Collaborative Research: Study of the Connections between Ordering, Dynamics and Glass Forming Ability in Metallic Liquid

Washington University, Saint Louis MO

Investigators

Abstract

Non-Technical Summary: Metallic glasses, which were only discovered about a half-century ago, have the potential to become transformative materials. However, two things are needed before this can happen - an improved understanding of which metallic liquids can be made into glasses and an ability to tailor these glasses to meet specific demands. There is evidence that the properties of metallic liquids near their melting temperatures are important for reaching these goals. Near the melting temperature, the shear viscosity (a measure of how easily a liquid flows) shows a change in how it increases with decreasing temperature. There is experimental evidence that this change is linked to changes in the atomic structure of the liquid. One goal of this research is to develop a deeper understanding of these processes at high temperature. A second goal is to combine this knowledge with measurements of the structures of the liquids and the crystal phases that can form from them to develop a model that predicts metallic glass formation. The new insight that will result from these studies will be of broad interest to the academic and industrial glass science community. A third goal is to develop a model of collaborative research that connects communities in different regions and of different sizes. This collaborative research effort between a small Liberal Arts College and a larger R1 University will work to combat national reductions in students seeking training in STEM fields in both communities. Undergraduate and graduate students will participate in research at academic institutions and at national laboratories, giving them valuable experience for deciding on their future educational and career paths. At the same time, the collaboration will develop a model for broad community engagement that uses modern technology to open up access routes for underserved communities to cutting-edge science and science education. Technical Summary: While metallic glasses have the potential to be transformative materials, an improved ability to identify and develop new glasses to meet changing demands is critically important. Studies suggest that the properties of the high temperature liquids are indicators of glass formation. Of particular importance is a structurally induced crossover in the properties of the shear viscosity of metallic alloy liquids at a temperature TA, which is near the liquidus temperature. Evidence suggests that the processes that begin at TA ultimately lead to the glass transition at lower temperatures. Predictions of the glass transition temperature based on the fragility of the liquid (determined from the shear viscosity) and the thermal expansion coefficient at TA are in good agreement with experimental data for the glasses studied. This research is focused on gaining a deeper understanding of the crossover at TA and developing a better predictor for glass formation that is based on fundamental properties of the liquid and the crystal phases that form from it. The experimental research will focus on quasi-elastic and inelastic neutron and high energy X-ray scattering studies of containerless-processed liquids and measurements of their viscosity and density as a function of temperature. Molecular dynamics studies will be used to guide these studies and to interpret the data obtained. The new insights developed in this proposal will be of interest to those interested in metallic alloy development as well as the broader glass community, including those working on silicate and chalcogenide glasses. These activities mirror a broad approach for accelerated materials development that is a national priority. The research collaboration between a Liberal Arts College and a R1 University will play an important role in the training of both undergraduate and graduate students in academia and at national laboratories, where they will learn cutting edge X-ray and neutron scattering techniques and computer modeling. 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.