DescriptionX-ray computed tomography (XCT) has become a very important method for non-destructive 3D-characterisation and evaluation of materials. Compact XCT systems are available that can reach resolutions down to 1 µm and even below. However, the polychromatic nature of the source, limited photon flux, cone beam artefacts and temperature instability lead to restrictions concerning the reachable CT-data quality; these restrictions are in particular pronounced for materials with a higher density like Al- and Fe-based alloys and for high resolutions. Synchrotron radiation offers significant advantages by its monochromatic and parallel beam of high brilliance. These advantages usually cause less artefacts, improved contrast and resolution. One goal of this investigation is the comparison of advanced cone beam XCT-systems with a µ-focus and a sub-µm (nano-focus) X-ray source with synchrotron computed tomography applied to a steel sample and to two multi-phase Al-samples (AlSi12Ni12, AlMg5Si7). For this reason high-resolution XCT-measurements with voxel sizes between 0.28 and 3.5 µm were performed. CT data features like beam hardening and ring artefacts, detectability of details, sharpness, contrast, signal to noise ratio and the grey value histogram were evaluated and compared systematically. µXCT reveals in all cases the lowest performance. Sub-µXCT gives excellent results regarding detectabilitiy of details, spatial and contrast resolution which are almost comparable to data measured by synchrotron-XCT. Only the signal-to-noise-ratio is for sub-µXCT usually significantly lower as compared to the two other methods. Concerning measurement costs, scanning volume, accessibility and user-friendliness sub-µXCT has significant advantages in comparison to synchrotron-XCT. The second goal is to optimize data quality by using a tube cooling for the Nanotom device. The heat generated at the target and at the deflection coils leads to an expansion of the whole tube and therefore to a movement of the focal spot. The effect of these movements was investigated by measuring the position of Copper wires that were mounted fixed to the tube and fixed to the turntable respectively. The usage of the cooling shows a significant decrease in movement of the tube. The image correction via first and last image also shows much less deviation. This makes it possible to increase measurement time by increasing the number of averaging or the number of projections which leads to an increased signal to noise ratio. A significant improvement in image quality could be shown for a filled polymer specimen at 0.7 µm Voxelsize and a measurement time of 7 hours.
|Period||1 Sep 2010|
|Event title||GE High Resolution X-ray CT Symposium: null|