Correlating atomic structure with metallic glass forming ability

当液体冷却成固体时，就像水在冰箱中冷却时凝固成冰一样，原子可以形成晶体固体，其中原子周期性排列，或者玻璃，其中原子随机排列。金属合金在快速冷却时可以形成金属玻璃。金属玻璃的性质表明在应用中的改进，例如用于电子产品，电池和氢气的外壳，用于医疗设备和植入物，以及用于机器人齿轮和卫星油箱的太空应用。液体是变成晶体还是玻璃取决于冷却速度;液体冷却得越快，就越有可能形成玻璃。 仍然允许玻璃形成的最慢冷却速率是临界冷却速率，这是任何材料的关键特性。确定临界冷却速率并因此量化玻璃形成能力（GFA）在过去一直是非常困难和复杂的任务。PI最近的工作表明，GFA可以通过X射线衍射测量从玻璃状固体的结构中确定，该测量给出了原子排列的信息。 将这些X射线衍射测量与GFA相关联提供了一种尖端工具，将大大推进玻璃和液体科学。 因此，这项研究有可能更快地开发新的金属玻璃，用于广泛的应用，并影响美国制造业。PI还将本着材料基因组计划（MGI）的精神，通过开放，互动的方法培养下一代科学家，与科学界广泛分享所有实验数据，并通过外展计划，高中学生通过制作YouTube视频学习和教授尖端材料科学研究。技术概述玻璃化，即在液态金属凝固时形成玻璃，其以临界冷却速率量化，并被称为玻璃形成能力GFA，是对于玻璃的物理、形成和加工至关重要的关键特征。然而，量化玻璃形成能力已经在实验上详细阐述，并且其复杂性阻碍了计算方法的使用。这些挑战阻碍了金属玻璃科学、发现和技术的进步，而金属玻璃科学、发现和技术是在一个巨大的潜在组成空间中进行的。 PI的初步结果表明，该补助金可以克服以前确定合金GFA的局限性。PI提供了GFA反映在玻璃呈现的结构中的证据，并且该结构可以容易地用标准X射线衍射测量来测量。合金的原子结构在XRD光谱中的第一衍射峰的半峰全宽Dq中被量化，PI的初步结果揭示了Dq和GFA之间的直接相关性;最佳玻璃形成体表现出最无序的非晶结构，反映在它们在离平衡最远的溅射状态下的最高Dq中。Dq-GFA关系表明，目前描述金属玻璃的原子结构的模型仅限于理想玻璃状态，但没有描述数量大得多的、占据势能景观中更高势能状态的真实的玻璃。为了描述这样的真实的玻璃，熵的贡献，并可能动力学也必须考虑。 另外，通过探索大的组成空间和温度或冷却速率下的Dq-GFA关系，将深入了解金属玻璃的形成图案。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYWhen a liquid is cooled to become a solid, like water solidifying into ice when cooled in a freezer, the atoms could form a crystalline solid, where the atoms are arranged periodically, or a glass, where the atoms are arranged randomly. Metal alloys can form metallic glasses when cooled rapidly. Metallic glasses have properties that suggest improvements in applications such as casings for electronics, batteries, and hydrogen, for medical devices and implants, and applications in space for robotics gears and satellite tanks. Whether the liquid becomes crystalline or a glass depends on the cooling rate; the faster the liquid is cooled, the more likely it will form a glass. The slowest cooling rate that still allows for glass formation is the critical cooling rate, which is a key characteristic of any material. Determining critical cooling rates and hence, quantifying the glass forming ability (GFA), has been a very difficult and elaborate task in the past. Recent work by the PI revealed that the GFA can be determined from the structure of the glassy solid through x-ray diffraction measurements that gives information on the arrangement of the atoms. Correlating these x-ray diffraction measurements to the GFA provides a cutting-edge tool that will advance the science of glasses and liquids significantly. Thereby, this research has the potential to develop new metallic glasses faster to be used in a wide range of applications and impact US manufacturing. The PI will also train the next generation of scientist through an open, interactive approach in the spirit of the Materials Genome Initiative (MGI) by broadly sharing all experimental data with the scientific community and through outreach programs where high-school students learn and teach about cutting edge materials science research by making YouTube videos. TECHNICAL SUMMARYVitrification, the formation of a glass upon solidification of a liquid metal, which is quantified in the critical cooling rate and referred to as the glass forming ability, GFA, is a key characteristic of paramount importance for the physics, formation and processing of glasses. However, quantifying glass forming ability has been experimentally elaborate and its complexity has prevented use of computational methods. These challenges have impeded progress in metallic glass science, discovery and technology which takes place in a vast potential compositional space. Preliminary results by the PI suggest that this grant can overcome previous limitations of identifying GFA of alloys. The PI provides evidence that the GFA is reflected in the structure the glass assumes and this structure can be readily measured with standard x-ray diffraction measurements. The alloy’s atomic structure is quantified in the full-width-half-max of the first diffraction peak in the XRD spectrum, Dq, and the PI’s preliminary results reveals a direct correlation between Dq and GFA; Best glass formers exhibit the most disordered amorphous structure, reflected in their highest Dq in their as-sputtered state which is furthest away from equilibrium. The Dq-GFA relationship suggested that current models to describe the atomic structure of metallic glasses are limited to the ideal glass state but do not describe the, vastly larger in number, real glasses that occupy the higher potential energy states in the potential energy landscape. To describe such real glasses, contributions of entropy, and possibly kinetics have to be considered as well. Separately, by exploring the Dq-GFA relationship over large compositional spaces and temperatures or cooling rates, will provide insight into formation motifs of 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.