Diffraction Across the Length Scale

This JOM special topic concerns advances in neutron and x-ray diffraction directed toward the study of the structural properties of materials at different length scales. This year, the scientific community is celebrating 100 years since the discovery of x-ray diffraction by Laue, Bragg, and the first experimental diffraction pattern obtained from a crystal by Friedrich and Knipping. After their experiment, it was immediately understood that x-rays could become one of the most powerful tools for material characterization, medicine, etc. During the last century, the importance of diffraction methods utilizing x-rays and later electrons, neutrons, and Mossbauer photons increased enormously, while their area of applicability significantly broadened. For example, compare the first laboratory x-ray tubes of 100 years ago with the ultrabrilliant synchrotron x-ray sources of today that have opened fantastic possibilities for the analysis of structure in a broad spectrum of materials. In the first decades of x-ray science, the studies of regular Laue–Bragg reflections, specifically their positions and intensities, were the primary focus of research. This allowed the characterization of crystallographic structure starting from simple lattices and moving toward complicated organic structures. Diffraction studies became the basis for the development of crystallography, physics, chemistry, etc. Later, the focus of x-ray science moved to the understanding of both static and dynamic lattice defects. In real crystals, thermal vibrations and other defects disturb periodic atomic arrangements and alter the diffracted intensity. Diffraction lines and reflections may broaden, their intensity weakens, and sometimes the so-called diffuse scattering appears around and between the Bragg peaks. The character of the scattered intensity relates to the shortand long-range order, type, and symmetry of defects, the interaction energy between different atoms, the Fermi surface, and phonons, and critical fluctuations near phase transitions, etc. The selected manuscripts present a slice of several x-ray and neutron diffraction applications that are currently the focus of research in different laboratories worldwide. These manuscripts demonstrate the possibilities of materials studies utilizing small local probes providing information about submicron volumes in those materials and larger beams probing statistically averaged properties of those materials. First, three manuscripts titled ‘‘Microscopic Deformation in Individual Grains in an Advanced High-Strength Steel’’ by Zhenzhen Yu, Roziliya Barabash, Oleg Barabash, Wenjun Liu, and Zhili Feng, ‘‘Acquisition, Sharing and Processing of Large Datasets for Strain Imaging: An Example of an Indented Ni3Al/Mo Composite’’ by N.S. McIntyre, R.I. Barabash, J. Qin, M. Kunz, N. Tamura, and H. Bei and ‘‘In Situ Observation of the Dislocation Structure Evolution During a Strain Path Change in Copper’’ by Christian Wejdemann, Henning Friis Poulsen, Ulrich Lienert, and Wolfgang Pantleon present example applications of different versions of x-ray microdiffraction with a beamsize 0.5 lm for in-depth understanding of the mechanical behavior at the mesoscale. Several versions of microdiffraction were developed: Polychromatic x-ray microdiffraction (PXM) and differential aperture x-ray microscopy (DAXM) were developed by Oak Ridge National Laboratory at the microdiffraction beamline 34-IDE at the Advanced Photon Source at Argonne National Laboratory. This method is directly based on Laue diffraction experiments. Modernization of the beam line apparatus and the high brilliance of synchrotron emissions create unusual opportunities to extract the mesoscale information about the materials. A slightly different version of this technique is described by McIntyre et al. where it is employed at the microdiffraction beamline at the Advanced Light Source. The PXM technique utilizes both a monochromatic beam and a white (pink) beam with an energy range of 5–25 keV. It is best suited to study defects in polycrystalline or multiphase materials Rozaliya I. Barabash is the guest editor for the Mechanical Behavior of Materials Committee of the TMS Structural Materials Division, and coordinated the topic Diffraction Studies across the Length Scales in this issue. JOM, Vol. 65, No. 1, 2013