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Parameter development for regeneration of high-pressure turbine components of two nickel-based superalloys by laser metal deposition (DED-LB/M)
Full text linkHigh-pressure turbine components in civil aircraft engines are economically highly relevant capital goods due to their single-crystalline material conditions and complex manufacturing. Their service life is directly determined by the degree of damage caused during use. To improve sustainability, there is a particular interest in optimizing the regeneration of damaged areas to ensure optimum use of these investments. Currently used methods such as arc or brazing processes result in a limited service-life extension with a corresponding degradation of component properties compared to the initial state. Novel repair strategies based on additive manufacturing (AM) techniques demonstrate considerable potential in this regard, due to their high degree of geometrical freedom and well-controllable process. Previous research has demonstrated the potential of the powder-based Laser Metal Deposition process (LMD; DED-LB/M) as a promising approach for epitaxial growth of similar materials through a series of successive deposition and remelting steps. It has been demonstrated that a turbine blade tip of up to 2.3 mm and a maximum single-crystalline proportion in the microstructure of 95 % can be regenerated. In addition, the approach for the regeneration of artificial crack-like structures was applied to successfully fill and close 300 μm depth. This study addresses the development of process parameters for two different nickel-based superalloys in use of similar powder compositions. The objective is to maintain and subsequently increase directionally solidified, single-crystalline microstructure in the regenerated areas. In addition, the increase of processing speed while maintaining the desired level of single crystallinity is a further objective. Therefore, the process development is performed on directionally solidified, single-crystalline substrates with a similar chemical composition to the high-pressure turbine components. After process development, verification is conducted in the form of multi-layered cubes. For both analyzed alloys, a maximum single crystallinity of 96.15 % can be achieved
Ozone production of low-frequency plasma using high-impedance high-voltage transformers for volume plasma generation for plasma-based air purification
Full text linkPlasma-based air purification was demonstrated to inactivate a range of pathogens, including viruses, bacteria and fungi, while also breaking down pollutants and odors. Plasma-based air purifiers can be used to clean industrial exhaust air, kitchens, food manufacturing facilities and in animal housing. One of the active mechanisms is attributable to the ozone produced by the plasma from atmospheric oxygen and subsequent ozone chemistry. Accordingly, a high ozone production rate is essential for an efficient process. In this study, the production rates of ozone were measured in a 3 m3 stainless steel chamber of a plasma-based air purifier. The plasma electrode is composed of two electrode stacks, each with 68 glass tubes (two rows of 34 tubes) and a gas gap of 2 mm. These stacks are alternately contacted with the two poles of a high-voltage (HV) transformer in a checkerboard pattern. When an alternating HV is applied, a volume plasma is generated between the glass tubes. The frequency and duty cycle (D), which is the control ratio of the transformer, was changed separately via the power electronics. The maximum electrical power consumption was achieved at the resonance frequency of 75 Hz with the D by 50%. The electrical power consumption decreased at higher and lower frequencies as well as by reducing the D. The results show that the ozone production rate increases with electrical power consumption and excitation frequency when the electrical power consumption is maintained at a constant level
A study on the integration of natural fiber in high-performance sustainable composites
Full text linkIn recent years, there has been an upsurge in environmentally friendly innovations due to the urgent need to address global warming and build a sustainable future. Natural fiber (NF) research is one area of interest that has gained significant attention in the composites industry, mainly due to its low carbon footprint compared to its synthetic counterpart. However, raw NFs currently do not have the same structural properties as their synthetic counterparts, such as carbon fiber (CF) and glass fiber (GF) composites. As a result, high-performance industries have been reluctant to adopt them due to their reduced stiffness in response to mechanical loading, which often limits their use in certain applications. To overcome this obstacle, innovative methods are being developed to improve the performance of these composites while maintaining a lower carbon footprint. This work falls into this category by creating a hybrid composite replacing conventional flow accelerators with NFs, taking advantage of their high permeability. Different natural fiber architectures are being tested for permeability, absorption, structure and infusion simulation. The generated data will be stored as a material library serving as a digital model for future applications. This work aims to combine NFs and CFs to achieve a sustainable design by balancing mechanical properties, manufacturing costs, and environmental footprint, resulting in a multi-objective problem that ultimately advances the general understanding of NFs and their potential in high-performance composites
Optimization of an air classifier coupled with triboelectric material sorting for fine powder separation
Full text linkDie Aufbereitung von Pulvermaterialien spielt in zahlreichen industriellen Anwendungen eine zentrale Rolle – sie umfasst nicht nur die Klassifikation von Partikeln in feine und grobe Fraktionen anhand der Partikelgröße, sondern auch die Materialsortierung unterschiedlicher Substanzen. Hierfür werden vielfach Abweiseradsichter eingesetzt, die in Kombination mit einem elektrostatischen Abscheider (ESP) gleichzeitig triboelektrische Aufladung und Materialsortierung ermöglichen und somit eine zweidimensionale Trennung realisieren. Im ersten Teil dieser Arbeit wird zunächst die eindimensionale, größenbasierte Partikeltrennung ohne Einsatz des ESP untersucht, bevor das gekoppelte System analysiert wird. Die partikelgrößenbasierte Trennung beruht auf dem Gleichgewicht zwischen zwei durch die Strömungsbewegung erzeugten Kräften: der Widerstandskraft, die die Partikel in Richtung des Sichterszentrums zieht, und der Zentrifugalkraft, die infolge der Rotation der Sichterschaufeln entsteht. Eine gleichmäßige Strömungsverteilung ist daher für eine effiziente Trennung unabdingbar. Mithilfe von numerischen Strömungssimulationen (CFD) sowie experimentellen Untersuchungen werden Herausforderungen identifiziert, die einer hohen Trennschärfe und einer Verringerung des Trennkorns im Wege stehen – etwa die Limitierungen, die durch zu hohe Schaufelndrehzahlen oder zu geringe Durchflussraten entstehen. Zur Behebung dieser Probleme wird eine Optimierung der Betriebsparameter vorgeschlagen, insbesondere durch das ausgewogene Verhältnis von Schaufelndrehzahlen und Durchflussrate, um die Bildung starker Strömungswirbel und die Rückmischung von Partikeln zu verhindern. Ergänzend dazu werden geometrische Modifikationen vorgenommen, etwa durch eine Erweiterung der Schaufeln in Richtung des Sichterszentrums sowie durch eine Anpassung ihrer Krümmung. Diese Veränderungen reduzieren die Wirbelintensität, erhöhen die Trennschärfe und ermöglichen die Erzeugung feinerer Pulver bei geringerem Energieaufwand. Die Ergebnisse zeigen, dass rückwärtsgekrümmte Schaufeln – also solche, die gegen die Strömungsrichtung gebogen sind – im Vergleich zu geraden oder vorwärtsgekrümmten Schaufeln konstant feinere Pulver mit einer höheren Trennschärfe liefern. Zudem verbessert eine Vergrößerung des Umwicklungswinkels der Schaufel die Effizienz bei der Feinpulvertrennung. Insgesamt bietet die CFD-basierte Analyse tiefgehende Einblicke in den Trennprozess und zeigt, wie durch die Optimierung von Betriebs- und Geometrieparametern eine effiziente Partikelklassifikation erreicht werden kann. Im zweiten Teil der Arbeit wird die gleichzeitige triboelektrische Aufladung der Partikel während des Klassifikationsvorgangs realisiert – dies erfolgt durch Kollisionen zwischen den Partikeln und den Sichterschaufeln oder anderen Systemkomponenten. Durch gezielte Optimierung von Parametern wie Schaufelndrehzahl und Durchflussrate werden häufige Partikel-Wand-Kollisionen induziert, was die triboelektrische Aufladung verstärkt und eine materialbasierte Trennung anhand der erworbenen Ladung ermöglicht. Dieses duale Trennungssystem bietet die Flexibilität, sowohl die Partikelgrößenverteilung als auch den Materialtyp gezielt zu steuern. Die Untersuchungen zeigen, dass eine Erhöhung der Durchflussrate oder der Schaufelndrehzahl zu höheren Partikelladungen führt – ein entscheidender Faktor für eine effektive Trennung im elektrostatischen Abscheider. Mit diesem Verfahren konnte eine Anreicherung von etwa 25–35 % bei einem 50:50-Gemisch zweier Materialien erzielt werden. Neben der Nutzung der triboelektrischen Aufladung innerhalb der Abweiseradsichter wird ein alternatives Verfahren vorgestellt, bei dem durch einen Zyklonlader eine erzwungene triboelektrische Aufladung erzielt wird. Diese Methode ermöglicht eine präzise Kontrolle sowohl über die Ladungsstärke als auch über die Polarität der Partikelladung und erweitert somit erheblich die Fähigkeit des Systems, mit einer breiten Materialvielfalt umzugehen.The processing of powder materials plays a vital role in various industrial applications, encompassing particle size-based classification into fine and coarse fractions as well as material sorting of powders from different substances. Deflector wheel classifiers are widely used for size-based classification, and when coupled with an electrostatic precipitator (ESP), they enable simultaneous triboelectric charging and material sorting, achieving a two-dimensional separation. This work first examines the one-dimensional particle size-based classification without the ESP, followed by the analysis of the coupled system. Particle size classification relies on the equilibrium between two forces generated by the flow movement: the drag force, which directs particles toward the center of the classifier, and the circumferential force produced by the rotation of the classifier blades. Therefore, efficient classification requires a uniform flow distribution. Through computational fluid dynamics (CFD) simulations and experimental investigations, the first objective of the study identifies challenges in achieving high separation sharpness and reduced cut size, such as the limitations posed by increased blade rotational speed or decreased flow rate. To address these issues, the study proposes optimizing operational parameters, particularly by balancing blade rotational speed with the flow rate to prevent the formation of strong flow vortices and reduce particle back-mixing. Additionally, geometrical modifications, including extending the blades towards the center and adjusting their curvature, are introduced. These changes reduce vortex intensity, improve separation sharpness, and enable the production of finer powders with lower energy consumption. The results reveal that backward-curved blades, bowed against the airflow direction, consistently yield finer powders with higher separation sharpness than straight or forward-curved blades. Furthermore, increasing the blades' wrap angle enhances the efficiency of fine powder separation. The study provides an in-depth analysis of the separation process using CFD simulations and offers insights into achieving efficient particle classification through optimization of operational and geometrical parameters. In the second part of the study, simultaneous particle triboelectric charging during classification is achieved through collisions between particles and the classifier blades or other system components. By optimizing the operational parameters, such as blade rotational speed and airflow rate, the system induces frequent particle-wall collisions, enhancing triboelectric charging and enabling material separation based on the acquired charge. This dual-mode separation system provides flexibility in controlling both particle size distribution and material type. The findings show that increasing either the flow rate or blade speed leads to higher particle charges, which are essential for efficient separation in the electrostatic separator. An enrichment of roughly 25–35% for a 50-50% mixture of two materials has been attained through this method. In addition to utilizing triboelectric charging within the classifier, an alternative mechanism through forced triboelectric charging via a cyclone charger is introduced. This method allows for precise control over both the magnitude and polarity of the particle charge, significantly enhancing the system’s ability to handle diverse materials
Rapid solidification of plant latices from Campanula glomerata driven by a sudden decrease in hydrostatic pressure
Full text linkMonitoring the solidification of droplets of plant latices with a fast quartz crystal microbalance with dissipation monitoring (QCM-D), droplets from Campanula glomerata were found to solidify much faster than droplets from Euphorbia characias and, also, faster than droplets from all technical latices tested. A similar conclusion is drawn from optical videos, where the plants were injured and the milky fluid was stretched (sometimes forming fibers) after the cut. Rapid solidification cannot be explained with physical drying because physical drying is transport-limited and therefore is inherently slow. It can, however, be explained with coagulation being triggered by a sudden decrease in hydrostatic pressure. A mechanism based on a pressure drop is corroborated by optical videos of both plants being injured under water. While the liquid exuded by E. characias keeps streaming away, the liquid exuded by C. glomerata quickly forms a plug even under water. Presumably, the pressure drop causes an influx of serum into the laticifers. The serum, in turn, triggers a transition from liquid-liquid phase separated state (an LLPS state) of a resin and hardener to a single-phase state. QCM measurements, optical videos, and cryo-SEM images suggest that LLPS plays a role in the solidification of C. glomerata
Einflussnahme auf die Gefügemorphologie additiv gefertigter Schichtsysteme
Full text linkDie Bestrebungen zur Ressourceneffizienz bei kostenintensiven und schwer zerspanbaren Werkstoffen erfordert den komplementären Einsatz additiver und abtragender Fertigungsschritte. Die Technologien müssen jedoch gezielt aufeinander abgestimmt werden. Die heterogene Mikrostruktur additiv gefertigter Bauteile, die zu instabilen Schnittbedingungen führt, soll durch Legierungsmodifikation positiv beeinflusst werden. Das Ziel dieser Arbeit ist es, eine Werkstoffmodifikation an Hochleistungslegierungen vorzunehmen und deren Einfluss auf den additiven Fertigungsprozess und die nachfolgende abtragende Bearbeitung zur Erzielung der Endkontur zu untersuchen. Um dieses Ziel zu erreichen, wurde an den Werkstoffen CoCr26Ni9Mo5W und FeNi36 eine Legierungsmodifikation mittels PTA-Verfahren mit den Elementen Ti, Zr und Hf durchgeführt. Es wurde untersucht, welche Auswirkungen die variierenden Massenanteile und Kombinationen der Modifikatoren auf die Gefügemorphologie, die Härte, die resultierende Zerspankraft sowie die Rauheit der bearbeiteten Oberfläche der beiden Legierungen haben. Nach Auswertung dieser Ergebnisse wurden die vielversprechendsten Legierungsmodifikationen entweder durch PVD-Beschichtung des Drahtes oder durch Fülldrahtmodifikation auf den MSG-Prozess übertragen und ebenfalls hinsichtlich der Kriterien bewertet. Zusätzlich wurde untersucht, ob die Legierungseigenschaften durch die Modifikationselemente beeinflusst werden. Aufgrund der Verschleißbeständigkeit von CoCr26Ni9Mo5W wird diese auf Dreikörperabrasiv- und Hochtemperaturstrahlverschleiß untersucht. FeNi36 weist über einen weiten Temperaturbereich einen niedrigen Wärmeausdehnungskoeffizienten auf und wird daher mittels Dilatometrie geprüft. Zusätzlich wird der Zweikörperabrasivverschleiß von FeNi36 getestet. Bei der Legierung CoCr26Ni9Mo5W führten die beiden Modifikationen mit 1 Gew.-% Zr und 1 Gew.-% Hf sowohl beim PTA- als auch beim MSG-Verfahren zu einem homogenen Gefüge, was sich in einer signifikanten Reduzierung der Zerspankräfte auswirkte. Darüber hinaus zeigte sich im Vergleich zur Ausgangslegierung ein geringerer Materialabtrag beim Dreikörperabrasivverschleiß. Bei der Prüfung der Beständigkeit gegen Hochtemperaturstrahlverschleiß wiesen sie einen geringfügig höheren, jedoch vernachlässigbaren Materialabtrag auf. Für die Legierung FeNi36 zeigten im PTA-Prozess keine Modifikationen einen positiven Einfluss auf die Mikrostruktur oder die resultierende Zerspankraft. Mit Hilfe einer Entscheidungsmatrix wurde die Modifikation mit 0,33 Gew.-\% Zr für die Übertragung auf den MSG-Prozess ausgewählt. Hierbei führte die Legierungsmodifikation zu einer deutlichen Veränderung der Gefügemorphologie sowie zu einer Reduktion der Zerspankraft. Hinsichtlich des Ausdehnungskoeffizienten im Bereich von 200 bis 600 °C zeigten die Legierungsmodifikationen kaum Auswirkungen auf dessen Verlauf. Im Hinblick auf die Beständigkeit gegen Zweikörperabrasivverschleiß führte die Modifikation mit 0,33 Gew.-\% Zr sowohl beim PTA- als auch beim MSG-Verfahren zu einem geringeren Materialabtrag. Es konnte gezeigt werden, dass eine Legierungsmodifikation zu einer homogeneren Mikrostruktur der additiv hergestellten Schichtsysteme und zu stabileren Zerspanungsbedingungen führt, wodurch die generativen und abtragenden Fertigungsschritte besser aufeinander abgestimmt werden können.Efforts to increase resource efficiency in the processing of cost-intensive and difficult-to-machine materials require the complementary use of additive and subtractive manufacturing steps. However, strict coordination of these technologies is required. Specifically, alloy modification aims to improve the heterogeneous microstructure of additively manufactured components, which typically leads to unstable cutting conditions. The objective of this study is to modify high-performance alloys and investigate the effects on both the additive manufacturing process and the subsequent subtractive machining required to achieve the final contour. To this end, alloy modifications were performed on CoCr26Ni9Mo5W and FeNi36 using the PTA process with Ti, Zr, and Hf. The study investigated the effects of varying mass fractions and elemental combinations on microstructural morphology, hardness, resulting cutting forces, and surface roughness. Based on these results, the most promising modifications were transferred to the GMAW process—either via PVD wire coating or flux-cored wire modification—and evaluated using the same criteria. Additionally, the influence of the modifying elements on intrinsic alloy properties was examined. Given its high wear resistance, CoCr26Ni9Mo5W was tested for three-body abrasive wear and high-temperature particle erosion. FeNi36, known for its low coefficient of thermal expansion over a wide temperature range, was analyzed using dilatometry. Furthermore, the two-body abrasive wear behavior of FeNi36 was investigated. For CoCr26Ni9Mo5W, modifications containing 1 wt.% Zr and 1 wt.% Hf produced a homogeneous microstructure in both PTA and GMAW processes, leading to significantly reduced cutting forces. Moreover, compared to the base alloy, lower material loss was observed during three-body abrasive wear testing. Regarding resistance to high-temperature particle erosion, material removal was slightly higher but negligible. In the case of FeNi36, none of the PTA modifications showed a positive influence on microstructure or cutting forces. However, using a decision matrix, the modification containing 0.33 wt.% Zr was selected for the GMAW process. Here, the modification resulted in a pronounced change in microstructural morphology and a reduction in cutting forces. The alloy modifications showed only minor effects on the coefficient of thermal expansion between 200 and 600 °C. Regarding two-body abrasive wear, the 0.33 wt.% Zr modification resulted in lower material removal in both PTA and GMAW processes. The study demonstrates that alloy modification leads to a more homogeneous microstructure in additively manufactured layers and more stable machining conditions, thereby facilitating better coordination between additive and subtractive manufacturing steps
Solar-based timekeeping for batteryless devices
Full text linkThe Internet of Things (IoT) is steadily gaining traction, but its reliance on battery power raises significant challenges. To address this, researchers are developing energyharvesting IoT devices that operate on intermittent power, eliminating the need for batteries but complicating accurate timekeeping due to unreliable energy supply. Traditional Real-Time Clocks (RTCs) and synchronization methods are ineffective under such conditions, hindering tasks that require precise timing. We propose timekeeping using TinyML to predict sunrise and sunset based on power usage patterns, enabling autonomous time inference without continuous power or external synchronization. We trained and evaluated multiple lightweight models through simulation and with real hardware, and we demonstrate their potential and shortcomings compared to conventional methods
A study of LoRa antennas for the 868 MHz ISM band: the Good, the Bad, and the Ugly
Full text linkThe rising popularity of long-range wireless networking has led to a global increase in LoRaWAN gateway deployments. Their interconnection to a common backend, such as The Things Network (TTN), establishes the foundation for a plethora of use cases. Especially the availability of low-cost Internet of Things (IoT) prototyping boards and platforms has led to an increasing distribution of LoRa transceivers. Their wireless communication range has, however, been reported to be starkly varying in practice. While a small part of this can be attributed to the natural spread in the manufacturing process of the chipsets, range discrepancies of up to hundreds of meters call for a better explanation. We have hence analyzed the typical components on commodity LoRa transceiver shields and noticed that many of them ship with antennas that are not perfectly matched to the frequency band of interest. This has motivated us to take a closer look at a range of commercially available LoRa antennas for the 868MHz frequency band, as used in European deployments. Our insights show that antennas pre-packed in 868MHz LoRa kits often seemed to be optimized for 902MHz to 928MHz operation. We perform a quantitative analysis of multiple commercially available antennas in different globally used frequency bands for LoRa. Our results show that poorly matched antennas can have severe impact on the transmission range and energy efficiency in LoRa networks. Thus, we highly recommend characterizing antennas prior deployment in order to increase the wireless coverage and reduce energy requirements
Measuring crop parameters via LoRa RSSI: a case study in a cornfield
Full text linkNowadays, precision agriculture and accurate irrigation/fertilization are becoming more and more important in agriculture. To improve the spatial and temporal resolution of traditional sensors, the use of "Networks as a Sensor" could be beneficial. Signal propagation is affected by various physical factors, including ambient humidity, plant biomass, and internal plant water content. This paper explores a longrange wireless sensing system designed to collect RSSI values in combination with biomass ground truth measurements in corn. Our deployment uses low-cost, commercially available sensor nodes and we focus on the feasibility of the long-term deployment. The system uses Long Range (LoRa) technology for wireless communication, enabling data to be transmitted over large distances in agricultural fields