Determining crystallographic microstructure of a given material in 2D can be challenging.  Further extending such an investigation to 3D on meaningful volumes (and without sample sectioning) can be even more so. Yet reaching this insight holds tremendous value for 3D materials science since the properties and performance of materials are intricately linked to microstructural morphology including crystal orientation. Achieving direct visualization of 3D crystallographic structure is possible by diffraction contrast tomography (DCT), albeit only available at a limited number of synchrotron X-ray facilities around the world. Recent developments, however, have made DCT possible on an X-ray microscope with a laboratory source. 

The introduction of diffraction contrast tomography as an additional imaging modality on the ZEISS Xradia 520 Versa laboratory X-ray microscope has opened up a whole new range of possibilities for studies of the effect of 3D crystallography on materials performance. The capability to link directly the crystallographic and grain microstructure information with that obtained via conventional absorption or phase contrast imaging, non-destructively in three-dimensions and all in the laboratory, creates a powerful and easy to access tool.   [1]  Using a polychromatic X-ray source, laboratory diffraction contrast tomography technique (LabDCT) takes advantage of the Laue focusing effect, improving diffraction signal detection and allows handling of many and closely spaced reflections. Additionally, LabDCT opens the way for routine, non-destructive and time-evolution studies of grain structure to complement destructive electron backscatter diffraction (EBSD) end-point characterization. Combination of grain information with microstructural features such as cracks, porosity, and inclusions all derived non-destructively in 3D presents new insights for materials characterization of damage, deformation and growth mechanisms. Furthermore, 3D grain orientation data is a valuable input into multi-scale, multi-layered modeling platforms that can virtually evaluate mechanical properties to produce high fidelity simulation results. Here, we introduce the LabDCT technique and demonstrate its unique capability through a selection of application examples for materials science as well as discuss innovative methods to extend the current capabilities of the technology for a better understanding of materials structure evolution in 3D.

[1] McDonald, S.A. et al. Non-destructive mapping of grain orientations in 3D by laboratory X-ray microscopy. Scientific Reports 5, 14665 (2015). doi: 10.1038/srep14665

Figures:

Schematic of the laboratory diffraction contrast tomography (LabDCT) implementation on the ZEISS Xradia 520 Versa X-ray microscope.

Laue-focusing effect of a grain fulfilling Bragg-reflection condition. Due to the divergence of the incident beam the reflected X-rays are focused in one dimension at a distance away from the sample that is equal to the distance between sample and source, causing line shaped diffraction spots.

Left: Reconstructed grain maps from sintering experiment with Cu powder. Grains are plotted as cubes at measured positions within absorption mask of the sample (shown transparent) revealing (relative) size and crystallographic orientation (by color). Right: Comparing the grain size distributions for time sintering steps.

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