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在离子辐照下形成非晶相的机制，并量化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。这部分的工作将有助于基本理解的辐射响应的金属玻璃，包括离子辐照引起的结构演变发生在不同的时间尺度，涉及损伤级联创建，热尖峰形成，和结构松弛的细节。该项目将利用纳米压痕和微柱压缩实验来量化由此产生的硬度、弹性模量和延展性。这部分工作将确定纳米晶体对金属玻璃力学响应的作用，并有助于对剪切带成核和传播的基本理解，不同机械强度和相互作用截面的纳米晶体的偏转和衰减。预计这项研究将有助于对金属玻璃中纳米晶体产生机制的新的基本理解，离子辐照，以及改变的结构在材料的机械响应的修改中的作用。离子辐照将被用作一种将过量自由体积精确引入金属玻璃的方法，因此将提供一种了解其内在性质的手段，即，自由体积在确定非晶到结晶转变中的作用。随着纳米晶体嵌入作为应力释放中心的无定形基质中，离子束改性的表面有望在恶劣环境中的广泛材料应用中表现出增强的延展性。这项研究代表了一个强有力的合作，跨越了机构界限（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）。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有助于研究成果的广泛传播。拟议的努力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。该项目旨在促进研究生和本科生等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.