Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Dokumenttyp
- Zeitschriftenartikel (29)
- Vortrag (8)
- Posterpräsentation (7)
- Beitrag zu einem Tagungsband (3)
Schlagworte
- Additive manufacturing (11)
- Laser powder bed fusion (8)
- Residual stress (5)
- Additive Manufacturing (4)
- AlSi10Mg alloy (4)
- AlSi10Mg (3)
- Computed tomography (3)
- EBSD analysis (3)
- Electron backscatter diffraction (EBSD) (3)
- Fatigue crack growth (3)
- In situ heating (3)
- Laser Powder Bed Fusion (3)
- Neutron diffraction (3)
- Residual Stress (3)
- Residual stress analysis (3)
- Creep (2)
- Diffraction (2)
- Diffraction elastic constants (2)
- Digital image correlation (DIC) (2)
- Electron backscatter diffraction (2)
- Fatigue crack propagation (2)
- Heat treatment (2)
- IN718 (2)
- Residual stress state (2)
- Residual stresses (2)
- Synchrotron X-Ray Refraction (2)
- Synchrotron refraction radiography (2)
- Thermally induced porosity (2)
- X-ray refraction (2)
- A357-T6 cast aluminum alloy (1)
- A357-T6 casting (1)
- AGIL (1)
- AISI 316L (1)
- AM IN718 (1)
- AM IN718 alloy (1)
- Al-3.85%Mg alloy (1)
- Aluminium alloys (1)
- As-built LPBF IN718 alloy (1)
- Bench braking sequence (1)
- Bragg-edge neutron 2D imaging (BENI) (1)
- Braking load history (1)
- Bulk properties ageing (1)
- Cellular structures (1)
- Components influence (1)
- Compression testing (1)
- Compressive test (1)
- Computed Tomography (1)
- Crack initiation period (1)
- Cracks (1)
- Crystal plasticity finite element modeling (CPFEM) (1)
- Crystallographic descriptor (1)
- Crystallographic texture control (1)
- Cyclic R-curve (1)
- DIC assisted compression (1)
- Damage tolerance (1)
- Denoising filter (1)
- Diffraction methods (1)
- Diffraction peak width (1)
- Diffraction-elastic constants (1)
- Diffusion (1)
- Digital image correlation (1)
- Dislocation-climb-controlled creep (1)
- Dislocations (1)
- Distortion (1)
- Distortion upon baseplate removal (1)
- Effect of scanning strategies (1)
- Electron microscopy (1)
- Energy dispersive X Ray diffraction (1)
- Ernel average misorientation (KAM) (1)
- Evolution of bulk properties (1)
- Fatigue performance (1)
- Fractals (1)
- Fractographic observations (1)
- Friction braking (1)
- Geometric descriptor (1)
- Graphite induced hysteresis (1)
- Hystersis (1)
- IN718 PBF-LB/M (1)
- Imaging (1)
- In situ testing (1)
- In-situ heat treatment (1)
- Inconel 718 (1)
- Interfaces (1)
- Keramik (1)
- L-PBF (1)
- L-PBF IN718 material (1)
- LPBF (1)
- Laboratory XµCT (1)
- Laminated metal composite (1)
- Laminated metallic composites (1)
- Laser Beam Melting (1)
- Laser Powder Bed Melting (1)
- Laser beam melting (1)
- Laser powder bed fusion (LPBF) (1)
- Laser-based additive manufacturing (1)
- Load history (1)
- Macroscopic stress (1)
- Mechanical behavior (1)
- Metal additive manufacturing (MAM) (1)
- Metallic matrix pad (1)
- Microstructural evolution (1)
- Microstructure (1)
- Microstructure and texture (1)
- Monoclinic to tetragonal transformation (1)
- Near-surface X-ray diffraction (1)
- Neutron Diffraction (1)
- Neutron and X-ray diffraction (1)
- Neutrons diffraction (1)
- Nickel-based superalloys (1)
- Nonlinear stress-strain curve (1)
- Online Process Monitoring (1)
- Pore size (1)
- Porosity growth (1)
- Post processing heat treatment (1)
- Powder analysis (1)
- Powder metallurgy (1)
- Power law and power-law breakdown (1)
- Power-law breakdown (1)
- Propagation modes (1)
- Pure aluminium (1)
- Qquantification and segmentation (1)
- Re-entrant surface feature (1)
- Refractory (1)
- Refractory zirconia (1)
- Residual stress in AM (1)
- Residual stress measurements (1)
- Röntgen-Refraktion (1)
- SIF evaluation (1)
- Scan strategies (1)
- Scan strategy influence (1)
- Scanning electron microscopy (1)
- Scanning electron microscopy (SEM) (1)
- Selective laser melted materials (1)
- Semi-metallic brake-pad material (1)
- Semi-metallic friction material (1)
- Semi-metallic sintered material (1)
- Si network disintegration (1)
- Sintering (1)
- Stainless Steel (1)
- Statistical image analysis (1)
- Statistically relevant volumes (1)
- Steady-state creep (1)
- Stiffness (1)
- Strain-free lattice references (1)
- Strain-free lattice spacing (1)
- Stress balance (1)
- Stress balance condition (1)
- Surface roughness analysis (1)
- Synchrotron Energy Dispersive Diffraction (1)
- Synchrotron X-ray computed tomography (1)
- Synchrotron X-ray diffraction (1)
- Synchrotron X-ray refraction radiography (1)
- Synchrotron computed tomography (1)
- Synchrotron refraction (1)
- Synchrotron tomography (1)
- Tensile testing (1)
- Texture (1)
- Thermally induced microcracking (1)
- Thermally induced porosity (TIP) (1)
- Thermography (1)
- Ti-6Al-4V (1)
- Tiatanium (1)
- Torsional fatigue (1)
- Torsional in situ fatigue testing (1)
- Toughening mechanism (1)
- Toughening mechanisms (1)
- Uniaxial compression tests (1)
- Verbundwerkstoffe (1)
- X-Ray refraction (1)
- X-ray Diffraction (1)
- X-ray analysis (1)
- X-ray and Neutron Diffraction (1)
- X-ray and neutron diffraction (1)
- X-ray synchrotron tomography (1)
- pure aluminum (1)
- subgrain (1)
Organisationseinheit der BAM
- 8 Zerstörungsfreie Prüfung (47)
- 8.5 Röntgenbildgebung (47)
- 9 Komponentensicherheit (14)
- 9.4 Integrität von Schweißverbindungen (13)
- 5 Werkstofftechnik (4)
- 5.1 Mikrostruktur Design und Degradation (2)
- 5.2 Metallische Hochtemperaturwerkstoffe (2)
- 8.0 Abteilungsleitung und andere (2)
- 9.0 Abteilungsleitung und andere (2)
- 9.6 Additive Fertigung metallischer Komponenten (2)
Eingeladener Vortrag
- nein (8)
Layer-by-layer additive manufacturing (AM) by means of laser-powder bed Fusion (L-PBF) offers many prospects regarding the design of lattice structures used, for example, in gas turbines. However, defects such as bulk porosity, Surface roughness, and re-entrant features are exacerbated in nonvertical structures, such as tilted struts. The characterization and quantification of these kinds of
defects are essential for the correct estimation of fracture and fatigue properties.
Herein, cylindrical struts fabricated by L-PBF are investigated by means of X-ray computed tomography (XCT), with the aim of casting light on the dependence of the three kinds of defects (bulk porosity, surface roughness, and re-entrant features) on the build angle. Innovative analysis methods are proposed to correlate shape and position of pores, to determine the angular-resolved Surface roughness, and to quantify the amount of re-entrant surface features, q. A meshing of the XCT surface enables the correlation of q with the classical Surface roughness Pa. This analysis leads to the conclusion that there is a linear correlation between q and Pa. However, it is conjectured that there must be a threshold of surface roughness, below which no re-entrant features can be build.
Metal Additive Manufacturing (AM) technologies such as Laser Powder Bed Fusion (LPBF) are characterized by layer wise construction, which enable advancements of component design, leading to potential efficiency and performance improvements. However, the rapid cooling rates associated with the process consequently leads to the generation of high magnitude residual stresses (RS). Therefore, a deep understanding of the formation of RS, the influence of process parameters on their magnitude and the impact on mechanical performance is crucial for widespread application. The experimental characterization of these RS is essential for safety related engineering application and supporting the development of reliable numerical models. Diffraction-based methods for RS analysis using high energy synchrotron X-rays and neutrons enable non-destructive spatially resolved characterization of both surface and bulk residual stresses in complex components. This presentation will provide an overview of recent research conducted by the BAM at large scale facilities for the characterization of residual stresses in LPBF metallic alloys. Special focus will be given to the challenges posed by textured LPBF materials for the reliable choice of the diffraction elastic constants (DECs), which is crucial to the accurate calculation of the level of RS.
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.
As opposed to reviewing results on experimental determination of residual stress by diffraction, this paper discusses the open issues when dealing with residual stress determination in additive manufactured parts, in particular those manufactured with laser powder bed fusion techniques. Three points are addressed in detail: (a) the proper determination of the strain-free reference d0, (b) the problem of the determination of the principal axes, and (c) the use of the correct diffraction elastic constants. It is shown that all methods to determine the strain-free reference d0 suffer from caveats, and care must be taken in evaluating the most suitable for the problem being tackled. In addition, it is shown that, in some systems, the principal axes do correspond to the geometrical axes of the specimen, but this needs to be systematically checked, especially in the case of uni- or bidirectional hatching strategies. Finally, the need to experimentally determine the proper diffraction elastic constants is underlined, especially in the case of strongly textured specimens, which again depends on the deposition strategy.
About the Role of Interfaces on the Fatigue Crack Propagation in Laminated Metallic Composites
(2021)
The influence of gradients in hardness and elastic properties at interfaces of dissimilar materials in laminated metallic composites (LMCs) on fatigue crack propagation is investigated experimentally for three different LMC systems: Al/Al-LMCs with dissimilar yield stress and Al/Steel-LMCs as well as Al/Ti/Steel-LMCs with dissimilar yield stress and Young’s modulus, respectively. The damage tolerant fatigue behavior in Al/Al-LMCs with an alternating layer structure is enhanced significantly compared to constituent monolithic materials. The prevalent toughening mechanisms at the interfaces are identified by microscopical methods and synchrotron X-ray computed tomography. For the soft/hard transition, crack deflection mechanisms at the vicinity of the interface are observed, whereas crack bifurcation mechanisms can be seen for the hard/soft transition. The crack propagation in Al/Steel-LMCs was studied conducting in-situ scanning electron microscope (SEM) experiments in the respective low cycle fatigue (LCF) and high cycle fatigue (HCF) regimes of the laminate. The enhanced resistance against crack propagation in the LCF regime is attributed to the prevalent stress redistribution, crack deflection, and crack bridging mechanisms. The fatigue properties of different Al/Ti/Steel-LMC systems show the potential of LMCs in terms of an appropriate selection of constituents in combination with an optimized architecture. The results are also discussed under the aspect of tailored lightweight applications subjected to cyclic loading.
Die Brechung von Röntgenstrahlen (Röntgenrefraktion) an Grenzflächen zwischen Materialien unterschiedlicher Dichte ist analog zur Ablenk-ung von sichtbarem Licht an z.B. Glasoberflächen. Es gibt jedoch zwei wesentliche Unterschiede:
a) konvexe Grenzflächen verursachen Divergenz (d.h. der Brechungsindex n ist kleiner als 1), und
b) die Ablenkungswinkel sind sehr klein, und reichen von einigen Bogensekunden bis zu einigen Bogenminuten (d.h. n ist nahe bei 1);
Wie auch bei sichtbarem Licht ist die Ablenkungsrichtung der Röntgenstrahlen abhängig von der Orientierung der durchstrahlten Grenzfläche. Aufgrund dieser Eigenschaften eignen sich Röntgenrefraktionsmethoden hervorragend für:
a) die Erkennung und Quantifizierung von Defekten wie Poren und Mikrorissen und
b) die Bewertung von Porosität und Partikeleigenschaften wie Orientierung, Größe und räumliche Verteilung.
Wir zeigen die Anwendung der Röntgenrefraktionsradiographie (2,5D Technik) und der -tomographie (3D Technik) für die Untersuchung verschiedener Probleme in der Werkstoffwissenschaft und -technologie:
a) Sintern von SiC-Grünkörpern
b) Porositätsanalyse in Dieselpartikelfiltersilikaten
c) Faser-Matrix-Haftung in Metall- und Polymermatrixverbundwerkstoffen
d) Mikrorissbildung in Glaskeramik.
Wir zeigen, dass der Einsatz von Röntgenrefraktionsmethoden quantitative Ergebnisse liefert, die direkt als Parameter in Werkstoffmodellen verwendet werden können.
Connecting Diffraction-Based Strain with Macroscopic Stresses in Laser Powder Bed Fused Ti-6Al-4V
(2020)
The laser powder bed fusion (LPBF) production process often results in large residual stress (RS) in the parts. Nondestructive techniques to determine RS are badly needed. However, a reliable quantification of macro-RS (i.e., stress at the component level) by means of diffraction-based techniques is still a great challenge, because the link between diffraction-based strain and macro-RS is not trivial. In this study, we experimentally determine (by means of in-situ synchrotron radiation diffraction) this link for LPBF Ti-6Al-4V. We compare our results with commonly used models to determine the so-called diffraction elastic constants (DECs). We show that LPBF materials possess different DECs than wrought alloys, simply because their microstructural and mechanical properties are different. We also show that the existing models can be used to calculate DECs only if high accuracy of the RS values is not required. If the peculiarities of the microstructure have to be taken into account (as is the case of additively manufactured materials), a radically new approach is desirable.
Laser based powder bed fusion additive manufacturing offers the flexibility to incorporate standard and userdefined scan strategies in a layer or in between the layers for the customized fabrication of metallic components. In the present study, four different scan strategies and their impact on the development of microstructure, texture, and residual stresses in laser powder bed fusion additive manufacturing of a nickel-based superalloy Inconel 718 was investigated. Light microscopy, scanning electron microscopy combined with electron backscatter diffraction, and neutron diffraction were used as the characterization tools. Strong textures with epitaxially grown columnar grains were observed along the build direction for the two individual scan strategies. Patterns depicting the respective scan strategies were visible in the build plane, which dictated the microstructure development in the other planes. An alternating strategy combining the individual strategies in the successive layers and a 67◦ rotational strategy weakened the texture by forming finer microstructural features. Von Mises equivalent stress plots revealed lower stress values and gradients, which translates as lower distortions for the alternating and rotational strategies. Overall results confirmed the scope for manipulating the microstructure, texture, and residual stresses during laser powder bed fusion additive manufacturing by effectively controlling the scan strategies.
Laser-based additive manufacturing methods allow the production of complex metal structures within a single manufacturing step. However, the localized heat input and the layer-wise manufacturing manner give rise to large thermal gradients. Therefore, large internal stress (IS) during the process (and consequently residual stress (RS) at the end of production) is generated within the parts. This IS or RS can either lead to distortion or cracking during fabrication or in-service part failure, respectively. With this in view, the knowledge on the magnitude and spatial distribution of RS is important to develop strategies for its mitigation. Specifically, diffraction-based methods allow the spatial resolved determination of RS in a non-destructive fashion. In this review, common diffraction-based methods to determine RS in laser-based additive manufactured parts are presented. In fact, the unique microstructures and textures associated to laser-based additive manufacturing processes pose metrological challenges. Based on the literature review, it is recommended to (a) use mechanically relaxed samples measured in several orientations as appropriate strain-free lattice spacing, instead of powder, (b) consider that an appropriate grain-interaction model to calculate diffraction-elastic constants is both material- and texture-dependent and may differ from the conventionally manufactured variant. Further metrological challenges are critically reviewed and future demands in this research field are discussed.
The electron backscatter diffraction (EBSD) technique is used to investigate the dislocation structures formed after steady-state creep deformation of an Al-3.85%Mg alloy. This material is crept at two different stress levels, corresponding to the so-called power-law and power-law breakdown regimes. The results show that, regardless of the creep stress level, the strain tends to localize, leading to the formation of intragranular bands. The thickness of such bands is larger when the material is tested at loads corresponding to the power-law breakdown. This suggests enhanced diffusion by dislocation pipes.