Collaborative Research: Ion Irradiation-Induced Nanocrystallization of Metallic Glasses and Its Effects on Their Mechanical Properties

该合作研究项目的主要目标是了解金属玻璃受到离子辐照时纳米晶相形成的机制，并量化其对材料力学行为的影响。本项目将采用单体离子辐照、高温离子辐照、簇离子辐照等方法，促进级联区直接结晶，实现晶体密度、尺寸和分布的可调。这部分工作将有助于基本理解金属玻璃的辐射响应，包括离子辐照引起的结构演化的细节，这些结构演化发生在不同的时间尺度上，涉及损伤级联的产生、热尖峰的形成和结构松弛。该项目将利用纳米压痕和微柱压缩实验来量化产生的硬度、弹性模量和延性。这部分工作将确定纳米晶体在金属玻璃力学响应中的作用，并有助于基本理解剪切带的成核和传播，以及不同机械强度和相互作用截面的纳米晶体的挠曲和衰减。期望本研究将有助于对离子辐照在金属玻璃中产生纳米晶体的机制的新的基本理解，以及改变的结构在材料力学响应的改变中的作用。离子辐照将被用作一种精确地将过多的自由体积引入金属玻璃的方法，因此将提供一种了解其内在性质的方法，即自由体积在确定非晶到结晶转变中的作用。由于纳米晶体嵌入在非晶基体中作为应力释放中心，离子束修饰表面有望在恶劣环境中展示出广泛的材料应用的增强延展性。这项研究代表了跨机构界限（大学和政府实验室）以及跨学科界限（材料科学，核工程，机械工程和应用物理）的强大合作。此外，这种跨学科合作的性质和来自多个学科的研究人员的参与支持了研究成果的广泛传播。拟议的工作还包括将我们的研究成果整合到参与大学的现有课程中，并开发有关主题的电子学习模块。该项目旨在促进代表性不足的群体参与研究，包括研究生和本科生。

The main objectives of this collaborative research project are to develop an understanding of the mechanisms responsible for nanocrystal phase formation when metallic glasses are subjected to ion irradiation, and to quantify the resulting effects on the materials' mechanical behavior. The project will employ monomer-ion irradiation, ion irradiation at elevated temperatures, and cluster ion irradiation to promote direct crystallization of cascade regions so as to achieve tunable crystal densities, sizes and distributions. This portion of the work will contribute to fundamental understanding of radiation responses of metallic glasses including details of ion irradiation induced structural evolution occurring over different time scales involving damage cascade creation, thermal spike formation, and structural relaxation. The project will utilize nanoindentation and micro pillar compression experiments to quantify resulting hardness, elastic modulus and ductility. This portion of work will identify the roles of nanocrystals on the mechanical response of metallic glasses, and contribute to fundamental understanding of shear band nucleation and propagation, and deflection and attenuation by nanocrystals of different mechanical strengths and interaction cross sections. It is expected that this study will contribute to new fundamental understanding of the mechanisms responsible for the creation of nanocrystals in metallic glasses by ion irradiation, and the role of the altered structures in the modification of the materials' mechanical response. Ion irradiation will be used as a method to precisely introduce excessive free volume into a metallic glass, and will therefore provide a means to understand its intrinsic properties, i.e., the role of free volume in determining amorphous-to-crystalline transitions. With nanocrystals embedded in an amorphous matrix acting as stress release centers, the ion beam modified surface is expected to demonstrate enhanced ductility for a wide range of materials applications in harsh environments. The study represents a strong collaboration which reaches across both institutional bounds (university and government laboratories) as well as interdisciplinary bounds (materials science, nuclear engineering, mechanical engineering and applied physics). In addition, the nature of this cross-disciplinary collaboration and the involvement of researchers from several disciplines support the broad dissemination of research results. The proposed effort also includes the integration of our research findings into existing courses at participant universities, and the development of an e-learning module on relevant topics. The project is planned to promote research involvement of underrepresented groups, both as graduate students and undergraduates.