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Three-Dimensional X-ray Diffraction Microscopy: Seeing microstructure inside of bulk materials Internal layer of aluminum polycrystal measured with x-ray diffraction microscopy at the Advanced Photon Source (R.M. Suter, C.M. Hefferan, S.F. Li, D. Hennessy, C. Xiao, U. Lienert, B. Tieman, submitted ): Colors correspond to different lattice orientations Circle indicates 1mm nominal sample size Hexagon indicates simulated region used in reconstruction

Table of Contents

1. Recent publications
2. Overview
3. Technique summary and schematic
4. Apparatus at the APS
5. The July 2004 crew

Related Publications

1. 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. Technol., 130, 021007 (2008); proceedings of the Materials Processing Defects-5 conference, Cornell University, July 2007).
   

2. 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).

3. Forward Modeling Method for Microstructure Reconstruction Using X-ray Diffraction Microscopy: Single Crystal Verification, R.M. Suter, D. Hennessy, C. Xiao, U. Lienert.  Reviews of Scientific Instruments, 77, 123905 (2006).

4. 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).

5. Three-dimensional maps of grain boundaries and the stess state of individual grains in polycrystals and powders, H.F. Poulsen, S.F. Nielsen, E.M. Laurdisen, S. Schmidt, R.M. Suter, U. Lienert, L. Margulies, T. Lorentzen, and D. Juul Jensen, J. Appl. Cryst., 34, 751-756 (2001).

6. Future Trends: Texture Analysis for Structure-Sensitive Properties, B.L. Adams, D. Juul Jensen, H.F. Poulsen, and R. Suter, Materials Science Forum, 273-275, 29-40 (1998).
   

Overview

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 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 on the horizon 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 m material. Similar to serial sectioning work, measurements are done layer-by-layer. However, 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, three dimensional x-ray diffraction microscopy promises to open up 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.

As a part of CMU's Mesoscale Interface Mapping Project (MIMP) (sponsored by the NSF MRSEC program) we are working to develop a facility for x-ray diffraction microscopy at the Advanced Photon Source at Argonne National Laboratory. We are specifically working to advance the state of non-destructive 3D microstructure mapping using high energy x-rays.

Schematic and Outline of the Technique

1. White (multi-wavelength) synchrotron radiation from an undulator source enters the experimental enclosure.

2. Bragg diffraction from a bent single crystal of silicon (in transmission) is used to generate a convergent monochromatic beam (50 -100keV) of x-rays.

3. The line focused high energy beam (red) illuminates a ~1 micron thick section of the sample (green).

4. Bragg spots (black) from individual grains are imaged on a CCD detector (gray); spots have the shape of the illuminated grain cross section projected onto the detector plane at the scattering angle.

5. Measuring a set of spots at multiple sample-to-detector distances yields the path of the diffracted beam and, by inversion, the position of the diffracting grain.

6. Step-wise measurements over a range of sample orientations, omega, yield multiple spots from each grain; this implies complete crystallographic orientation information and projected images of each grain from multiple points of view.

7. After image processing, our analysis code performs a simulation of the entire measurement and microstructure. The sample space is gridded and the crystallographic (or chemical) phase and orientation at each grid element is adjusted to optimize the overlap of simulated Bragg scattering with the experimental data.

Apparatus at APS beamline XOR-1

The following images were taken during our July 2004 beam time:

The experimental hutch. The white beam enters from the right and travels in an evacuated pipe into the monochromator box (roughly cubical box on optical table). Slits before the sample (see below)  reduce background and can be used to limit the horizontal width of the line focused beam.  The sample stage and detector system follow (the horizontal stainless steel cylinder with funnel on top is the liquid nitrogen chamber that cools the CCD.

The heavy slits are at right followed by an ion chamber for monitoring the incident beam intensity (white, blue and red cables are attached). The sample rotation (Huber green), omega, and translation stages (XY) are seen next. The CCD lens (coming in from left) is pointing at a mirror that directs light from an x-ray detector crystal (see below).  The entire CCD system is mounted on a translation stage so that the sample-to-detector distance can be varied.

Close-up of a mounted sample (in the drill chuck), Ta beam stop (perpendicular to sample and mounted in a goniometer at right), transparent x-ray detector crystal (Ce doped YAG), mirror, and lens that couples light to the CCD (out of view to left).