Session K2: Experimental Developments VI: X-ray II

In situ x-ray diffraction and imaging studies of structural and geological materials under dynamic loading

New opportunities to study the evolution of microstructure of materials in response to dynamic loading are enabled by the development of new x-ray sources and detectors. This talk will focus on recent experiments on structural and geological materials under loading at strain rates of on the order of 10$^{3}$ s$^{-1}$. Examples will include diffraction studies of texture evolution in polycrystalline magnesium alloys and martensitic phase transformations in steel and Ni-Ti, along with preliminary static phase contrast imaging studies of defects in single-crystal quartz and sandstone. The talk will emphasize general principles and experimental considerations in developing \textit{in situ} x-ray experiments. Two primary themes will be how to take best advantage of the characteristics of the x-ray source and detector, and the limits that these characteristics place on the samples and loading conditions that can be studied. The talk will conclude with a discussion of prospects for future developments in the field in light of continuing advances in x-ray sources and detectors.   

Fast Compression and Decompression capabilities at HPCAT

Materials behavior and phase transformation pathways are strongly influenced by the time dependence of the driving mechanism (compression, thermal transfer, strain, irradiation, etc). While shock compression and static compression are well established techniques available for a long time, the techniques filling the compression rate gap and studying materials behavior as a function of compression rates at intermediate rates remain scarce. Recent advances in synchrotron sources, x-ray optics, fast area detectors, and sample environment control have enabled many time-resolved experimental techniques for studying materials at extreme pressure and temperature conditions. The High Pressure Collaborative Access Team (HPCAT) at the Advanced Photon Source has made a sustained effort to develop and assemble a powerful collection of high-pressure apparatus for time-resolved research and developing techniques for collecting high-quality time-resolved x-ray scattering data at compression rates intermediate between static and shock compression experiments. In this talk we will outline recently developed capabilities at HPCAT for synthesis of metastable and amorphous materials and studying properties (EOS, lattice relaxation, etc.) and phase transition mechanisms of materials using fast unidirectional and cyclic compression-decompression with variable strain rates up to extreme compression of tens of TPa per second.   

Single Hit Energy-resolved Laue Diffraction

In-situ white light Laue diffraction is a technique to interrogate the structure of materials undergoing dynamic compression up to megabar pressures. We present an extension to the existing Laue diffraction platform in which CCD cameras are used in single photon mode enabling a measurement of the energy of a subset of diffraction peaks. Careful choice of which diffraction peaks are observed allows for a measurement of the longitudinal and transverse strains. This allows for the measurement of absolute volume of the unit cell in addition to its aspect ratio. We present results for silicon, where only longitudinal elastic strain has been observed. VISAR measurements show the presence of a two wave structure and measurements made from the diffraction patterns on the CCD show that material downstream of the second wave does not contribute to the observed diffraction peaks, suggesting that this material may be highly disordered, or has undergone large scale rotation.   

Time Resolved X-Ray Diffraction of Reactive Solids Under Dynamic Loadings

We present novel time-resolved (TR) x-ray diffraction and TR Raman spectroscopy capable of probing structural and chemical evolutions of solids undergoing chemical and phase transformations. These methods are applicable to a wide range of dynamic experiments to study both single event phenomena of solids under thermal, electric or mechanical impact conditions and non-single event phenomena under dynamic-diamond anvil cell (\textit{d}-DAC) and high frequency pulse (or ramp) laser-heated DAC. In this talk, relevant technology developments are described with several examples of our recent studies on reactive metals and dense molecular systems, which are synergistic to many proposed activities to develop dynamic synchrotron x-ray diffraction capabilities centered at advanced third and fourth generation light sources.