms in bulk metallic glasses (BMGs) at experimentally relevant time scales. Because their elastic moduli are of the same order as many metals, BMGs offer the tantalizing possibility of a material that exhibits both high strength and moderate toughness at room temperature, with a range of potential applications in fuel cells, aerospace, auto parts, sporting goods, and medical devices. One key unresolved issue for BMGs is that the atomistic details governing the formation of shear transformation zones (STZ), which are the unit plastic deformation mechanism, have not been identified. This lack of a mechanistic, atomistically-based understanding of BMG plasticity has significantly inhibited the further development and application of BMGs. Accomplishment of the research objectives will be made possible by the development of a novel numerical technique, called the autonomous basin climbing (ABC) method, which will generate an autonomous escape trajectory on the 3N-dimensional potential energy surface from any metastable initial state. Specifically, the PI will (1) develop a coupled ABC/kinetic Monte Carlo algorithm that enables the study of shear localization at experimentally-relevant strain rates, (2) develop novel non-local instability criteria to identify the sizes, shapes, and dynamics of interacting STZs, and (3) develop a unified self-learning scheme to substantially reduce the computational cost such that the ABC method, when applied to BMGs or any other atomistic system, can access length scales that are comparable to classical molecular dynamics (i.e. tens of nanometers) while also being able to access time scales far beyond that of classical molecular dynamics.If successful, this research will make original contributions to understanding the fundamental inelastic deformation mechanisms that lead to localized shear deformation and thus catastrophic failure in BMGs specifically, and amorphous solids in general. Furthermore, knowledge of these atomistic deformation mechanisms and their relationship to the structure of amorphous solids will lead to new, atomistically-informed continuum deformation and plasticity theories for amorphous solids. Education and outreach objectives will focus on (1) recruitment of women and underrepresented minorities to participate in the exciting and rapidly expanding field of nanomaterials research, (2) outreach to high school students to encourage future careers in science and engineering, (3) novel web-based dissemination of both new course materials and software interfaces that are developed through this interdisciplinary modeling effort to link research, education, and broader impacts, and (4) course development at the undergraduate level to encourage freshmen to pursue majors in science and engineering.