Coherent X-Ray Scattering Studies of Phase Transitions in Metals

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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.