Elastic and inelastic scattering studies of supercooled metallic glass-forming liquids - the connection between ordering and fragility

过冷金属玻璃形成液体的弹性和非弹性散射研究——有序性和脆性之间的联系

• 批准号: 1506553
• 负责人: Kenneth Kelton
• 金额: $ 40.8万
• 依托单位: Washington University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1506553&HistoricalAwards=false
• 关键词: Elastic; inelastic; scattering; studies; supercooled

NON-TECHNICAL SUMMARY:In addition to the novel properties of metallic glasses, including strengths greater than steel, high hardness and resistance to corrosion, they can be thermo-plastically formed, in much the same way that a glass blower forms traditional silicate glasses. This allows them to be molded into complex shapes using a process that is not possible for conventional alloys. To realize their full potential, however, new methods are needed for the quick identification of potential metallic glasses to meet emerging technological needs. A property, fragility, corresponding to the change in the liquid viscosity with temperature, is frequently taken to correlate with glass-formability. However, the microscopic meaning of fragility is unclear; it appears to correlate with the rate of structural change of the liquid with cooling below the melting temperature. These structural changes can be measured by scattering high-energy X-rays from liquids that are levitated in a high-vacuum environment, avoiding reactions between the liquid and its container. Using a novel facility these are extended to neutron scattering studies at the Spallation Neutron Source, the most intense pulsed neutron source on Earth, allowing a direct comparison between structural changes and liquid flow. The insights gained from this work lead to an improved ability to predict glass formation and a deeper understanding of the process of glass formation itself, which remains a key unsolved problem in condensed matter science. Following the guidelines of the Materials Genome Initiative, the results also yield new structural and physical property data for computer modeling, necessary for advanced materials development. The research is an integral part of the scientific training of both graduate and undergraduate students, and contributes to the PI's ongoing outreach activities to regional secondary school teachers, which are focused on discussions of common materials to convey basic scientific principles to students. TECHNICAL SUMMARY:While metallic glasses are now poised for many novel technological applications, new methods are needed to rapidly identify and develop new glasses to meet changing demands, as well as to probe the fundamental nature of glass formation. Fragility, related to the temperature dependence of the viscosity, frequently correlates with glass formability. However, the microscopic origin of fragility and why it may be important for glass formation are poorly understood. Fundamental investigations of the relations between liquid structure and flow and how these are related to the glass transition and glass formation can illuminate this. Based on recent work from this research team: (i) fragility is reflected in the rate of structural ordering with temperature, (ii) a high temperature crossover in the viscosity, Tcoop, is related to the onset of cooperative flow and (iii) Tcoop is strongly correlated with the glass transition temperature, Tg, confirming that glass formation is the final step in a cooperative process that actually begins at a much higher temperature. Some key questions emerging from these results are: (i) Is chemical or topological ordering more closely related to fragility? (ii) What is the structural relation to the onset of cooperative flow? (iii) How can Tcoop and a high temperature measure of liquid fragility be best used to develop new search approaches to identify good glass-forming liquids? These questions can be addressed by elastic and inelastic neutron scattering studies on levitated liquids using a new electrostatic levitation (ESL) facility constructed by this team for use at the Spallation Neutron Source. The high intensity of the SNS allows measurements to be made in shorter times and hence to deeper liquid supercoolings. These data can be correlated with measurements of the liquid viscosity at high temperature, giving a deeper understanding of fragility from a better understanding of the connections between topological/chemical ordering processes and liquid dynamics, and the processes that connect Tcoop with the glass transition. Clues can also be found for glass formation in the high temperature liquid, giving new search schemes to identify good glass formers, beyond the insight-guided trial and error or combinatorial methods commonly used. Relations between liquid ordering and glass formability are of broad interest to the glass community, extending beyond metallic glasses to the silicate and chalcogenide glasses as well.

非技术摘要：除了金属玻璃的新型特性（包括大于钢的强度，高硬度和对腐蚀的耐药性）外，它们还可以是层状形成的，与玻璃鼓风机形成传统的硅酸盐玻璃一样。这使它们可以使用常规合金无法使用的过程将它们模制成复杂的形状。 但是，为了实现其全部潜力，需要新的方法来快速识别潜在的金属眼镜以满足新兴的技术需求。 与温度液体粘度变化相对应的脆弱性，经常与玻璃的合理性相关。但是，脆弱性的微观含义尚不清楚。它似乎与液体的结构变化速率相关，冷却低于熔化温度。 这些结构变化可以通过从高空环境中悬浮的液体中散射高能X射线来测量这些变化，从而避免了液体及其容器之间的反应。使用新颖的设施，这些设施扩展到散布中子源的中子散射研究，是地球上最激烈的脉冲中子源，从而可以直接比较结构变化和液体流动。 从这项工作中获得的见解导致了预测玻璃形成的能力，并对玻璃形成的过程进行了更深入的了解，这仍然是凝结物质科学中的关键未解决问题。 遵循材料基因组倡议的指南，结果还产生了用于计算机建模的新结构和物理属性数据，这是高级材料开发所必需的。 这项研究是研究生和本科生科学培训不可或缺的一部分，并为PI的持续外展活动做出了为区域中学教师的持续宣传活动，该教师的重点是讨论常见材料，以向学生传达基础科学原理。 技术摘要：尽管现在已经为许多新型技术应用提供了金属眼镜，但需要新的方法来迅速识别和开发新的眼镜以满足不断变化的需求，并探测玻璃形成的基本性质。 与粘度的温度依赖性有关的脆弱性通常与玻璃的形成性相关。 但是，脆弱性的微观起源以及为什么对玻璃形成可能很重要的原因很少。 对液体结构与流动之间关系以及它们与玻璃转变和玻璃形成如何相关的基本研究可以阐明这一点。 基于该研究团队的最新工作：（i）脆弱性反映在与温度的结构排序速率上，（ii）粘度的高温交叉与TCOOP有关，TCOOP与合作流的发作有关，（iii）TCOOP与玻璃过渡，TG，TG，TG，TG，TG，TG，TG，TG的温度相关，在最终的过程中，该过程实际上是在一个较高的过程中，它实际上是在一个较高的过程中，该过程实际上是在一个启动的一项启动的过程。 从这些结果中提出的一些关键问题是：（i）化学或拓扑排序与脆弱性更紧密相关？ （ii）与合作流的开始有什么结构关系？ （iii）如何最好地使用TCOOP和高温液体脆弱的量度来开发新的搜索方法来识别良好的玻璃形成液体？ 这些问题可以通过使用该团队构建的新静电悬浮（ESL）设施对悬浮的液体进行弹性和非弹性中子散射研究来解决，供散布中子中子源使用。 SNS的高强度允许在较短的时间进行测量，从而使其具有更深的液体超冷。这些数据可以与高温下液体粘度的测量相关联，从更好地理解拓扑/化学有序过程与液体动力学之间的连接，以及将TCOOP与玻璃转变相关联的过程。还可以在高温液体中找到玻璃形成的线索，提供新的搜索方案，以识别出良好的玻璃形成器，除了常见的洞察力引导的反复试验和错误或组合方法。 液体订购与玻璃的形成性之间的关系对玻璃社区引起了广泛的兴趣，将金属玻璃超越金属玻璃和硅酸盐玻璃杯。