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Metals
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Metal Powder for Additive Manufacturing: Manufacturing, Properties and Degradation
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Metal Powder for Additive Manufacturing: Manufacturing, Properties and Degradation

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Powder Metallurgy".

Deadline for manuscript submissions: closed (30 June 2022) | Viewed by 15043

Special Issue Editors

Prof. Dr. Eduard Hryha

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Guest Editor
Director of the Competence Centre for Additive Manufacturing - Metal (CAM2), Division of Materials and Manufacture, Industrial and Materials Science, Chalmers University of Technology, SE-41296 Gothenburg, Sweden
Interests: metal additive manufacturing and powder metallurgy; metal powder development for AM; novel materials for AM; quality assurance in AM
Prof. Dr. Lars Nyborg

E-Mail Website
Guest Editor
Director of Chalmers Production Area of Advance, Researcher at the Division of Materials and Manufacture, Department of Industrial and Materials Science, Chalmers University of Technology, Göteborg, Sweden
Interests: powder metallurgy; additive manufacturing; surface science and engineering

Special Issue Information

Dear Colleagues,

Additive manufacturing (AM) is widely acknowledged to be revolutionary, altering the manufacturing and logistics landscape. When it comes to metal AM, metal powder-based technologies have attracted the largest amount of research and industrial attention, and their industrial application has grown significantly during the last decade. Metal additive manufacturing is a relatively new technology. However, significant technological development during the last two decades has allowed us to achieve significant progress when it comes to AM hardware development, allowing to manufacture metal AM components with properties compared to or even exceeding those of materials produced via conventional manufacturing processes for established materials. Further development and wider implementation of metal AM requires significant expansion of the material portfolio offered by the technology, decreasing the cost of the feedstock material as well as improving powder reuse during AM processing, requiring deeper understanding of powder degradation during powder handling and AM processing. However, focus on development of the metal powder for AM, as well as correlation between powder properties, AM process robustness, and properties of AM components has been rather limited to date. This Special Issue of Metals welcomes review and original research articles covering manufacturing, characterization, and degradation of metal powder feedstock with a focus on:

  • Powder manufacturing for AM;
  • Characterization of powder properties;
  • Effect of powder properties on the properties of AM components;
  • New materials for additive manufacturing;
  • Powder degradation in AM;
  • Fundamental investigations on the powder properties–AM process–AM component properties relationship;
  • Modelling and simulation applied to metal powders for AM;
  • Standardization of metal powders for AM;
  • Life cycle assessment.

Prof. Dr. Eduard Hryha
Prof. Dr. Lars Nyborg
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • additive manufacturing
  • metal powder
  • powder manufacturing
  • powder properties
  • powder degradation
  • powder characterization
  • powder reuse in AM

Published Papers (5 papers)

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Research

14 pages, 5502 KiB  
Article
Rheological Behavior of Inconel 718 Powder for Electron-Beam Melting
by Laura Cordova, Ahmad Raza and Eduard Hryha
Metals 2022, 12(7), 1231; https://doi.org/10.3390/met12071231 - 21 Jul 2022
Cited by 2 | Viewed by 2255
Abstract
Understanding the impact of powder reuse in powder-bed-fusion electron beams (PBF-EB) is key to maintain the processability and yield. Powder oxidation, due to exposure to high temperatures for a prolonged period of time, can lead to a decrease in electrical conductivity of the [...] Read more.
Understanding the impact of powder reuse in powder-bed-fusion electron beams (PBF-EB) is key to maintain the processability and yield. Powder oxidation, due to exposure to high temperatures for a prolonged period of time, can lead to a decrease in electrical conductivity of the powder and, hence, electrostatic forces that originate during interaction with the electron beam. The effect of oxidation on physical properties as powder rheological properties, apparent/tap density and charging are studied in this work. The analysis using Scanning Electron Microscopy (SEM) shows thermodynamically stable Al-rich oxide particulates (sized 100–200 nm) covering the surface of the reused powder particles, with an increase of 20% in bulk oxygen in comparison to the virgin powder and, measured by X-ray Photoelectron Spectroscopy (XPS), average oxide thickness of circa 13 nm in the reused powder. On the one hand, reusing the powder positively impacted the flowability studied using the Revolution Powder Analyzer (RPA), in which the avalanche angle was decreased from 37 deg to 30 deg, for virgin and reused powder, respectively. The volume fraction of loose powder was similar for both virgin and reused powder, 57% and 56%, respectively, while the packed volume fraction was measured lower in the reused (57%) than the virgin powder (60%). On the other hand, the charging behavior, studied using the ION Charge Module of the powder, worsened; this almost doubled in the reuse powder (−9.18 V/g) compared to the virgin powder (−5.84 V/g). The observation of ejected particles from the build volume is attributed to the charging behavior and lower packing volume fraction in the reused powder. Full article
(This article belongs to the Special Issue Metal Powder for Additive Manufacturing: Manufacturing, Properties and Degradation)
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22 pages, 3081 KiB  
Article
Exploration of the Effects of Metallic Powder Handling and Storage Conditions on Flowability and Moisture Content for Additive Manufacturing Applications
by Jack Grubbs, Bryer C. Sousa and Danielle Cote
Metals 2022, 12(4), 603; https://doi.org/10.3390/met12040603 - 31 Mar 2022
Cited by 8 | Viewed by 2870
Abstract
Metal powder-based additive manufacturing (AM) relies on consistently successful processing of feedstock powder, necessitating through-process predictability in powder properties and behavior. However, routine powder handling and storage may degrade powder performance by influencing flowability and moisture content through exposure to ambient conditions. Therefore, [...] Read more.
Metal powder-based additive manufacturing (AM) relies on consistently successful processing of feedstock powder, necessitating through-process predictability in powder properties and behavior. However, routine powder handling and storage may degrade powder performance by influencing flowability and moisture content through exposure to ambient conditions. Therefore, this study aimed to evaluate the effects of repeated environmental exposure on the flowability and moisture content of Al 5056 and Ta powders for AM applications. Using Carney Funnel flow tests, thermogravimetric analysis, and particle size/shape analysis, powder characterization helped elucidate powder property and behavioral changes with exposure. Results indicated inconsistent flowability and moisture content changes for both material types when exposure conditions were altered. Correlational statistics highlighted the most influential particle characteristics on powder behavior after exposure; particle morphology was most impactful for the semi-spherical Al 5056, whereas moisture content and particle size were most significant for the angular Ta. While exposure to laboratory conditions minimally changed powder performance in this study, caution is advised when handling and storing powders in more “extreme” environments. Powder users are urged to implement quality controls alongside powder characterization to pinpoint how specific powders should be treated, handled, and stored in a given environment for successful processing in AM. Full article
(This article belongs to the Special Issue Metal Powder for Additive Manufacturing: Manufacturing, Properties and Degradation)
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14 pages, 2299 KiB  
Article
Laser Powder Bed Fusion of an Al-Mg-Sc-Zr Alloy: Manufacturing, Peak Hardening Response and Thermal Stability at Peak Hardness
by Bharat Mehta, Arvid Svanberg and Lars Nyborg
Metals 2022, 12(1), 57; https://doi.org/10.3390/met12010057 - 27 Dec 2021
Cited by 6 | Viewed by 2701
Abstract
This study shows a rapid and systematic approach towards identifying full density and peak hardness for an Al-Mg-Sc-Zr alloy commonly known as Scalmalloy®. The alloy is tailored for the laser powder bed fusion process and has been shown to be printable [...] Read more.
This study shows a rapid and systematic approach towards identifying full density and peak hardness for an Al-Mg-Sc-Zr alloy commonly known as Scalmalloy®. The alloy is tailored for the laser powder bed fusion process and has been shown to be printable with >99.8% relative density. The microstructure suggests Al grain refinement in melt pool boundaries, associated with formation of primary Al3(Sc,Zr) particles during solidification. Peak hardening response was identified by heat treatment tests at 573,598 and 623 K between 0 and 10 h. A peak hardness of 172 HV0.3 at 598 K for 4 h was identified. The mechanical properties were also tested with yield and ultimate strengths of 287 MPa and 364 MPa in as-printed and 468 MPa and 517 MPa in peak hardened conditions, respectively, which is consistent with the literature. Such an approach is considered apt when qualifying new materials in industrial laser powder bed fusion systems. The second part of the study discusses the thermal stability of such alloys post-peak-hardening. One set of samples was peak hardened at the conditions identified before and underwent secondary ageing at three different temperatures of 423,473 and 523 K between 0 and 120 h to understand thermal stability and benchmark against conventional Al alloys. The secondary heat treatments performed at lower temperatures revealed lower deterioration of hardness over ageing times as compared to the datasheets for conventional Al alloys and Scalmalloy®, thus suggesting that longer ageing times are needed. Full article
(This article belongs to the Special Issue Metal Powder for Additive Manufacturing: Manufacturing, Properties and Degradation)
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16 pages, 4339 KiB  
Article
Linking In Situ Melt Pool Monitoring to Melt Pool Size Distributions and Internal Flaws in Laser Powder Bed Fusion
by Claudia Schwerz and Lars Nyborg
Metals 2021, 11(11), 1856; https://doi.org/10.3390/met11111856 - 18 Nov 2021
Cited by 15 | Viewed by 3310
Abstract
In situ monitoring of the melt pools in laser powder bed fusion (LPBF) has enabled the elucidation of process phenomena. There has been an increasing interest in also using melt pool monitoring to identify process anomalies and control the quality of the manufactured [...] Read more.
In situ monitoring of the melt pools in laser powder bed fusion (LPBF) has enabled the elucidation of process phenomena. There has been an increasing interest in also using melt pool monitoring to identify process anomalies and control the quality of the manufactured parts. However, a better understanding of the variability of melt pools and the relation to the incidence of internal flaws are necessary to achieve this goal. This study aims to link distributions of melt pool dimensions to internal flaws and signal characteristics obtained from melt pool monitoring. A process mapping approach is employed in the manufacturing of Hastelloy X, comprising a vast portion of the process space. Ex situ measurements of melt pool dimensions and analysis of internal flaws are correlated to the signal obtained through in situ melt pool monitoring in the visible and near-infrared spectra. It is found that the variability in melt pool dimensions is related to the presence of internal flaws, but scatter in melt pool dimensions is not detectable by the monitoring system employed in this study. The signal intensities are proportional to melt pool dimensions, and the signal is increasingly dynamic following process conditions that increase the generation of spatter. Full article
(This article belongs to the Special Issue Metal Powder for Additive Manufacturing: Manufacturing, Properties and Degradation)
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13 pages, 6601 KiB  
Article
Effect of the Process Atmosphere Composition on Alloy 718 Produced by Laser Powder Bed Fusion
by Camille Pauzon, Andreas Markström, Sophie Dubiez-Le Goff and Eduard Hryha
Metals 2021, 11(8), 1254; https://doi.org/10.3390/met11081254 - 07 Aug 2021
Cited by 10 | Viewed by 2475
Abstract
The detrimental effect of nitrogen and oxygen when it comes to the precipitation of the strengthening γ’’ and γ’ phases in Alloy 718 is well-known from traditional manufacturing. Hence, the influence of the two processing atmospheres, namely argon and nitrogen, during the laser [...] Read more.
The detrimental effect of nitrogen and oxygen when it comes to the precipitation of the strengthening γ’’ and γ’ phases in Alloy 718 is well-known from traditional manufacturing. Hence, the influence of the two processing atmospheres, namely argon and nitrogen, during the laser powder bed fusion (L-PBF) of Alloy 718 parts was studied. Regardless of the gas type, considerable losses of both oxygen of about 150 ppm O2 (≈30%) and nitrogen on the level of around 400 ppm N2 (≈25%) were measured in comparison to the feedstock powder. The utilization of nitrogen as processing atmosphere led to a slightly higher nitrogen content in the as-built material—about 50 ppm—compared to the argon atmosphere. The presence of the stable nitrides and Al-rich oxides observed in the as-built material was related to the transfer of these inclusions from the nitrogen atomized powder feedstock to the components. This was confirmed by dedicated analysis of the powder feedstock and supported by thermodynamic and kinetic calculations. Rapid cooling rates were held responsible for the limited nitrogen pick-up. Oxide dissociation during laser–powder interaction, metal vaporization followed by oxidation and spatter generation, and their removal by processing atmosphere are the factors describing an important oxygen loss during L-PBF. In addition, the reduction of the oxygen level in the process atmosphere from 500 to 50 ppm resulted in the reduction in the oxygen level in as-built component by about 5%. Full article
(This article belongs to the Special Issue Metal Powder for Additive Manufacturing: Manufacturing, Properties and Degradation)
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