Abstract
The quality of components made by laser beam melting (LBM) additive manufacturing is naturally influenced by the quality of the powder bed. A packing density <1 and porosity inside the powder particles lead to intrinsic voids in the powder bed. Since the packing density is determined by the particle size and shape distribution, the determination of these properties is of significant interest to assess the printing process. In this work, the size and shape distribution, the amount of the particle’s intrinsic porosity, as well as the packing density of micrometric powder used for LBM, have been investigated by means of synchrotron X-ray computed tomography (CT). Two different powder batches were investigated: Ti–6Al–4V produced by plasma atomization and stainless steel 316L produced by gas atomization. Plasma atomization particles were observed to be more spherical in terms of the mean anisotropy compared to particles produced by gas atomization. The two kinds of particles were comparable in size according to the equivalent diameter. The packing density was lower (i.e., the powder bed contained more voids in between particles) for the Ti–6Al–4V particles. The comparison of the tomographic results with laser diffraction, as another particle size measurement technique, proved to be in agreement.
Highlights
Powder bed additive manufacturing (PB-AM) techniques, such as electron beam melting (EBM) and laser beam melting (LBM), require process control of each manufacturing step [1]
The quality of components made by laser beam melting (LBM) additive manufacturing is naturally influenced by the quality of the powder bed
The size and shape distribution, the amount of the particle’s intrinsic porosity, as well as the packing density of micrometric powder used for LBM, have been investigated by means of synchrotron X-ray computed tomography (CT)
Summary
Powder bed additive manufacturing (PB-AM) techniques, such as electron beam melting (EBM) and laser beam melting (LBM), require process control of each manufacturing step [1]. Since the techniques are based on metallic powder, powder characterization is one of the main steps for process optimization. Powder properties, such as heat conduction [2], flowability [3], packing density [4], internal porosity [5], size, and shape [6], may influence the powder bed quality [7]. A variety of powder characteristics (e.g., size distribution, flowability) are certificated by the manufacturer. The discussion about particle shape becomes even more critical when recycled powder has to be used during the process, since the mean particle size and shape changes after first use [12,13,14] and certificates are not reliable any longer. As shown in [15], the usage of realistic powder characteristics during modeling of PB-AM processes is necessary for accurate prediction of porosity and melt pool dimensions
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