Abstract
Laboratory diffraction contrast tomography (LabDCT) is a recently developed technique for 3D nondestructive grain mapping using a conical polychromatic beam from a laboratory-based X-ray source. The effects of experimental parameters, including accelerating voltage, exposure time and number of projections used for reconstruction, on the characterization of the 3D grain structure in an iron sample are quantified. The experiments were conducted using a commercial X-ray tomography system, ZEISS Xradia 520 Versa, equipped with a LabDCT module; and the data analysis was performed using the software package GrainMapper3D, which produces a 3D reconstruction from binarized 2D diffraction patterns. It is found that the exposure time directly affects the background noise level and thus the ability to distinguish weak spots of small grains from the background. With the assistance of forward simulations, it is found that spots from the first three strongest {hkl} families of a large grain can be seen with as few as 30-40 projections, which is sufficient for indexing the crystallographic orientation and resolving the grain shape with a reasonably high accuracy. It is also shown that the electron current is a more important factor than the accelerating voltage to be considered for optimizing the photon numbers with energies in the range of 20-60 keV. This energy range is the most important one for diffraction of common metals, e.g. iron and aluminium. Several suggestions for optimizing LabDCT experiments and 3D volume reconstruction are finally provided.
Highlights
Laboratory X-ray diffraction contrast tomography (LabDCT) is an emerging characterization technique allowing nondestructive 3D crystallographic orientation mapping (Bachmann et al, 2019; King et al, 2013, 2014)
102 Adam Lindkvist et al Optimizing LabDCT for grain structure characterization diffraction image collected with an exposure time of 20 s has more of a ‘salt and pepper’ look of the background than the rest of the images, indicating a higher level of background noise
The results show that LabDCT experiments can be optimized with respect to the three experimental parameters studied here
Summary
Laboratory X-ray diffraction contrast tomography (LabDCT) is an emerging characterization technique allowing nondestructive 3D crystallographic orientation mapping (Bachmann et al, 2019; King et al, 2013, 2014). It adapts principles of synchrotron DCT (Ludwig et al, 2008; Reischig et al, 2013) and has been implemented in a commercially available X-ray microtomography (m-CT) microscope (Holzner et al, 2016; McDonald et al, 2017, 2015). During a LabDCT experiment, the sample is rotated 360 around the vertical axis at a selected number of intervals, through which many diffraction spots from different crystallographic lattice planes of the same grain are recorded and used for indexing of crystallographic orientations and reconstruction of the grain structure in the sample in three dimensions
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