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

非技术综述：金属玻璃在大约半个世纪前才被发现，它有可能成为变革性材料。然而，在这种情况发生之前，需要两件事--提高对哪些金属液体可以制成玻璃的理解，以及能够定制这些玻璃以满足特定需求。有证据表明，金属液体在熔化温度附近的性质对于实现这些目标很重要。在熔化温度附近，剪切粘度(衡量液体流动难易程度的指标)显示出其随温度降低而增加的变化。有实验证据表明，这种变化与液体原子结构的变化有关。这项研究的目标之一是加深对高温下这些过程的理解。第二个目标是将这一知识与对液体结构和由它们形成的晶相的测量相结合，以开发一个预测金属玻璃形成的模型。这些研究将产生的新见解将引起学术界和工业玻璃科学界的广泛兴趣。第三个目标是开发一种合作研究模式，将不同地区和不同规模的社区联系起来。这项由一所小型文理学院和一所规模较大的R1大学合作开展的研究工作，将致力于应对在两个社区寻求STEM领域培训的学生人数在全国范围内的减少。本科生和研究生将参加学术机构和国家实验室的研究，为他们决定未来的教育和职业道路提供宝贵的经验。同时，合作将开发一个广泛社区参与的模式，利用现代技术为服务不足的社区开辟获得尖端科学和科学教育的途径。技术摘要：虽然金属玻璃具有潜在的变革性材料，但提高识别和开发新玻璃的能力以满足不断变化的需求是至关重要的。研究表明，高温液体的性质是玻璃形成的指示器。尤其重要的是，金属合金液体的剪切粘度特性在接近液相线温度的温度TA下发生了结构诱导的交叉。证据表明，在TA开始的过程最终导致较低温度下的玻璃化转变。根据液体的脆性(由剪切粘度确定)和TA处的热膨胀系数预测的玻璃化转变温度与所研究玻璃的实验数据符合得很好。这项研究的重点是更深入地了解TA的交叉，并根据液体的基本性质和由此形成的晶相开发更好的玻璃形成预测因子。实验研究将侧重于无容器加工液体的准弹性和非弹性中子和高能X射线散射研究，以及测量其粘度和密度随温度的变化。分子动力学研究将被用来指导这些研究并解释所获得的数据。本提案中提出的新见解将使那些对金属合金开发感兴趣的人以及更广泛的玻璃界，包括那些从事硅酸盐和硫化物玻璃工作的人感兴趣。这些活动反映了加速材料开发的广泛方法，这是国家的优先事项。文理学院和R1大学之间的研究合作将在学术界和国家实验室的本科生和研究生的培训中发挥重要作用，他们将在那里学习尖端的X射线和中子散射技术以及计算机建模。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.