Ingenieurwissenschaften und zugeordnete Tätigkeiten
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- 2019 (4) (entfernen)
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- AM IN718 alloy (1)
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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.
Evolution of a friction material with braking sequence: properties related to the microstructure
(2019)
The microstructural complexity (multi-component and multi-scale) of friction materials, such as those used in braking applications,usually limits the characterization to the pristine state, even when they are to be submitted to high loading brake sequences. The understanding of properties ageing as a function of load history and microstructure is an important step to gain further knowledge on the tribological mechanisms occurring at the contact surface, as well as on the braking performances. To do so, the bulk mechanical and microscopical properties of a semi-metallic friction material are investigated before and after a braking sequence. Uniaxial compression tests combined with DIC are used to study the axial evolution of the mechanical behaviour (i.e., from the contact surface to the backplate). A significant mechanical evolution is observed in the after-braking material, which develops a layered behaviour along the depth. The layers (three) exhibit distinct mechanical/microstructural features that can be related to the braking thermal gradients and the occurrence of local damage.