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

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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.