Special Issue "Additive Manufacturing of Ferrous Materials"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 July 2018).

Special Issue Editors

Prof. Dr. Pavel Krakhmalev
E-Mail Website
Guest Editor
Department of Engineering and Physics, Karlstad University, SE-651 88, Karlstad, Sweden
Interests: microstructure property relationships in advanced metallic materials; wear and failure analysis; additive manufacturing; new titanium alloys for medical applications; additive manufacturing of ferrous materials
Prof. Igor Yadroitsev
E-Mail Website
Guest Editor
Department of Mechanical and Mechatronic Engineering, Bloemfontein, Central University of Technology, Free State, South Africa, 9300
Interests: optimization of additive manufacturing process; development of process parameters; development of new alloys; biomedical materials; titanium alloys

Special Issue Information

Dear Colleagues,

Laser additive manufacturing (AM) is acknowledged as being a resource-efficient sustainable technology, providing the manufacturing of objects of complex shapes, containing internal channels and cavities, with less wastage of materials and shorter lead times. Two large branches of laser additive manufacturing technology are powder bed fusion, often referred to as selective laser melting (SLM), and directed energy deposition, also called laser metal deposition (LMD).

Ferrous materials are well-known structural, tool, automotive, and civil materials. In general, steels and cast irons are cheaper than nonferrous alloys, are widely used and cover very broad range of properties and applications. Because of this, ferrous materials attract high interest as cost-effective materials for AM.

During AM manufacturing, powder material is remolten, rapidly cooled, subjected to thermal shock and repeatable thermal cycling due to layer-by-layer maturing of the manufacturing process. As such, selection of materials for laser additive manufacturing is a challenge. Presently, a limited number of ferrous materials, steels, has been proven to be perfectly suitable for additive manufacturing. Substantial research and development efforts are, therefore, directed to the development of process parameters suitable for pore-free manufacturing of existing materials or to design new material grades tolerant to AM.

This Special Issue is dedicated to all aspects of additive manufacturing of ferrous materials to show recent advances in this field. We are looking forward to receiving submissions dedicated to both, powder bed fusion and directed energy deposition of ferrous materials for structural, tooling, medical and other applications. Original contributions related to development of process parameters, manufacturing strategies, development of new steel grades for AM, formation of microstructure, characterization of defects, microstructure-properties relationship in AM manufactured ferrous alloys are welcome in a form of short communications, full-length articles, and reviews.

Prof. Dr. Pavel Krakhmalev
Prof. Dr. Igor Yadroitsev
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 papers will be 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 1600 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
  • powder bed fusion
  • directed energy deposition
  • new ferrous alloy for AM
  • processing strategies and optimization of process parameters
  • defects and porosity
  • microstructure formation and evolution
  • mechanical properties

Published Papers (7 papers)

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Research

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Open AccessFeature PaperArticle
Investigation of Heat Treatment Strategies for Additively-Manufactured Tools of X37CrMoV5-1
Metals 2018, 8(10), 854; https://doi.org/10.3390/met8100854 - 19 Oct 2018
Cited by 3
Abstract
For cost-intensive products like automobiles, clients often wish to personalize their product, what forces the industry to create a large diversity of combinable parts. Additionally, the life cycles of many components become shorter. For highly-stressable parts, which are commonly manufactured by forging, the [...] Read more.
For cost-intensive products like automobiles, clients often wish to personalize their product, what forces the industry to create a large diversity of combinable parts. Additionally, the life cycles of many components become shorter. For highly-stressable parts, which are commonly manufactured by forging, the short changeover cycles result in expensive products, as the costs of tools must be offset by the sale of only a few parts. To reduce the tool cost, new, flexible processes have to be established in tool manufacturing. Laser-based additive manufacturing is noted for its high flexibility; notably, Laser Metal Deposition (LMD) is gaining increasing relevance in research, as it is already used for coating and repairing forming tools, this technology makes it possible to add material onto free-formed surfaces. Therefore, investigations are being conducted to qualify this process to produce forging tools. Due to the thermal processes which are required during additive manufacturing, the microstructure of the material differs from that of wrought material. This, in turn, affects the strategy of post heat treatment in order that the required mechanical properties for tools be attained. Within this manuscript, the influence of additive manufacturing on performance characteristics of hot work tool steel X37CrMoV5-1 (1.2343) is analyzed. To investigate the behavior of additively manufactured material during the process chain of tool manufacturing, properties for different states of a heat treatment are characterized by hardness and strength. It was shown that the strength of the additively manufactured material could be increased compared to wrought material by using a tailored heat treatment. The effects that cause this behavior are investigated by comparing the microstructure at different states of heat treatment. Full article
(This article belongs to the Special Issue Additive Manufacturing of Ferrous Materials)
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Open AccessArticle
Processing of AISI H11 Tool Steel Powder Modified with Carbon Black Nanoparticles for the Additive Manufacturing of Forging Tools with Tailored Mechanical Properties by Means of Laser Metal Deposition (LMD)
Metals 2018, 8(9), 659; https://doi.org/10.3390/met8090659 - 23 Aug 2018
Cited by 1
Abstract
Within the scope of the presented work the processing of AISI H11 (1.2343 or X37CrMoV5-1) tool steel powder modified by adding carbon black nanoparticles in varying concentrations by means of Laser Metal Deposition (LMD) is extensively investigated. On the basis of single weld [...] Read more.
Within the scope of the presented work the processing of AISI H11 (1.2343 or X37CrMoV5-1) tool steel powder modified by adding carbon black nanoparticles in varying concentrations by means of Laser Metal Deposition (LMD) is extensively investigated. On the basis of single weld track experiments, multi-layered cuboid-shaped samples made out of pure AISI H11 tool steel powder as well as modified tool steel powder mixtures were manufactured by applying various process parameters. The main scientific aim of the investigations was to achieve a basic understanding of the influence of the added carbon black nanoparticles on the resulting sample properties. For that purpose, the generated specimens were first analyzed with respect to relative density, inner defects, microstructure, Vickers hardness and chemical composition. Subsequently, the mechanical properties of post-heat-treated specimens were investigated, with the focus on the yield strength (Y0.2%), by means of compression tests. We prove that by adding carbon black nanoparticles to the initial AISI H11 powder, the formation of martensitic and bainitic phases, as well as the precipitation of carbides at the grain boundaries, are enhanced. As a result, a significant increase of Vickers hardness and of the compression yield strength by up to 11% can be achieved in comparison to samples made out of the unmodified AISI H11 powder. Furthermore, it can be fundamentally demonstrated that the fabrication of parts with layer-specific variable hardness can be realized by the controlled changing of the powder mixtures used during the layer-by-layer manufacturing approach. Full article
(This article belongs to the Special Issue Additive Manufacturing of Ferrous Materials)
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Open AccessCommunication
Evaluation of Strain-Rate Sensitivity of Selective Laser Melted H13 Tool Steel Using Nanoindentation Tests
Metals 2018, 8(8), 589; https://doi.org/10.3390/met8080589 - 28 Jul 2018
Cited by 2
Abstract
This paper demonstrates the successful printing of H13 tool steel by a selective laser melting (SLM) method at a scan laser speed of 200 mm/s for the best microstructure and mechanical behavior. Specifically, the nanoindentation strain-rate sensitivity values were 0.022, 0.019, 0.027, 0.028, [...] Read more.
This paper demonstrates the successful printing of H13 tool steel by a selective laser melting (SLM) method at a scan laser speed of 200 mm/s for the best microstructure and mechanical behavior. Specifically, the nanoindentation strain-rate sensitivity values were 0.022, 0.019, 0.027, 0.028, and 0.035 for SLM H13 at laser scan speeds of 100, 200, 400, 800, and 1600 mm/s, respectively. This showed that the hardness increases as the strain rate increases and, practically, the hardness values of the SLM H13 at the 200 mm/s laser scan speed are the highest and least sensitive to the strain rate as compared to H13 samples at other scan speeds. The SLM processing of this material at 200 mm/s laser scan speed therefore shows the highest potential for advanced tool design. Residual stress is expected to affect the hardness and shall be investigated in future research. Full article
(This article belongs to the Special Issue Additive Manufacturing of Ferrous Materials)
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Open AccessArticle
Characterization of 17-4PH Single Tracks Produced at Different Parametric Conditions towards Increased Productivity of LPBF Systems—The Effect of Laser Power and Spot Size Upscaling
Metals 2018, 8(7), 475; https://doi.org/10.3390/met8070475 - 22 Jun 2018
Cited by 7
Abstract
Global industrial adoption of laser-based powder bed fusion (LPBF) technology is still limited by the production speed, the size of the build envelope, and therefore the maximum part size that can be produced. The cost of LPBF can be driven down further by [...] Read more.
Global industrial adoption of laser-based powder bed fusion (LPBF) technology is still limited by the production speed, the size of the build envelope, and therefore the maximum part size that can be produced. The cost of LPBF can be driven down further by improving the build rates without compromising structural integrity. A common approach is that the build rate can be improved by increasing the laser power and beam diameter to instantly melt a large area of powder, thus reducing the scanning time for each layer. The aim of this study was to investigate the aspects of upscaling LPBF processing parameters on the characteristic formation of stable single tracks, which are the primary building blocks for this technology. Two LPBF systems operating independently, using different parameter regimes, were used to produce the single tracks on a solid substrate deposited with a thin powder layer. The results obtained indicate that higher laser power and spot size can be used to produce stable tracks while the linear energy input is increased. It was also shown statistically that the geometrical characteristics of single tracks are mainly affected by the laser power and scanning speed during the scanning of a thin powder layer. Full article
(This article belongs to the Special Issue Additive Manufacturing of Ferrous Materials)
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Open AccessArticle
Crystallographic Features of Microstructure in Maraging Steel Fabricated by Selective Laser Melting
Metals 2018, 8(6), 440; https://doi.org/10.3390/met8060440 - 09 Jun 2018
Cited by 7
Abstract
This study characterizes the microstructure and its associated crystallographic features of bulk maraging steels fabricated by selective laser melting (SLM) combined with a powder bed technique. The fabricated sample exhibited characteristic melt pools in which the regions had locally melted and rapidly solidified. [...] Read more.
This study characterizes the microstructure and its associated crystallographic features of bulk maraging steels fabricated by selective laser melting (SLM) combined with a powder bed technique. The fabricated sample exhibited characteristic melt pools in which the regions had locally melted and rapidly solidified. A major part of these melt pools corresponded with the ferrite (α) matrix, which exhibited a lath martensite structure with a high density of dislocations. A number of fine retained austenite (γ) with a <001> orientation along the build direction was often localized around the melt pool boundaries. The orientation relationship of these fine γ grains with respect to the adjacent α grains in the martensite structure was (111)γ//(011)α and [-101]γ//[-1-11]α (Kurdjumov–Sachs orientation relationship). Using the obtained results, we inferred the microstructure development of maraging steels during the SLM process. The results depict that new and diverse high-strength materials can be used to develop industrial molds and dies. Full article
(This article belongs to the Special Issue Additive Manufacturing of Ferrous Materials)
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Open AccessArticle
An Investigation of the Microstructure and Fatigue Behavior of Additively Manufactured AISI 316L Stainless Steel with Regard to the Influence of Heat Treatment
Metals 2018, 8(4), 220; https://doi.org/10.3390/met8040220 - 28 Mar 2018
Cited by 11
Abstract
To exploit the whole potential of Additive Manufacturing, it is essential to investigate the complex relationships between Additive Manufacturing processes, the resulting microstructure, and mechanical properties of the materials and components. In the present work, Selective Laser Melted (SLM) (process category: powder bed [...] Read more.
To exploit the whole potential of Additive Manufacturing, it is essential to investigate the complex relationships between Additive Manufacturing processes, the resulting microstructure, and mechanical properties of the materials and components. In the present work, Selective Laser Melted (SLM) (process category: powder bed fusion), Laser Deposition Welded (LDW) (process category: direct energy deposition) and, for comparison, Continuous Casted and then hot and cold drawn (CC) austenitic stainless steel AISI 316L blanks were investigated with regard to their microstructure and mechanical properties. To exclude the influence of surface topography and focus the investigation on the volume microstructure, the blanks were turned into final geometry of specimens. The additively manufactured (AM-) blanks were manufactured in both the horizontal and vertical building directions. In the horizontally built specimens, the layer planes are perpendicular and in vertical building direction, they are parallel to the load axis of the specimens. The materials from different manufacturing processes exhibit different chemical composition and hence, austenite stability. Additionally, all types of blanks were heat treated (2 h, 1070 °C, H2O) and the influence of the heat treatment on the properties of differently manufactured materials were investigated. From the cyclic deformation curves obtained in the load increase tests, the anisotropic fatigue behavior of the AM-specimens could be detected with only one specimen in each building direction for the different Additive Manufacturing processes, which could be confirmed by constant amplitude tests. The results showed higher fatigue strength for horizontally built specimens compared to the vertical building direction. Furthermore, the constant amplitude tests show that the austenite stability influences the fatigue behavior of differently manufactured 316L. Using load increase tests as an efficient rating method of the anisotropic fatigue behavior, the influence of the heat treatment on anisotropy could be determined with a small number of specimens. These investigations showed no significant influence of the heat treatment on the anisotropic behavior of the AM-specimens. Full article
(This article belongs to the Special Issue Additive Manufacturing of Ferrous Materials)
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Review

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Open AccessFeature PaperReview
Microstructure, Solidification Texture, and Thermal Stability of 316 L Stainless Steel Manufactured by Laser Powder Bed Fusion
Metals 2018, 8(8), 643; https://doi.org/10.3390/met8080643 - 15 Aug 2018
Cited by 9
Abstract
This article overviews the scientific results of the microstructural features observed in 316 L stainless steel manufactured by the laser powder bed fusion (LPBF) method obtained by the authors, and discusses the results with respect to the recently published literature. Microscopic features of [...] Read more.
This article overviews the scientific results of the microstructural features observed in 316 L stainless steel manufactured by the laser powder bed fusion (LPBF) method obtained by the authors, and discusses the results with respect to the recently published literature. Microscopic features of the LPBF microstructure, i.e., epitaxial nucleation, cellular structure, microsegregation, porosity, competitive colony growth, and solidification texture, were experimentally studied by scanning and transmission electron microscopy, diffraction methods, and atom probe tomography. The influence of laser power and laser scanning speed on the microstructure was discussed in the perspective of governing the microstructure by controlling the process parameters. It was shown that the three-dimensional (3D) zig-zag solidification texture observed in the LPBF 316 L was related to the laser scanning strategy. The thermal stability of the microstructure was investigated under isothermal annealing conditions. It was shown that the cells formed at solidification started to disappear at about 800 °C, and that this process leads to a substantial decrease in hardness. Colony boundaries, nevertheless, were quite stable, and no significant grain growth was observed after heat treatment at 1050 °C. The observed experimental results are discussed with respect to the fundamental knowledge of the solidification processes, and compared with the existing literature data. Full article
(This article belongs to the Special Issue Additive Manufacturing of Ferrous Materials)
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