Correlating atomic structure with metallic glass forming ability

当液体冷却成固体时，就像水在冰箱里冷却后凝固成冰一样，原子可以形成原子周期性排列的结晶固体，也可以形成原子随机排列的玻璃。金属合金迅速冷却时可形成金属玻璃。金属玻璃的性能表明，在电子产品、电池和氢气外壳、医疗设备和植入物以及机器人齿轮和卫星储罐在太空中的应用方面，金属玻璃的性能可以得到改进。液体变成结晶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杯。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。在过去，确定临界冷却速率，从而量化玻璃形成能力（GFA）一直是一项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，这可以提供原子排列的信息。将这些x射线衍射测量与GFA相关联提供了一个尖端的工具，将显著推进玻璃和液体的科学。因此，这项研究有可能更快地开发出新的金属玻璃，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、互动的方式，与科学界广泛分享所有实验数据，并通过外展项目，让高中生通过制作YouTube视频，学习和教授最前沿的材料科学研究，培养下一代科学家。技术概述：玻璃化，即液态金属凝固后形成的玻璃，用临界冷却速率来量化，称为玻璃形成能力，GFA，是对玻璃的物理、形成和加工至关重要的关键特性。然而，量化玻璃形成能力的实验已经很复杂，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，这些进步发生在一个巨大的潜在成分空间中。PI的初步结果表明，这项拨款可以克服以前鉴定合金GFA的局限性。PI提供了GFA在玻璃结构中反射的证据，这种结构可以很容易地用标准x射线衍射测量来测量。通过XRD谱图中第一个衍射峰Dq的全宽半max来定量合金的原子结构，PI的初步结果揭示了Dq与GFA之间的直接关系；最佳的玻璃成形物表现出最无序的非晶态结构，这反映在其溅射状态下的Dq最高，而溅射状态离平衡态最远。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状态，而没有描述在势能景观中占据更高势能状态的数量大得多的真实玻璃。为了描述这样的真实玻璃，熵的贡献，以及可能的动力学也必须考虑在内。另外，通过在大的成分空间和温度或冷却速率上探索Dq-GFA关系，将提供对金属玻璃形成图案的见解。该奖项反映了美国国家科学基金会的法定使命，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.