Special Issue "Progress in Metals Additive Manufacturing: From New Design to New Materials and Post Processing"

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

Deadline for manuscript submissions: closed (15 July 2020).

Special Issue Editor

Dr. Abdollah Saboori
E-Mail Website
Guest Editor
Department of Management and Production Engineering (DIGEP), Politecnico Di Torino, Corso Duca Degli Abruzzi 24, 10129 Torino, Italy
Interests: metal additive manufacturing; selective laser melting; electron beam melting; directed energy deposition; stainless steel; titanium alloys; metal matrix composites; materials characterization
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Special Issue Information

Dear Colleagues,

Additive manufacturing (AM) includes a set of processes in which a complex component can be produced in a layerwise fashion using the heating provided by a laser or electron source. Metals Additive Manufacturing (AM) is a rapidly growing manufacturing capability. This technology is expected to revolutionize the fabrication of metallic parts, in particular for application fields, where complex geometries, highly customized parts, small part production numbers and/or lead-time saving, play a decisive role. Nonetheless, despite all the remarkable efforts, there are significant challenges that are limiting the wider uptake and exploitation of metals AM, spanning across the entire metal AM supply chain. These include a lack of AM design and modelling skills and software, a gap in understanding in properties obtained from different machines and technologies, and an incomplete understanding of the causes of part quality variation and their effect on part failure. This Special Issue is dedicated to disseminate these recent scientific efforts.

For this Special Issue in Materials, it is my pleasure to invite you to submit reviews and articles in the areas of material supply, part design, process modelling, process technology, post-processing techniques and applications of metals AM.

Dr. Abdollah Saboori
Guest Editor

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. Materials is an international peer-reviewed open access semimonthly 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 2000 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
  • Metals and alloys
  • New alloys
  • Design for AM
  • Materials characterization

Published Papers (5 papers)

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Research

Article
Further Studies into Crack Growth in Additively Manufactured Materials
Materials 2020, 13(10), 2223; https://doi.org/10.3390/ma13102223 - 12 May 2020
Cited by 6 | Viewed by 830
Abstract
Understanding and characterizing crack growth is central to meeting the damage tolerance and durability requirements delineated in USAF Structures Bulletin EZ-SB-19-01 for the utilization of additive manufacturing (AM) in the sustainment of aging aircraft. In this context, the present paper discusses the effect [...] Read more.
Understanding and characterizing crack growth is central to meeting the damage tolerance and durability requirements delineated in USAF Structures Bulletin EZ-SB-19-01 for the utilization of additive manufacturing (AM) in the sustainment of aging aircraft. In this context, the present paper discusses the effect of different AM processes, different build directions, and the variability in the crack growth rates related to AM Ti-6Al-4V, AM Inconel 625, and AM 17-4 PH stainless steel. This study reveals that crack growth in these three AM materials can be captured using the Hartman–Schijve crack growth equation and that the variability in the various da/dN versus ΔK curves can be modeled by allowing the terms ΔKthr and A to vary. It is also shown that for the AM Ti-6AL-4V processes considered, the variability in the cyclic fracture toughness appears to be greatest for specimens manufactured using selective layer melting (SLM). Full article
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Article
Influences of Horizontal and Vertical Build Orientations and Post-Fabrication Processes on the Fatigue Behavior of Stainless Steel 316L Produced by Selective Laser Melting
Materials 2019, 12(24), 4203; https://doi.org/10.3390/ma12244203 - 14 Dec 2019
Cited by 4 | Viewed by 1046
Abstract
In this paper, the influences of build orientation and post-fabrication processes, including stress-relief, machining, and shot-peening, on the fatigue behavior of stainless steel (SS) 316L manufactured using selective laser melting (SLM) are studied. It was found that horizontally-built (XY) and machined (M) test [...] Read more.
In this paper, the influences of build orientation and post-fabrication processes, including stress-relief, machining, and shot-peening, on the fatigue behavior of stainless steel (SS) 316L manufactured using selective laser melting (SLM) are studied. It was found that horizontally-built (XY) and machined (M) test pieces, which had not been previously studied in the literature, in both stress-relieved (SR) or non-stress-relieved (NSR) conditions show superior fatigue behavior compared to vertically-built (ZX) and conventionally-manufactured SS 316L. The XY, M, and SR (XY-M-SR) test pieces displayed fatigue behavior similar to the XY-M-NSR test pieces, implying that SR does not have a considerable effect on the fatigue behavior of XY and M test pieces. ZX-M-SR test pieces, due to their considerably lower ductility, exhibited significantly larger scatter and a lower fatigue strength compared to ZX-M-NSR samples. Shot-peening (SP) displayed a positive effect on improving the fatigue behavior of the ZX-NSR test pieces due to a compressive stress of 58 MPa induced on the surface of the test pieces. Fractography of the tensile and fatigue test pieces revealed a deeper understanding of the relationships between the process parameters, microstructure, and mechanical properties for SS 316L produced by laser systems. For example, fish-eye fracture pattern or spherical stair features were not previously observed or explained for cyclically-loaded SLM-printed parts in the literature. This study provides comprehensive insight into the anisotropy of the static and fatigue properties of SLM-printed parts, as well as the pre- and post-fabrication parameters that can be employed to improve the fatigue behavior of steel alloys manufactured using laser systems. Full article
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Article
Analysis of Density, Roughness, and Accuracy of the Atomic Diffusion Additive Manufacturing (ADAM) Process for Metal Parts
Materials 2019, 12(24), 4122; https://doi.org/10.3390/ma12244122 - 09 Dec 2019
Cited by 6 | Viewed by 1623
Abstract
Atomic Diffusion Additive Manufacturing (ADAM) is a recent layer-wise process patented by Markforged for metals based on material extrusion. ADAM can be classified as an indirect additive manufacturing process in which a filament of metal powder encased in a plastic binder is used. [...] Read more.
Atomic Diffusion Additive Manufacturing (ADAM) is a recent layer-wise process patented by Markforged for metals based on material extrusion. ADAM can be classified as an indirect additive manufacturing process in which a filament of metal powder encased in a plastic binder is used. After the fabrication of a green part, the plastic binder is removed by the post-treatments of washing and sintering (frittage). The aim of this work is to provide a preliminary characterisation of the ADAM process using Markforged Metal X, the unique system currently available on the market. Particularly, the density of printed 17-4 PH material is investigated, varying the layer thickness and the sample size. The dimensional accuracy of the ADAM process is evaluated using the ISO IT grades of a reference artefact. Due to the deposition strategy, the final density of the material results in being strongly dependent on the layer thickness and the size of the sample. The density of the material is low if compared to the material processed by powder bed AM processes. The superficial roughness is strongly dependent upon the layer thickness, but higher than that of other metal additive manufacturing processes because of the use of raw material in the filament form. The accuracy of the process achieves the IT13 grade that is comparable to that of traditional processes for the production of semi-finished metal parts. Full article
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Article
Additive Manufacturing of Alloy 718 via Electron Beam Melting: Effect of Post-Treatment on the Microstructure and the Mechanical Properties
Materials 2019, 12(1), 68; https://doi.org/10.3390/ma12010068 - 25 Dec 2018
Cited by 21 | Viewed by 3261
Abstract
Alloy 718 finds application in gas turbine engine components, such as turbine disks, compressor blades and so forth, due to its excellent mechanical and corrosion properties at elevated temperatures. Electron beam melting (EBM) is a recent addition to the list of additive manufacturing [...] Read more.
Alloy 718 finds application in gas turbine engine components, such as turbine disks, compressor blades and so forth, due to its excellent mechanical and corrosion properties at elevated temperatures. Electron beam melting (EBM) is a recent addition to the list of additive manufacturing processes and has shown the capability to produce components with unique microstructural features. In this work, Alloy 718 specimens were manufactured using the EBM process with a single batch of virgin plasma atomized powder. One set of as-built specimens was subjected to solution treatment and ageing (STA); another set of as-built specimens was subjected to hot isostatic pressing (HIP), followed by STA (and referred to as HIP+STA). Microstructural analysis of as-built specimens, STA specimens and HIP+STA specimens was carried out using optical microscopy and scanning electron microscopy. Typical columnar microstructure, which is a characteristic of the EBM manufactured alloy, was observed. Hardness evaluation of the as-built, STA and HIP+STA specimens showed that the post-treatments led to an increase in hardness in the range of ~50 HV1. Tensile properties of the three material conditions (as-built, STA and HIP+STA) were evaluated. Post-treatments lead to an increase in the yield strength (YS) and the ultimate tensile strength (UTS). HIP+STA led to improved elongation compared to STA due to the closure of defects but YS and UTS were comparable for the two post-treatment conditions. Fractographic analysis of the tensile tested specimens showed that the closure of shrinkage porosity and the partial healing of lack of fusion (LoF) defects were responsible for improved properties. Fatigue properties were evaluated in both STA and HIP+STA conditions. In addition, three surface conditions were also investigated, namely the ‘raw’ as-built surface, the machined surface with the contour region and the machined surface without the contour region. Machining off the contour region completely together with HIP+STA led to significant improvement in fatigue performance. Full article
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Article
Development of Laser-Based Powder Bed Fusion Process Parameters and Scanning Strategy for New Metal Alloy Grades: A Holistic Method Formulation
Materials 2018, 11(12), 2356; https://doi.org/10.3390/ma11122356 - 22 Nov 2018
Cited by 11 | Viewed by 1705
Abstract
In spite of the fast growth of laser-based powder bed fusion (L-PBF) processes as a part of everyday industrial practice, achieving consistent production is hampered by the scarce repeatability of performance that is often encountered across different additive manufacturing (AM) machines. In addition, [...] Read more.
In spite of the fast growth of laser-based powder bed fusion (L-PBF) processes as a part of everyday industrial practice, achieving consistent production is hampered by the scarce repeatability of performance that is often encountered across different additive manufacturing (AM) machines. In addition, the development of novel feedstock materials, which is fundamental to the future growth of AM, is limited by the absence of established methodologies for their successful exploitation. This paper proposes a structured procedure with a complete test plan, which defines step-by-step the standardized actions that should be taken to optimize the processing parameters and scanning strategy in L-PBF of new alloy grades. The method is holistic, since it considers all the laser/material interactions in different local geometries of the build, and suggests, for each possible interaction, a specific geometry for test specimens, standard energy parameters to be analyzed through a design of experiment, and measurable key performance indicators. The proposed procedure therefore represents a sound and robust aid to the development of novel alloy grades for L-PBF and to the definition of the most appropriate processing conditions for them, independent of the specific AM machine applied. Full article
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