Structure, Properties and Relaxation of Shear Bands in Metallic Glasses

技术：单剪切带的灾难性破坏对金属玻璃的结构应用提出了挑战。虽然许多研究工作都是为了防止这种失败，但对剪切带行为的基本理解仍然不完整。这项工作的目的是为了更深入地了解剪切带的结构和性质之间的关系，以及两者对热松弛的依赖。这一目标将通过有针对性的实验和建模相结合来实现。剪切带将在不同的条件下形成，其结构和热力学性能将被表征。将使用的实验技术包括常规和高分辨率透射电子显微镜、x射线衍射、差示扫描量热法、纳米压痕、回弹测量和常规机械测试。化学无序将作为透射电子显微镜衍射对比的来源进行探讨。将探讨同步加速器x射线纳米探针在剪切带表征中的应用。剪切带处大量的自由体积为研究金属玻璃在高度非松弛状态下的行为提供了机会。将进行旨在直接表征剪切带局部特性的实验。在包含剪切带的样品中的变形模式将在应变速率范围内进行探索。大块金属玻璃的高稳定性使人们可以广泛地研究弛豫对其性能的影响。一个目标将是根据剪切带的“记忆”可以通过松弛消除的程度的几个特性来确定。将应用和扩展先前的理论模型来分析结果。非技术：金属玻璃由于其独特的物理性质而引起了许多科学和技术的兴趣。它们的高弹性极限和屈服强度对结构应用具有吸引力，随着体合成技术的发展已成为现实。更广泛的影响是科学、技术和教育。预期的结果将提高对金属玻璃结构-性能关系的基本认识。他们将为金属玻璃结构应用的知识库做出贡献。这些研究将有助于教育和培养研究生。他们将学习材料基础知识，发展计划和开展研究的能力，并精通最先进的电子显微镜、x射线衍射和结构材料的性能表征。此外，研究生将学习以口头和书面形式将他们的研究结果传达给科学界

TECHNICAL: Catastrophic failure at a single shear band has posed challenges to structural applications in metallic glasses. While much research effort is directed at preventing such a failure, the fundamental understanding of shear-band behavior is still incomplete. The goal of this work is to obtain a deeper understanding of the relationships between the structure and properties of shear bands, and the dependence of both on thermal relaxation. This goal will be achieved by a combination of targeted experiments and modeling. Shear bands will be formed under varying conditions, and their structure and thermal and mechanical properties will be characterized. Experimental techniques to be used include conventional and high-resolution transmission electron microscopy, x-ray diffraction, differential scanning calorimetry, nanoindentation, spring-back measurements and conventional mechanical tests. Chemical disorder will be explored as a source of diffraction contrast in transmission electron microscopy. The use of a synchrotron x-ray nanoprobe for shear-band characterization will be explored. The high amount of free volume at shear bands offers an opportunity for studying the behavior of metallic glasses in a highly unrelaxed state. Experiments aimed at direct characterization of the local properties of shear bands will be performed. Deformation modes in samples containing shear bands will be explored for a range of strain rates. The high stability of bulk metallicglasses will allow an extensive study of the effect of relaxation on properties. One goal will be a determination, based on several properties of the extent to which the "memory" of shear bands can be erased by relaxation. Previous theoretical models will be applied and extended to analyze the results. NON-TECHNICAL: Metallic glasses have generated much scientific and technological interest due to their unique physical properties. Their high elastic limit and yield strength are attractive for structural applications, which have become a reality with the development of bulk synthesis. The broader impacts are scientific, technological and educational. The expected results will improve the fundamental understanding of the structure-property relationship in metallic glasses. They will contribute to the knowledge base for structural applications of metallic glasses. These studies will help educate and train graduate students. They will learn materials fundamentals, develop the ability to plan and conduct research, and will become proficient in state-of-the-art electron microscopy, x-ray diffraction and property characterization of structural materials. In addition, graduate students will learn to communicate their results to the scientific community orally and in writing