Advanced Photon Source

An Office of Science National User Facility

Techniques

1-ID techniques leverage the high-brilliance of synchrotron x-rays in the 42<E<120 keV range to non-destructively evaluate bulk materials.Often the techniques listed below can be combined on a single specimen, which is particularly beneficial for in-situ experiments.

High-energy x-ray diffraction

This technique employs a transmission geometry and large area detector (s) to measure quantities such as the phase fraction, internal strain and crystallographic texture in each phase of a polycrystalline material. Such materials encompass the vast majority of structural materials, ranging from aircraft wings to engine crankshafts to bones and teeth.The high-flux of synchrotron x-rays allows for weak phases to be detected, such as Zr-H phases in Zr alloys with H concentrations on the 100 parts-per-million level, and rapid data collection with less than 1sec/detector image common. 

At the low bragg angles associated with these high-energies (2theta(typ) < 10 degrees) the area detector captures diffraction information from a 2D plane of sample orientations which are nearly perpendicular to the incident beam. The incident x-ray beamsize can be decreased to approximately 2 (V) x 10 (H) microns using slits and/or focusing elements, allowing gradients transverse to the incident beam to be probed by translating the sample relative to the fixed beam.In the longitudinal direction, diffraction is typically averaged over the entire sample thickness traversed by the x-ray beam; however diffracted beam apertures may be used to produce longitudinal resolutions down to ~100 microns.

By taking diffraction patterns as a function of a rotation, about an axis perpendicular to the incident beam (omega),3D quantities may be measured including the orientation distribution function (macro-texture) and full strain tensor.In addition, this rotation provides 3D reconstructions with the techniques of high-energy diffraction microscopy and scattering tomography described below.

High-energy x-ray diffraction microscopy

HEDM_derived_grain_mapIn the HEDM technique, individual grains within a polycrystalline aggregate can be mapped by taking diffraction patterns as a function of rotation angle.HEDM requires that diffraction spots from individual grains can be identified, meaning that there is an upper limit to the number of grains which can be measured in a given diffraction volume.In non-deformed samples as many as thousands of grains may be indexed, while this number decreases with crystallite disorder (e.g. plastic deformation). The output is a grain-by-grain map of crystallographic parameters in the irradiated volume including lattice parameters, orientations, positions and volumes and, in certain cases, grain shape.Currently only a few synchrotron facilities are available worldwide which can generate this type of diffraction data. The closest non-x-ray analogue is electron-backscatter diffraction, available much more widely, which provides 2D (surface) information with higher spatial resolution but poorer resolution of crystallographic parameters.

High-energy x-ray scattering tomography
This technique is based on collecting position-resolved 'powder-like' diffraction data at a number of angular orientations of the specimen, with positional intervals generally matching the beam-size and number chosen to cover the entire specimen cross-section.Through subsequent reconstruction of this data, the cross-section is partitioned, or voxellated, such that powder diffraction data can be attributed to each voxel.Three-dimensional imaging can be performed by an orthogonal specimen translation and repeating the process. This method is particualrly appropriate when grain sizes are too small to be individually resolved with HEDM (roughly this limit is in the 1-5 micron range), and thus valuable for studying inhomogeneities in nano-grained materials including bio-materials and many energy-storage materials.