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Grain Boundaries in a Highly Pure Iron Sample

September 01, 2017

New HEDM Project at ANL

Jocelyn Duffy

The National Science Foundation Major Research Infrastructure program announced funding of a $1.5M project to build a new High Energy Diffraction Microscope (HEDM) at the Advanced Photon Source (APS) synchrotron at Argonne National Laboratory. The project will be carried out by a consortium led by Robert M. Suter of the CMU Physics Department and involves faculty at Purdue University, Colorado School of Mines, and the University of Utah, as well as participants at the Advanced Photon Source.

This second generation instrument builds upon technological developments in which the CMU departments of Physics and of Materials Science and Engineering have taken a leading role for over more than a decade. Recent technology and software developments will allow enhanced experimental control and feedback as well as accelerated data reduction to produce microscope output on the time scale of the data collection. Once commissioned, the new instrument will be available to a broad international materials science community and help relieve the high demand on the current facility at the APS 1-ID beamline.

High-Energy Diffraction Microscopy (HEDM) uses spatially resolved diffraction to non-destructively map crystal orientation fields inside bulk samples such as metals. The figure shows a single slice through a three-dimensional map of orientations within highly pure iron. Three parameters specifying the local crystal unit cell orientations are mapped onto an RGB color scale.
Successive measurements determine the evolution of the network of boundaries between different orientations at high temperature or under mechanical load. Such dynamic changes have not been directly observable before the development of HEDM. This new technology is therefore critical to develop more accurate and reliable predictive models of materials, their responses and properties.




The current HEDM at APS

The existing facility, where the technique was developed, is shown in the photo. X-rays generated 75 meters upstream by a superconducting undulator pass through a monochromator which selects the x-ray wavelength (or energy). An evacuated beam transport pipe brings the beam (shown schematically in red) in from the right. Major components of the instrument are silicon sawtooth refractive lenses that focus the 300 μm tall beam down to 1.5 μm in the vertical direction, the sample stack with sample positioning and rotation stages and facilities to apply tensile or compressive forces, a near-field diffraction and tomographic imaging detector with 1.5 μm resolution over a three millimeter field of view, and a far-field detector. The sample position/orientation is computer controlled from a station outside the radiation-tight hutch, providing a data collection robot programmed to perform a variety of measurement protocols. In the new HEDM implementation, data streams will be pipelined to supercomputer systems as the measurement proceeds.