$crystaldiffract file types$

$crystaldiffract file types$

This is due to unpaired dislocations of a single sign accumulating on the slip plane, causing the lattice to develop an orientation gradient. Nye (1953 ▶) showed that heterogeneous slip will cause the lattice to develop orientation gradients, which depend on which slip systems were active. In order to identify slip system activity from measured diffraction peak evolution, a model that relates the two is necessary. Simply put, the regions of different lattice state within the crystal diffract X-rays to different regions on the detector, changing the distribution of diffracted intensity. The observed peak evolution is due to the distribution of the lattice state developing within the crystal as dislocation glide proceeds. Observations of sets of diffraction peaks from plastically deformed crystals using both monochromatic and polychromatic X-ray beams have shown that diffraction peaks from different sets of lattice planes evolve by varying amounts (Joffe & Kirpitcheva, 1922 ▶ Cahn, 1950 ▶ Lienert et al., 2009 ▶), with the evolution dictated by the specific distributions of state in the crystal.

$crystaldiffract file types$

In diffraction images from deforming crystals, the change in state is reflected in changes of the distribution of diffracted intensity measured on a detector. Dislocation glide occurs when a sufficient shear stress is resolved upon the slip system, allowing lattice planes to move relative to one another. The most prevalent mechanism of plastic deformation is dislocation glide (slip) upon a specific slip system or sets of slip systems. This analysis will allow for new information about plasticity to be gathered at the crystal scale from HEDM techniques.ĭuring the plastic deformation of crystalline materials, the lattice state evolves, subsequently changing the mechanical response of the crystal. In this work, a new forward modeling technique is presented to be used to determine slip system activity within deforming crystals at the onset of plastic deformation using diffraction data from intermediate- and far-field geometries. Inversion techniques use models to process diffraction data to determine quantities of interest such as lattice strain or orientation. Forward-modeling techniques use models to completely represent the material, then simulate conditions of the diffraction experiment in order to generate synthetic diffraction data, which can be directly compared with experimental results. Once the diffraction data have been collected, the methods of interpreting the data fall under two broad categories: forward modeling (Suter et al., 2006 ▶ Ludwig et al., 2009 ▶ Wong et al., 2013 ▶ Gonzalez et al., 2013 ▶) and direct inversion (Poulsen, 2004 ▶ Bernier et al., 2011 ▶). The high-energy stations at the Cornell High Energy Synchrotron Source (CHESS) are currently well suited to conduct intermediate- and far-field HEDM experiments. In intermediate-field geometries, diffraction data are equally sensitive to the real-space topology and the reciprocal space of the crystal. Near-field experiments tend to be sensitive to the real-space topology of grains within a sample, while far-field experiments are more sensitive to the reciprocal-space distributions of lattice strain and orientation within grains.

$crystaldiffract file types$

HEDM experiments are usually classified according to the sample-to-detector distance: near-field experiments, where the area detector is close to the sample (Li et al., 2012 ▶ Johnson et al., 2008 ▶) far-field (Poulsen, 2004 ▶ Margulies et al., 2002 ▶ Lienert et al., 2009 ▶) experiments, where the detector is far from the sample and intermediate field, where the detector sits between these two extremes. The lattice state is described by the local lattice orientation, lattice strain and dislocation density, which can vary across the crystal. The distribution of intensity of each diffraction peak contains information about both the real-space topology and the lattice state of the grains (Poulsen, 2004 ▶). Generally, these experiments are rotating crystal diffraction experiments, conducted in a transmission geometry, with an area detector placed behind the sample. High-energy diffraction microscopy (HEDM) techniques allow for the study of deformation of polycrystalline engineering materials at the crystal scale where the origins of failure modes such as fatigue and fracture occur. The ability to produce high-flux high-energy monochromatic X-ray beams, in addition to area detectors with rapid collection times, is enabling a new generation of in situ characterization experiments for crystalline materials.

$crystaldiffract file types$

Crystaldiffract file types