Multi-laser powder bed fusion (M-LPBF) systems, characterized by large building envelopes and multiple lasers, have become increasingly prevalent in industrial additive manufacturing. The increased build rate of these machines relative to single laser systems offers the potential to drastically reduce the cost per part. However, one major challenge with M-LPBF is that often multiple lasers are needed to build a single part. Therefore, the exposure area must be divided, and the segments must be assigned to different lasers. Various strategies for splitting the exposure area are available, but their influence on part quality remains yet to be determined. This study aims to investigate the impact of the fixed exposure border, variable exposure border, and segmented stripes M-LPBF exposure strategy on the part quality of samples built with two lasers compared to samples built with one laser. Therefore, the porosity, microstructure, and mechanical properties of IN718 samples were evaluated. The research shows that the fixed exposure border strategy resulted in a localized increase in porosity at the border or within the overlap area between segmented exposure areas, as well as grain coarsening and increased texture within the remelted areas. The variable exposure strategy also resulted in a higher porosity level, but the microstructure was more like the single laser reference sample. These changes resulted in a minor decrease in mechanical properties. The segmented stripes strategy exhibited a similar microstructure and mechanical properties to the single laser reference, making it the most suitable approach for M-LPBF in industrial applications.
Synchrotron phase-contrast micro-tomography is considered the gold standard in non-destructive volumetric imaging of millimeter and centimeter-sized objects. Micro-tomography beamlines are operating at many synchrotron radiation facilities, including the Extremely Brilliant Source (EBS) at the European Synchrotron Radiation Facility (ESRF). Applications favor objects which cannot be sufficiently resolved by state-of-the-art industrial micro-CT scanners. Synchrotron tomography features much superior time resolution, e.g., for in situ micro-CT, as well as superior photon flux, thus making this method suitable for Region of Interest scanning (i.e., multiresolution tomography). This report presents first results from the EBS' latest industrial beamline BM18, which was built for hierarchical propagation phase-contrast tomography. BM18 makes use of the exceptionally high coherence of the new ESRF-EBS lattice. Thanks to the wide polychromatic high-energy beam, one can scan and zoom into larger parts, e.g., from additive manufacturing or battery packs. In particular, BM18 allows for recording multiple scans at different resolutions ranging from 42 μm down to 0.6 μm, without the need to remove the object or manually change detectors. Free space propagation of up to 36 m yields excellent phase-contrast which in turn enhances the resolving power of the system. BM18 is generating an unprecedented amount of very large datasets. Consequently, novel strategies for data processing, storage and visualization are under development for this particular instrument.
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