| 1. |
- Müller, M., et al.
(författare)
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Multimaterial direct energy deposition: From three-dimensionally graded components to rapid alloy development for advanced materials
- 2023
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Ingår i: Journal of laser applications. - : AIP Publishing. - 1042-346X .- 1938-1387. ; 35:1
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Tidskriftsartikel (refereegranskat)abstract
- Laser-based direct energy deposition (L-DED) with blown powder enables the simultaneous or sequential processing of different powder materials within one component and, thus, offers the possibility of additive multimaterial manufacturing. Therefore, the process allows a spatially resolved material allocation and fabrication of sharp or even graded material transitions. Within this contribution, the latest results from two major research fields in multimaterial L-DED—(I) automation and (II) rapid alloy development of high entropy alloys (HEAs) by in situ synthesis—shall be presented. First, an automated multimaterial deposition process was developed, which enables the automated manufacturing of three-dimensionally graded specimens. For this, a characterization of the deposition system regarding powder feeding dynamics and resulting powder mixtures in the process zone was conducted. The obtained system characteristics were used to achieve a three-dimensional deposition of specified powder mixtures. The fabricated specimens were analyzed by energy-dispersive x-ray spectroscopy, scanning electron microscopy, and micro hardness measurement. The research demonstrates the increasing readiness of L-DED for the fabrication of multimaterial components. Second, the latest results from rapid alloy development for HEAs by DED are presented. By the simultaneous usage of up to four powder feeders, a vast range of alloy compositions within the Al–Ti–Co–Cr–Fe–Ni HEA system was investigated. For this, tailored measurement systems such as an in-house developed powder sensor were beneficially used. The study shows the influence of a variation of Al on the phase formation and resulting mechanical properties and demonstrates the potential of L-DED for reducing development times for new alloys.
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| 2. |
- Riede, M., et al.
(författare)
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Material characterization of AISI 316L flexure pivot bearings fabricated by additive manufacturing
- 2019
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 12:15
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Tidskriftsartikel (refereegranskat)abstract
- Recently, additive manufacturing (AM) by laser metal deposition (LMD) has become a key technology for fabricating highly complex parts without any support structures. Compared to the well-known powder bed fusion process, LMD enhances manufacturing possibilities to overcome AM-specific challenges such as process inherent porosity, minor build rates, and limited part size. Moreover, the advantages aforementioned combined with conventional machining enable novel manufacturing approaches in various fields of applications. Within this contribution, the additive manufacturing of filigree flexure pivots using 316L-Si by means of LMD with powder is presented. Frictionless flexure pivot bearings are used in space mechanisms that require high reliability, accuracy, and technical cleanliness. As a contribution to part qualification, the manufacturing process, powder material, and fabricated specimens were investigated in a comprehensive manner. Due to its major impact on the process, the chemical powder composition was characterized in detail by energy dispersive X-ray spectroscopy (EDX) and inductively coupled plasma optical emission spectrometry (ICP-OES). Moreover, a profound characterization of the powder morphology and flowability was carried out using scanning electron microscopy (SEM) and novel rheological investigation techniques. Furthermore, quantitative image analysis, mechanical testing, laser scanning microscopy, and 3D shape measurement of manufactured specimens were conducted. As a result, the gained knowledge was applied for the AM-specific redesign of the flexure pivot. Finally, a qualified flexure pivot has been manufactured in a hybrid manner to subsequently ensure its long-term durability in a lifetime test bench.
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| 3. |
- Brueckner, Frank, et al.
(författare)
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Phenomena in multi-material fabrication using laser metal deposition
- 2019
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Ingår i: Laser 3D Manufacturing VI. - : SPIE - The International Society for Optics and Photonics.
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Konferensbidrag (refereegranskat)abstract
- Additive Manufacturing (AM) processes as Laser Metal Deposition (LMD) addresses various benefits such as the build-up of complex shaped parts, the possibility of functional integration, reduced lead times or the use of difficult machinable materials compared to conventional manufacturing possibilities. Beside mentioned advantages, the use of more than one material in a component strongly increases the field of applications. Similar to structures in nature, multi-material arrangements can be realized by (I) sharp intersections from one material to the other (e. g. in the case of a thin corrosion protection), (II) graded structures enabling smoother material transitions (e. g. dissimilar materials joined together without defects), (III) composite structures with enclosed particles in a matrix material as well as by (IV) in-situ alloying of different material compositions. Due to varying material properties (e.g. thermo-physical, mechanical, optical), the combination of materials often requires a detailed investigation of occurring process phenomena and well-chosen modifications of the process regimes. Within this paper, (a) the right material feeding as well as powder interaction between various materials in Laser Metal Deposition, (b) the suitable selection of laser wavelengths for different materials, (c) process window adjustments by means of additional sensor equipment, (d) limitations of material combinations as well as (e) results and material characterization of multi-material parts are discussed. Phenomena are discussed by means of exemplary industrial applications, e.g. from the jet engine or medical business.
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| 4. |
- Haack, M, et al.
(författare)
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Investigation on the formation of grain boundary serrations in additively manufactured superalloy Haynes 230
- 2020
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Ingår i: Journal of laser applications. - : American Institute of Physics (AIP). - 1042-346X .- 1938-1387. ; 32:3
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Tidskriftsartikel (refereegranskat)abstract
- Solid-solution and carbide-strengthened superalloys such as Haynes 230 are the materials of choice for the hot-section components of gas turbines, e.g., combustion cans and transition ducts. Under severe thermal conditions, to which those parts are exposed, creep strength is a crucial property of the related materials during their lifetime. Recently, the introduction of serrated grain boundaries in Haynes 230 has been intensively studied [J. G. Yoon, H. W. Jeong, Y. S. Yoo, and H. U. Hong, "Influence of initial microstructure on creep deformation behaviors and fracture characteristics of Haynes 230 superalloy at 900 °C,"Mater. Charact. 101, 49-57 (2015); L. Jiang, R. Hu, H. Kou, J. Li, G. Bai, and H. Fu, "The effect of M23C6 carbides on the formation of grain boundary serrations in a wrought Ni-based superalloy,"Mater. Sci. Eng. A 536, 37-44 (2012)], and nearly a triplication of the time to creep failure at high temperature and low stress conditions has been observed [J. G. Yoon, H. W. Jeong, Y. S. Yoo, and H. U. Hong, "Influence of initial microstructure on creep deformation behaviors and fracture characteristics of Haynes 230 superalloy at 900 °C,"Mater. Charact. 101, 49-57 (2015)]. The aim of this paper is to achieve serrated grain boundaries in Haynes 230 through an appropriate thermal process chain including the intrinsic heat treatments of the laser metal deposition (LMD) process, subsequent hot isostatic pressing and suitable heat treatments. The formation of serrations is a relatively new technique for Haynes 230 (i.e., first paper in 2012), and similar alloys and thus serrations have only been introduced in conventionally cast or wrought alloys so far. Optical and scanning electron microscopies are employed in this work to investigate the created microstructures, whose grain and carbide structure is finer compared to the recently studied conventionally processed alloys. Within the LMD samples, serrations were already found on almost all of the observed grain boundaries even in the as-build condition. This result was rather unexpected, as literature reports slow-cooling to be responsible for the formation of serrations, while fast-cooling is prevalent in LMD. Some authors associated the formation of serrations to the precipitation of M23C6-carbides at the grain boundaries during slow cooling conditions [L. Jiang, R. Hu, H. Kou, J. Li, G. Bai, and H. Fu, "The effect of M23C6 carbides on the formation of grain boundary serrations in a wrought Ni-based superalloy,"Mater. Sci. Eng. A 536, 37-44 (2012)]. The lower density of carbides along grain boundaries in the as-build state, however, makes this mechanism seem unlikely. Other authors attributed the emergence of serrations to a phenomenon similar to the faceting mechanism [J. G. Yoon, H. W. Jeong, Y. S. Yoo, and H. U. Hong, "Influence of initial microstructure on creep deformation behaviors and fracture characteristics of Haynes 230 superalloy at 900 °C,"Mater. Charact. 101, 49-57 (2015)]. It can be said that no uniform theory for the emergence of grain boundary serrations exists as of now. The electron backscatter diffraction (EBSD) investigations performed in this work indicated a correlation between serrated grain boundary segments, the {111}-directions of the crystal lattice, and possibly segregations along dendritic subgrain boundaries for a two-dimensional case. Serial sectioning in combination with EBSD analysis confirmed an agreement between the three-dimensional orientation of serrated grain boundary segments and the {111}-direction of adjacent grains. Hence, a mechanism different from the ones described in previous works is proposed for the formation of grain boundary serrations in the additively manufactured Haynes 230 alloy.
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| 5. |
- Kolsch, N., et al.
(författare)
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Novel local shielding approach for the laser welding based additive manufacturing of large structural space components from titanium
- 2020
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Ingår i: Journal of laser applications. - : American Institute of Physics (AIP). - 1042-346X .- 1938-1387. ; 32:2
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Tidskriftsartikel (refereegranskat)abstract
- The Advanced Telescope for High-ENergy Astrophysics (ATHENA) will observe “the hot and energetic universe,” which was determined as one of the most urgent scientific topics for a major future space mission by The European Space Agency (ESA). One of its three main components is the optical bench, a monolithic titanium structure that accommodates 678 mirror modules and keeps them accurately aligned. The immense but slender structure in the range of 2.5–3 m diameter at a height of 300 mm proves a challenge to manufacturing. A hybrid robot cell is developed using additive buildup via laser welding, combined with high-performance machining and the state of the art process and metrology monitoring and control. The present work focuses on the shielding of the laser induced melt pool, a key concern when processing titanium. The sensitive metal with unusual low heat conductivity requires a large area of high purity atmosphere to prevent embrittlement. However, the large hybrid system prohibits the use of a sealed enclosure, and therefore, a local shielding system is developed for the challenging case of the ATHENA optical bench’s hollow-chamber design. Since the present thin wall design poses a worst-case scenario in terms of heat dissipation and shielding flow for the shielding system, its effectiveness here can be applied to most other geometries enabling the flexibility for lot size one. The key features of the novel approach are the prevention of turbulence while keeping operation economical despite the large shielding area. The first is achieved by means of an integrated honeycomb screen and the latter by employing a layered flow with a higher velocity outer curtain and an air deflecting coflow. This system was numerically optimized, tested, and effectiveness proven by means of visual inspection, microstructural analysis, and measurement of material properties.
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| 6. |
- Moritz, J., et al.
(författare)
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Functional integration approaches via laser powder bed processing
- 2019
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 31:2
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing design rules are different from those of conventional fabrication techniques. These allow geometries that would not be possible to achieve otherwise. One example of application is the integration of functional parts as part of the manufacturing process. Conceivable applications range from mechanical functions like integration of moving parts or thermodynamic functions, for example, cooling channels or incorporation of electric circuits for electrical functionalization [J. Glasschroeder, E. Prager, and M. F. Zaeh, Rapid Prototyping J. 21, 207–215 (2015)]. Nevertheless, the potential of functional integration using powder-bed processes is far from being exhausted. The present approach addresses the generation of inner cavities and internal structures of titanium-based parts or components by the use of selective laser melting. This paper focusses on the investigation of voids and cavities regarding their capabilities to add new functions to the material. To this end, comprehensive characterization is performed using destructive as well as nondestructive testing methods. These include 3D scanning, computed tomography, and surface roughness measurements as well as microscopic analysis. Voids and cavities were filled with different thermoplastic materials, followed by the qualitative assessment of the mold filling and resulting material properties. Finally, applications are derived and evaluated with respect to the field of lightweight design or damping structures.
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| 7. |
- Mueller, M., et al.
(författare)
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Influence of process parameter variation on the microstructure of thin walls made of Inconel 718 deposited via laser-based directed energy deposition with blown powder
- 2023
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Ingår i: Journal of Materials Science. - : Springer Nature. - 0022-2461 .- 1573-4803. ; 58:27, s. 11310-11326
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Tidskriftsartikel (refereegranskat)abstract
- In laser-based directed energy deposition (L-DED) of Inconel 718 the microstructure of the fabricated components strongly depends on the applied process parameters and the resulting solidification conditions. Numerous studies have shown that the process parameters deposition speed and laser power have a major influences on microstructural properties, such as dendrite morphology and segregation behavior. This study investigates how changes in these process parameters affect the microstructure and hardness when the line mass, and thus the resulting layer height, are kept constant. This enables the microstructural comparison of geometrically similar specimens that were manufactured with the same number of layers but severely different process parameters. This approach yields the benefit of almost identical geometrical boundary conditions, such as the layer-specific build-height and heat conducting cross section, for all specimens. For microstructural analysis scanning electron microscopy and energy dispersive X-ray spectroscopy were applied and the results evaluated in a quantitative manner. The microstructural features primary dendritic arm spacing, fraction and morphology of precipitated Laves phase as well as the spatially resolved chemical composition were measured along the build-up direction. The occurring cooling rates were calculated based on the primary dendritic arm spacing using semi-empirical models. Three different models used by others researchers were applied and evaluated with respect to their applicability for L-DED. Finally, microhardness measurements were performed for a baseline evaluation of the influence on the materials’ mechanical properties.
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| 8. |
- Polenz, S., et al.
(författare)
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Wavelength dependent laser material processing of ceramic materials
- 2019
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 31:2
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Tidskriftsartikel (refereegranskat)abstract
- In the future, ceramic materials will find even more applications in aerospace, energy, and drive technology. Reasons for this are the comparatively low density and good long-term stability at high temperatures for applications for components exposed to high temperatures, e.g., of engines. By using increasing combustion temperatures through the use of ceramics increases the efficiency of modern drive systems [Ohnabe, Masaki, Onozuka, Miyahara, and Sasa, Compos. Part A Appl. Sci. Manuf. 30, 489–496 (1999)]. Despite the high interest of the aviation industry to increase the use of ceramic materials, the time- and energy-consuming classical production of these materials and the concomitant limiting factors in terms of shape and size are still a drawback [Krenkel, Ceramic Matrix Composites Fiber Reinforced Ceramics and their Applications (WIY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2008)]. This paper follows a new approach to producing ceramic matrix composites (CMCs). The laser material deposition (LMD) and selective laser melting techniques were used to investigate the coupling of different laser wavelengths into ceramic materials. By combining different energy sources and utilizing wavelength-dependent energy coupling, the additive manufacturing application of ceramic materials to metallic substrates was tested. With the knowledge gained from wavelength-dependent energy coupling, the potential for the production of CMCs should be demonstrated by means of LMD
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| 9. |
- Schneider, J., et al.
(författare)
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Additive manufacturing of a metallic optical bench—process development, material qualification and demonstration
- 2023
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Ingår i: CEAS Space Journal. - : Springer Nature. - 1868-2502 .- 1868-2510. ; 15:1, s. 55-68
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Tidskriftsartikel (refereegranskat)abstract
- With the large-class science mission ATHENA, the European Space Agency (ESA) aims at exploring the hot and energetic universe with advanced X-Ray technology. As a central component of the telescope, hundreds of silicon pore optic (SPO) modules will be assembled in an optical bench with a diameter of about 2.5 m. Several approaches are under investigation for the manufacturing of this supporting structure, and for handling the challenging constraints with respect to size, geometry and material. In cooperation with ESA, the Fraunhofer IWS is currently investigating the manufacturing of the optical bench made from Ti-6Al-4 V by means of Additive Manufacturing using Laser Metal Deposition (LMD) followed by subtractive finishing. Several development steps have been covered in a holistic manner starting with the system engineering of the production site. The main focus of the activity was on the process development for the Additive Manufacturing as well as the subtractive finishing. Furthermore, the properties of the produced material were also investigated. Within the scope of this publication, a general overview is given about the project related developments, achievements, and flanking activities for solving various challenges. The suitability of the developed technologies and workflows are now being evaluated through the manufacture of a representative, large-scale breadboard.
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| 10. |
- Schneider, J., et al.
(författare)
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Advanced manufacturing approach via the combination of selective laser melting and laser metal deposition
- 2019
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 31:2
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing processes are frequently discussed in a competitive manner instead of being considered synergetically. This is particularly unfavorable since advanced machining processes in combination with additive manufacturing can be brought to the point that the results could not be achieved with the individual constituent processes in isolation [K. Gupta, R. F. Laubscher, and N. K. Jain, Hybrid Machining Processes—Perspectives on Machining and Finishing (Springer, New York, 2016), p. 68]. On that basis, boundary conditions from selective laser melting (SLM) and laser metal deposition (LMD) are considered in mutual contemplation [A. Seidel et al., in Proceedings of 36th International Congress on Applications of Laser & Electro-Optics, Atlanta, GA, 22–26 October 2017(Fraunhofer IWS, Dresden, 2017), pp. 6–8]. The present approach interlinks the enormous geometrical freedom of powder-bed processing with the scalability of the LMD process. To demonstrate the potential of this approach, two different strategies are pursued. Firstly, a hollow structure demonstrator is manufactured layer wise via LMD with powder and subsequently joined with geometrically complex elements produced via SLM. Afterward, possibilities for a microstructural tailoring within the joining zone via the modification of process parameters are theoretically and practically discussed. Therefore, hybrid sample materials have been manufactured and interface areas are subjected to microstructural analysis and hardness tests. The feasibility of the introduced approach has been demonstrated by both fields of observation. The process combination illustrates a comprehensive way of transferring the high geometric freedom of powder-bed processing to the LMD process. The adjustment of process parameters between both techniques seems to be one promising way for an alignment on a microstructural and mechanical scale.
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| 11. |
- Seidel, A., et al.
(författare)
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Novel Approach for Suppressing of Hot Cracking Via Magneto-fluid Dynamic Modification of the Laser-Induced Marangoni Convection
- 2020
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Ingår i: Superalloys 2020. - Cham : Springer. ; , s. 972-981
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Konferensbidrag (refereegranskat)abstract
- The occurrence of hot cracking is a significant problem during welding processing of highly heat resistant nickel-base superalloys. Hot cracking is most often associated with liquid films that are present along grain boundaries in the fusion zone and the partially melted zone and can only be suppressed to a very limited extent. The latter is the case despite remarkable studies and analyses of the phenomenon. In this work, a new approach is presented which intends the suppression of hot cracking by using a non-contact method to influence the solidification process. It is based on the idea of a modification of the laser-induced melt pool convection (Marangoni convection) using customized magnetic fields. As a consequence, special system technology is derived on the basis of theoretical considerations while the effectiveness to be expected is estimated on the basis of the information available in the literature. The implemented system technology is described in detail. The focus of this description is on the magnetic flux density distribution or the temporal change, respectively, with respect to the laser-induced melt pool. The presented experimental results provide a comparative view of samples welded with and without the influence of a magnetic field while a significant difference is evident. The outlook of this work describes key data of a test stand specially developed for examining the identified topic in in-depth investigations.
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| 12. |
- Seidel, A., et al.
(författare)
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Surface modification of additively manufactured gamma titanium aluminide hardware
- 2019
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 31:2
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Tidskriftsartikel (refereegranskat)abstract
- A major part of additive manufacturing focuses on the fabrication of metallic parts in different fields of applications. Examples include components for jet engines and turbines and also implants in the medical sector. Titanium alloys represent a material group which is used cross-sectoral in a large number of applications. The present paper addresses the titanium aluminides in particular. These materials have a low density in combination with a comparatively high-temperature resistance [G. Sauthoff, Intermetallics (Wiley-VCH Verlag, Weinheim, Germany, 2008)]. Nevertheless, the laser material processing is rather challenging because of their distinct tendency to lamellar interface cracking. This requires tailored processing strategies and equipment [C. Leyens et al., in Ti-2015: The 13th World Conference on Titanium, Symposium 5. Intermetallics and MMCs, 16–20 August 2015, San Diego, CA (The Minerals, Metals & Materials Society, Pittsburgh, PA, 2016)]. This work focusses on tailored processing of titanium aluminides with focus on the process-dependent surface characteristics. This includes the as-built status for powder bed processing and direct laser metal deposition but also the surface modification via post and/or advanced machining. Finally, comprehensive characterization is performed using destructive as well as nondestructive testing methods. The latter includes 3D scanning, computed tomography, microscopic analysis, and, in particular, surface roughness measurements.
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