Investigating the Shear Localization Mechanisms in Bulk Metallic Glasses via Novel Energy Landscape Exploration Techniques

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The research objective of this grant is to develop novel atomistic modeling approaches to explore the potential energy landscape in order to elucidate the fundamental atomistic shear deformation and localization mechanisms in bulk metallic glasses (BMGs) at experimentally relevant time scales. Because their elastic moduli are of the same order as many metals, BMGs offer the tantalizing possibility of a material that exhibits both high strength and moderate toughness at room temperature, with a range of potential applications in fuel cells, aerospace, auto parts, sporting goods, and medical devices. One key unresolved issue for BMGs is that the atomistic details governing the formation of shear transformation zones (STZ), which are the unit plastic deformation mechanism, have not been identified. This lack of a mechanistic, atomistically-based understanding of BMG plasticity has significantly inhibited the further development and application of BMGs. Accomplishment of the research objectives will be made possible by the development of a novel numerical technique, called the autonomous basin climbing (ABC) method, which will generate an autonomous escape trajectory on the 3N-dimensional potential energy surface from any metastable initial state. Specifically, the PI will (1) develop a coupled ABC/kinetic Monte Carlo algorithm that enables the study of shear localization at experimentally-relevant strain rates, (2) develop novel non-local instability criteria to identify the sizes, shapes, and dynamics of interacting STZs, and (3) develop a unified self-learning scheme to substantially reduce the computational cost such that the ABC method, when applied to BMGs or any other atomistic system, can access length scales that are comparable to classical molecular dynamics (i.e. tens of nanometers) while also being able to access time scales far beyond that of classical molecular dynamics.If successful, this research will make original contributions to understanding the fundamental inelastic deformation mechanisms that lead to localized shear deformation and thus catastrophic failure in BMGs specifically, and amorphous solids in general. Furthermore, knowledge of these atomistic deformation mechanisms and their relationship to the structure of amorphous solids will lead to new, atomistically-informed continuum deformation and plasticity theories for amorphous solids. Education and outreach objectives will focus on (1) recruitment of women and underrepresented minorities to participate in the exciting and rapidly expanding field of nanomaterials research, (2) outreach to high school students to encourage future careers in science and engineering, (3) novel web-based dissemination of both new course materials and software interfaces that are developed through this interdisciplinary modeling effort to link research, education, and broader impacts, and (4) course development at the undergraduate level to encourage freshmen to pursue majors in science and engineering.