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

这一合作研究项目的主要目标是了解金属玻璃在离子辐照下形成纳米晶相的机制，并量化由此对材料力学行为的影响。该项目将采用单体离子辐照、高温离子辐照和团簇离子辐照来促进级联区的直接结晶，从而实现可调的晶体密度、尺寸和分布。这部分工作将有助于从根本上理解金属玻璃的辐射响应，包括离子辐照诱导的结构演化在不同时间尺度上发生的细节，包括损伤级联产生、热峰形成和结构弛豫。该项目将利用纳米压痕和微柱压缩实验来量化所产生的硬度、弹性模数和延展性。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，并有助于从根本上理解不同机械强度和相互作用截面的纳米晶体的剪切带成核和传播，以及纳米晶体的偏转和衰减。预计这项研究将有助于从新的基础上理解离子辐照在金属玻璃中产生纳米晶体的机制，以及改变的结构在改变材料力学响应中的作用。离子辐照将被用作一种精确地将过量自由体积引入金属玻璃的方法，因此将提供一种理解其内在性质的手段，即自由体积在决定非晶态到晶态转变中的作用。由于纳米晶嵌入在无定形基质中作为应力释放中心，离子束修饰表面有望在恶劣环境下显示出更高的延展性，适用于广泛的材料应用。这项研究代表着一项跨越机构边界(大学和政府实验室)以及跨学科边界(材料科学、核工程、机械工程和应用物理)的强有力的合作。此外，这种跨学科合作的性质和来自几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纳入参与大学的现有课程，以及开发有关主题的电子学习模块。该项目计划促进研究生和本科生中代表性不足的群体参与研究。

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.