Unraveling the Fundamental Mechanisms of Nanoscale Deformation in Bulk Metallic Glasses

尽管块体金属玻璃中缺乏周期性原子排列是多种所需性质的原因，例如高强度、上级弹性和容易形成几乎无限形状的能力，但它们的无序原子结构和相关的缺乏限定的剪切平面也导致较差的室温延展性。因此，金属玻璃作为结构材料的实际应用目前仅限于少数应用，例如眼镜架、手术工具或高尔夫球杆。在这个奖项中，实验和理论的方法相结合，以提高我们的知识的原子尺度的过程管理的大块金属玻璃变形的响应。提高对微观结构损伤机制的理解是建立结构-性能关系的必要先决条件，这将允许定制设计的合金以最佳匹配其预期应用的特性进行生产。从事该项目的学生将有独特的机会在一个结合了微观和纳米力学跨学科技能的领域接受培训，在单原子尺度上进行材料研究，实施新的实验方法，并开发新的原子尺度分子动力学模拟。研究团队还将与当地学校合作，举办讲座和演示，旨在鼓励学生从事科学和工程事业。金属玻璃通过剪切转变区的出现来容纳塑性流动，剪切转变区是非均匀塑性流动中最小的可识别单元。如果许多这样的区域聚集，则可以形成剪切带，该剪切带将大的剪切应变局部化在材料的薄区域内。金属玻璃中的这种剪切带类似于晶体中的剪切面。在这里，联合实验和计算建模研究调查的剪切转变区，它们形成的剪切带，和它们控制的机械性能的启动和增长。为此，将对通过创新制备方法生产的样品进行纳米级机械测试，如压痕和压缩，以研究塑性流动如何受到应变率，样品尺寸，探测体积以及变形过程中材料的结构特性的影响，然后将其结果与计算机模拟进行比较。这项工作旨在开发定量预测剪切带的产生和传播的能力，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查进行评估，被认为值得支持的搜索.

Although the lack of periodic atomic arrangements in bulk metallic glasses is responsible for multiple desirable properties such as high strength, superior elasticity, and an ability to be easily formed into virtually unlimited shapes, their disordered atomic structure and associated absence of defined shear planes also give rise to inferior room temperature ductility. As a result, the practical use of metallic glasses as structural materials is currently limited to only a few applications such as eyeglass frames, surgical tools, or golf clubs. In this award, experimental and theoretical approaches are combined to advance our knowledge of the atomic-scale processes governing the response of bulk metallic glasses to deformation. An improved understanding of microstructural damage mechanisms is a necessary pre-requisite to establish structure-property relationships that will allow custom-designed alloys to be produced with characteristics tailored to best match their intended applications. The students working on the project will have the unique opportunity to be trained in an area that combines interdisciplinary skills in micro- and nanomechanics, to perform investigations of materials at the scale of single atoms, to implement new experimental approaches, and to develop novel atomic scale molecular dynamics simulations. The research team will also engage with local schools to give lectures and demonstrations designed to encourage students to pursue careers in science and engineering.Metallic glasses accommodate plastic flow through the emergence of shear transformation zones, which are the smallest identifiable units in inhomogeneous plastic flow. If many such zones aggregate, shear bands can form that localize large shear strain inside a thin region of material. Such shear bands in metallic glasses are analogous to shear planes in crystals. Here, joint experimental and computational modeling studies are employed to investigate the initiation and growth of shear transformation zones, the shear bands they form, and the mechanical properties they control. Towards this end, nanoscale mechanical testing such as indentation and compression will be carried out on samples produced by innovative preparation methods to study how plastic flow is affected by strain rate, sample size, probing volume, and the structural properties of the material during deformation, the results of which will then be compared to computer simulations. This work seeks to develop an ability to quantitatively predict the initiation and propagation of shear bands, which is a critical step towards a mechanistic understanding of deformation and failure properties as well as identifying ductility and toughness enhancement methods for metallic glasses.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.