Direct Deposition Research Articles

Microstructural analysis of Inconel 718 manufactured via direct energy deposition: response surface methodology for process parameters optimisation and post-heat treatment

Microstructural analysis of Inconel 718 manufactured via direct energy deposition: response surface methodology for process parameters optimisation and post-heat treatment

Fatigue Performance of Ti-6Al-4V Processed by Wire-Arc Directed Energy Deposition

AbstractTi-6Al-4V has a wide range of applications, but long lead times and low-efficiency processing of the material leads to limitations. Through additive manufacturing, such as wire-arc directed energy deposition, higher processing efficiency, and lower lead times are possible. To fully realize the benefits, an important parameter for application is the fatigue performance, which needs to be better documented and performance shortcomings improved. Currently, available results on fatigue performance of wire-arc directed energy deposition of Ti-6Al-4V are limited. Therefore, wire-arc directed energy deposition of Ti-6Al-4V was used with the following approach. Samples were characterized using scanning electron microscopy and optical light microscopy, and mechanically tested for tensile and fatigue performance. Minimal pore density and a fine α microstructure within coarsened epitaxial columnar β-grains was observed. Additionally, elemental burn-off and oxygen contamination was assessed, showing a loss of 0.2 wt.% aluminum during processing and no oxygen pick-up. Compared to other cold metal transfer-based wire-arc directed energy deposition results available in the literature, the results present significant improvements. Fractography indicated mixed fracture modes, which are likely due to the macro-zones of α having varying orientations. Our work provides an advancement in fatigue performance and processing, further showing the potential of the technology.

Electrophoretic deposition of carbon-ionomer layers on proton conducting membranes.

Synthetic and natural carbons are widely used as carrier for electrodes in electrochemical applications. They need to have a controlled morphology in order to facilitate mass and charge transport, so the process of film formation is of uttermost importance. Here we show, how carbons (after proper preconditioning) can be codeposited with an ionomer by electrophoretic deposition, a method that does allow full control of deposition conditions during the process. In view of potential applications, we focus on the direct deposition on proton-conducting membranes. Ionomers and membranes applied are based on established per-fluorinated polyethylene with SO3H-terminated side chains (PFSA). Conditions for reproducible deposition are reported in terms of optimal charge on the carbon particles, field strength in the deposition cell and necessary deposition times for a given film thickness. Additionally, a horizontal cell arrangement is suggested to avoid gravitational effects.

Spider waste enhances soil nutrient content, soil respiration, and plant growth

Abstract Predators can alter the movement of nutrients through ecosystems by depositing waste products following predation. Whilst the benefits of predator waste for large predators (e.g. bears) or dense accumulations of predators (e.g. seabirds on islands) seem clear, less is known about whether smaller, solitary predators can have measurable effects on local ecosystem processes. In separate experiments with web‐building and wandering spiders, we tested if the presence of predators affected soil nutrient content, soil respiration, soil microbial communities, and plant growth. In the first experiment with black widow spiders, total nitrogen and nitrate were not affected by spider presence, but ammonia and phosphorus were higher from soil under the edge of the spider web than soil away from the spider. Soil respiration and plant growth were both higher in soil collected from under the spider retreat compared with soil collected away from the spider web. In a second experiment with wolf spiders, we tested for interactions between spiders and soil microbial communities. There were positive effects of wolf spider presence on all soil nutrients and there were interactions between spiders and soil type (i.e. field‐collected versus autoclaved) for total carbon, total nitrogen, nitrate, and pH. Spider presence and soil type also affected soil respiration and spider presence had a large effect on the composition of the microbial community of the soil. There were also positive effects of wolf spider presence on plant biomass and plant height, with a significant interaction between spiders and soil type for plant height. Overall, our results show that two spiders with different life histories (i.e. web‐building and wandering) both have significant positive effects on plant growth through the deposition of their waste products. These effects may occur through the direct deposition of nutrients and changes in soil microbial communities. Although, further work is needed to resolve these interactions. Read the free Plain Language Summary for this article on the Journal blog.

Integrated top-down process and voxel-based microstructure modeling for Ti-6Al-4 V in laser wire direct energy deposition process

Laser-wire metal additive manufacturing (AM) is one of the ideal direct energy deposition (DED) processes for creating large-scale parts with a medium level of complexity. However, the DED process involves complex thermal signatures and wide length scales making the fabrication of realistic AM components and part qualification often reliant on experimental trial-and-error optimization. While experimental measurements over the full volume of a part are valuable and necessary, measuring the entire area of a part is significantly laborious and practically infeasible, particularly for large parts in terms of cost and rapid qualification. Therefore, in this work, we developed an effective thermal and microstructure modeling framework based on the Johnson–Mehl-Avrami-Kolmogorov (JMAK) and Koistinen & Marburger (KM) models through a top-down approach that considers plate distortion-affected thermal profiles. A voxel-by-voxel simulation method is used to predict individual phase fractions of Ti-6Al-4 V. The predicted results were validated through detailed metallurgical measurements. A combined voxel-by-voxel approach with a sparse data reconstruction technique produced a near-perfect reconstruction of the original data. This approach anticipates a significant reduction in data points and computation time and resources. Lastly, we conclude with potential extensions of this work to other modeling efforts.

Studies on hardness, elastic modulus and high temperature oxidation resistance of TiC and TiB2 dispersed titanium aluminide (Ti45Al5Nb0.5Si) composites developed by laser direct energy deposition

In this study, TiC (5 to 10wt.%) and TiB2 (5 to 10wt.%) reinforced TiAl (Ti45Al5Nb0.5Si) composites have been developed by laser direct energy deposition (LDED) process. The microstructures of TiAl/TiC and TiAl/TiB2 composites consist of TiC and TiB2 particles dispersed in γ and α2 matrix. The microhardness of the composites is improved from 571 HV to 634-683 HV (for TiC dispersion) and 649-694 HV (for TiB2 dispersion). The activation energy of cyclic oxidation is increased from 228kJ/mol (Ti45Al5Nb0.5Si) to 271-301kJ/mol (TiC dispersion) and 262-296kJ/mol (TiB2 additions). The mechanism of oxidation of the composites is established.

Circumventing cracking in grading 316L stainless steel to Monel400 through compositional modifications in directed energy deposition

In joining Fe-alloys and Cu-containing alloys to access the high strength of steels and corrosion resistance of Cu-alloy, cracking is widely observed due to the significant Cu microsegregation during the solidification process, resulting in an interdendritic Cu-rich liquid film at the end of solidification. By fabricating functionally graded materials (FGMs) that incorporate additional elements like Ni in the transition region between these terminal alloy classes, the hot cracking can be reduced. In the present work, the joining of stainless steel 316L (SS316L) and Monel400 by modifying the Ni concentration in the gradient region was studied. A new hot cracking criterion based on hybrid Scheil-equilibrium approach was developed and validated with monolithic multi-layer samples within the SS316L-Ni-Monel400 three-alloy system and a SS316L to 55/45 wt% SS316L/Ni to Monel400 FGM sample fabricated by direct energy deposition (DED). The new hot cracking criterion, based on the hybrid Scheil-equilibrium approach, is expected to help design FGM paths between other Fe-alloys and Cu-containing alloys as well.

Laser Directed Energy Deposition Additive Manufacturing of Al7075 alloy: Process Development, Microstructure, and Porosity

7xxx series aluminum alloys are priority materials adopted in aerospace because of their lightweight property and excellent mechanical performance. The combination of lightweight material and additive manufacturing techniques can significantly promote lightweight design in many industries. This study developed the optimal process for manufacturing Al7075 alloy by laser-aided directed energy deposition and revealed the material properties of the as-deposited Al7075 specimens. Firstly, single-track experiments were conducted by varying laser power, printing speed, and powder delivery rate in broad ranges. Results indicated that the printing speed and powder delivery rate impact the surface finish and shape of single-track beads considerably. Block specimens printed with the optimal parameters selected from the single-track experiments present crack-free quality and have a high relative density of up to 99.89%. Second phases with rich Cu, Mg, and Zn elements along the inter-dendritic regions and grain boundaries were observed from the microstructure inspection. The composition of zinc in the deposited samples is lower than usual, which leads to a relatively low microhardness.

Microstructure and mechanical properties of Mg-Nd-Zn-Zr alloy fabricated by TIG-based wire - arc directed energy deposition with pulsed current

In this study, the Mg-2.16Nd-0.49Zn-0.48Zr (wt%) alloy thin-wall specimens were prepared by tungsten inert gas (TIG) based wire-arc directed energy deposition (WA-DED) with different pulsed currents. The arc characteristics, microstructures, and mechanical properties of as-deposited (AD), 5 Hz, 10 Hz, 15 Hz, and 20 Hz specimens were systematically analyzed and evaluated. The uniformly equiaxed crystals with random grain orientations and intergranular network Mg-Nd-Zn eutectics were found in the WA-DED fabricated Mg-Nd-Zn-Zr alloy thin-wall specimens. No significant voids were found. The microstructure is regulated, and the mechanical properties are improved by adjusting the pulsed current frequency. The 10 Hz specimen had the optimal microstructure with an average grain size of 10.35 μm. Concurrently, the 10 Hz specimen exhibits excellent strength-ductility synergy and isotropic, benefiting from the finely equiaxed crystals. The average microhardness of the 10 Hz specimen was 68.51 HV0.2, and the ultimate tensile strengths in the building and traveling directions were 223 MPa and 229.7 MPa, respectively, and the yield strengths in the building and traveling directions were 138.3 MPa and 145.3 MPa, respectively. Notably, the elongations in the building and traveling directions of the 10 Hz specimen were 16.8% and 17.4%, respectively. The local strain evolution and fracture surfaces of AD and 10 Hz specimens in the building and traveling directions were observed. The mechanisms of grain refinement and mechanical property improvement were revealed.

Effect of ultrasonic vibrations on mass efficiency and microstructure of laser direct deposition Inconel 718 superalloy

Laser direct deposition (LDD) is widely used to repair and manufacture high-value industrial components. However, it faces various defects, such as porosity, cracks, non-uniform microstructure, lack of fusion, keyhole phenomenon, element segregation, and undesirable secondary phases. A method to manage these defects is to concurrently apply ultrasonic vibrations (USV) during the LDD process. This study investigates the effect of USV on the mass efficiency and microstructure of LDD Inconel 718 superalloy to understand how incorporating USV can change the performance and structural integrity of single passes produced using the LDD process. For this purpose, USV is applied to a substrate during the LDD process. The resulting samples are characterized and analyzed using optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results indicate that applying USV below a threshold power value increases mass deposition by over 25%, while exceeding this threshold reduces it. Attention to this threshold power value is crucial for determining the process parameters, including laser power and speed. Additionally, USV transforms the microstructure from columnar to equiaxed and increases subgrain formation. This implementation also enhances the cooling rate, significantly decreasing the Laves phase by over 30% in all process parameters.

Sources and Fates of Sedimentary Polycyclic Aromatic Hydrocarbons in the East Siberian Arctic Shelf: Implications for Input Pathways and Black Carbon Constraint

AbstractThe Arctic region is experiencing more rapid climate changes than the other parts of the world and serves as a sink for semi‐volatile persistent organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), which can be utilized as molecular markers for pyrogenic carbon, such as black carbon (BC). As the sea ice retreats and increased terrestrial inputs with widespread wildfires, the PAH concentrations in the Arctic Ocean are rising. In this study, the sources and fates of PAHs together with BC in surface sediments from the East Siberian Arctic Shelf (ESAS) were analyzed. Positive matrix factorization (PMF) elucidated a mixed petrogenic and pyrogenic sources and distinct PAH fates associated with diverse input pathways including coastal permafrost erosion contribution (∼30%), petrogenic‐related emission (∼34%), fossil fuel combustion (∼26%), and biomass burning (∼10%). Correlation analysis indicated that BC plays a key role in affecting the behavior and fates of PAHs. In the Chukchi Sea, PAHs are closely associated with soot‐BC, whereas in the Laptev Sea (LS) and west East Siberian Sea (W‐ESS), they exhibit a coupling process with char‐BC. The presence of these carbonaceous materials in the sediments of CS is likely influenced by atmospheric deposition and biological activity, whereas the LS and W‐ESS regions are mainly affected by long‐distance river transport and direct deposition from coastal permafrost. As global warming continues, permafrost thawing induces the remobilization and retranslocation of PAHs, thereby becoming a significant PAH contributor and input pathway in the rapidly changing Arctic coastal margin.

Microstructure Refinement of Bulk Inconel 718 Parts During Fabrication with EB-PBF Using Scanning Strategies: Transition from Bidirectional-Raster to Stochastic Point-Based Melting

Inconel 718 is a widely popular aerospace superalloy known for its high-temperature performance and resistance to oxidation, creep, and corrosion. Traditional manufacturing methods, like casting and powder metallurgy, face challenges with intricate shapes that can result in porosity and uniformity issues. On the other hand, Additive Manufacturing (AM) techniques such as Powder Bed Fusion (PBF) and Direct Energy Deposition (DED) can allow the creation of intricate single-part components to reduce weight and maintain structural integrity. However, AM parts often exhibit directional solidification, leading to anisotropic properties and potential crack propagation sites. To address this, post-processing treatments like HIP and heat treatment are necessary. This study explores the effects of the raster and stochastic spot melt scanning strategies on the microstructural and mechanical properties of IN718 parts fabricated using Electron Beam Powder Bed Fusion (EB-PBF). This research demonstrates that raster scanning produces columnar grains with higher mean aspect ratios. Stochastic spot melt scanning facilitates the formation of equiaxed grains, which enhances microstructural refinement and lowers anisotropy. The highest microstructural values were recorded in the raster-produced columnar grain structure. Conversely, the stochastic melt-produced transition from columnar to equiaxed grain structure demonstrated increased hardness with decreasing grain size; however, the hardness of the smallest equiaxed grain structure was slightly less than that of the columnar grain structure. These findings underscore the vital importance of scanning strategies in optimizing the EB-PBF process to enhance material properties.

A Short Review on the Wire-Based Directed Energy Deposition of Metals: Mechanical and Microstructural Properties and Quality Enhancement

Wire-based directed energy deposition (WDED) is an emerging additive manufacturing process garnering significant attention due to its potential for fabricating metal components with tailored mechanical and microstructural properties. This study reviews the WDED process, focusing on fabrication techniques, mechanical behaviors, microstructural characteristics, and quality enhancement methods. Utilizing data from the Web of Science, the study identifies leading countries in WDED research and highlights a growing interest in the field, particularly in materials engineering. Stainless steel, titanium, aluminum, and copper-based alloys are prominent materials for WDED applications. Furthermore, the study explores post-processing techniques such as machining, heat treatment, and surface finishing as integral steps for quality enhancement in WDED components.

Printing the Future Layer by Layer: A Comprehensive Exploration of Additive Manufacturing in the Era of Industry 4.0

In the era of Industry 4.0, 3D printing, or additive manufacturing (AM), has revolutionized product design and manufacturing across various sectors. This review explores the evolution of 3D printing technology and its impact on industrial innovation, highlighting advancements in aeronautics, the automotive industry, and biomedicine. Various AM processes, such as binder jetting, direct energy deposition, and powder bed fusion, and materials like metals, polymers, ceramics, and composites, are discussed. Innovations like high-speed sintering, continuous liquid interface production, and bioprinting demonstrate ongoing advancements. The potential of 3D printing in personalized medical applications is emphasized due to its flexibility in geometry and materials. Despite progress, challenges like standardization, material quality, recycling, sustainability, and economic feasibility hinder widespread adoption. Overcoming these challenges is crucial for optimizing 3D printing technologies, ensuring high-quality, efficient, and affordable production. The review also addresses the future prospects of 4D and 5D printing technologies and their potential applications in various industries. This overview underscores 3D printing’s role in shaping the future of manufacturing within the context of Industry 5.0, emphasizing human–machine collaboration and sustainability.

Synthesis of Ultrathin Film PEGDMA Hydrogels Coated onto Different Surfaces by Atmospheric Pressure Plasma: Characterization and Potential Features for the Biomedical Field

AbstractThe preparation of resistant ultrathin film (utf) hydrogels coated onto different working surfaces (e.g., fabrics) is paying increasing attention as an advantageous strategy for customizing their resultant properties. More specifically, poly(ethylene glycol) (PEG)‐based utf‐hydrogels are relevant for their superior biocompatibility or antibiofouling properties. However, promoting the generation of poly(ethylene glycol) dimethacrylate (PEGDMA) cross‐links ideally without the use of initiators or other cross‐link agents, which might compromise the final bioactivity of the system, is complicated. Moreover, the actual synthesis techniques used for the preparation of such utf‐hydrogels face important drawbacks like high scale‐up costs or important geometrical restrictions, completely hindering its technological transfer. Herein, for the first time and easy and technologically scalable technology is reported for the synthesis and direct deposition of PEGDMA400 utf‐hydrogels onto different substrates based on atmospheric pressure nanosecond pulsed plasma approach. The advantages of the technology are explored and discussed, reporting the ready‐to‐use transparent coating of fabrics. After washing the samples using washing programs of a commercial laundry machine, coatings are still well adhered, showing excellent stability. Finally, the resultant properties of PEGDMA400 utf‐hydrogels are exhaustively characterized using in operando conditions in order to elucidate their potential capabilities in the biomedical field.

Two-Dimensional X-Ray Diffraction (2D-XRD) and Micro-Computed Tomography (Micro-CT) Characterization of Additively Manufactured 316L Stainless Steel

In-depth quality assessment of 3D-printed parts is vital in determining their overall characteristics. This study focuses on the use of 2D X-Ray diffraction (2D-XRD) and X-Ray micro-computed tomography (micro-CT) techniques to evaluate the crystallography and internal defects of 316L SS parts fabricated by the powder-based direct energy deposition (DED) technique. The test samples were printed in a controlled argon environment with variable laser power and print speeds, using a customized deposition pattern to achieve a high-density print (>99%). Multiple features, including hardness, elastic modulus, porosity, crystallographic orientation, and grain morphology and size were evaluated as a function of print parameters. Micro-CT was used for in-depth internal defect analysis, revealing lack-of-fusion and gas-induced (keyhole) pores and no observable micro-cracks or inclusions in most of the printed body. Some porosity was found mostly concentrated in the initial layers of print and decreased along the build direction. 2D-XRD was used for phase analysis and grain size determination. The phase analysis revealed single phase γ-austenitic FCC phase without any detectable presence of the δ-ferrite phase. A close correlation was found between Electron Backscatter Diffraction (EBSD) and 2D-XRD results on the average size distribution and the crystallographic orientation of grains in the sample. This work demonstrates the fast and reliable as-printed crystallography analysis using 2D-XRD compared to the EBSD technique, with potential for in-line integration.

Prediction of catchment efficiency in direct energy deposition using dimensional analysis and machine learning

Direct Energy Deposition (DED) is an additive manufacturing process used to fabricate thin/thick-walled structures and high-value component restorations. As blown powder-based DED gains prominence, catchment efficiency becomes imperative for enhancing material utilization and process effectiveness. This study focuses on predicting catchment efficiency within a DED process by investigating four significant process parameters: laser power, powder feed rate, carrier gas flow rate, and deposition speed. The primary objective is to devise a dimensionless number capable of predicting catchment efficiency based on a combination of these parameters, categorizing efficiency into low, medium, and high regions. This approach reduces the need for resource-intensive experimentation. The experimental validation of the proposed dimensionless number was conducted, showing an error rate of around 8%. Additionally, six machine learning classifier algorithms – Support Vector Machines, K-Nearest Neighbours, Decision Tree, Random Forest, Linear Regression, and Gaussian Naive Bayes – were employed to categorize catchment efficiency zones. Support Vector Machine demonstrated the best performance with a predictive accuracy of 0.98. This study provides a methodology for catchment efficiency prediction, enhancing decision-making and resource optimization, and can be used to optimize process parameters for thin-wall or relatively thin-wall fabrication.

Correction: Investigation of Ti2AlNb Added TiAl Composite Prepared by Direct Laser Deposition

Correction: Investigation of Ti2AlNb Added TiAl Composite Prepared by Direct Laser Deposition

Integrated Control of Thermal Residual Stress and Mechanical Properties by Adjusting Pulse-Wave Direct Energy Deposition

Directed energy deposition with laser beam (DED-LB) components experience significant residual stress due to rapid heating and cooling cycles. Excessive residual tensile stress can lead to cracking in the deposited sample, resulting in service failure. This study utilized digital image correlation (DIC) and thermal imaging to observe the in situ temporal evolution of strain and temperature gradients across all layers of a deposited 316 L stainless steel thin wall during DED-LB. Both continuous-wave (CW) and pulsed-wave (PW) laser modes were employed. Additionally, the characteristics of thermal cracks and geometric dislocation density were examined. The results reveal that PW mode generates a lower temperature gradient, which in turn reduces thermal strain. In CW mode, the temperature–stress relationship curve of the additive manufacturing sample enters the “brittleness temperature zone”, leading to the formation of numerous hot cracks. In contrast, PW mode samples are almost free of cracks, as the metal avoids crack-sensitive regions during solidification, thereby minimizing hot crack formation. Overall, these factors collectively contribute to reduced residual stress and improved mechanical properties through the adjustment of pulsed-wave laser deposition.

Characterization and simulation of AlSi10Mg reinforcement structures by direct energy deposition by means of laser beam and powder

Among metal additive manufacturing technologies, direct energy deposition (DED) processes have the advantage to be easily integrable in a manufacturing chain with other conventional technologies. This characteristic can be exploited by designing reinforcement structures to be added by DED onto pre-existing subcomponents to tailor the part’s mechanical properties while keeping the part lightweight. This study focuses on DED by means of laser beam and powder process optimization to improve material quality and geometrical accuracy of AlSi10Mg reinforcement structures while preventing excessive thermal deformations and material dilution into the substrate. These results are compared with finite elements numerical simulations of the deposition process, comprising thermo-elastic deformation and material deposition, to predict the bending and reinforcement of the processed substrate. In particular, the model includes the deterministic prediction of the deposition profile as a function of the process parameters and a few condition-specific coefficients: once calibrated, the model was used to compare the numerical and experimental residual deformation of the reinforced sample, obtaining promising agreement. The reinforcement provided to a 1.5 mm thick substrate by a single wall of deposited materials, with cross-sectional dimensions of 2 mm in width and 2.5 mm in height, was evaluated by three points bending. With the reinforcement on the tensile side of the stresses, the energy absorbed by the material plastic deformation increased by 2.4% as compared to the substrate alone, while with the reinforcement on the compression side of the stresses the energy absorption increased by 75.8% on average.