Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Erscheinungsjahr
Dokumenttyp
- Vortrag (3104)
- Posterpräsentation (802)
- Beitrag zu einem Tagungsband (698)
- Zeitschriftenartikel (429)
- Forschungsbericht (245)
- Sonstiges (110)
- Dissertation (108)
- Forschungsdatensatz (104)
- Zeitschriftenheft (Herausgeberschaft für das komplette Heft) (80)
- Buchkapitel (59)
Sprache
- Englisch (3868)
- Deutsch (1921)
- Mehrsprachig (18)
- Russisch (7)
- Spanisch (5)
- Französisch (2)
- Italienisch (2)
- Chinesisch (2)
- Portugiesisch (1)
Referierte Publikation
- nein (5826) (entfernen)
Schlagworte
- Korrosion (186)
- Corrosion (181)
- Additive manufacturing (174)
- Additive Manufacturing (162)
- Additive Fertigung (136)
- Nanoparticles (103)
- Microstructure (82)
- Nichtrostender Stahl (82)
- Eigenspannungen (80)
- Laser beam welding (74)
Organisationseinheit der BAM
- 6 Materialchemie (1020)
- 9 Komponentensicherheit (999)
- 5 Werkstofftechnik (660)
- 7 Bauwerkssicherheit (580)
- 8 Zerstörungsfreie Prüfung (491)
- 9.4 Integrität von Schweißverbindungen (389)
- 7.6 Korrosion und Korrosionsschutz (329)
- 9.3 Schweißtechnische Fertigungsverfahren (329)
- 6.1 Oberflächen- und Dünnschichtanalyse (279)
- 8.5 Röntgenbildgebung (252)
Paper des Monats
- ja (2)
The damage mechanisms of metallic components produced by process laser powder bed fusion differ significantly from those typically observed in conventionally manufactured variants of the same alloy. This is due to the unique microstructures of additively manufactured materials. Herein, the focus is on the study of the evolution of creep damage in stainless steel 316L specimens produced by laser powder bed fusion. X-ray computed tomography is used to unravel the influence of the process-specific microstructure from the influence of the initial void distribution on creep damage mechanisms. The void distribution of two specimens tested at 600 °C and 650 °C is analyzed before a creep test, after an interruption, and after fracture. The results indicate that the formation of damage is not connected to the initial void distribution. Instead, damage accumulation at grain boundaries resulting from intergranular cracking is observed.
Laser powder bed fusion (PBF-LB/M) of metallic alloys is a layer-wise additive manufacturing process that provides significant scope for more efficient designs of components, benefiting performance and weight, leading to efficiency improvements for various sectors of industry. However, to benefit from these design freedoms, knowledge of the high produced induced residual stress and mechanical property anisotropy associated with the unique microstructures is critical. X-ray and neutron diffraction are considered the benchmark for non-destructive characterization of surface and bulk internal residual stress. The latter, characterized by the high penetration power in most engineering alloys, allows for the use of a diffraction angle close to 90° enabling a near cubic sampling volume to be specified. However, the complex microstructures of columnar growth with inherent crystallographic texture typically produced during PBF-LB/M of metallics present significant challenges to the assumptions typically required for time efficient determination of residual stress. These challenges include the selection of an appropriate set of diffraction elastic constants and a representative lattice plane suitable for residual stress analysis. In this contribution, the selection of a suitable lattice plane family for residual stress analysis is explored. Furthermore, the determination of an appropriate set of diffraction and single-crystal elastic constants depending on the underlying microstructure is addressed.
In-situ loading experiments have been performed at the Swiss Spallation Neutron Source with the main scope to study the deformation behaviour of laser powder bed fused Inconel 718. Cylindrical tensile bars have been subjected to an increasing mechanical load. At pre-defined steps, neutron diffraction data has been collected. After reaching the yield limit, unloads have been performed to study the accumulation of intergranular strain among various lattice plane families.
Metallbasierte additive Fertigungsverfahren werden zunehmend industriell zur Anfertigung von komplex geformten Komponenten eingesetzt. In diesem Zusammenhang ist das Laser-Pulverbettschweißen von Metall (PBF-LB/M) ist ein weitläufig genutztes Verfahren. Im PBF-LB/M-Prozess werden lagenweise aufgetragene Metallpulverschichten selektiv mittels eines Lasers aufgeschmolzen. Die Entstehung von internen Fehlstellen (bspw. Porosität, Lunker oder Risse) während des Fertigungsvorgangs stellt ein ernstzunehmendes Risiko für die Bauteilsicherheit und somit für die weitere industrielle Etablierung des Verfahrens dar. Die Entstehung von Fehlstellen hängt eng mit lokalen Änderungen der thermischen Historie des Bauteils zusammen. Mit Hilfe von thermografischen Kameras zur Prozessüberwachung kann die thermische Historie bereits während der Fertigung erfasst werden. Damit eröffnet sich die Möglichkeit, die Entstehung von Fehlstellen anhand der thermografischen Daten vorherzusagen und somit potenziell Kosten für eine nachgelagerte Qualitätssicherung einzusparen.
In diesem Beitrag soll die Modellierung der Fehlstellenvorhersage anhand thermografischer Prozessdaten diskutiert werden. Hierbei liegt ein Schwerpunkt auf der Fragestellung, mit welcher Genauigkeit unterschiedliche Formen von Fehlstellen, im speziellen Anbindungsfehler und Keyhole-Porosität, auf lokaler Bauteilebene vorhergesagt werden können. Weiterhin werden verschiedenen Modelltypen aus dem Bereich des Maschinellen Lernens auf ihre Eignung für die Fehlstellenvorhersage verglichen. Ein weiterer zentraler Aspekt in diesem Zusammenhang ist die Untersuchung der Eingangsdaten des Modells auf ihre Relevanz für das Vorhersageergebnis.
Als Datengrundlage für die durchgeführten Untersuchungen dienen die Fertigungsprozesse von zwei identischen Haynes-282-Bauteilen (Nickel-Basislegierung), welche mit Hilfe einer im kurzwelligen Infrarotbereich arbeitenden Thermografiekamera überwacht wurden. Das Bauteildesign umfasste lokale Bereiche, in denen mit Hilfe einer Parametervariation die Entstehung von Fehlstellen forciert wurde. Um die Position und Größe der entstandenen Defekte zu quantifizieren, wurden beide Bauteile nach erfolgter Fertigung mittels Computertomografie (CT) geprüft. Im Rahmen der Datenvorbereitung für die Modellierung erfolgte eine Reduzierung der erhobenen Thermogramme zu physikalisch-interpretierbaren Merkmalen (bspw. Schmelzbadfläche oder Zeit-über-Schwellwert). Weiterhin erfolgte eine Registrierung der thermografischen Daten mit den Fehlstellen-Referenzdaten der CT, um eine exakte örtliche Überlagerung von thermischer Information und lokalem Fehlstellenbild zu erzielen. Zur Ermöglichung einer lokalen Fehlstellenvorhersage wurden die thermografischen Daten schichtweise in kleinteiligen Volumina angeordnet, welche als Eingangsgröße für die genutzten ML-Algorithmen dienten.
Die Ergebnisse der Untersuchungen zeigen, dass sich die Porosität auf Bauteilschichtebene mit einer hohen Genauigkeit vorhersagen lässt. Eine Vorhersage der Porosität auf lokaler Bauteilebene erweist sich noch als herausfordernd. Die erprobten ML-Algorithmen zeigen vergleichbare Ergebnisse, obwohl ihnen unterschiedliche Modellierungsannahmen zugrunde liegen und sie variierende Komplexität aufweisen. Mit Hilfe der erzielten Erkenntnisse eröffnet sich die Möglichkeit, Rückschlüsse auf die gewählte Prozessüberwachungshardware und Datenvorverarbeitung zu ziehen und somit langfristig die Leistungsfähigkeit von Modellen zur Fehlstellenvorhersage zu verbessern.
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.
Compound semiconductors (CS) are promising materials for the development of high-power electrical applications. They have low losses, can withstand high temperatures and can operate at very high voltages and currents. This makes them a key technology for the electrification of many high energy applications, especially electromobility and HVDC power lines.
The challenge with CS technology is that most of the process technology has to be developed anew to the high standards required by electronic applications. Today, compound semiconductors can be produced in thin layers on top of substrates fabricated from classical crystal growth processes that are already well established. A promising method for this is metal organic vapour phase epitaxy (MOVPE). With this method, many different compounds with semiconducting properties can be synthesized. Additionally, this process technology is a direct thin layer deposition method. Therefore, complex multilayer systems can be generated directly by the deposition process and without the need of doping after growing.
There are a number of critical defects that can originate from the deposition process of these thin film devices. Within this project, we intend to develop new correlative imaging and analysis techniques to determine defect types, to quantify defect size and number density, as well as to characterise defects for process optimisation.
We report here on the use of spectroscopic ellipsometry and imaging ellipsometry to investigate defects in several different compound semiconductor materials used in high-power electronic devices. The materials we investigated are β-Ga2O3, SiC, GaN, AlN, and AlGaN materials as well as oxidised SiC surfaces. All of these materials have their typical defects and require optimised measurement and analysis schemes for reliable detection and analysis. Spectroscopic ellipsometry is a highly sensitive method for determining the thicknesses and dielectric function of thin layers, yielding potentially a high number of microscopic properties. The combined method between ellipsometry and optical microscopy is called imaging ellipsometry and is especially powerful for the large amount of data it produces. We have analysed defects in SiC- and AlN-based thin film semiconductors as well as characterised the properties of different types of SiO2 layers created on top of SiC monocrystals. We developed ellipsometric models for the data analysis of the different semiconductor materials.
If the defects have geometric features, it is useful to combine the ellipsometric analysis with topometry method like interference microscopy and scanning probe microscopy. We have successfully characterised function-critical defects in MOVPE SiC layers and correlated the findings with topography from WLIM measurements. We have developed an imaging ellipsometric measurement methodology that allows to estimate the relative defect area on a surface by a statistical raw data analysis.
Compound semiconductors (CS) are promising materials for the development of high-power electrical applications. They have low losses, can withstand high temperatures and can operate at very high voltages and currents. This makes them a key technology for the electrification of many high energy applications, especially electromobility and HVDC power lines.
The challenge is that most of the process technology has to be developed specifically and tailored to the high standards required by electronic applications. Today, many different CS materials can be produced in thin layers on top of substrates fabricated from classical crystal growth processes that are already well established. A promising method for this is metal organic vapour phase epitaxy (MOVPE). This technology is a direct thin layer deposition method capable of producing complex multilayer systems directly from one deposition process without the need of doping after growing.
There are a number of critical defects that can originate from the deposition process when targeting electronic thin film devices. Within this project, we intend to develop new correlative imaging and analysis techniques to determine defect types, to quantify defect size and density, as well as to characterise defects for further process optimisation.
We report here on the use of spectroscopic and multispectral imaging ellipsometry to investigate defects in several different compound semiconductor materials used in high-power electronic devices. The materials we investigated are β-Ga2O3, SiC, GaN, AlN, and AlGaN as well as oxidised SiC. All of these materials have their typical defects and require optimised measurement and analysis schemes for reliable detection and analysis. Spectroscopic ellipsometry is a highly sensitive method for determining the thicknesses and dielectric function of thin layers, yielding potentially a high number of microscopic properties. The combined method between ellipsometry and optical microscopy is known as imaging ellipsometry and is especially powerful for the large amount of data it produces. We have analysed defects in SiC- and AlN-based thin film semiconductors as well as characterised the properties of different types of SiO2 layers created on top of SiC monocrystals. We developed ellipsometric models for the data analysis of the different semiconductor materials.
If the defects have geometric features, it is useful to combine the ellipsometric analysis with topometry methods like interference microscopy and scanning probe microscopy. We have successfully characterised function-critical defects in MOVPE SiC layers and correlated the findings with topography from WLIM measurements. We have developed an imaging ellipsometric measurement methodology that allows to estimate the relative defect area on a surface by a statistical raw data analysis.
Development of representative test specimens by thermal history transfer in laser powder bed fusion
(2024)
The use of components manufactured by laser powder bed fusion (PBF LB/M) and subjected to fatigue loading is still hampered by the uncertainty about the homogeneity of the process results. Numerous influencing factors including the component’s geometry contribute to the risk of process instability and resulting inhomogeneity of properties. This drastically limits the comparability of different built parts and requires expensive full component testing. The thermal history as the spatiotemporal temperature distribution has been identified as a major cause for flaw formation. Therefore, it can be hypothesized that a similar thermal history between components and test specimens enhances their comparability. Following this assumption, a strategy is developed to transfer the intrinsic preheating temperature as a measure of comparability of thermal histories from a region of interest of a complex component to a simple test specimen. This transfer concept has been successfully proved by the use of FEM-based macroscale thermal simulations, validated by calibrated infrared thermography. An adoption of the specimen manufacturing process by the adjustment of the inter layer times was established to manufacture specimens which are representatives of a specific region of a large-scale component in terms of the thermal history similarity criterion. The concept is schematically illustrated in Figure 1 and was demonstrated using a pressure vessel geometry from the chemical industry.
Ellipsometry as optical metrology method for analysis of reference materials for nanoelectronics
(2024)
Electrical properties of materials at the nanoscale can be characterized using scanning microwave microscopes (SMM) and conductive atomic force microscopes (C AFM). However, the measurement results are difficult to compare since different setups and different reference standards are used. The development of new “out-of-lab” reference standards can contribute to the traceability and reliability of these scanning probe microscopy methods (SPM) and facilitate their broader industrial application.
In this study, we discuss the capability of optical methods such as ellipsometry for the characterization of existing and the development of new reference calibration samples for scanning microwave microscopy. Ellipsometry is a fast and non-destructive method, which enables very accurate determination of the layer thickness and the dielectric functions of the materials. Imaging ellipsometry is suitable for spatially resolved measurements when analyzing thin layers in microstructured samples.
We show how the electrical resistivity of indium tin oxide (ITO) layers in newly designed resistive calibration samples can be obtained from spectroscopic ellipsometric measurements. The extension of the measurement range into the mid-infrared region was necessary when analyzing ITO layers with low conductivity. This parameter was obtained by fitting a Drude function describing the absorption of the free carriers. The impact of the coating process conditions on the layer properties is discussed.
Imaging ellipsometry was applied for the characterisation of thin ITO and SiO2 layers in microstructured resistive and capacitance calibration kits. The uncertainties of determined layer thicknesses were specified according to standardized practice guides used in ellipsometry. We show how statistical fingerprint analysis of the measured ellipsometric transfer quantities can be used to validate the quality of potential reference materials for nano-electronics and to monitor the processing of structured samples.
As industries move for ever faster development and adoption cycles of emerging new technologies in the field of welding, the meticulous and longer-winded approach of the scientific research process can feel harder to integrate. To help bridge this gap and increase the speed, quality, and adoption rate of publicly funded research, the Bundesanstalt für Materialforschung und -prüfung (BAM) continues to work towards enabling scientists with direct access to necessary software tools and - in the future – highest quality welding research reference data to further foster collaborations.
On the experimental side, the arc welding group at BAM division 9.3 “welding technologies” is continuing to expand and upgrade its capacities of robotic welding systems with integrated state of the art sensor technologies and software solutions. This allows all experiments to be recorded and measured in micro-millimeter accuracy and at sub-millisecond precision, including welding process data, complete spatial geometry and temperature measurements, process video recordings and more. The custom software-based solutions and interfaces allow scaling of the welding systems from large thick plate offshore applications to small additive repair weldments in wind turbine blades to multi-hour continuous weldments in additive manufacturing applications. In addition to the data gathered during the welding process itself, the relevant testing results and materials properties produced at BAM or externally can be integrated seamlessly. This allows detailed traceability of all results back to the actual welding process.
Regardless of the scope and application, complete datasets can be made accessible for research or industry partners in the highest resolution based on the open source WelDX (welding data exchange) file format.
Figure 1. Welding experiment representation including dynamic process data, cross-section imaging and hardness measurements from a single weldx file.
The talk will give an overview of the experimental facilities and workflows as well as current software developments with a focus on research data quality assurance, traceability, and accessibility.
Based on the integration into latest research trends and activities of the “welding technologies” division, the path to publishing reference datasets for arc welding process for various applications and materials is outlined and discussed.
Es wurde untersucht, ob und unter welchen Bedingungen sich Kurzfasern aus Hanf heimischer Produktion für die Erzeugung einer Faser-Antifoulingbeschichtung auf Schiffsrümpfen sowie für die Beflockung anderer technischer Oberflächen verwenden lassen.
Das Grundprinzip der Beflockungstechnik besteht darin, Kurzfasern im Längenbereich zwischen 0.5 und 15 mm in einem elektrischen Feld auf eine frisch mit einem Lack oder Kleber beschichtete ebene oder profilierte bzw. gekrümmte Oberfläche aufzubringen und dort bevorzugt senkrecht zu verankern. Auf diese Weise entsteht ein dichter, die Oberfläche vollständig bedeckender Faserflor. Als Flockfasermaterial finden bisher vorwiegend Polyamid (Nylon, Perlon), Viskose, Polyester sowie Baumwolle als nachwachsende Faser Verwendung. Nach der Herstellung unterscheidet man Schnitt- und Mahlflockfasern. Beflockungsmaschinen größerer Leistungsfähigkeit sind in der Regel keine mobilen Aggregate, sondern stationäre, für einen bestimmten Anwendungszweck spezialisierte Aufbauten, auf denen z.B. Gehäuse, PKW-Innenausbauteile, Profile, Bezugsstoffe und andere Textilien beschichtet werden.
Die Besonderheit dieses Vorhabens liegt einerseits in der Verwendung einer neuen Faserart - Hanfkurzfasern - für Beflockungszwecke und andererseits in der Notwendigkeit ein eher mobiles Beflockungsaggregat zu entwickeln, um die Beflockung von Schiffsrümpfen und anderen größeren Objekten prinzipiell zu ermöglichen.
Direct energy deposition additive manufacturing technologies that utilize an electric arc have great potential for generating large volume metal components. However, selecting process parameters that yield the desired near net shape design and requested mechanical component behavior is not a trivial task due to the complex relationship between all process parameters and material characteristics. This presentation exemplifies the application of a newly developed solid welding wire doped with TiB to enhance grain refinement in the deposited metal for additive manufacturing based on DED-Arc of high-strength precipitation hardening AlMgSi-aluminum alloys. It is worth noting that the solid wire is the result of our preliminary metallurgical studies on grain refinement in aluminum weld metal.
Consequently, research focuses on the correlation between process parameters and component quality to understand the underlying mechanisms. This is crucial for evaluating a robust process parameter space that yields component quality in line with corresponding standards which are mainly taken from welding technology.
Specifically, we examine component quality by analyzing pore size and distribution, as well as grain morphology. To enhance the mechanical properties of the deposited metal, a post-weld heat treatment was conducted, comprising of solution treatment, quenching, and artificial aging. The study also evaluates the effects of various heat treatment strategies on the final mechanical properties of the material.
To demonstrate the applicability of 3D metal printing of high-strength aluminium alloys, a more complex demonstrator was created. It has been shown that DED-Arc can produce high-volume aluminium parts with the same quality as the corresponding subtractive processing strategy.
Additionally, the entire additive manufacturing chain has been digitally integrated, enabling traceability of all relevant process steps, which is essential for reliable subsequent quality assessment.