Skalenübergreifende Charakterisierung des Ausscheidungs- und Auflösungsverhaltens in mikrolegierten Stählen

Eine geringe Zugabe von sogenannten Mikrolegierungselementen wie Niob, Titan oder Vanadium verbessert die mechanischen Eigenschaften von niedriglegierten Stählen deutlich. Thermomechanische Umformung, z.B. Walzen, vereinigt die mechanische Formgebung mit kontrollierten Wärmebehandlungen und ermöglicht dadurch die gezielte Einstellung der Stahlmikrostruktur. Die verbesserten mechanischen Eigenschaften können vielfach zur Reduktion der benötigten Stahlmenge eingesetzt werden, wodurch ökonomisch und ökologisch große Einsparpotentiale entstehen. Hinsichtlich der maßgeschneiderten Entwicklung immer neuer Stahlsorten mit optimierten Eigenschaften und einem immer wichtiger werdenden nachhaltigen Ressourceneinsatz ist es in der Forschung und Industrie von großer Bedeutung, zu jedem Zeitpunkt im Herstellungsprozess den Zustand der Legierungselemente und deren Wirkung auf die Mikrostruktur quantifizierbar zu machen. Die vorliegende Arbeit fokussiert sich auf die Entwicklung einer Methodik zur präzisen Quantifizierung von Niob und dessen Ausscheidungen während der thermomechanischen Umformung. Die elektrische Widerstandsmessung erlaubt dabei die schnelle und gleichzeitig hoch sensitive Messung des gelösten bzw. ausgeschiedenen Niobgehalts in einer Vielzahl von Stadien des thermomechanischen Umformprozesses und bei variierten Umformparametern. Durch die Korrelation mit anderen hochauflösenden Charakterisierungsverfahren werden die Grenzen und Annahmen des elektrischen Widerstandes als Maß für die Quantifizierung von Niob diskutiert. Modellrechnungen nutzen die experimentellen Realdaten und beschreiben die Niob-Löslichkeit und seine Ausscheidungskinetik. Dadurch werden valide Aussagen über die werkstoffphysikalischen Prozesse in industriell relevanten Stahlsorten getroffen.A small addition of so-called microalloying elements such as niobium, titanium or vanadium significantly improves the mechanical properties of low-alloy steels. Thermomechanical forming, e.g. rolling, combines mechanical shaping and heat treatment and thus enables tayloring of the steel microstructure. This results in major potential savings because the amount of steel required can be reduced through improved mechanical properties. With regard to the customized development of ever new steel grades with optimized properties and the increasingly important sustainable use of resources, it is very important in research and industry to be able to quantify the state of the alloying elements and their effect on the microstructure at any point in the manufacturing process. The present work focuses on the development of a methodology to precisely quantify niobium and its precipitates during thermomechanical rolling. In this context, electrical resistivity measurement allows the quick and highly sensitive measurement of the dissolved or precipitated niobium on the macro-scale and at a variety of stages of the thermomechanical process and varied deformation parameters. By correlation with other high-resolution characterization techniques, the limitations and assumptions of electrical resistivity as a measure for niobium quantification are discussed. Model calculations employ the experimental real data and describe the niobium solubility and its precipitation kinetics. By this, valid conclusions are drawn about the material physics in industrially relevant steel grades

Precipitate number density determination in microalloyed steels by complementary atom probe tomography and matrix dissolution

Particle number densities are a crucial parameter in the microstructure engineering of microalloyed steels. We introduce a new method to determine nanoscale precipitate number densities of macroscopic samples that is based on the matrix dissolution technique (MDT) and combine it with atom probe tomography (APT). APT counts precipitates in microscopic samples of niobium and niobium-titanium microalloyed steels. The new method uses MDT combined with analytical ultracentrifugation (AUC) of extracted precipitates, inductively coupled plasma–optical emission spectrometry, and APT. We compare the precipitate number density ranges from APT of 137.81 to 193.56 × 1021 m−3 for the niobium steel and 104.90 to 129.62 × 1021 m−3 for the niobium-titanium steel to the values from MDT of 2.08 × 1021 m−3 and 2.48 × 1021 m−3. We find that systematic errors due to undesired particle loss during extraction and statistical uncertainties due to the small APT volumes explain the differences. The size ranges of precipitates that can be detected via APT and AUC are investigated by comparison of the obtained precipitate size distributions with transmission electron microscopy analyses of carbon extraction replicas. The methods provide overlapping resulting ranges. MDT probes very large numbers of small particles but is limited by errors due to particle etching, while APT can detect particles with diameters below 10 nm but is limited by small-number statistics. The combination of APT and MDT provides comprehensive data which allows for an improved understanding of the interrelation between thermo-mechanical controlled processing parameters, precipitate number densities, and resulting mechanical-technological material properties. Graphical abstract: [Figure not available: see fulltext.

Quantitative analysis of mixed niobium-titanium carbonitride solubility in HSLA steels based on atom probe tomography and electrical resistivity measurements

Solubility of mixed niobium-titanium carbonitrides in commercially relevant High Strength Low-Alloy (HSLA) steel was investigated by combined use of electrical re sistivity measurements and APT after interrupted quenching from soaking temperatures between 950 and 1250 C. Increasing electrical resistivity of the bulk material towards higher soaking temperatures was proportional to the nominal niobium addition which was varied between 0.002 and 0.022e0.043e0.085 wt.-%. Correlative APT analysis of the solutes in the steel matrix showed good agreement with electrical resistivity. Investigating numerous precipitate particles, APT also derived a precise composition for mixed niobium titanium-carbonitrides which constitute the steel microstructure after casting/before soaking. The scavenging of microalloy elements by insoluble titanium nitrides was cor rected by means of combined APT analysis of such precipitate and a quantitative image analysis for the estimation of the total volume fraction of titanium nitrides. For the first time, solute and precipitate composition together were used for solubility calculations of such mixed carbonitrides to derive an experimental solubility product. This was compared to solubility products of well-established simple carbides and nitrides and theoretical calculations of the solubility of multicomponent carbonitrides. The large discrepancy between experimentally derived and modelled solubility emphasizes the ne cessity of a robust methodology for the quantification of microalloy precipitation in HSLA steels

Development of a Protective Coating for Evaluating the Sub-surface Microstructure of a Worn Material

In the current study, electrolytic deposition using two diferent electrodes, copper (Cu) and nickel (Ni) was investigated with the aim of protecting the worn surface during mechanical sectioning and polishing, for a posterior examination of the sub-surface microstructure. The efcacies of the two coatings were visually assessed based on its adhesivity and the ability to protect the wear tracks of an as-cast 26% Cr high chromium cast iron (HCCI) alloy. It was observed that electrodeposition using Cu as the electrode was inefective owing to a poor adhesivity of the coating on the HCCI surface. The coating had peeled of at several regions across the cross-section during the mechanical sectioning. On the other hand, Ni electroplating using Ni strike as the electrolyte was successfully able to protect the wear track, and the sub-surface characteristics of the wear track could be clearly visualized. A uniform coating thickness of about 8 µm was deposited after 30–40 min with the current density maintained between 1 and 5 A/dm2 . The presence of the Ni coating also acted as a protective barrier prevent ing the ejection of the broken carbide fragments underneath the wear track

Tracing Microalloy Precipitation in Nb-Ti HSLA Steel during Austenite Conditioning

The microalloying with niobium (Nb) and titanium (Ti) is standardly applied in low carbon steel high-strength low-alloy (HSLA) steels and enables austenite conditioning during thermo-mechanical controlled processing (TMCP), which results in pronounced grain refinement in the finished steel. In that respect, it is important to better understand the precipitation kinetics as well as the precipitation sequence in a typical Nb-Ti-microalloyed steel. Various characterization methods were utilized in this study for tracing microalloy precipitation after simulating different austenite TMCP conditions in a Gleeble thermo-mechanical simulator. Atom probe tomography (APT), scanning transmission electron microscopy in a focused ion beam equipped scanning electron microscope (STEM-on-FIB), and electrical resistivity measurements provided complementary information on the precipitation status and were correlated with each other. It was demonstrated that accurate electrical resistivity measurements of the bulk steel could monitor the general consumption of solute microalloys (Nb) during hot working and were further complemented by APT measurements of the steel matrix. Precipitates that had formed during cooling or isothermal holding could be distinguished from strain-induced precipitates by corroborating STEM measurements with APT results, because APT specifically allowed obtaining detailed information about the chemical composition of precipitates as well as the elemental distribution. The current paper highlights the complementarity of these methods and shows first results within the framework of a larger study on strain-induced precipitation

A proteomics sample metadata representation for multiomics integration and big data analysis

The amount of public proteomics data is rapidly increasing but there is no standardized format to describe the sample metadata and their relationship with the dataset files in a way that fully supports their understanding or reanalysis. Here we propose to develop the transcriptomics data format MAGE-TAB into a standard representation for proteomics sample metadata. We implement MAGE-TAB-Proteomics in a crowdsourcing project to manually curate over 200 public datasets. We also describe tools and libraries to validate and submit sample metadata-related information to the PRIDE repository. We expect that these developments will improve the reproducibility and facilitate the reanalysis and integration of public proteomics datasets.publishedVersio

Tracing Microalloy Precipitation in Nb-Ti HSLA Steel during Austenite Conditioning

The microalloying with niobium (Nb) and titanium (Ti) is standardly applied in low carbon steel high-strength low-alloy (HSLA) steels and enables austenite conditioning during thermo-mechanical controlled processing (TMCP), which results in pronounced grain refinement in the finished steel. In that respect, it is important to better understand the precipitation kinetics as well as the precipitation sequence in a typical Nb-Ti-microalloyed steel. Various characterization methods were utilized in this study for tracing microalloy precipitation after simulating different austenite TMCP conditions in a Gleeble thermo-mechanical simulator. Atom probe tomography (APT), scanning transmission electron microscopy in a focused ion beam equipped scanning electron microscope (STEM-on-FIB), and electrical resistivity measurements provided complementary information on the precipitation status and were correlated with each other. It was demonstrated that accurate electrical resistivity measurements of the bulk steel could monitor the general consumption of solute microalloys (Nb) during hot working and were further complemented by APT measurements of the steel matrix. Precipitates that had formed during cooling or isothermal holding could be distinguished from strain-induced precipitates by corroborating STEM measurements with APT results, because APT specifically allowed obtaining detailed information about the chemical composition of precipitates as well as the elemental distribution. The current paper highlights the complementarity of these methods and shows first results within the framework of a larger study on strain-induced precipitation

Auslegung und Verifikation neuer Verfahren der Kabinenbelüftung für Verkehrsflugzeuge

Zielsetzung dieses Vorhabens war die Validierung der Vorteile des Konzepts der Quellbelüftung für Flugzeugkabinen unter realen Flugbedingungen im „Advanced Technology Research Aircraft“ (ATRA) des DLR sowie die Evaluation neuartiger Verdrängungslüftungskonzepte für Flugzeugkabinen in dem bodengebundenen Versuchsträger Do 728 des DLR. Ferner sollte ein aktives Lining zur Reduzierung des Lärmeintrags in die Kabine entwickelt und erforscht werden. Die Themen wurden im Rahmen des SINTEG-Verbundprojektes mit den Projektpartnern Airbus Operations GmbH und Diehl Aircabin bearbeitet. Erstmalig wurde ein flugfähiges Quellbelüftungssystem in eine A320 Flugzeugkabine integriert. Zur experimentellen Simulation und messtechnischen Erfassung der resultierenden Kabinenströmung wurde ein für Flugversuche zugelassenes Kabinenmesssystem entwickelt und aufgebaut. In Boden- und Flugversuchen konnten die erwarteten Vorteile der Kabinen Quellbelüftung bestätigt werden. Parallel zu den experimentellen Untersuchungen wurden die relevanten Strömungsfälle mittels numerischer, zeitaufgelöster Rechenverfahren simuliert, um genaueren Aufschluss über die dreidimensionalec Strömungsstrukturen in der ATRA-Kabine zu erhalten. Aufbauend auf den Erfahrungen der Flugversuche wurde ein Deckenluftauslasses entwickelt, der die Möglichkeit bietet, Luft gleichmäßig und impulsarm über die Decke in die Kabine zu bringen sowie in zukünftigen Ausbaustufen als multifunktionale Interieurkomponente parallel Licht oder Geräusche in die Kabine einzukoppeln. Die aerodynamischen Möglichkeiten, die sich hieraus für die Kabinenbelüftung ergeben wurden in dem Do 728 Versuchsträger experimentell untersucht. Schließlich wurde ein aktives Lining entwickelt, das die Schallabstrahlenden Schwingungen eines Linings durch aktive Struktur-Akustik Regelung deutlich reduziert

Virtual and augmented reality training platforms for transfer of skills

Within the European project SKILLS Virtual and Augmented Reality platforms have been developed that are used for the realization of different training simulators in the field of sports (training of rowing and juggling), surgery (training of maxillofacial and telerobotic surgery), rehabilitation (rehabilitation of upper limp), maintenance (training of assembly procedures) and robotics (training of robot programming). These platforms are integrating capturing and rendering technologies. The capturing technologies are used to register specific criteria of skills to be hold in a digital representation. Thus, parameters relevant for specific skills are qualified and used as evaluation factors within the training simulators. The training simulators not only can simulate the virtual environment of the training situation, but this environment can be enhanced via multimodal renderings, fostering the training process and accelerating the training effect. The integrative platforms from scalable and adaptable frameworks that can be used to realize different training protocols and that can be adapted to the trainee's degree of skill. Therefore the training protocol can be specified via standardized application scripts