Unraveling the Fundamental Mechanisms of Nanoscale Deformation in Bulk Metallic Glasses

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Although the lack of periodic atomic arrangements in bulk metallic glasses is responsible for multiple desirable properties such as high strength, superior elasticity, and an ability to be easily formed into virtually unlimited shapes, their disordered atomic structure and associated absence of defined shear planes also give rise to inferior room temperature ductility. As a result, the practical use of metallic glasses as structural materials is currently limited to only a few applications such as eyeglass frames, surgical tools, or golf clubs. In this award, experimental and theoretical approaches are combined to advance our knowledge of the atomic-scale processes governing the response of bulk metallic glasses to deformation. An improved understanding of microstructural damage mechanisms is a necessary pre-requisite to establish structure-property relationships that will allow custom-designed alloys to be produced with characteristics tailored to best match their intended applications. The students working on the project will have the unique opportunity to be trained in an area that combines interdisciplinary skills in micro- and nanomechanics, to perform investigations of materials at the scale of single atoms, to implement new experimental approaches, and to develop novel atomic scale molecular dynamics simulations. The research team will also engage with local schools to give lectures and demonstrations designed to encourage students to pursue careers in science and engineering.Metallic glasses accommodate plastic flow through the emergence of shear transformation zones, which are the smallest identifiable units in inhomogeneous plastic flow. If many such zones aggregate, shear bands can form that localize large shear strain inside a thin region of material. Such shear bands in metallic glasses are analogous to shear planes in crystals. Here, joint experimental and computational modeling studies are employed to investigate the initiation and growth of shear transformation zones, the shear bands they form, and the mechanical properties they control. Towards this end, nanoscale mechanical testing such as indentation and compression will be carried out on samples produced by innovative preparation methods to study how plastic flow is affected by strain rate, sample size, probing volume, and the structural properties of the material during deformation, the results of which will then be compared to computer simulations. This work seeks to develop an ability to quantitatively predict the initiation and propagation of shear bands, which is a critical step towards a mechanistic understanding of deformation and failure properties as well as identifying ductility and toughness enhancement methods for metallic glasses.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.