A comparative study of high resolution cone beam X-ray tomography and synchrotron tomography applied to Fe- and Al-alloys

TLDR

X‑ray computed tomography, especially cone‑beam systems with μ‑focus detectors, has become essential for non‑destructive 3‑D material characterization, yet their polychromatic beams and limited photon flux impose artefacts and resolution limits, particularly for dense metals, whereas synchrotron sources provide monochromatic, high‑brilliance beams that mitigate these issues. The study recorded steel and two multi‑phase aluminum alloys with μ‑focus and sub‑μ‑focus cone‑beam XCT systems (voxel sizes 0.4–3.5 µm) and compared the resulting data to synchrotron XCT at 0.3 µm/voxel, systematically evaluating beam hardening, ring artefacts, detail detection, sharpness, contrast, SNR, and grey‑value histograms. Results show μ‑focus XCT performed worst, sub‑μ‑focus XCT achieved detail detection, spatial and contrast resolution comparable to synchrotron XCT but with lower SNR, and offered significant industrial advantages in cost, volume, accessibility, and user‑friendliness.

Abstract

X-ray computed tomography (XCT) has become a very important method for non-destructive 3D-characterization and evaluation of materials. Due to measurement speed and quality, XCT systems with cone beam geometry and matrix detectors have gained general acceptance. Continuous improvements in the quality and performance of X-ray tubes and XCT devices have led to cone beam CT systems that can now achieve spatial resolutions down to 1 μm and even below. However, the polychromatic nature of the source, limited photon flux and cone beam artefacts mean that there are limits to the quality of the CT-data achievable; these limits are particularly pronounced with materials of higher density like metals. Synchrotron radiation offers significant advantages by its monochromatic and parallel beam of high brilliance. These advantages usually cause fewer artefacts, improved contrast and resolution.Tomography data of a steel sample and of two multi-phase Al-samples (AlSi12Ni1, AlMg5Si7) are recorded by advanced cone beam XCT-systems with a μ-focus (μXCT) and a sub-μm (nano-focus, sub-μXCT) X-ray source with voxel dimensions between 0.4 and 3.5 μm and are compared with synchrotron computed tomography (sXCT) with 0.3 μm/voxel. CT data features like beam hardening and ring artefacts, detection of details, sharpness, contrast, signal-to-noise ratio and the grey value histogram are systematically compared. In all cases μXCT displayed the lowest performance. Sub-μXCT gives excellent results in the detection of details, spatial and contrast resolution, which are comparable to synchrotron-XCT recordings. The signal-to-noise ratio is usually significantly lower for sub-μXCT compared with the two other methods. With regard to measurement costs "for industrial users", scanning volume, accessibility and user-friendliness sub-μXCT has significant advantages in comparison to synchrotron-XCT.