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| High Energy X-ray
Diffraction Microscopy (HEDM):
Observing microstructure evolution inside of bulk materials
3D representation of local misorientations in a copper wire that has undergone light tensile strain (reference 3, below).
of Contents (modified November 2010)
Probing Microstructure Dynamics With X-ray
Diffraction Microscopy, R.M. Suter, C.M.
Hefferan, S.F. Li, D. Hennessy, C. Xiao, U. Lienert, B.
Tieman, J. Eng. Mater.
021007 (2008); proceedings of the Materials Processing
Defects-5 conference, Cornell University, July 2007).
3-Dimensional Characterization of Polycrystalline Bulk Materials Using High-Energy Synchrotron Radiation, U. Lienert, J. Almer, B. Jakobsen, W. Pantleon, H.F. Poulsen, D. Hennessy, C. Xiao, and R.M. Suter, Materials Science Forum 539-543, 2353-2358 (2007).
Tracking: a method for structural characterization of grains in powders or polycrystals, E.M. Laurdisen, S. Schmidt, R.M. Suter, and H.F. Poulsen, J. Appl. Cryst., 34, 744-750 (2001).
Three-dimensional maps of grain boundaries and the stress state of individual grains in polycrystals and powders, H.F. Poulsen, S.F. Nielsen, E.M. Lauridsen, S. Schmidt, R.M. Suter, U. Lienert, L. Margulies, T. Lorentzen, and D. Juul Jensen, J. Appl. Cryst., 34, 751-756 (2001).
Schematic and Outline of the Technique
Apparatus at APS beamline 1-ID
|Sample stage at 1-IDB.
|The measurement crew (March 2010) at 1-ID command central|
Some examples of
microstructure measurements using x-ray diffraction microscopy
(updates are coming soon...Nov 2010)
All data shown here
were collected at the Advanced Photon Source, beamline 1-ID
at Argonne National Laboratory. Participants include Chris
Hefferan, Frankie Li, Robert Suter (CMU) and Ulrich Lienert
(APS). Important computational assistance was provided by
Brian Tieman of the APS; analysis was performed using custom
software developed at CMU running on a 68 node cluster at
1. A section through the middle of a NIST certified
152 micron diameter single crystal ruby sphere. a) The
color map on the left shows misorientations from the average
orientation. Red-green-blue color contributions are
proportional to the Rodrigues vector describing the
misorientation. The maximum
rotation angle is 0.3 degrees. The
green circle shows the nominal 152 micron sample cross-section
while the hexagon shows the entire region included in the
analysis. The maximum radial deviations are roughly 8 microns.
b) The map on the right shows the 'confidence' fitting
parameter indicating maximal overlap of the simulation with
the experimental data in the central region and reduced
overlap near the edges. This reduction is due to background
subtraction removing weak edges of the imaged diffraction
spots. This fit is based on simulation of 1118 ruby Bragg
peaks about 115 of which could be observed at more than one
detector distance in the experimental data set. A confidence
of 0.79 means that over 90 simulated peaks overlap
experimentally observed peaks; 0.33 confidence implies 38
|Ruby sphere orientation map
||Relative confidence map for
image at left
2. Near surface sections through an aluminum 1050 alloy polycrystal sample. Colors indicate grain orientations, again coded by Rodrigues vector components. The blue circle indicates the 1 mm nominal sample diameter while the hexagon is the analysis box. Black lines in the maps are draw between elements with more than 5 degree misorientation.
| z = 0
|z = -10um|
crystallographic misorientation between the above two
layer measurements. Black lines show boundaries in the z
= 0 layer.
Overview of relevance of HEDM microstructure mapping techniuqe
Polycrystals are aggregates of single crystals joined together by a network of internal interfaces called grain boundaries. Polycrystalline materials, in both single and multi-phase forms, are ubiquitous in engineered systems: integrated circuits, aircraft and automotive components, communications devices, machine tools, and many others. The three dimensional geometry, arrangement, and relative orientation of the grains and the consequent grain boundary network (i.e., the microstructure) are crucial determinants of mechanical, chemical, thermal, and electrical properties. While there has been dramatic progress made in gaining three dimensional information about microstructure from two dimensional measurements made at surfaces (CMU MRSEC), it remains a great challenge to be able to watch microstructural evolution in response to external stimuli. With such observations made deep inside bulk materials, we should be able to deepen our understanding of phenomena and develop accurate constitutive relations governing the evolution and thereby learn how to do predictive calculations and to tailor microstructures to specific applications.
Three Dimensional X-ray Diffraction Microscopy (see articles listed above and the monograph by H.F. Poulsen, "Three Dimensional X-ray Diffraction Microscopy," Springer, 2004) is the only method available that can non-destructively image macroscopic volumes of internal microstructures. Based simply on Bragg diffraction, it is as versatile as, for example, electron backscatter diffraction analysis of surface microstructures. But by using high energy x-rays, it looks through millimeters of material without the need for destructive serial sectioning. Similar to serial sectioning work, measurements are done layer-by-layer. After the measurement, the sample still exists and can be re-measured after processing. Real-time dynamics can be monitored. The x-rays can penetrate sample chambers, making in-situ measurements possible. In sum, high energy x-ray diffraction microscopy (HEDM) promises to open the world of microstructure dynamics and response to a new light. In combination with powerful new computational tools, one can look forward to a new level of understanding and a new level of "dynamic three dimensional command over materials structure," (ONR BAA 04-024) processing, and properties.