Coherent X-Ray Scattering Studies of Phase Transitions in Metals

技术：X射线散射/衍射长期以来一直是研究材料原子结构和演化的主要工具。传统的X射线散射使用的是有效相干长度远小于光束本身大小的光子束。然而，来自第三代同步加速器源的高亮度硬X射线束的可获得性使得制造在整个散射体中表现出显著相干性的小X射线束(通常直径约为10毫米)成为可能。目前可用的硬X射线束使一些传统上在光学系统中使用的技术现在可以用于硬X射线系统。该程序扩展了相干x射线散射的应用，以研究金属和合金相变的动力学、动力学和微观可逆性。它将检测表现出位移相变的合金的微观可逆性和记忆性，包括铜-锌-铝形状记忆合金。它还将研究波动、缺陷钉扎和这些系统中的动力学以及合金排序之间的关系。最后，将考察外差技术的发展，以研究在固有的样品散射相对较弱和扩散的情况下的波动动力学。非技术：这项研究计划将提高对纳米尺度动力学的理解，即原子如何在纳米长度尺度上运动。这些知识对于理解和开发先进材料非常重要，这些材料将成为未来通信、计算、化学加工和其他行业的基础。作为这项研究计划的一部分，研究生、本科生和高中学生将学习新的X射线技术和材料问题，这些技术和材料问题是当前材料研究的前沿。通过与美国国内外其他机构的科学家继续合作，这些学生将有机会看到各种研究环境。

Technical: X-ray scattering/diffraction has long been a primary tool for investigating the atomic structure and evolution of materials. Traditional x-ray scattering uses photon beams that have effective coherence lengths significantly smaller than the size of the beam itself. The availability of high brilliance hard x-ray beams from 3rd generation synchrotron sources, however, has opened the possibility of making small x-ray beams (typically of order 10 mm in diameter) that exhibit significant coherence throughout the scattering volume. Currently available hard x-ray beams enable some of the techniques traditionally used in the optical regime to now be used in the hard x-ray regime. This program expands the applications of coherent x-ray scattering to investigate dynamics, kinetics and microscopic reversibility in metal and alloy phase transitions. It will examine microscopic reversibility and memory in alloys exhibiting displacive phase transitions, including the Cu-Zn-Al shape memory alloys. It will also examine the relationships between fluctuations, defect pinning and kinetics in these systems as well as in ordering alloys. Finally, the development of heterodyne techniques will be examined for the study of fluctuation dynamics in cases where the inherent sample scattering is relatively weak and diffuse. Non-Technical: This research program will improve understanding of nanoscale dynamics, i.e. how atoms move on the nanometer length scale. Such knowledge is important for understanding and developing advanced materials that will form the basis of future communications, computing, chemical processing and other industries. As part of this research program, students at the graduate, undergraduate and high school levels will be involved in learning about new x-ray techniques and materials issues that are at the forefront of current materials research. Through continuing collaborations with scientists at other institutions, both inside and outside the US, these students will have an outstanding opportunity to see a variety of research environments.