Correlating atomic structure with metallic glass forming ability

非技术总结当液体冷却成固体时，就像水在冰柜中冷却时凝固成冰一样，原子可能会形成晶体固体，原子在其中周期性排列，或者形成玻璃，原子在玻璃中随机排列。金属合金在快速冷却时可以形成金属玻璃。金属玻璃的性能表明，在电子产品、电池和氢气的外壳、医疗设备和植入物的外壳，以及机器人齿轮和卫星坦克的太空应用方面都有改进。液体是结晶的还是玻璃的取决于冷却速度；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度是临界冷却速度，这是任何材料的关键特性。确定临界冷却速度，从而量化玻璃形成能力(GFA)，在过去一直是一项非常困难和复杂的任务。PI最近的工作表明，通过给出原子排列信息的X射线衍射测量，可以从玻璃固体的结构中确定GFA。将这些X射线衍射测量与GFA相关联提供了一种尖端工具，将极大地推动玻璃和液体科学的发展。因此，这项研究有可能更快地开发出新的金属玻璃，以便在广泛的应用中使用，并影响美国制造业。国际和平研究所还将本着材料基因组倡议(MGI)的精神，通过开放、互动的方式培训下一代科学家，与科学界广泛分享所有实验数据，并通过推广计划，让高中生通过制作YouTube视频来学习和教授尖端材料科学研究。技术总结玻璃化，即液态金属凝固时形成的玻璃，以临界冷却速度表示，称为玻璃形成能力，对玻璃的物理、形成和加工至关重要。然而，玻璃形成能力的量化一直在实验上精心设计，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，这些科学、发现和技术发生在一个巨大的潜在成分空间。PI的初步结果表明，这项拨款可以克服以前在鉴定合金GFA方面的局限性。等电点提供了证据，证明玻璃所呈现的结构反映了GFA，这种结构可以很容易地用标准的X射线衍射测量来测量。合金的原子结构在X射线衍射谱的第一个衍射峰的全宽半极大值DQ中被量化，PI的初步结果表明DQ与GFA之间存在直接的相关性；最好的玻璃成型体表现出最无序的非晶态结构，反映在它们在溅射时离平衡最远的状态下的DQ最高。DQ-GFA关系表明，目前描述金属玻璃原子结构的模型仅限于理想的玻璃态，而不是描述在势能图景中占据更高势能态的真实玻璃的数量要多得多。为了描述这种真实的玻璃，还必须考虑到熵的贡献，以及可能的动力学。另外，通过探索大型成分空间和温度或冷却速度的DQ-GFA关系，将提供对金属玻璃形成主题的洞察。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 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.