Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Eingeladener Vortrag
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Dieses Dokument fasst den Projekfortschritt des BAM-Projektes "Ermittlung geeigneter Wärmeführungen zur Wasserstoffreduktion beim Schweißen höherfester Feinkornbaustähle mit modifiziertem Sprühlichtbogen" im Rahmen des Fachausschusses 1 "Schweißmetallurgie & Werkstoffverhalten" des DVS e. V. zusammen.
Um den wachsenden Anforderungen nach Leichtbau und Ressourceneffizienz im Kran-, Nutzfahrzeug- und Brückenbau gerecht zu werden, kommen in diesen Industriebranchen vermehrt hochfeste Feinkornbaustähle mit Streckgrenzen von mehr als 690 MPa zum Einsatz. Allerdings erfordern diese Stähle bei der schweißtechnischen Verarbeitung äußerste Sorgfalt, weil gerade die Sensibilität gegenüber einer Degradation der mechanischen Eigenschaften, durch den im Lichtbogen aufgenommenen Wasserstoff, mit steigender Festigkeit signifikant zunimmt und zur wasserstoffunterstützten Kaltrissbildung führen kann. In diesem Vortrag werden Ergebnisse vorgestellt, die den Einfluss von Kontaktrohrabstand, Drahtvorschub sowie Schweißspannung auf den Wasserstoffeintrag in Ein- und Mehrlagenschweißungen aus hochfestem Feinkornbaustahl zeigen. Dabei wird der konventionelle Lichtbogen mit dem modernen modifizierten Sprühlichtbogen verglichen. Ziel ist es, durch geeignete Wärmeführungen die Wasserstoffkonzentration in Schweißverbindungen zu reduzieren, um somit die Gefahr einer wasserstoffunterstützten Kaltrissbildung zu minimieren.
Die BAM-Liste - Anforderungen an Tanks für die Beförderung gefährlicher Güter – mit den Beständigkeitsbewertungen metallischer und polymerer Werkstoffe ist Grundlage für die stoffbezogenen Baumusterzulassungen für Tankcontainer und ortsbewegliche Tanks zur Beförderung gefährlicher Güter durch die BAM seit der Herausgabe der 1. Auflage 1989. Diese Beständigkeitsbewertungen werden nicht nur bundesweit, sondern weltweit als Erkenntnisquelle genutzt. Für die Zulassung von Kesselwagen und Tankfahrzeugen werden diese Daten auch herangezogen. Die Werkstoffbeständigkeitsdaten und der damit verbundene Informationsservice der BAM haben mit Sicherheit dazu beigetragen, Leckagen von Tanks aufgrund des Einsatzes von Tanks/Kesselwagen aus einem gegenüber dem Füllgut unbeständigem Tankwerkstoff oder Dichtungswerkstoff zu vermeiden.
Interlaboratory comparison: optical property classification of carbon-based films by ellipsometry
(2017)
The paper addresses the “INTERLABORATORY COMPARISON: OPTICAL PROPERTY CLASSIFICATION OF CARBON-BASED FILMS BY ELLIPSOMETRY” and the following points are discussed in more detail: Established classification for mechanical properties, Complementary classification for optical properties, Ellipsometry for determination of optical constants n-k plane as material fingerprint, Samples, participants & set-ups (samples: Japan, participants: Japan, Germany, France, set-ups: Japan, Germany, USA) and Results of interlaboratory comparison: thickness, n & k.
Easy to handle and stretchable polymer optical fibres for sensor applications
Basic idea of stimulated Brillouin scattering
Brillouin threshold for PMMA-POF and PFGI-POF in comparison
Sensorial behavior of Brillouin scattering in PFGI-POF and silica SMF
Basics and classification of distributed Brillouin sensing methods
Basic idea of dynamic Brillouin sensing
Ein neuer Ansatz bei elektrochemischen Korrosionsuntersuchungen kann durch den Einsatz von gelartigen Elektrolyten als Alternative zu wässrigen Prüfelektrolyten beschritten werden. Gelartige Elektrolyte ermöglichen minimalinvasive Untersuchungen an natürlich gebildeten Zinkdeckschichten. Dadurch können korrosionsrelevante Kennwerte ermittelt werden, die Aussagen zur Deckschichtbildung und zur Stabilität der gebildeten Deckschichten unter verschiedenen klimatischen Bedingungen erlauben. In diesem Beitrag wird anhand verschiedener Deckschichtzustände an Zink der Mehrwert von Untersuchungen mit gelartigen Elektrolyten für die Korrosionsforschung verdeutlicht.
In-situ ED-XRD und Radiographie während eines Zugversuchs an wasserstoffbeladenem Supermartensit
(2017)
Die Ergebnisse von in-situ Experimenten am Berliner Elektronenspeicherring (BESSY II) werden vorgestellt. Es wurden Zugversuche an wasserstoffbeladenen und wasserstofffreien supermartensitischen Proben durchgeführt und Diffraktionsspektren und radiographische Bilder aufgenommen. Die energiedispersive Röntgendiffraktion ermöglichte dabei die dehnungsinduzierte Phasenumwandlung von Restaustenit zu Martensit in-situ zu beobachten. Die Radiographiebilder der zerreisenden Probe gaben Einblicke in das Bruchverhalten in Abhängigkeit vom Wasserstoffgehalt des Supermartensits.
Im deutschen Bundesautobahnnetz treten vor allem an den vor 2005 errichteten Betonfahrbahndecken vermehrt Schäden auf, die mit einer AKR in Verbindung gebracht werden. Sie äußern sich zunächst in einer Dunkelfärbung in den Fugenbereichen der Betonfahrbahndecke. Oft wird diese Erscheinung von einer von der Fuge ausgehenden horizontalen Rissbildung parallel zur Fahrbahnoberfläche begleitet. Durch den Einsatz der NMR-Technik konnte erstmals zerstörungsfrei der erhöhte Feuchtegehalt in der Betonrandzone als Ursache für diese Erscheinung nachgewiesen werden. Zusätzlich durchgeführte Radaruntersuchungen und Darr-Wäge-Versuche zeigten, dass die erhöhte Durchfeuchtung in der Betonrandzone in der Regel den gesamten Fahrbahnquerschnitt erfasst. Weiterhin wurde aufgezeigt, dass vor allem die akustischen Verfahren eine zerstörungsfreie Detektion der von der Fuge ausgehenden lateralen Ausdehnung der oberen Rissebene in die Fahrbahnplatte ermöglichen. Im Gegensatz zum Impakt-Echo-Verfahren erlaubt das Ultraschall-Echo-Verfahren zusätzlich die Ermittlung der Tiefenlage der oberen Rissebene. Es wird eine weitere Ertüchtigung der akustischen Verfahren für die Strukturaufklärung in Betonfahrbahndecken angeregt.
The reinforcement of concrete with polymer fibers provides resistance to crack formation. The orientation distribution of these fibers has a significant influence on the mechanical behavior of the material. To optimize material performance, micromechanical models that are capable of making accurate predictions of the mechanical behavior of composite materials are needed. These models must be calibrated using experimental results from microstructural characterization. For the fiber orientation distribution analysis in the present study, computed tomography (CT) data were used to evaluate the properties of a fiber-reinforced cement mortar. The results have indicated that the fibers in this material have highly anisotropic orientation characteristics and that there is a clear tendency for the polymer fibers to agglomerate during mixing and casting. The incorporation of this experimental data into micromechanical models will increase the accuracy of those models for material simulation and optimization.
Shock tube systems are non-electric explosive fuses employed in blasting and demolition applications to trigger the detonation of explosive charges. Their working principle is based on the explosive reaction of a fine powder on the tubing´s inner surface, generating a percussive wave travelling at a velocity of 2,100 m/s along the length of the tube, without destroying it. One of the key aspects of the manufacturing process of these shock tubes is the size and morphology of the explosive powder grains and their distribution on the inner wall of the tube, in order to propagate the shockwave efficiently and reliably. For the first time, synchrotron X-ray computed tomography has been used to characterize non-destructively the explosive powder grains, typically Al/HMX between 10 and 20 μm in size, in terms of morphology and 3D distribution but also to characterise the presence and location of defects within the shock tube walls.
Der Vortrag gibt einen Überblick zu aktuellen Projektaktivitäten im BAM-Fachbereich 6.4 Technologien mit Nanowerkstoffen. Der Einsatz von Femtosekunden-Laserpulsen zur Mikro- und Nanostrukturierung, für Prozessschritte in der Photovoltaik und zur Reinigung und Dekontamination von Oberflächen wird beschrieben. Darüber hinaus werden Laser-Zerstörschwellenmessungen erläutert.
Photoluminescence techniques are amongst the most widely used tools in the life sciences, with new and exciting applications in medical diagnostics and molecular imaging continuously emerging. Advantages include their comparative ease of use, unique sensitivity, non-invasive character, and potential for multiplexing, remote sensing, and miniaturization. General drawbacks are, however, signals, that contain unwanted wavelength- and polarization contributions from instrument-dependent effects, which are also time-dependent due to aging of instrument-components, and difficulties to measure absolute fluorescence intensities. Moreover, scattering systems require special measurement geometries and the interest in new optical reporters with emission > 1000 nm strategies for reliable measurements in the second diagnostic for the comparison of material performance and the rational design of new fluorophores with improved properties.
Here, we present strategies to versatile method-adaptable liquid and solid fluorescence standards for different fluorescence parameters including traceable instrument calibration procedures and the design of integrating sphere setups for the absolute measurement of emission spectra and quantum yields in the wavelength region of 350 to 1600 nm. Examples are multi-emitter glasses, spectral fluorescence standards, and quantum yield standards for the UV/vis/NIR
Lanthanide-doped up-converting nanoparticles (UCNPs) are promising reporters for medical diagnostics and bioimaging, which are excited in the near infrared (NIR) by multiphoton absorption processes, and show multiple narrow emission bands in the visible (vis) and NIR, long luminescence lifetimes in the μs range, and excellent photostability. Current limitations present their relative low absorption cross sections and low fluorescence efficiencies, with the latter being affected by particle size, surface chemistry, and microenvironment, particularly water.
Here, we present results from systematic studies of the excitation power density dependent upconversion luminescence spectra, intensities/intensity ratios of the individual emission bands, slope factors, and quantum yields of UCNPs of varying size, dopant concentration, and surface chemistry in different microenvironments as well as the up- and downconversion luminescence decay kinetics of the different emission bands. Moreover, first studies of the energy transfer from UCNPs to surface-bound organic dyes acting as fluorescence acceptors are shown. Based upon these measurements, fluorescence deactivation channels are identified and spectroscopic parameters for the screening of material performance are derived.
Lanthanide-doped up-converting nanoparticles (UCNPs) are promising reporters for medical diagnostics and bioimaging. Current limitations present their relative low absorption cross sections and low fluorescence efficiencies, with the latter being affected by particle size, surface chemistry, and microenvironment, particularly water.
Here, we present results from systematic studies of the excitation power density dependent upconversion luminescence spectra, intensities/intensity ratios of the individual emission bands, slope factors, and quantum yields of UCNPs of varying size, dopant concentration, and surface chemistry in different microenvironments as well as the up- and downconversion luminescence decay kinetics of the different emission bands. Moreover, first studies of the energy transfer from UCNPs to surface-bound organic dyes acting as fluorescence acceptors are shown. Based upon these measurements, fluorescence deactivation channels are identified and spectroscopic parameters for the screening of material performance are derived.
Der Vortrag widmet sich der Validierung der Verbundfestigkeit von optischen Schicht-/Substrat-systemen mittels Zentrifugentechnologie und diskutiert Versagensbilder und gemessene Werte der Verbundfestigkeit ausgewählter feinoptischer bzw. ophtalmischer Schichten in Abhängigkeit von den plasto-elastischen Eigenschaften und der Dicke der Substrate.
A laser induced breakdown spectroscopy (LIBS) system was combined with the Gas Tungsten Arc (TIG) Welding process for the in situ monitoring of chemical compositions in austenitic stainless steels during welding. The purpose of this project is to develop a prototype of an online chemical composition control system for welding applications. One of the use cases of this new LIBS-based measurement system can be the controlling of potentially dangerous emissions during the welding process in order to improve the working safety conditions.
Synchrotron Radiation with its high intensity and the opportunity to tune the wavelength offers unique possibilities to investigate real catalysts, even under industry-like conditions.
A good example is a XAFS study performed at supported Ni catalysts used for the dimerization of butene at elevated temperature and pressure. Another example are investigations at titania supported Pd based catalyst elucidating the role of co-components (e.g. Sb, Co, Mn and Au) which are necessary to get the desired promising performance in the gas phase acetoxylation of toluene to benzyl acetate, an environmentally benign alternative for the conventional process using chlorine.
Furthermore, investigations about the redox properties of different Cu catalysts will be presented. It could be shown that the redox properties of Cu have a great impact on the performance of such catalysts, not only in some gas phase reactions, but also in photocatalytic applications, e.g. water splitting.
The work aims at addressing the modelling and implementation of criteria for multiple crack propagation, including interaction and coalescence, for a more reliable fracture mechanics-based prediction of stress-life curves for weldments.
A large experimental work is presented in which micro-cracks have been made visible by heat-tinting at successive stages of fatigue life of the welded specimens. Here the correlation between the number of initiation sites and the applied stress level has been also investigated.
The criteria have been implemented in in-house software, which allows multiple fatigue crack propagation, and validated against selected experimental tests. The results have shown that the modelling of multiple crack propagation and interaction is crucial for the prediction of the fatigue strength of weldments, both in finite and infinite life regime.
Faser-Kunststoff-Verbunde werden zunehmend in der Luft- und Raumfahrt, der Automobil- und Windenergieindustrie eingesetzt. Die hier entwickelten Bauteile sind oft nicht nur multiaxialen mechanischen Belastungen, sondern auch hohen klimatischen Beanspruchungen ausgesetzt. Einsatztemperaturen zwischen -60°C und 100°C bei 10-90% relativer Feuchte sind keine Seltenheit, in der Raumfahrt sind die thermischen Belastungen sogar noch extremer. Die Auswirkungen einer Wechselwirkung extremer klimatischer Beanspruchungen mit multiaxialen mechanischen Belastungen wurden bisher kaum betrachtet. Das Ziel des Projektes ist die Untersuchung des Ermüdungsverhaltens der Faser-Kunststoff-Verbunde in Abhängigkeit von multiaxialer mechanischer Belastung, Temperatur und Feuchte. Dazu werden umfangreiche experimentelle Untersuchungen an Flach- und Rohrproben sowie numerische und analytische Berechnungen durchgeführt.
Für die Durchführung der Experimente werden zunächst Glasfaser-Preforms in einem an der BAM entwickelten Haspelverfahren ohne nominelle Ondulation hergestellt. Aus diesen Preforms werden anschließend in einem vakuumunterstützten Resin Transfer Molding (RTM)-Prozess die GFK-Probekörper gefertigt.
Bisher wurden die thermoelastischen Eigenschaften und die Festigkeiten des Faser-Kunststoff-Verbundes und der Matrix mit Zug- und Druckversuchen unter paralleler Temperaturlast im Bereich von -60°C bis +80°C ermittelt. Auf der Basis eines Konzeptes zur Berechnung der Matrixbeanspruchung wurde ein Modell zur Bestimmung des Schädigungsbeginns von Laminaten unter quasistatischer thermomechanischer Belastung weiterentwickelt und experimentell validiert.
Im weiteren Verlauf des Projekts wird das Verhalten von Glasfaser-Kunststoff-Verbunden unter schwingender Belastung und paralleler Temperaturlast untersucht. Hier wurden bereits Experimente bei Raumtemperatur durchgeführt. Mit dem Verfahren der Grauwertanalyse ist es dabei möglich, in-situ die Schädigung des Werkstoffs zu messen. Des Weiteren wird das Verhalten von Faser-Kunststoff-Verbunden unter zyklischer Temperaturlast ohne mechanische Belastung untersucht. Auch hier zeigen sich bereits nach wenigen Lastwechseln erste Zwischenfaserbrüche.
Borosilicate glass has a wide range of technical applications due to its high chemical durability and thermal-shock resistivity. Here the effect of H2O on 16 Na2O, 10 B2O3,74 SiO2 glass is studied over a wide range of water contents from 0 to 8 wt.%. MIR spectra give evidence for the coexistence of strongly and weakly H-bonded hydrous species. Evaluation of NIR bands at 5200 cm-1 (molecular H2O), 4700 cm-1 (B-OH), and 4500 cm-1 (Si-OH) reveal that OH groups dominate up to ~6 wt.% H2O, with B-OH/Si-OH of ≈ 0.8. The incorporation of low amounts of H2O has strong impact on structure. NMR spectra of nominally dry glasses indicate a significant fraction (12 %) of 3-coordinated boron, but almost all boron is 4-coordinated after addition of 3 wt.% H2O. Raman spectra show that hydration results preferentially in transformation of Q4 to Q2 while Q3 remain unchanged, probably stabilized by bonding to BO4 tetrahedra. Viscosity measurements and differential thermal analysis give consistent results, confirming strong decrease of the glass transition temperature with addition of water from 849 K (dry) to 540 K (5 wt% H2O). An additional relaxation mechanism in hydrous glasses is inferred from dynamic mechanical analysis and is assigned to cooperative processes involving hydrous species. It is postulated that this relaxation mechanism plays an important role in crack growth kinetics.
Surface water-induced broadening of crack initiation probability of zinc aluminosilicate glasses
(2017)
The crack generation probability by Vickers indentation of glass surfaces is known to be influenced by the atmospheric conditions under which the Vickers experiment is performed [1]. However, the effect of surface water due to preparation and storage of the glass surfaces prior to the indentation is less understood. Therefore, zinc aluminosilicate glasses of perzinc, peraluminous as well as nominally NBO-free meta-aluminous composition were prepared by melt quenching. Surfaces of cut and polished specimens of these glasses were either stored for seven days under constant atmosphere (50 °C; 55% RH) or etched (HF: 20vol%; 20 min) shortly before indentation. The obtained results show a strong variation of crack initiation behavior depending on chemical composition of the glasses as well as sample preparation. All experiments were performed in dry nitrogen gas to minimize the influence of atmospheric humidity during indentation. While the regular glass surfaces exposed to humid air prior to Vickers indentation show a broad distribution of crack initiation probability, this distribution narrows down if etched glass surfaces are tested. SNMS depth profiling shows a water enriched layer at the surface (150 μm) for the non-etched and stored specimens leading to the conclusion that surface water causes broadening of the crack initiation probability of glass surfaces.
Borosilicate glass has a wide range of technical applications due to its high chemical durability and thermal-shock resistivity. Here the effect of H2O on 16 Na2O, 10 B2O3,74 SiO2 glass is studied over a wide range of water contents from 0 to 8 wt.%. MIR spectra give evidence for the coexistence of strongly and weakly H-bonded hydrous species. Evaluation of NIR bands at 5200 cm-1 (molecular H2O), 4700 cm-1 (B-OH), and 4500 cm-1 (Si-OH) reveal that OH groups dominate up to ~6 wt.% H2O, with B-OH/Si-OH of ≈ 0.8. The incorporation of low amounts of H2O has strong impact on structure. NMR spectra of nominally dry glasses indicate a significant fraction (12 %) of 3-coordinated boron, but almost all boron is 4-coordinated after addition of 3 wt.% H2O. Raman spectra show that hydration results preferentially in transformation of Q4 to Q2 while Q3 remain unchanged, probably stabilized by bonding to BO4 tetrahedra. Viscosity measurements and differential thermal analysis give consistent results, confirming strong decrease of the glass transition temperature with addition of water from 849 K (dry) to 540 K (5 wt% H2O). An additional relaxation mechanism in hydrous glasses is inferred from dynamic mechanical analysis and is assigned to cooperative processes involving hydrous species. It is postulated that this relaxation mechanism plays an important role in crack growth kinetics.
Diverse animal species consume toxins, minerals or secondary compounds as an adaptive response to pathogen infection – a process termed self-medication. Recent studies have also shown that macronutrients can play an important role in an individual’s infection response. For instance African army worm caterpillars select a diet rich in protein and low in carbohydrate upon baculovirus infection. Here we investigate whether dietary choice of macronutrients also plays a role in immunity in the omnivorous cockroach: Blatta orientalis. After challenging individual cockroaches with a common entomopathogenic soil bacterium, Pseudomonas entomophila, we conducted food-choice experiments using two artificial diets differing in their relative protein to carbohydrate ratio. We show for the first time that cockroaches are able to self-select a protein-enriched diet as a response to bacterial infection. This is driven by a sharp decline in carbohydrate intake rather than an increase in protein intake. Additionally, infected cockroaches reduced their overall nutrient intake, which is consistent with an illness-induced anorexia-like response. The feeding pattern of bacteria-challenged individuals returned to normality approx 4 days after challenge. We also investigate whether cockroach survival and hemolymph immunity are enhanced in individuals when restricted to a protein-rich vs. carbohydrate-rich diet. Overall, our findings demonstrate that macronutrient preferences follow a general pattern independent of pathogen type. Furthermore, we show that interactions between nutrition and immunity are highly conserved in evolution, highlighted by the fact that caterpillars and cockroaches diverged some 386 million years ago.
Several Additive Manufacturing (AM) processes are based on the deposition of a powder to form a powder bed layer-by-layer, which typically has a low packing density (35-50%) and consequently hinders the ability of sintering ceramic parts to full density.
The layerwise slurry deposition (LSD) is an innovative process for the deposition of layers in AM. In the LSD, a slurry with no or small organic content is repetitively spread as thin layers on each other by means of a doctor blade. During the deposition, the ceramic particles settle to form thin layers with a high packing density (55-60%). When coupled with a printing head or with a laser, the LSD enables novel AM technologies inspired to the 3D printing or selective laser sintering, but taking advantage of having a highly dense powder-bed.
The LSD combined with inkjet binder printing (LSD-print) was applied to a submicron Al2O3 powder to produce samples which had a comparable density to uniaxially pressed samples, both in the green and in the sintered state.
Recent studies have shown that host-microbiota interactions can lead to dramatic changes in host phenotype. We investigate the causal drivers of microbe-associated shifts in host phenotype by examining how feeding behaviour is modulated by microbiota interactions in two omnivorous cockroaches: Blatta orientalis and Blatella germanica. We conducted food-choice experiments after challenging hosts with a common entomopathogenic soil bacterium to understand the impact of pathogens on host macronutrient preference. We find that immune challenge by a pathogenic microbe drives a sharp decline in carbohydrate intake and results in a relative increase in the ratio of protein to carbohydrate (P:C) consumed. Additionally, infected cockroaches reduce their overall nutrient intake, which is consistent with an illness-induced anorexia-like response. We show for the first time that cockroach feeding behaviour is dynamically modulated by a pathogen, and examine the influence of modified feeding behaviour on host immunity. We also investigate whether in addition to pathogens, gut commensals are causally responsible for shifts in host behavioural phenotype. Here, we conduct food-choice and immune-challenge experiments in germ-free cockroaches, which have been refaunated with gut microbiota that are experimentally adapted to variable macronutrient (P:C) diets.
Recent studies have shown that host-microbiota interactions can lead to dramatic changes in host phenotype. We investigate the causal drivers of microbe-associated shifts in host phenotype by examining how feeding behaviour is modulated by microbiota interactions in two omnivorous cockroaches: Blatta orientalis and Blatella germanica. We conducted food-choice experiments after challenging hosts with a common entomopathogenic soil bacterium to understand the impact of pathogens on host macronutrient preference. We find that immune challenge by a pathogenic microbe drives a sharp decline in carbohydrate intake and results in a relative increase in the ratio of protein to carbohydrate (P:C) consumed. Additionally, infected cockroaches reduce their Overall nutrient intake, which is consistent with an illness-induced anorexia-like response. We show for the first time that cockroach feeding behaviour is dynamically modulated by a pathogen, and examine the influence of modified feeding behaviour on host immunity. We also investigate whether in Addition to pathogens, gut commensals are causally responsible for shifts in host behavioural phenotype. Here, we conduct food-choice and immune-challenge experiments in germ-free cockroaches, which have been refaunated with gut microbiota that are experimentally adapted to variable macronutrient (P:C) diets.
185 cracks were initiated in a soda-lime-silica glass by Vickers indentation and grown under controlled dry nitrogen atmosphere. Direct observation of subcritical crack growth (SCCG) upon indentation was performed using a video camera with an image acquisition rate of 3 ms. The results show that the validity of K(c) relations used to determine the indentation fracture toughness from a single imprint is questionable. It seems that correlation of crack length to stress intensity necessitate the use of statistical significant data of multiple crack events.
Hydrous silicate and borate glasses of up to 8 wt% water were prepared using wet condition of melting under external pressure. Rheological experiments were conducted to determine the effect of the total water content on viscous flow and kinetic fragility. The findings indicate that dissolved water acts as a strong fluxing agent in both glass types. Water decreases particularly viscosity at the glass transition range, makes the viscosity-temperature curve "longer" and thus decreases kinetic fragility. Recent IR and NMR data are presented to link the dynamics of hydrous silicate and borate glasses with their structure particularly with regard to changes in the water-, silicon- and boron-speciation.
Um das Risswachstum in Gläsern zu untersuchen, sind in einer Glovebox 185 Risse ausgehen von Vickers-Eindrücken in Kalk-Natron-Glas initiiert und gewachsen. Die direkte Beobachtung des unterkritischen Risswachstums erfolgte mit einer Hochgeschwindigkeitskamera. Die Ergebnisse zeigen, dass die statistische Auswertung vieler radialer Risse von multiplen Rissevents notwendig ist, um eine Korrelation zum Spannungsintensitätsfaktor ziehen zu können.
Glasig-kristalline Werkstoffe für Schlüsseltechnologien - Prozessbegleitende Prüfung und Simulation
(2017)
Eigenschaftsprofile und Kennwertstreuungen keramischer und glaskeramischer Komponenten und Bauteile werden durch ihren Herstellungsprozess wesentlich mitbestimmt. Prozessbegleitende Prüf- und Simulationsmethoden gewinnen so wachsenden Einfluss auf die Erschließung neuer Applikationsfelder dieser Werkstoffe. Eine wichtige Rol¬le spielen hierbei oft thermokinetische Prozesse, die u. a. Wärmetransport- und Diffusionsvorgänge, Phasengrenzflächenreaktionen, das rheologische Verhalten heterogener Systeme sowie deren Gefügeevolution beim Sintern umfassen. Ziel des Vortrages ist es, diesen Trend anhand ausgewählter Bei-spiele aus der Arbeit des Fachbereichs Glas der BAM zu illustrieren.
Up to now, the mechanisms of surface nucleation and surface-induced texture formation are far from being understood. Corresponding phenomena are discussed hypothetically or even controversial, and related studies are restricted to very few glasses. As a main drawback, the vast majority of previous work on oriented growth of surface crystals do not consider the possible effects of glass surface treatments (like polishing defects, adhered particles and cracks, …) or ambient annealing conditions (vacuum or atmospheric pressure) which both can influence crystal nucleation and growth. Moreover, very few observations of crystal orientation related to surface crystallization were focused on separately growing crystals. In conclusion, up to now, no systematic studies on initially oriented crystal growth or nucleation from defined active nucleation sites have been pursued.
Therefore, the main objective of the proposed project is to gain a basic understanding of the mechanisms of surface-induced microstructure formation in glass ceramics. We shall answer the question whether preferred orientation of surface crystals is the result of oriented nucleation or caused by other orientation selection mechanisms acting during early crystal growth. In both cases, crystal orientation may be caused by the orientation of the glass surface itself or the anisotropy and orientation of active surface nucleation defects.
New techniques of experimental characterization of surface-crystallized glasses shall be applied to find answers to the questions posed above. Based on a controlled preparation and annealing of the glass sample surfaces, that includes the defined creation of active nucleation defects, and followed by the microstructural characterization especially during the very early growth stages of separated surface crystals, the orientation relations between defect and initiated surface crystal will be analyzed. In order to gain new insights, a couple of entirely new microstructure diagnostics techniques, including chemically contrasted XRM, laser-based sample preparation for XRM, and 3D electron backscatter diffraction shall be developed or applied.
This way, using X-ray microscopy as a pivotal technique for the non-destructive 3D characterization of relatively large samples at superior spatial resolution (but also complemented by other microstructure diagnostics techniques, e.g. TEM elemental mappings at cross-sectioned samples) unprecedented insights into the microstructure evolution upon surface crystallization of model glasses will be gained.
The manufacture of sintered glasses and glass-ceramics, glass Matrix composites and glass-bounded ceramics or pastes is often affected by gas bubble formation. Against this background, we studied sintering and foaming of barium silicate glass powders used as SOFC sealants using different powder milling scenarios. Sintering was measured by means of heating microscopy backed up by XPD, DTA, Vacuum Hot Extraction (VHE) and optical and electron microscopy. Foaming increased significantly as milling progressed. For moderately milled glass powders, subsequent storage in air could also promote foaming. Although the powder compacts were uniaxially pressed and sintered in air, the milling environment significantly affected foaming. The strength of this effect increased in the order Ar >> N2 < air < CO2. Conformingly, VHE studies revealed that the pores of aerated samples predominantly encapsulated CO2, even for powders milled in Ar and N2. Results of this study thus indicate that foaming is caused by carbonaceous species trapped on the glass powder surface. Foaming could be substantially reduced by milling in water and 10 wt% HCl.
The layer-wise slurry deposition (LSD) is an innovative process for the deposition of powder layers with a high packing density for Additive Manufacturing (AM). A slurry with small organic content is repetitively spread as thin layers on top of each other by means of a doctor blade. During the deposition, the ceramic particles settle to form thin layers with a high packing density (55-60%). Each layer is then dried, resulting in the stacking of a dry powder bed with high powder packing. When coupled with a printing head or with a laser source, the LSD enables novel AM technologies inspired to the 3D printing or selective laser sintering, but taking advantage of having a highly dense powder bed.
The LSD -3D printing, in particular, offers the potential of producing large (> 100 mm) and high quality ceramic parts, with microstructure and properties similar to traditional processing.
This presentation will give an overview of the milestones in the development of this technology, with focus on the latest results applied both to silicate and to technical ceramics.
Damage development and damage tolerance of structures manufactured by selective laser melting
(2017)
The additive manufacturing technology of Selective Laser Melting (SLM) experiences a rapid development within an increasing marked of quite different application fields. The properties of SLM materials and structures are influenced by a number of tech-nological parameters such as the metal powder (particle size, homogeneity, cleanliness), the laser tool (power, beam diameter, pulse lengths), the scanning operation (speed, sequence and orientation of melting paths), parameters of the over-all equipment (design and preheating of the base plate, currents and turbulence in the protective gas atmosphere) and, last not least, the hatching strategy including the build-up direction of the structure with respect to the loading direction of the component.
For the perspective use of SLM structures as load carrying, safety-relevant components the knowledge of their mechanical properties is necessary. It is essential to understand these in the context of the manufacturing-related features and at the back-ground of the basic characteristics of metallic materials: crystal lattice, microstructure and material defects. The paper provides an overview on factors which affect the mechanical parameters stiffness, strength, ductility, toughness, fatigue crack propagation and fatigue strength in the context of selective laser melting.
Presentation of the work of division 9.4 with focus on the Key aspects of component welding applying higher-strength fine-grained structural steels. The increased application of higher-strength steels and filler materials necessitates a more profound understanding of the interactions between the welding process, the heat input, the cooling conditions and the resulting metallurgical processes in the weld and its surroundings. Strategies, which help to improve the strength properties and life-time of welded structures to such an extent that the utilisation of higher-strength materials can be justified and their lightweight construction potential can thus be exploited to the full, can only be derived from the interaction between all the influencing factors. Examples of a few investigations on welded joints between higher-strength fine-grained structural steels with regard to the interactions between the main variables influencing the cold cracking are presented.
Laser metal deposition is described with its applications for additive manufacturing. The necessary process chain is discussed, with regard to weld bead dimensions and 3D build-up strategy. Metallurgical cross sections, x-ray and tensile tests are conducted. As demonstrative components, a gas turbine burner and a turbine blade are shown
Die zerstörungsfreie Prüfung von austenitischen Mischnähten, wie sie beispielsweise im Primärkreislauf von Kernkraftwerken vorkommen, stellt besondere Anforderungen an die eingesetzte Ultraschallprüfung. Voraussetzung für die positions- und größenrichtige Darstellung von Bauteilfehlern, insbesondere bei bildgebenden Ultraschallverfahren, ist die genaue Kenntnis der Materialparameter auf dem gesamten Schalllaufweg vom Sender zum Empfänger. Im Rahmen eines Forschungsprojekts entwickeln wir ein zerstörungsfreies, inverses Verfahren, das die Schweißnahtparameter entsprechend des Ogilvy-Modells aus der Schallschnelleverteilung bestimmt, die eine Longitudinalwelle an der Oberfläche erzeugt, nachdem sie durch die Schweißnaht gelaufen ist.
Lumineszenzmethoden und funktionelle Chromophore erlangten in den letzten Jahren breite Anwendungen in den Material- und Lebenswissenschaften wie z.B. in der medizinischen Diagnostik, der Beleuchtungs- und Displaytechnologie, der Photovoltaik oder im Sicherheitsbereich für die Echtheitskodierung. Entscheidend für eine hohe Effizienz und Nachweisempfindlichkeit funktioneller Chromophore ist eine große Helligkeit bzw. Brillanz. Brillante Stoffe zeichnen sich durch eine hohe Absorption des anregenden Lichtes (messbar über den molaren Extinktionskoeffizienten) aus sowie durch eine effiziente Umwandlung des absorbierten Lichtes in Lumineszenzlicht bzw. durch eine große Photolumineszenzquantenausbeute aus. Die Bestimmung der Schlüsselgröße Fluoreszenzquantenausbeute erfolgt i.a. relativ zu einem Farbstoff bekannter Fluoreszenzquantenausbeute über einen Vergleich der absorptionsgewichteten integralen Fluoreszenzspektren von Probe und Standard. Hierfür werden Referenzmaterialien mit zertifizierten Fluoreszenzquantenausbeuten benötigt, die bislang nicht verfügbar sind. Im folgenden werden die laufenden Forschungsarbeiten an einer Serie an Fluoreszenzquantenausbeutestandard vorgestellt, die im Spektralbereich von 350 nm – 1050 nm emittieren. Diese Materialien können auch zur Überprüfung von Ulbrichtkugelmessplätzen eingesetzt werden.
The ageing of Fe-Cr model alloys in 0.5 % SO2 and 99.5 % Ar atmosphere was investigated to aim in a fundamental and systematic analysis of the combined oxidation and sulfidation mechanism. The crystallization and reaction paths for oxide and sulfide formation were followed in-situ by energy dispersive X-ray diffraction (EDXRD) in an early stage of corrosion (30 s – 24 h). For this technique, high energetic white synchrotron X-ray radiation (10-100 keV) was used as radiation source. Diffraction pattern were collected continuously in an early stage of corrosion up to 24 h during the complete ageing experiment.
The crystalline phases, growing on top of the coupons, were identified directly via their specific dhkl values. The evolution of the extracted integral intensities of specific reflections of the corrosion products as a function of time access direct information about the kinetics of the nucleation and growth. The results presented here show for iron with 2 wt% Cr wuestite formation first. Wuestite vanishes after 10 min of reaction only and magnetite and hematite appear. Magnetite formation proceeds simultaneously with sulfide formation. Sulfides growth proceeds after an incubation time, which differs for low alloyed (2 wt% Cr) and high alloyed (9 wt% Cr) material.
Die Ergebnisse von in-situ Experimenten am Berliner Elektronenspeicherring (BESSY II) werden vorgestellt. Es wurden Zugversuche an wasserstoffbeladenen und wasserstofffreien supermartensitischen Proben durchgeführt und Diffraktionsspektren und radiographische Bilder aufgenommen. Die energiedispersive Röntgendiffraktion ermöglichte dabei die dehnungsinduzierte Phasenumwandlung von Restaustenit zu Martensit in-situ zu beobachten. Die Radiographiebilder der zerreisenden Probe gaben Einblicke in das Bruchverhalten in Abhängigkeit vom Wasserstoffgehalt des Supermartensits.
The presentation focuses on the current state of the optical spectroscopic studies on plasmon enhanced upconversion luminescent processes of silica-metal core-shell nanocomposites. A general introduction of the upconversion process, the theoretical basis of plasmonic enhancement, the theoretical requirements in regard to NP architecture for plasmon enhanced UC will be outlined. The first proof-of-concept measurements show the difficulty in realization the theoretical measurement parameters in laboratory conditions and underline the need for shifting the experiments to single particle level.“
Im Rahmen eines BMWi Projekts der Fa. Innovent Jena, bei dem ein neuartiger optischer Sensor zur Bewertung der Oberflächenqualität und Reinheit von optischen Gläsern im Fokus stand, wurden die abbildende Ellipsometrie, die IR-Mikroskopie und die Weißlichtinterferenzmikroskopie als Referenzverfahren herangezogen. Mittels Brewster-Winkelmessungen konnten „Wolkenstrukturen“ identifiziert werden, die bei nachfolgenden Beschichtungsprozessen zu Schichtdefekten führen können. Außerdem wurden mittels Ellipsometrie Änderungen im Brechungsindex der Floatgläser (Luft- bzw. Zinnseite) nachgewiesen. Topographie Oberflächenmerkmale wie Welligkeit, Rauheit und Kreuzrillen konnten mittels Weißlichtinterferenzmikroskopie bzw. abbildender Ellipsometrie identifiziert werden.
Advanced spray drying process by controlled slurry destabilization and ultrasonic atomization
(2017)
Spray drying of ceramic slurries aims for soft and free-flowing granules with homogenous microstructure suitable for uniaxial and isostatic pressing. A stable and continuous spray drying process of slurries with maximized solids content is a further development target, since a reduction of the energy intensive drying procedure is desirable.
First part of the investigation focuses on the development of an appropriate zirconia slurry for spray drying with optimized organic additive contents (dispersant + binder + pressing and lubricating agents). Characterization and improvement of slurries are based on zeta potential measurements and investigations of the sedimentation behavior in an optical centrifuge. Therefor the slurries were spray dried with a conventional spray dryer with a two stream nozzle run in fountain mode. The controlled destabilization of the slurries was introduced, since the unwanted formation of hard granules with donut-like shape could be circumvented. Spray drying of such modified slurries resulted in soft granules without voids and finally leaded to sintered bodies with improved microstructure, density and bending strength.
Expectedly, the destabilization process causes a significant increase in viscosity of the ceramic slurry. Hence, an alternative spraying concept utilizing an ultrasonic nozzle was tested. Indeed, the ultrasonic nozzle seems able to atomize slurries with viscosities beyond the capability of the regular two stream nozzles due to the slurry’s shear thinning behavior. In second part of the investigation the integration of the ultrasonic nozzle in a commercial spray dryer is shown and first results of the spraying tests are discussed. Continuous spraying processes of highly viscous alumina, zirconia and ZTA slurries were realized over an extended production period.
Ermittlung eines allgemeingültigen Erstarrungsrisskennwerts durch Abstraktion gängiger Heißrisstests
(2017)
Ergebnisse von Untersuchungen zur Heißrissanfälligkeit metallischer Werkstoffe, die aus gängigen Heißrisstests gewonnen wurden, sind i.A. schlecht mit Ergebnissen aus anderen Testverfahren vergleichbar. Darüber hinaus ist die Fehlererkennungsgenauigkeit der etablierten Testverfahren mitunter dürftig. Auch die Übertragbarkeit der rein Werkstoff-orientieren Testergebnisse auf reale Bauteile gestaltet sich schwierig. Insgesamt ist das Phänomen der Heißrissbildung nicht ausreichend erforscht und verstanden, als dass es in Konstruktion und/oder Bauteilfertigung vorhergesagt werden könnte.
Die vorliegende Arbeit befasst sich mit der Abstraktion gängiger Testverfahren, um verfahrensspezifische Einflüsse möglichst zu eliminieren, sodass eine universellere Beurteilung von Werkstoffen vorgenommen werden kann. Die gewonnenen Ergebnisse können so besser für Simulationen bzw. Vorhersagen der Heißrissanfälligkeit realer Bauteile herangezogen werden.
Die Angabe der Messunsicherheit wird im Rahmen von Konformitätsbewertungen gefordert. Die Messunsicherheit gibt an, wie sicher der wahre Wert der Messgröße getroffen wird. Für ihre Ermittlung gibt es unterschiedliche Ansätze, allen voran der „Guide to the Expression of Uncertainty in Measurement“ (GUM). In der geplanten Auditoren- und Bewerterschulung sollen in einem Übersichtsvortrag "Uncertainty Budgets in Measurement and Testing for Surface Characterization: Ellipsometry, Hardness and Adhesion Testing" Herangehensweisen und Methoden zur Ermittlung der Messunsicherheit vorgestellt und anschließend anhand beispielhafter Anwendungen aus den Arbeitsbereichen der BAM erklärend untersetzt werden.
Mit dieser Schulung sollen die Auditoren und Bewerter der BAM befähigt werden, geltende Anforderungen zur Messunsicherheit handhaben und beurteilen zu können.