Materials World Network: Structures and Mechanical Behavior of Nanocrystalline Phase-Containing Glass-Forming Thin Films

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This Materials World Network award by the Metallic Materials and Nanostructures program in the Division of Materials Research to University of Tennessee Knoxville is to establish a fundamental understanding of the processing and fabrication of amorphous/nanocrystalline metallic thin-film coatings, and the mechanisms responsible for the resulting ductility and fatigue-resistance enhancements. This award is cofunded by the Office of Special Projects-DMR and the Office of International Science and Engineering. This collaborative experimental and theoretical project is carried out between the University of Tennessee and the team in the Republic of China (Taiwan) consisting of National Taiwan University of Science and Technology, National Taiwan Ocean University and National Cheng Kung University. This project is motivated by two novel and preliminary observations that the two teams recently discovered that: 1) metallic-glass coatings with or without the presence of nanocrystalline phases can be prepared by an annealing-induced amorphization process; and 2) these coatings on structural materials demonstrate excellent mechanical properties and fatigue resistance. In the experimental program, the Taiwan team will develop and improve the thin-film preparation method that realizes the controllable amorphization and nanocrystallization during annealing, and the USA team will focus on the deformation and fatigue behavior of these film-on-substrate systems. Advanced characterization tools, such as the high-resolution transmission-electron microscopy, will be employed to study (1) the microstructural evolution during the thin-film preparation and (2) the interaction of the strain localization and the nanocrystalline phase in the metallic-glass film during mechanical testing. From the modeling point of view, the Taiwan team will emphasize a molecular-dynamics study of the kinetic processes in the annealing-induced amorphization, while the USA team will work on the relationship between the shear-band characteristics and the mechanical behavior of the film, and the effect of the film on the fatigue behavior. The connection of these models to and comparisons with the experimental observations will lead to the basic understanding of fatigue mechanisms. The collaborative research will advance and enhance the focused research and teaching activities on both the USA and Taiwan sides. Research projects from this joint program will be designed and used as a teaching unit for both middle- and high-school students and teachers, especially women and minority students involved in the outreach programs. These efforts are designed, not only to increase the public awareness of advanced structural materials and their scientific importance, but also to stimulate the interests of the broader public in science, engineering, and technology careers. Educational materials will be developed and disseminated through two newly-developed graduate-level classes. The present integrated research and education activities will promote the public awareness of the international-scientific collaboration.