Maschinenbau, Umwelt- und Gebäudetechnik
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Directed energy deposition–electron beam (DED-EB) additive manufacturing is a highly promising process for the fabrication of titanium components, offering high deposition rates and precise process control under vacuum conditions. However, optimizing the deposition characteristics, such as dimensional accuracy, surface quality, and layer uniformity, remains a key challenge, partly due to the complex dynamics of heat input and melt pool behavior. This study examines the influence of electron beam modulation on these deposition characteristics by systematically varying beam deflection parameters, including frequency and pattern, during the wire-based additive manufacturing of titanium. The effects of beam modulation on wire melting, melt pool stability, layer formation, and overall build geometry were thoroughly evaluated. The results demonstrate that carefully controlled electron beam modulation enables significant improvements in deposition stability, surface finish, and control over geometric features, thereby enhancing process reliability and enabling the production of near-net-shape titanium components. Notably, a parameter set consisting of a circular beam deflection at an oscillation frequency of 500Hz and an overfocus setting of + 40 mA effectively minimized surface ripples and waviness, thereby enhancing process stability and yielding defect-free components. These insights contribute to advancing DED-EB as a viable solution for applications where high geometric accuracy and process efficiency are demanded.
Laser cladding is an essential method for strengthening and restoring component surfaces. To increase its efficacy and provide a reliable surface treatment technique, it is necessary to optimize process parameters, enhance material adhesion, and guarantee high-quality, reliable coatings. These measures help to extend the lifespan of components. In this study, the surfaces of AISI 904L stainless steel samples were cladded to prepare various Co-based composite coatings with single and multiple layers reinforced with WC–CoCr–Ni powder. The phases within the newly developed layers were investigated using X-ray Diffraction (XRD), while the microstructure was examined using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). Further tests were performed to assess the hardness, wear resistance and corrosion performance of the deposited coatings. Analyzing and comparing the coatings, it was observed that the coating performance increased with increasing thickness and generally due to a lower amount of Fe present within the microstructure.
This study examines the effect of elevated printing speeds (100–600 mm/s) on the dimensional accuracy and tensile strength of PLA components fabricated via fused deposition modeling (FDM). To isolate the influence of printing speed, all other parameters were kept constant, and two filament variants—natural (unpigmented) and black PLA—were analyzed. ISO 527-2 type 1A specimens were produced and tested for dimensional deviations and ultimate tensile strength (UTS). The results indicate that printing speed has a marked impact on both geometric precision and mechanical performance. The optimal speed of 300 mm/s provided the best compromise between dimensional accuracy and tensile strength for both filaments. At speeds below 300 mm/s, under-extrusion caused weak layer bonding and air gaps, while speeds above 300 mm/s led to over-extrusion and structural defects due to thermal stress and rapid cooling. Black PLA yielded better dimensional accuracy at higher speeds, with cross-sectional deviations between 2.76% and 5.33%, while natural PLA showed larger deviations of up to 8.63%. However, natural PLA exhibited superior tensile strength, reaching up to 46.59 MPa, with black PLA showing up to 13.16% lower UTS values. The findings emphasize the importance of speed tuning and material selection for achieving high-quality, reliable, and efficient FDM prints.
Many components in industry are subjected to high loads during operation and therefore often do not reach their intended service life. Conventional steels frequently do not provide sufficient protection against wear and corrosion. One solution is to coat these components using methods like thermal spraying to apply cermet coatings such as Cr3C2-NiCr or WC-Co-Cr. In light of increasingly strict environmental regulations, more eco-friendly alternatives are needed, especially ones that use little or no Cr, Ni, Co, or W. Another alternative is the recycling of powder materials, which is the focus of this research project. This study investigated whether filter dust from an HVOF system could be used to develop a new coating suitable for use in applications requiring resistance to wear and corrosion. This is challenging as the filter dusts have heterogeneous compositions and irregular particle sizes. Nevertheless, this recycled material, referred to as “Green Cermets” (GCs), offers previously untapped potential that may also be of ecological interest. An established WC-Co-Cr coating served as a reference. In addition to friction wear and corrosion resistance, the study also examined particle size distribution, hardness, microstructure, and susceptibility to crack formation at the interface and inside the coating. Even though the results revealed a diminished performance of the GC coatings relative to the conventional WC-CoCr, they may still be applicable in various industrial applications.
High-entropy alloys are known for their promising mechanical properties, wear and corrosion resistance, which are maintained across a wide range of temperatures. In this study, a CoCrFeNiCu-based high-entropy alloy, distinguished from conventional CoCrFeNi systems by the addition of Cu, which is known to enhance toughness and wear resistance, was investigated to better understand the effects of compositional modification on processability and performance. The influence of key process parameters, specifically laser power and scan speed, on the processability of CoCrFeNiCu-based high-entropy alloys produced by laser powder bed fusion additive manufacturing was investigated, with a focus of low laser power, which is critical for minimizing defects and improving the resulting microstructure and mechanical performance. The printed sample density gradually increases with higher volumetric energy density, achieving densities exceeding 99.0%. However, at higher energy densities, the samples exhibit susceptibility to hot cracking, an issue that cannot be mitigated by adjusting the process parameters. Mechanical properties under optimized parameters were further evaluated using Charpy impact and (in situ) tensile tests. These evaluations were supplemented by in situ tensile experiments conducted within a scanning electron microscope to gain insights into the behavior of defects, such as hot cracks, during tensile testing. Despite the sensitivity to hot cracking, the samples exhibited a respectable ultimate tensile strength of 662 MPa, comparable to fine-grained steels like S500MC (070XLK). These findings underscore the potential of CoCrFeNiCu-based high-entropy alloys for advanced applications. However, they also highlight the necessity for developing strategies to ensure stable and reliable processing methods that can mitigate the susceptibility to hot cracking.
Abstract
This study signifies the development and characterization of a composite material with a metallic matrix of aluminum reinforced with a steel mesh, utilizing centrifugal casting technology. An evaluation was conducted to ascertain the influence of the formulation process and the presence of the insert on the mechanical behavior with regard to tensile strength. The aluminum matrix was obtained from commercial and scrap alloys, elaborated by advanced methods of degassing and chemical modification. Meanwhile, the steel mesh reinforcement was cleaned, copper plated, and preheated to optimize wetting and, consequently, adhesion. The structural characterization was performed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy analyses (EDX), which highlighted a well-defined interface and uniform copper distribution. The composite was produced by means of horizontal-axis centrifugal casting in a fiberglass mold, followed by cold rolling to obtain flat specimens. A total of eight tensile specimens were examined, with measured ultimate tensile strengths ranging from 78.5 to 119.8 (MPa). A thorough examination of the fractured specimens revealed a brittle fracture mechanism, devoid of substantial plastic deformation. The onset of failures was frequently observed at the interface between the aluminum matrix and the steel mesh. The use of SEM and EDX investigations led to the confirmation of the uniformity of the copper coating and the absence of significant porosity or interfacial defects. A bimodal distribution of tensile strength values was observed, a phenomenon that is likely attributable to variations in mesh positioning and local differences in solidification. A correlation was established between the experimental results and an analytical polynomial model, thereby confirming a reasonable fit. In sum, the present study provides a substantial foundation for the development of metal matrix composites with enhanced performance, specifically designed for challenging structural applications. This method also demonstrates potential for recycling aluminum scrap into high-performance composites with controlled microstructure and mechanical integrity.
Die Optimierung mechanischer Bauteile nimmt in der Entwicklung technischer Produkte einen immer größer werdenden Stellenwert ein. Ziel dieses Prozesses ist herauszufinden, welche Form und Topologie eine Struktur besitzen muss, um die an sie gestellte Konstruktionsaufgabe besonders gut zu erfüllen. Damit die optimierten Strukturen auch herstellbar sind, ist das Bestreben aktueller Forschung, Informationen über die Fertigungsprozesse direkt in die entsprechenden Optimierungsverfahren in Form von Fertigungsrestriktionen zu integrieren. In dieser Arbeit wird eine Methodik zur Integration von Fertigungsrestriktionen bei 3D-Fräsverfahren in die Topologieoptimierung mit der Level-Set-Methode entwickelt. Berücksichtigt werden dabei die Gewährleistung der Werkzeugzugänglichkeit aller Bearbeitungspunkte sowie die Einhaltung einer Mindestwandstärke. Die Methodik basiert auf der Induktion eines Strukturwachstums in Bereichen, die entweder unzugänglich oder zu dünn sind. Um diese Bereiche zu identifizieren, wird ein Verfahren entwickelt, bei dem die Level-Set-Funktion entlang der Außenkonturen realistischer Werkzeuggeometrien interpoliert wird. Zur Induktion des Strukturwachstums wird regelmäßig ein Potential definiert. Dieses besitzt innerhalb der Struktur größere Werte als außerhalb und ändert sich normal zum Strukturrand linear. Eine Minimierung des auf dem Strukturrand vorliegenden Potentials wird in ein Strukturwachstum überführt. Dazu werden die Sensitivitäten des Potentials bezüglich Verschiebungen des Strukturrandes ermittelt und mit den Entwicklungsgeschwindigkeiten der Level-Set-Funktion gekoppelt. Dadurch werden beide Fertigungsrestriktionen in eine gemeinsame mathematische Restriktion überführt und schließlich explizit in das Optimierungsproblem integriert.
Femtosecond laser-induced nano structuring offers a novel approach to enhance the performance of porous transport layers (PTLs) in anion-exchange membrane water electrolysis. By applying ultrashort laser pulses to nickel felts, distinct surface morphologies were generated, including high-spatial-frequency laser-induced periodic surface structures (HSFL-LIPSS), irregular ablated surfaces, and hybrid structures. Surface area analysis revealed increases of up to 4-fold for LIPSS, 6-fold for hybrid structures (LIPSS+Ablation), and 9-fold for ablated surfaces compared to untreated fibers. Electrochemical testing showed reduced overpotentials for laser-treated samples, comparable to state-of-the-art electrodes despite the absence of catalyst layers. Overpotentials could be reduced by up to 6.5 % at 10 mA cm−2 and by up to 9.6 % at 100 mA cm−2 compared to the unprocessed felt. Notably, ablated structures, with the highest surface areas, exhibited microcavities that may entrap oxygen bubbles, limiting active site and reaction rates. The LIPSS structures demonstrated the lowest activation losses and highest current density (1.32 A cm⁻² at 2.0 V) due to their periodic morphology and enhanced electrolyte flow, representing a 17 % improvement at 2.0 V compared to the untreated felts. Moreover, Tafel slopes down to 66 mV dec−1 denote a performant kinetic while oxidation charge measurements revealed pronounced peaks for laser-treated samples, with ablated surfaces achieving the highest charge of 16.76 ± 1.64 C cm⁻². Chronopotentiometry revealed the LIPSS structures showing the highest resistance to degradation among the structured samples.
These findings suggest femtosecond laser nano structuring as a promising method to improve PTL performance. Further application of catalyst layers could amplify the electrochemical efficiency of these advanced materials.
To enhance the operational life of hydraulic machinery, protective coatings against wear, particularly cavitation erosion, and corrosion might be applied on the surfaces of components. The experiments conducted in this study aimed to assess the suitability of 80/20 NiCrBSi/WC-Co composite coatings for this purpose. A coating of NiCrBSi self-fluxing alloy, which served as the reference material, was deposited alongside a NiCrBSi coating reinforced with 20% WC-Co, both applied by flame spraying onto X3CrNiMo13-4 substrates, the martensitic stainless steel type frequently utilized in turbine blade manufacturing. The improved density of the coatings and adhesion to the substrate was achieved by remelting with an oxyacetylene flame. The cavitation and corrosion performance of both the reference and composite coating were evaluated through cavitation tests and electrochemical measurements conducted in the laboratory. The results demonstrate that the addition of 20% WC-Co significantly enhances the cavitation resistance of the composite material, as evidenced by the reduction to 3.76 times of the cumulative erosion (CE), while the stabilization rate remained at half the value observed for the reference self-fluxing alloy coating. Conversely, the addition of WC-Co into the NiCrBSi coating resulted in a slight decrease in the corrosion resistance of the self-fluxing alloy. Nevertheless, the corrosion rate of the composite coating (124.80 µm/year) did not significantly exceed the upper limit for excellent corrosion resistance (100 µm/year).

