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Eingeladener Vortrag
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The Binder Jetting BJ process is one of the most versatile additive manufacturing technologies in use. In this process a binder is locally jetted into a powder bed for the consolidation of a 3D structure, layer by layer. Basically, all materials which can be provided as a flowable powder and, thus, spreadable to a thin layer, can be processed. Metals, ceramics and polymers are processable, but also materials from nature, such as sand, wood sawdust and insect frass. Moreover, the BJ technology is adapted to large building volumes of some cubic meters easily. Besides these striking advantages, the manufacture of ceramic parts by BJ is still challenging, as the packing density of the powder bed is generally too low and the particle size of a flowable powder too large for a successful densification of printed parts in a subsequent sintering step to an advanced ceramic product. After an introduction of binder jetting in general and highlighting some examples, strategies for obtaining dense ceramic parts by BJ will be introduced.
The presentation demonstrates an application of multi-scale optical imaging methods such as spectroscopic imaging ellipsometry and white light interference microscopy for the investigation of wide-bandgap semiconductors for power electronics. The capabilities of these methods for the development of new reference calibration samples for scanning microwave microscopes (SMM) and conductive atomic force microscopes (C AFM) are discussed.
The variability and heterogeneity in their structural composition is significant for nearly all synthetic and natural polymers. Beside molar mass also functionality type distribution, copolymer composition distribution and architectural features are responsible for changing the material properties.
A wide range of analytical techniques are available to get insight into these parameters. However, in most cases it is essential to combine different sophisticated techniques to get closer to actual structures and to avoid statistical averages.
Different liquid chromatographic separation modes and their coupling in a two-dimensional way (SEC, LCCC, HILIC, 2D-LC) in combination with suitable detection techniques (e.g. UV, RI, LS, IR, MALDI/ESI-MS) as well as techniques like BET, DCS, SEM/TEM were applied to make structural features visible.
A few aspects are discussed for structural different polylactides from various synthesis routes and their behavior in LC-MS.
Manipulating ceramic powder compacts and ceramic suspensions (slurries) within their volume with light requires a minimum transparency of the materials. Compared to polymers and metals, ceramic materials are unique as they offer a wide electronic band gap and thus a wide optical window of transparency. The optical window typically ranges from below 0.3 µm up to 5µm wavelength. Hence, to penetrate with laser light into the volume of a ceramic powder compound its light scattering properties need to be investigated and tailored. In the present study we introduce the physical background and material development strategies to apply two-photon-polymerization (2PP) for the additive manufacture of filigree structures within the volume of ceramic slurries.
Preliminary results of an interlaboratory comparison on microplastics organised by plasticsfate
(2023)
Microplastics are everywhere in the environment, but analytics is challenging. Since harmonisation is missing as well es suitable reference materials, BAM did under th umbrella of VAMAS funded by the EU Horizon 2020 project PlasticsFate a ILC for microplastic detection methods. Methods adressed were IR, Raman, Py-GC/MS and TED-GC/MS. The talk gives a first presentation and evaluation on the results.
The presentation will start with an overview of ceramic additive manufacturing (AM) technologies and will discuss the potential of AM in the field of bioceramics.
The presentation will then focus on two possible use cases of binder jetting technologies.
In the first example, standard powder-based binder jetting is used to manufacture a porous implant design for large scale bone defects. The related challenges in the process chain will be discussed, from powder synthesis to sintering and characterization of the printed part.
In the second example, the LSD-print slurry-based binder jetting technology is presented as a possibility to adapt powder-bed AM to produce dense ceramic parts. The use case will focus on an application in the field of dental ceramics, specifically for the manufacturing of patient individualized single tooth restorations (veneers, crowns) with a high throughput process chain.
The variability and heterogeneity in their structural composition is significant for nearly all synthetic and natural polymers. Beside molar mass also functionality type distribution, copolymer composition distribution and architectural features are responsible for changing the material properties.
A wide range of analytical techniques are available to get insight into these parameters. However, in most cases it is essential to combine different sophisticated techniques to get closer to actual structures and to avoid statistical averages.
Different liquid chromatographic separation modes and their coupling in a two-dimensional way (SEC, LCCC, HILIC, 2D-LC) in combination with suitable detection techniques (e.g. UV, RI, LS, IR, MALDI/ESI-MS) as well as techniques like BET, DCS, SEM/TEM were applied to make structural features visible.
A few aspects are discussed for structural different polylactides from various synthesis routes and their behavior in LC-MS. Moreover, some analytical results for technical lignins valorized by mechanochemical treatment or modified by functional polymers are presented.
Der Vortrag gibt einen Überblick über die vielfältigen Möglichkeiten der Oberflächenfunktionalisierung mittels Mikro- und Nanostrukturierung durch Ultrakurzpuls-Lasermaterialbeabeitung. Dies schließt eine Diskussion des Phänomens der Laser-induzierten periodischen Oberflächenstrukturen (LIPSS, engl.: Laser-induced Periodic Surface Structures, Ripples), sowie deren Klassifikation und Bildungsmechanismen mit ein. Ein Schwerpunkt der Präsentation liegt auf der Diskussion verschiedener Anwendungsmöglichkeiten der LIPSS in Bereichen der Optik, Fluidik, Tribologie und Medizin, sowie auf einem Ausblick auf die industrielle Skalierbarkeit der LIPSS-Technologie.
Die additive Fertigung mittels Schweißverfahren bietet große ökonomische Vorteile für eine ressourceneffiziente Bauteilherstellung. Offene Fragen bezüglich Homogenität, Anisotropie der Schweißgefüge und den damit verbundenen Bauteileigenschaften stehen einer wirtschaftlichen Verarbeitung oftmals im Wege. Finale Bauteilgeometrie und Oberflächengüte erfordern meist komplementäre subtraktive Fertigungsschritte. Werkstoffe für hochbelastbare Komponenten sind oftmals schwer spanbar. In einem Vorhaben der BAM und des ISAF wurde untersucht, wie die Modifikation der AM-Schweißzusätze und das ultraschallunterstützte Fräsen (US) die Zerspanungssituation verbessern. Der vorliegende Artikel stellt wesentliche Zusammenhänge zwischen Legierung, Gefüge und Zerspanung zweier schwer spanbarer Hochleistungslegierungen (FeNi und CoCr) dar. Großes Potenzial zeigte neben dem US die Modifikation mit Zr und Hf bei Zulegierung in das Schweißgut mittels Beschichtung von Massivdrähten bzw. Herstellung von Fülldrähten.
Unlike conventional alloys, which typically consist of one main element, high-entropy alloys (HEAs) contain five or more principal elements, which broaden chemical complexity and with it a realm of synergistic mechanisms. The AlMo0.5NbTa0.5TiZr HEA initiated a subclass of Al-containing refractory (r)HEAs that has recently drawn attention [2]. The alloy has a superalloy-resembling B2/bcc nanostructure, which inspired its name refractory high entropy superalloy (RSA). With high-temperature (HT) compressive strengths beyond conventional Ni-based superalloys, this nanostructure could be used for improved HT structural applications. However, in the application-relevant HT regime the Al-Zr-rich B2 phase decomposes to form a hexagonal Al-Zr-based intermetallic (Al4-xZr5; x: 0..1) [3,4]. This work explores the fascinating yet fatal micromechanisms associated to this phase transformation, in the context of creep, annealing and oxidation experiments performed between 800 and 1200 °C.
The material was produced by arc-melting and heat treatment in argon, which lead to grain boundaries decorated with up to 7%. Interrupted constant-load creep tests were performed under vacuum (at 10-4 Pa), at 900–1100 °C with external tensile stresses of 30–120 MPa. Oxidation experiments were separately conducted for 24 hours at 800 and 1000 °C in both dry (21% O2 + 79% N2) and humid (8% O2 + 74% N2 + 18% H2O) air. After the experiments, the samples were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy to reveal degradation mechanisms. Crystallographic texture, orientation relationships and stabilization of an oxygen-containing iso structure (Al4-xZr5(Ox-y); y: 0..x) of the Al-Zr-rich intermetallic are found and discussed.
Im Rahmen des Vortrags wurden die Ergebnisse und die Methodik zur Erhebung von Forschungsbedarfen und Fähigkeitslücken bei den Behörden und Organisationen mit Sicherheitsaufgaben, welche im Rahmen des Projektes InnoBOSK durchgeführt wurden, vorgestellt. Den Schwerpunkt bildete dabei die Umsetzung der Workshops gemeinsam mit den Einsatzkräften und die Umsetzung der problemorientierten Erhebungsmethodik.
Microplastic reference material is required for validation and harmonization purposes. This includes the analysis of the pure polymer particles and the validation of the respective measurement methods. In addition, there is the harmonization of different laboratories. On the other hand, sample preparation methods must be validated and harmonized with regard to their recovery and subsequent analysis in the respective matrices. For this purpose, we produce reference material candidates in the form of tablets with different mass fractions and particle numbers of polyethelene terephthalate. In the presentation first measurement results by µ-Raman, µ-FTIR, pyrolysis-GC-MS and TED-GC/MS will be presented.
The presentation gives an overview of BAM's activities on processing influences and application properties of MPEAs in the form of joined and machined high and medium entropy alloys (CoCrFeMnNi and CoCrNi). In the case of welding, the focus is on defect-free welded joints with sufficient mechanical properties. In the case of machining, the focus is on the possible influence on the surface quality of the materials through adequate milling parameters. In addition, the hydrogen absorption and diffusion properties as well as the electrochemical corrosion behavior are fundamentally examined.
Since microplastics (MPs) can be found everywhere and are becoming a problem of high concern, it is necessary to understand their physico-chemical properties. To obtain reliable analytical data a set of validated methods for sampling, sample preparation, detection, and data evaluation are needed.
To meet these needs an interlaboratory comparison (ILC) with 84 participants worldwide has been organized under the international pre-standardisation platform VAMAS (www.vamas.org/twa45/) as Project 2 “Development of standardized methodologies for characterisation of microplastics with microscopy and spectroscopy methods” within the Technical Working Area TWA 45 “Micro and Nano Plastics in the Environment”. In this ILC thermo-analytical methods (Py-GC/MS and TED-GC/MS) and vibrational methods (µ-Raman and µ-FTIR) have been tested and compared by providing a set of microplastic representative test materials and measurement protocols developed at BAM. The defined measurands were: particle number concentration, particle size distribution (PSD), and polymer identity and mass content. To increase the statistical quality, 6 samples were shipped together with blank samples. Hence, the ILC provides information on precision and accuracy of the results obtained with different methods as well as strengths and limitations of the proposed protocols.
Motivated by the aim of developing an additive manufacturing (AM) technology easily integrated in the process chains of the ceramic industry, the LSD-print technology was conceived as a slurry-based variation of binder jetting (BJ).
BJ and other powder bed technologies (such as powder bed fusion) are amongst the most successful AM techniques, especially for metals and polymers, thanks to their high productivity and scalability. The possibility to use commercially available feedstocks (in the form of powders or granules) makes BJ also attractive for ceramic materials. The application of these techniques to most advanced ceramics has however been difficult so far, because of the limitations in depositing homogeneous layers with fine, typically poorly flowable powders.
In this context, the "layerwise slurry deposition" (LSD) was proposed at TU Clausthal (Germany) as a slurry-based deposition of ceramic layers by means of a doctor blade. Combined with layer-by-layer laser sintering of the material, the LSD process was originally demonstrated for the rapid prototyping of silicate ceramics. Due to the difficulties in controlling the microstructure and the defect formation in laser-sintered technical ceramics, the LSD process was later combined with inkjet printing in the LSD-print technology, which has been further developed at BAM (Germany) in the past decade.
The LSD-print technology combines the high speed of inkjet printing, typical of BJ, with the possibility of producing a variety of high-quality ceramics with properties comparable to those achieved by traditional processing. Due to the mechanical stability of the powder bed, the process can also be carried out with continuous layer deposition on a rotating platform, which further increases its productivity.
This presentation will delve into 10 years of research on the LSD-print of a wide variety of technical ceramics including alumina, silicon carbides and dental ceramics. The discussion highlights how a seemingly small process and feedstock modification (from powders to slurries) has great influence on the challenges and potential of this process, which are being addressed on its path to industrialization.
The talk summarizes challenges in microplastic analysis. It shows the preparation of microplastic reference materials as well as the testing on homogeneity and stability. The reference material is used in an international laboratory comparison to compare different detection methods used for microplastic analysis. The methods used were µ-IR (FTIR+LDIR) for number-based methods and TED-GC/MS and Py-GC/MS for mass-based methods. The ILC was done under the umbrella of VAMAS TWA 45. Results of the participants are presented.
The presentation includes aspects of material design and characterization with a focus on lignin. Examples are the structural elucidation of lignosulfonates by means of two-dimensional chromatography, the mechanochemical degradation and functionalization of Kraft-Lignin with accompanying analytics. Future projects involving the incorporation of lignin into polymers will be presented.
This contributions shows the first results of the ongoing interlaboratory comparisons under VAMAS/TWA 34 Nanoparticle populations related on the determination of pasrticle size distribution and relative concentration of nanoparticles and an example of an ILC running under VAMAS/TWA 41 Graphene and Related 2D Materials on the determination of the lateral diemsnions of graphene oxide flakes by Scanning Electron Microscopy. The link to related standardisation projects at ISO/TC Nanotechnologies are explained.
Advanced materials, such as nanomaterials, 2D materials, or thin films, play a crucial role in driving economic development and addressing major challenges in the coming years. These challenges include mitigating the impact of climate change, advancing lightweight engineering, enhancing catalysis, and improving medical applications.
To comprehend the performance of these materials and ensure their acceptance across various sectors as safe and sustainable for both humans and the environment, the availability of reference procedures, materials, and data is essential. One versatile tool for establishing such references and evaluating the proficiency of individual laboratories and their competencies is through (international) interlaboratory comparisons (ILC). Notably, initiatives like the Versailles Project on Advanced Materials and Standards (VAMAS) provide a platform for conducting ILCs.
This webinar will showcase various examples of interlaboratory comparisons, illustrating their impact on the development of reference products.
In recent years, many protocols in computational materials science have been automated and made available within software packages (primarily Python-based). This ranges from the automation of simple heuristics (oxidation states, coordination environments) to the automation of protocols, including multiple DFT and post-processing tools such as (an)harmonic phonon computations or bonding analysis. Such developments also shorten the time frames of projects after such developments have been made available and open new possibilities. For example, we can now easily make data-driven tests of well-known rules and heuristics or develop quantum chemistry-based materials descriptors for machine learning approaches. These tests and descriptors can have applications related to magnetic ground state predictions of materials relevant for spintronic applications or for predicting thermal properties relevant for thermal management in electronics. Combining high-throughput ab initio computations with fitting, fine-tuning machine learning models and predictions of such models within complex workflows is also possible and promises further acceleration in the field. In this talk, I will show our latest efforts to link automation with data-driven chemistry and materials science.
Der Vortrag gibt eine Übersicht zum Stand des Projekts zum Thema Gefügeveränderung bei trockener Grobbearbeitung. Es wurden vier verschiedene trockene Oberflächenbearbeitungsverfahren an 2 Werkstoffen eingesetzt um Testoberflächen zu schaffen. Die so gefertigten Oberflächen wurden lichtmikroskopisch untersucht und die jeweiligen Rauhigkeitskennwerte bestimmt. Weiterhin wurden metallografische Querschliffe angefertigt um die verfahrens- bzw. materialabhängigen Einflüsse auf mögliche Gefügeveränderungen zu untersuchen. Zusätzlich wurden elektrochemische Polarisationsversuche durchgeführt um die oberflächenspezifische Korrosionsbeständigkeit der nichtrostenden Stahlproben zu quantifizieren.
Bonds and local atomic environments are crucial descriptors of material properties. They have been used to create design rules and heuristics and as features in machine learning of materials properties. Implementations and algorithms (e.g., ChemEnv and LobsterEnv) for identifying local atomic environments based on geometrical characteristics and quantum-chemical bonding analysis are nowadays available. Fully automatic workflows and analysis tools have been developed to use quantum-chemical bonding analysis on a large scale. The lecture will demonstrate how our tools, that assess local atomic environments and perform automatic bonding analysis, help to develop new machine learning models and a new intuitive understanding of materials.[5,6] Furthermore, the general trend toward automation in density functional-based materials science and some of our recent contributions will be discussed.
Bonds and local atomic environments are crucial descriptors of material properties. They have been used to create design rules and heuristics and as features in machine learning of materials properties. Implementations and algorithms (e.g., ChemEnv and LobsterEnv) for identifying local atomic environments based on geometrical characteristics and quantum-chemical bonding analysis are nowadays available. Fully automatic workflows and analysis tools have been developed to use quantum-chemical bonding analysis on a large scale. The lecture will demonstrate how our tools, that assess local atomic environments and perform automatic bonding analysis, help to develop new machine learning models and a new intuitive understanding of materials. Furthermore, the general trend toward automation in density functional-based materials science and some of our recent contributions will be discussed.
Der Vortrag gibt einen Überblick zu ultrakurzen Laserpulsen, der Ultrakurzpulslaser-Materialbearbeitung und der dabei ggf. auftretenden unerwünschten Röntgenstrahlung. Es wird die Laserbearbeitung von technischen und biologischen Materialien diskutiert. Schutzmöglichkeiten gegenüber der Röntgenstrahlung werden erörtert.
Advances in ultrafast laser manufacturing: nanostructures, thin films, and scaling perspectives
(2024)
Advanced ultrafast laser technology is a rapidly growing field that currently enables many new industrial and scientific applications. During the last decades, this has been significantly driven by the availability of high-repetition-rate laser sources and novel beam delivery concepts. At the laser side, Moore’s law equally manifests for ultrafast laser technologies, since the average output power of such lasers doubles approximately every two years. This development is mainly driven by the increase of the pulse repetition rates of energetic laser pulses, currently enforcing the development of smart beam control and novel scanning strategies for preventing heat-accumulation and plasma-shielding effects during laser-based materials processing. This keynote presentation addresses the advantages, recent developments, and perspectives of laser processing with ultrashort laser pulses. A special focus is laid on the tailored structuring of thin films as well as the manufacturing and probing of sub-diffraction surface nanostructures – an ongoing race to extreme scales. Current limitations are identified and an outlook to future scaling perspectives will be provided.
Ziel des FuE-Vorhabens ist die Entwicklung, Aufbau und Validierung eines gasto-mographischen Messsystems basierend auf stationärer und mobiler Sensorik zum Emissionsmonitoring in kommunalen Kläranlagen. Die Gastomographie basiert hierbei im Wesentlichen auf, aus unterschiedlichen Sichtwinkeln aufgenommenen, integralen Konzentrationsmessungen, anhand derer eine Rekonstruktion der Gasverteilung erfolgt. Das FuE-Projekt kombiniert hierfür stationäre Sensornetzwerke mit luftgestützten und bodengebundenen Robotersystemen in einem System. Letztere werden mit Reflektoren und/oder Gasdetektoren ausgestattet. Hierfür werden Open-Path-Gasmesstechnik basierend auf Tunable Diode Laser Ab-sorption Spectroscopy (TDLAS, primär CH4 in ppm·m) und In-situ-Gassensorik (CH4, ppm) auf Basis von z.B. Infrarot eingesetzt. Dies sind zwei komplementäre Methoden der Gasmessung: Die In-situ-Gassensorik ermöglicht Punktmessungen, wohingegen TDLAS-Sensoren Gaskonzentrationen integral über offene Messstre-cken von bis zu 60 m gegen Oberflächen messen. Die In-situ-Gassensorik wird für Referenzmessungen und ggf. zur Erhöhung der Rekonstruktionsqualität zum Ein-satz kommen. Die wesentlichen Neuheiten des Projekts sind:
• 2D-Gastomographie auf Basis eines mit TDLAS-basierter Open-Path-Gasmesstechnik und Reflektoren ausgestatteten heterogenen Messsystems.
• CT-basierte Rekonstruktionsalgorithmen, adaptiert an die komplexen Rahmenbedingungen.
• Validierung des Messsystems anhand realer Messungen auf Kläranlagen.
In order to be able to manipulate ceramic powder compacts and ceramic suspensions (slurries) within their volume with light, a minimum transparency of the materials is required. Compared to polymers and metals, ceramic materials are characterized by the fact that they have a wide electronic band gap and therefore a wide optical window of transparency. The optical window generally ranges from less than 0.3 µm to 5 µm wavelength. In order to focus light into the volume of a ceramic powder compact, its light scattering properties must therefore be tailored. In this study, we present the physical background and material development strategies for the application of two-photon polymerization (2PP) and selective volumetric sintering for the additive manufacturing of structures in the volume of ceramic slips and green compacts.
Die Integration und Wiederverwendung von Wissen und Daten aus der Herstellung, Bearbeitung und Charakterisierung von Materialien wird im Zuge der digitalen Transformation in der Materialwissenschaft und Werkstofftechnologie in verschiedenen Projekten behandelt. Dabei liegt der Fokus auf der Interoperabilität von Daten und Anwendungen, die nach den FAIR-Prinzipien erstellt und veröffentlicht werden. Zur Umsetzung eines komplexen Datenmanagements und der Digitalisierung im Bereich der Materialwissenschaften gewinnen Ontologien zunehmend an Bedeutung. Sie ermöglichen sowohl menschenlesbare als auch maschinenverständliche und -interpretierbare Wissensrepräsentationen durch semantische Konzeptualisierungen.
Im Rahmen des Projektes Plattform MaterialDigital (PMD, materialdigital.de), welches in dieser Präsentation vorgestellt wird, werden Ontologien verschiedener Ebenen entwickelt (verbindende mid-level sowie Domänen-Ontologien). Die PMD-Kernontologie (PMD Core Ontology - PMDco) ist eine Ontologie der mittleren Ebene, die Verbindungen zwischen spezifischeren MSE-Anwendungsontologien und domänenneutralen Konzepten herstellt, die in bereits etablierten Ontologien höherer Ebenen (top-level Ontology) verwendet werden. Sie stellt somit einen umfassenden Satz von durch Konsensbildung in der Gemeinschaft (geteiltes Vokabular) entstanden Bausteinen grundlegender Konzepte aus der Materialwissenschaft und Werkstofftechnik (MSE) dar. In dieser Präsentation wird die PMDco adressiert.
Weiterhin wird eine auf die PMDco bezogene normenkonforme ontologische Repräsentation zur Speicherung und Weiterverarbeitung von Zugversuchsdaten – die Tensile Test Ontology (TTO) – präsentiert, die in enger Zusammenarbeit mit dem zugehörigen DIN-Standardisierungsgremium NA 062-01-42 AA erstellt wurde. Dies umfasst den Weg von der Entwicklung einer Ontologie nach Norm, der Konvertierung von Daten aus Standardtests in das interoperable RDF-Format bis hin zur Verbindung von Ontologie und Daten. Auf Grundlage der dabei entwickelten Struktur und Vorgehensweise können weitere Materialcharakterisierungsmethoden semantisch beschrieben werden, woraus sich in diesem Zusammenhang Kooperationsmöglichkeiten ergeben.
Die thermische Historie beim additiven Aufbau von komplexen Realkomponenten und geometrisch primitiven Prüfkörpern unterscheidet sich signifikant. Daraus können Eigenschaftsunterschiede resultieren, die zu unterschiedlichem Materialverhalten führen können. In diesem Vortrag wird das Konzept repräsentativer Probekörper eingeführt, das eine Übertragung thermischer Historien von komplexen Geometrien auf einfache Geometrien ermöglicht und hierdurch zu einer besseren Vergleichbarkeit der Werkstoffeigenschaften führen soll.
Bislang wird das Phänomen der orientierten Oberflächenkristallisation kontrovers diskutiert und entsprechende Studien beschränken sich auf nur wenige Gläser. Für Silikatgläser haben wir eine gute Korrelation zwischen der berechneten Oberflächenenergie von Kristallflächen und der orientierten Oberflächenkeimbildung gefunden. Die Oberflächenenergien wurden unter der Annahme abgeschätzt, dass die Kristalloberflächen bei der Keimbildung den Kristallebenen mit minimaler Energie entsprechen, denen ein Riss beim Bruch folgt. Dieses Konzept wurde am Institut für Physik in Rennes erfolgreich bei der Berechnung der Bruchflächenenergien von Gläsern angewandt. Mehrere orientierte Keimbildungsphänomene lassen sich dadurch erklären, dass man annimmt, dass Kristalloberflächen mit hoher Energie dazu neigen, von der Schmelze benetzt zu werden. Dies minimiert die gesamte Grenzflächenenergie des Keims. Darüber hinaus werden wir die Entwicklung der Mikrostruktur beim weiteren Kristallwachstum und ihre Auswirkungen auf die bevorzugte Kristallorientierung diskutieren.
The general term additive manufacturing (AM) encompasses processes that enable the production of parts in a single manufacturing step. Among these, laser powder bed fusion (PBF-LB) is one of the most commonly used to produce metal components. In essence, a laser locally melts powder particles in a powder bed layer-by-layer to incrementally build a part. As a result, this process offers immense manufacturing flexibility and superior geometric design capabilities compared to conventional processes. However, these advantages come at a cost: the localized processing inevitably induces large thermal gradients, resulting in the formation of large thermal stress during manufacturing. In the best case, residual stress remains in the final parts produced as a footprint of this thermal stress. Since residual stress is well known to exacerbate the structural integrity of components, their assessment is important in two respects. First, to optimize process parameter to minimize residual stress magnitudes. Second, to study their effect on the structural integrity of components (e.g., validation of numerical models). Therefore, a reliable experimental assessment of residual stress is an important factor for the successful application of PBF-LB. In this context, diffraction-based techniques allow the non-destructive characterization of the residual stress. In essence, lattice strain is calculated from interplanar distances by application of Braggs law. From the known lattice strain, macroscopic stress can be determined using Hooke’s law. To allow the accurate assessment of the residual stress distribution by such methods, a couple of challenges in regard of the characteristic PBF-LB microstructures need to be overcome.
This presentation highlights some of the challenges regarding the accurate assessment of residual stress in PBF-LB on the example of the Nickel-based alloy Inconel 718. The most significant influencing factors are the use of the correct diffraction elastic constants, the choice of the stress-free reference, and the consideration of the crystallographic texture. Further, it is shown that laboratory X-ray diffraction methods characterizing residual stress at the surface are biased by the inherent surface roughness. Overall, the impact of the characteristic microstructure is most significant for the selection of the correct diffraction elastic constants. In view of the localized melting and solidification, no significant gradients of the stress-free reference are observed, even though the cell-like solidification sub-structure is known to be heterogeneous on the micro-scale.
The thermal history during additive manufacturing of complex components differs significantly from the thermal history of geometrically primitive test specimens. This can result in differences in properties that can lead to different material behavior. In this talk, the concept of representative test specimens is introduced, which enables the transfer of thermal histories from complex geometries to simple geometries, which can lead to better comparability of material properties.