Josefine Lemke, Max Biegler, Michael Rethmeier
Powder properties are considered a key factor in part quality in laser additive manufacturing, although few studies have investigated the effects in directed energy deposition (DED). Water atomized (WA) and gas atomized (GA) powders are frequently used but may result in different part properties due to powder properties. To examine their qualification for DED-LB, this work examines powders and build quality of AISI 316L. Also, examination techniques are compared. The results show that the powder production has no relevant influence on porosity and Archimedian density of built parts. WA powders show good processability in DED-LB, despite unfavorable morphology. In contrast, WA specimen reach only 10% fracture elongation in tensile testing whereas GA-based specimen achieve 30%. Tensile strength of both is above 500 MPa. The reason for the lower mechanical property values can be attributed to defects and oxides. WA powders may provide a cost-effective alternative for DED-LB when mechanical load requirements are not important.
Keywords: DED-LB; porosity; AISI 316L; water atomized; gas atomized; powder
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Influence of TiC-nanoparticles in Laser Metal Deposition of EN AW-7075
Finn Bendixen, Annika Bohlen, Thomas Seefeld
EN AW-7075 (AlZn5,5MgCu) is a high strength aluminum alloy for aerospace applications suffering from poor weldability due to solidification cracking susceptibility. In this study, crack free Laser Metal Deposition (LMD) of EN AW-7075 is enabled by adding up to 1 vol% of TiC-nanoparticles (35-55 nm) to the powder feedstock. It was found that nanoparticles are successfully incorporated into the melt pool where they provide grain refinement due to inoculation and thereby eliminate hot cracking.
Moreover, the addition of nanoparticles enhances the absorption of the laser wavelength in the powder (as measured with an Ulbricht sphere). It was found that the coupling efficiency of the processing laser beam was increased for the alloy to a small extent and no challenges due to reduced flowability occurred.
Keywords: Laser Metal Deposition; grain refinement; hot cracking; nanoparticles
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E. Weisser, P. Kiefer, V. Glushych, R. Hama-Saleh Abdullah
This study investigates the influence of process gases on the laser material deposition process, with a particular focus on their effects on geometric characteristics of single tracks, process temperature and microhardness. The research aims to analyze the interactions between the selected process gases argon, helium, nitrogen, and carbon dioxide and the powder material 316L. A comparative evaluation with laser welding techniques highlights shared principles and distinct effects, providing a comprehensive understanding of process dynamics. Experimental investigations and literature analyses reveal the critical impact of gas flow rates, chemical reactivity, and thermal conductivity on the resulting layer quality and structural properties. The findings contribute to optimizing process parameters, ensuring enhanced material performance and reliability in industrial applications. This work serves as a foundation for future studies on tailored gas applications in laser-based manufacturing processes.
Keywords: Laser Material Deposition; Process Gases; 316L; Argon; Helium; Nitrogen; Carbon Dioxide; Microstructure; Dilution Zone; Heat-Affected Zone; Microhardness; Process Temperature
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Akshay Ashok Benni, Pietro Antonio Martelli, Vasile Luchin, Ilchat Sabirov, Andrea Crosato, Alper Kanyilmaz, Ali Gokhan Demir, Barbara Previtali
Additive manufacturing (AM) of steel is gaining traction in the construction industry, offering the ability to fabricate complex geometries and optimize resource use. Among the AM techniques, Laser-Based Powder Directed Energy Deposition (DED-LB) is notable as it provides a compromise of relatively high productivity with respect to powder bed fusion and fine resolution with respect to arc based DED processes. However, the common steel grades often encounter challenges in meeting construction requirements, including limited compatibility with conventional structural steels concerning bolted and welded assemblies. This study tackles these challenges by developing the DED-LB process with a novel high-strength steel powder feedstock. Through an extensive experimental campaign, the research evaluates the processability of the material, focusing on achieving dense and crack-free steel components. The results highlight optimized deposition strategies providing high mechanical strength, opening new possibilities for its adoption in the construction sector for medium to large sized products.
Keywords: Laser Metal Deposition, DED-LB, high strength steel, steel structures
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Laser-Based Powder Fixation on Textiles for Highly Functionalized Coatings
Yashas Shivakumar, Annika Gambke, Dr. Andreas Neudeck, Julia Ullrich
In recent years, the demand for Smart and Technical Textiles has increased, especially with the incorporation of sensors and actuators. However, current conductive textile structures, achieved by integrating conductive yarns, wires, and strands or by conventional coating and printing technologies, lack kink resistance, reliability, and the required grade of functionalization. The proposed process allows the application of a multi-material powder comprising a blend of polymer powders and functional pigments, e.g., metal particles. The technology is characterized by a nozzle-based application of the loose powder mixture and a subsequent laser fixation step. This enables the fabrication of individualized and highly functionalized coated substrates based on a digital data set. However, it was noticed that the laser beam path overshoots the targeted tracks for various reasons, such as substrate surface, heat-affected zone, different powder types used, and their interaction with the laser are discussed here.
Keywords: Powder; Coating; Multi-material; Additive Manufacturing; Smart textiles
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Annika Bohlen, Thomas Seefeld
In laser-based directed energy deposition (DED), a well-aligned powder stream relative to the laser beam is essential for maximizing process efficiency and minimizing material loss. A detailed understanding of powder stream propagation is therefore critical. In this study, high-speed imaging was used to investigate particle behavior within the powder stream. Using a multi-step evaluation method, the mean velocity, velocity variations, and flight direction of individual particles were determined. Powder channels with varying surface roughness—ranging from Ra = 2.16 µm to 0.27 µm—were tested to assess their influence on stream characteristics. The results reveal that lower channel roughness leads to increased mean particle velocity and significantly narrower flight angles. Specifically, the divergence angle decreased by approximately 61 %, which suggests the potential for a more focused powder stream and reduced material loss. In addition to these findings, 70-hour endurance tests confirmed the long-term stability of particle flow and divergence, with no measurable changes observed. Surface topography evolved slightly due to particle impact, but roughness values remained stable and no structural degradation occurred. These findings offer valuable insights into optimizing powder delivery systems for enhanced efficiency and precision in laser-based DED processes.
Keywords: Laser-based Directed Energy Deposition, Powder Nozzle, Powder Stream Propagation