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Additive Manufacturing of Alloys Using Electron Beam Powder Bed Fusion

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Manufacturing Processes and Systems".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 33474

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Prof. Dr. Carolin Koerner

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Chair of Materials Science and Engineering for Metals, Department of Material Science and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Martensstr. 5, 91058 Erlangen, Germany
Interests: additive manufacturing; electron beam powder bed fusion; alloy development; high-performance alloys; nickel-base superalloys; casting of lightweight alloys

Dr. Matthias Markl

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Chair of Materials Science and Engineering for Metals, Department of Materials Science and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Martensstr. 5, 91058 Erlangen, Germany
Interests: additive manufacturing; powder bed fusion; numerical simulation; numerical alloy development

Special Issue Information

Dear Colleagues,

Electron beam powder bed fusion of alloys (PBF-EB/M) is one of many additive manufacturing technologies, which are expected to revolutionize future industrial production. Starting from computer-aided designed data, components are built layer by layer within a powder bed by selectively melting the powder with a high-power electron beam. The application field of the electron beam is restricted to metallic components, since electric conductivity is required. However, the electron beam works under vacuum conditions and can be moved at extremely high velocities, and a high beam power is available. These features make PBF-EB/M especially interesting for the processing of high-performance alloys.

This Special Issue aims to present the latest research related to PBF-EB/M technology. It will collect the most impressive contributions during the “3rd International Conference on Electron Beam Additive Manufacturing” EBAM 2020 (www.ebam.fau.de) but is open to all researchers who wish to submit additional journal contributions. The topics cover but are not limited to powder manufacturing and recovery, process observation and control, new/modified process/beam technologies, processing/properties of all kinds of metallic/intermetallic alloys, as well as modeling and simulation.

Prof. Dr. Carolin Koerner
Dr. Matthias Markl
Guest Editors

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Keywords

additive manufacturing
powder bed fusion
electron beam

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Published Papers (11 papers)

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Research

14 pages, 16982 KiB

Open AccessArticle

Basic Mechanism of Surface Topography Evolution in Electron Beam Based Additive Manufacturing

by Christoph Breuning, Julian Pistor, Matthias Markl and Carolin Körner

Materials 2022, 15(14), 4754; https://doi.org/10.3390/ma15144754 - 7 Jul 2022

Cited by 7 | Viewed by 2225

Abstract

This study introduces and verifies a basic mechanism of surface topography evolution in electron beam additive manufacturing (E-PBF). A semi-analytical heat conduction model is used to examine the spatio-temporal evolution of the meltpool and segment the build surface according to the emerging persistent meltpool domains. Each persistent domain is directly compared with the corresponding melt surface, and exhibits a characteristic surface morphology and topography. The proposed underlying mechanism of topography evolution is based on different forms of material transport in each distinct persistent domain, driven by evaporation and thermocapillary convection along the temperature gradient of the emerging meltpool. This effect is shown to be responsible for the upper bound of the standard process window in E-PBF, where surface bulges form. Based on this mechanism, process strategies to prevent the formation of surface bulges for complex geometries are proposed. Full article

(This article belongs to the Special Issue Additive Manufacturing of Alloys Using Electron Beam Powder Bed Fusion)

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15 pages, 5535 KiB

Open AccessArticle

PBF-EB of Fe-Cr-V Alloy for Wear Applications

by Marie Franke-Jurisch, Markus Mirz, Thomas Wenz, Alexander Kirchner, Burghardt Klöden and Thomas Weißgärber

Materials 2022, 15(5), 1679; https://doi.org/10.3390/ma15051679 - 23 Feb 2022

Cited by 6 | Viewed by 2483

Abstract

Due to the small variety of materials, the areas of application of additive manufacturing in the toolmaking industry are currently still limited. In order to overcome these material restrictions, AM material development for high carbon-containing iron-based materials, which are characterized by high strength, hardness, and wear resistance, must be intensified. However, these materials are often susceptible to crack formation or lack of fusion defects during processing. Therefore, these materials are preferentially suited for electron beam powder bed fusion (PBF-EB). In this paper, an Fe-Cr-V alloy with 10% vanadium is presented. Investigations were carried out on the PBF-EB system Arcam A2X. Specimens and demonstrators are characterized by a three-phase microstructure with an Fe-rich matrix and VC and M₇C₃ reinforcements. The resulting microstructures were characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Furthermore, mechanical and physical properties were measured. A final field test was conducted to evaluate durability in use. Full article

(This article belongs to the Special Issue Additive Manufacturing of Alloys Using Electron Beam Powder Bed Fusion)

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11 pages, 3581 KiB

Open AccessArticle

Electron Beam Powder Bed Fusion of Water Atomized Iron and Powder Blends

by Alexander Kirchner, Burghardt Klöden, Marie Franke-Jurisch, Gunnar Walther and Thomas Weißgärber

Materials 2022, 15(4), 1567; https://doi.org/10.3390/ma15041567 - 19 Feb 2022

Viewed by 2196

Abstract

In the present state of the art, highly spherical alloy powders are employed as feedstock in powder bed fusion processes. These powders are characterized by high flowability and apparent density. Their elaborate fabrication process is reflected in high powder price, adding a significant fraction to the cost of additively manufactured parts. Thus, the use of non-spherical powders, such as water atomized material, can lower costs significantly. Here, the electron beam powder bed fusion (PBF-EB) of standard water atomized iron powder used for press-and-sinter is studied. Despite raking problems, using the coating mechanism in standard configuration samples with densities exceeding 99% were fabricated. In a further step, the addition of alloying elements by powder blending is explored. Important powder properties of feedstock blended from irregular and spherical powders are characterized. The PBF-EB processing of two alloys is presented. The first represents a low carbon steel. Samples were characterized by metallographic cross-section, energy dispersive X-ray (EDX) mapping, and mechanical testing. The second alloy system is a FeCrAl. After PBF-EB processing of the powder mixture, chemical homogeneity was achieved. Besides the low cost, this approach of using water atomized powder mixed with master alloy offers the advantage of high flexibility for potential application. Full article

(This article belongs to the Special Issue Additive Manufacturing of Alloys Using Electron Beam Powder Bed Fusion)

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19 pages, 12802 KiB

Open AccessArticle

Electron-Optical In Situ Imaging for the Assessment of Accuracy in Electron Beam Powder Bed Fusion

by Christopher Arnold, Christoph Breuning and Carolin Körner

Materials 2021, 14(23), 7240; https://doi.org/10.3390/ma14237240 - 26 Nov 2021

Cited by 10 | Viewed by 2606

Abstract

The current study evaluates the capabilities of electron-optical (ELO) in situ imaging with respect to monitoring and prediction of manufacturing precision in electron beam powder bed fusion. Post-process X-ray computed tomography of two different as-built parts is used to quantitatively evaluate the accuracy and limitations of ELO imaging. Additionally, a thermodynamic simulation is performed to improve the understanding of ELO data and to assess the feasibility of predicting dimensional accuracy numerically. It is demonstrated that ELO imaging captures the molten layers accurately (deviations <100 μm) and indicates the creation of surface roughness. However, some geometrical features of the as-built parts exhibit local inaccuracies associated with thermal stress-induced deformation (deviations up to 500 μm) which cannot be captured by ELO imaging. It is shown that the comparison between in situ and post-process data enables a quantification of these effects which might provide the possibility for developing effective countermeasures in the future. Full article

(This article belongs to the Special Issue Additive Manufacturing of Alloys Using Electron Beam Powder Bed Fusion)

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20 pages, 10488 KiB

Open AccessArticle

In Situ Monitoring of Powder Bed Fusion Homogeneity in Electron Beam Melting

by Marco Grasso

Materials 2021, 14(22), 7015; https://doi.org/10.3390/ma14227015 - 19 Nov 2021

Cited by 15 | Viewed by 2347

Abstract

Increasing attention has been devoted in recent years to in situ sensing and monitoring of the electron beam melting process, ranging from seminal methods based on infrared imaging to novel methods based on backscattered electron detection. However, the range of available in situ monitoring capabilities and solutions is still quite limited compared to the wide number of studies and industrial toolkits in laser-based additive manufacturing processes. Some methods that are already industrially available in laser powder bed fusion systems, such as in situ detection of recoating errors, have not yet been investigated and tested in electron beam melting. Motivated by the attempt to fill this gap, we present a novel in situ monitoring methodology that can be easily implemented in industrial electron beam melting machines. The method is aimed at identifying local inhomogeneity and irregularities in the powder bed by means of layerwise image acquisition and processing, with no external illumination source apart from the light emitted by the hot material underneath the currently recoated layer. The results show that the proposed approach is suitable to detect powder bed anomalies, while also highlighting the link between the severity of in situ detected errors and the severity of resulting defects in the additively manufactured part. Full article

(This article belongs to the Special Issue Additive Manufacturing of Alloys Using Electron Beam Powder Bed Fusion)

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13 pages, 2871 KiB

Open AccessArticle

Cyclic Crack Growth in Chemically Tailored Isotropic Austenitic Steel Processed by Electron Beam Powder Bed Fusion

by Matthias Droste, Ruben Wagner, Johannes Günther, Christina Burkhardt, Sebastian Henkel, Thomas Niendorf and Horst Biermann

Materials 2021, 14(21), 6544; https://doi.org/10.3390/ma14216544 - 1 Nov 2021

Cited by 1 | Viewed by 1589

Abstract

The present study analyzes the cyclic crack propagation behavior in an austenitic steel processed by electron beam powder bed fusion (PBF-EB). The threshold value of crack growth as well as the crack growth behavior in the Paris regime were studied. In contrast to other austenitic steels, the building direction during PBF-EB did not affect the crack propagation rate, i.e., the crack growth rates perpendicular and parallel to the building direction were similar due to the isotropic microstructure characterized by equiaxed grains. Furthermore, the influence of significantly different building parameters was studied and, thereby, different energy inputs causing locally varying manganese content. Crack growth behavior was not affected by these changes. Even a compositional gradation within the same specimen, i.e., crack growth through an interface of areas with high and areas with low manganese content, did not lead to a significant change of the crack growth rate. Thus, the steel studied is characterized by a quite robust cyclic crack growth behavior independent from building direction and hardly affected by typical parameter deviations in the PBF-EB process. Full article

(This article belongs to the Special Issue Additive Manufacturing of Alloys Using Electron Beam Powder Bed Fusion)

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11 pages, 3965 KiB

Open AccessArticle

Characterization of Spatter and Sublimation in Alloy 718 during Electron Beam Melting

by Ahmad Raza and Eduard Hryha

Materials 2021, 14(20), 5953; https://doi.org/10.3390/ma14205953 - 10 Oct 2021

Cited by 7 | Viewed by 2611

Abstract

Due to elevated temperatures and high vacuum levels in electron beam melting (EBM), spatter formation and accumulation in the feedstock powder, and sublimation of alloying elements from the base feedstock powder can affect the feedstock powder’s reusability and change the alloy composition of fabricated parts. This study focused on the experimental and thermodynamic analysis of spatter particles generated in EBM, and analyzed sublimating alloying elements from Alloy 718 during EBM. Heat shields obtained after processing Alloy 718 in an Arcam A2X plus machine were analyzed to evaluate the spatters and metal condensate. Comprehensive morphological, microstructural, and chemical analyses were performed using scanning electron microscopy (SEM), focused ion beam (FIB), and energy dispersive spectroscopy (EDS). The morphological analysis showed that the area coverage of heat shields by spatter increased from top (<1%) to bottom (>25%), indicating that the spatter particles had projectile trajectories. Similarly, the metal condensate had a higher thickness of ~50 μm toward the bottom of the heat shield, indicating more significant condensation of metal vapors at the bottom. Microstructural analysis of spatters highlighted that the surfaces of spatter particles sampled from the heat shields were also covered with condensate, and the thickness of the deposited condensate depended on the time of landing of spatter particles on the heat shield during the build. The chemical analysis showed that the spatter particles had 17-fold higher oxygen content than virgin powder used in the build. Analysis of the metalized layer indicated that it was formed by oxidized metal condensate and was significantly enriched with Cr due to its higher vapor pressure under EBM conditions. Full article

(This article belongs to the Special Issue Additive Manufacturing of Alloys Using Electron Beam Powder Bed Fusion)

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24 pages, 9621 KiB

Open AccessArticle

Smoke Suppression in Electron Beam Melting of Inconel 718 Alloy Powder Based on Insulator–Metal Transition of Surface Oxide Film by Mechanical Stimulation

by Akihiko Chiba, Yohei Daino, Kenta Aoyagi and Kenta Yamanaka

Materials 2021, 14(16), 4662; https://doi.org/10.3390/ma14164662 - 18 Aug 2021

Cited by 34 | Viewed by 3429

Abstract

In powder bed fusion–electron beam melting, the alloy powder can scatter under electron beam irradiation. When this phenomenon—known as smoking—occurs, it makes the PBF-EBM process almost impossible. Therefore, avoiding smoking in EBM is an important research issue. In this study, we aimed to clarify the effects of powder bed preheating and mechanical stimulation on the suppression of smoking in the powder bed fusion–electron beam melting process. Direct current electrical resistivity and alternating current impedance spectroscopy measurements were conducted on Inconel 718 alloy powder at room temperature and elevated temperatures before and after mechanical stimulation (ball milling for 10–60 min) to investigate changes in the electrical properties of the surface oxide film, alongside X-ray photoelectron spectroscopy to identify the surface chemical composition. Smoking tests confirmed that preheating and ball milling both suppressed smoking. Furthermore, smoking did not occur after ball milling, even when the powder bed was not preheated. This is because the oxide film undergoes a dielectric–metallic transition due to the lattice strain introduced by ball milling. Our results are expected to benefit the development of the powder bed fusion–electron beam melting processes from the perspective of materials technology and optimization of the process conditions and powder properties to suppress smoking. Full article

(This article belongs to the Special Issue Additive Manufacturing of Alloys Using Electron Beam Powder Bed Fusion)

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14 pages, 5797 KiB

Open AccessArticle

A Single Crystal Process Window for Electron Beam Powder Bed Fusion Additive Manufacturing of a CMSX-4 Type Ni-Based Superalloy

by Julian Pistor, Christoph Breuning and Carolin Körner

Materials 2021, 14(14), 3785; https://doi.org/10.3390/ma14143785 - 6 Jul 2021

Cited by 19 | Viewed by 4062

Abstract

Using suitable scanning strategies, even single crystals can emerge from powder during additive manufacturing. In this paper, a full microstructure map for additive manufacturing of technical single crystals is presented using the conventional single crystal Ni-based superalloy CMSX-4. The correlation between process parameters, melt pool size and shape, as well as single crystal fraction, is investigated through a high number of experiments supported by numerical simulations. Based on these results, a strategy for the fabrication of high fraction single crystals in powder bed fusion additive manufacturing is deduced. Full article

(This article belongs to the Special Issue Additive Manufacturing of Alloys Using Electron Beam Powder Bed Fusion)

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12 pages, 5355 KiB

Open AccessArticle

Microstructural and Mechanical Evaluation of a Cr-Mo-V Cold-Work Tool Steel Produced via Electron Beam Melting (EBM)

by Carlos Alberto Botero, Aydın Şelte, Markus Ramsperger, Giulio Maistro, Andrey Koptyug, Mikael Bäckström, William Sjöström and Lars-Erik Rännar

Materials 2021, 14(11), 2963; https://doi.org/10.3390/ma14112963 - 31 May 2021

Cited by 8 | Viewed by 3370

Abstract

In this work, a highly alloyed cold work tool steel, Uddeholm Vanadis 4 Extra, was manufactured via the electron beam melting (EBM) technique. The corresponding material microstructure and carbide precipitation behavior as well as the microstructural changes after heat treatment were characterized, and key mechanical properties were investigated. In the as-built condition, the microstructure consists of a discontinuous network of very fine primary Mo- and V-rich carbides dispersed in an auto-tempered martensite matrix together with ≈15% of retained austenite. Adjusted heat treatment procedures allowed optimizing the microstructure by the elimination of Mo-rich carbides and the precipitation of fine and different sized V-rich carbides, along with a decrease in the retained austenite content below 2%. Hardness response, compressive strength, and abrasive wear properties of the EBM-manufactured material are similar or superior to its as-HIP forged counterparts manufactured using traditional powder metallurgy route. In the material as built by EBM, an impact toughness of 16–17 J was achieved. Hot isostatic pressing (HIP) was applied in order to further increase ductility and to investigate its impact upon the microstructure and properties of the material. After HIPing with optimized protocols, the ductility increased over 20 J. Full article

(This article belongs to the Special Issue Additive Manufacturing of Alloys Using Electron Beam Powder Bed Fusion)

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18 pages, 6289 KiB

Open AccessArticle

Quasi-Static Tensile Properties of Unalloyed Copper Produced by Electron Beam Powder Bed Fusion Additive Manufacturing

by Prithwish Tarafder, Christopher Rock and Timothy Horn

Materials 2021, 14(11), 2932; https://doi.org/10.3390/ma14112932 - 29 May 2021

Cited by 12 | Viewed by 4232

Abstract

Mechanical properties of powder bed fusion processed unalloyed copper are reported majorly in the as-fabricated condition, and the effect of post-processes, common to additive manufacturing, is not well documented. In this study, mechanical properties of unalloyed copper processed by electron beam powder bed fusion are characterized via room temperature quasi-static uniaxial tensile test and Vickers microhardness. Tensile samples were extracted both perpendicular and parallel to the build direction and assigned to three different conditions: as-fabricated, hot isostatic pressing (HIP), and vacuum annealing. In the as-fabricated condition, the highest UTS and lowest elongation were obtained in the samples oriented perpendicular to the build direction. These were observed to have clear trends between sample orientation caused primarily by the interdependencies between the epitaxial columnar grain morphology and dislocation movement during the tensile test. Texture was insignificant in the as-fabricated condition, and its effect on the mechanical properties was outweighed by the orientation anisotropy. The fractographs revealed a ductile mode of failure with varying dimple sizes where more shallow and finely spaced dimples were observed in the samples oriented perpendicular to the build direction. EDS maps reveal that grain boundary oxides coalesce and grow in HIP and vacuum-annealed specimens which are seen inside the ductile dimples and contribute to their increased ductility. Overall, for the post-process parameters chosen in this study, HIP was observed to slightly increase the sample’s density while vacuum annealing reduced the oxygen content in the specimens. Full article

(This article belongs to the Special Issue Additive Manufacturing of Alloys Using Electron Beam Powder Bed Fusion)

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