Special Issue "New Materials and Understandings in Selective Laser Melting (SLM)"

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

Deadline for manuscript submissions: 1 July 2020.

Special Issue Editors

Prof. Christopher Tuck
Website
Guest Editor
Faculty of Engineering, University of Nottingham, UK
Interests: Additive Manufacturing; 3D Printing; Materials Science; Materials Engineering; Metals; Polymers
Dr. Nesma Aboulkhair
Website
Guest Editor
Faculty of Engineering, University of Nottingham, UK
Interests: Additive Manufacturing; Metals, Materials Science; Mechanical peformance; Materials Engineering

Special Issue Information

Dear Colleagues,

Selective laser melting (SLM) is a powder-bed fusion additive manufacturing technique used to fabricate intricate structures with unmatched degrees of complexity. Critical to this process is the feedstock material. Immense research efforts have been spent on using readily available alloys. However, in SLM, the material is irradiated with a laser beam causing rapid melting and solidification, imposing significantly different thermal experiences. Therefore, designing new alloys specifically tailored to the process or modifying available alloys is sought.

The process–material–property relationship in SLM is markedly complex. An understanding of how SLM affects the process of designing new alloys is essential to heightening the momentum in this field. The focus of this Special Issue is on approaches to developing new materials tailored to SLM and the new understandings needed to overcome the barriers to wider adoption.

It is our pleasure to invite you to submit a manuscript to this Special Issue. Full papers, communications and reviews are all welcome.

Prof. Christopher Tuck
Dr. Nesma Aboulkhair
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. 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

  • selective laser melting
  • alloy development
  • metallurgy
  • mechanical properties
  • melt pool dynamics
  • powderbed fusion.

Published Papers (4 papers)

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Research

Open AccessFeature PaperArticle
Heat Treatments and Critical Quenching Rates in Additively Manufactured Al–Si–Mg Alloys
Materials 2020, 13(3), 720; https://doi.org/10.3390/ma13030720 - 05 Feb 2020
Abstract
Laser powder-bed fusion (LPBF) has significantly gained in importance and has become one of the major fabrication techniques within metal additive manufacturing. The fast cooling rates achieved in LPBF due to a relatively small melt pool on a much larger component or substrate, [...] Read more.
Laser powder-bed fusion (LPBF) has significantly gained in importance and has become one of the major fabrication techniques within metal additive manufacturing. The fast cooling rates achieved in LPBF due to a relatively small melt pool on a much larger component or substrate, acting as heat sink, result in fine-grained microstructures and high oversaturation of alloying elements in the α-aluminum. Al–Si–Mg alloys thus can be effectively precipitation hardened. Moreover, the solidified material undergoes an intrinsic heat treatment, whilst the layers above are irradiated and the elevated temperature in the built chamber starts the clustering process of alloying elements directly after a scan track is fabricated. These silicon–magnesium clusters were observed with atom probe tomography in as-built samples. Similar beneficial clustering behavior at higher temperatures is known from the direct-aging approach in cast samples, whereby the artificial aging is performed immediately after solution annealing and quenching. Transferring this approach to LPBF samples as a possible post-heat treatment revealed that even after direct aging, the outstanding hardness of the as-built condition could, at best, be met, but for most instances it was significantly lower. Our investigations showed that LPBF Al–Si–Mg exhibited a high dependency on the quenching rate, which is significantly more pronounced than in cast reference samples, requiring two to three times higher quenching rate after solution annealing to yield similar hardness results. This suggests that due to the finer microstructure and the shorter diffusion path in Al–Si–Mg fabricated by LPBF, it is more challenging to achieve a metastable oversaturation necessary for precipitation hardening. This may be especially problematic in larger components. Full article
(This article belongs to the Special Issue New Materials and Understandings in Selective Laser Melting (SLM))
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Open AccessArticle
The Effects of Feature Sizes in Selectively Laser Melted Ti-6Al-4V Parts on the Validity of Optimised Process Parameters
Materials 2020, 13(1), 117; https://doi.org/10.3390/ma13010117 - 26 Dec 2019
Cited by 1
Abstract
Ti-6Al-4V is a popular alloy due to its high strength-to-weight ratio and excellent corrosion resistance. Many applications of additively manufactured Ti-6Al-4V using selective laser melting (SLM) have reached technology readiness. However, issues linked with metallurgical differences in parts manufactured by conventional processes and [...] Read more.
Ti-6Al-4V is a popular alloy due to its high strength-to-weight ratio and excellent corrosion resistance. Many applications of additively manufactured Ti-6Al-4V using selective laser melting (SLM) have reached technology readiness. However, issues linked with metallurgical differences in parts manufactured by conventional processes and SLM persist. Very few studies have focused on relating the process parameters to the macroscopic and microscopic properties of parts with different size features. Therefore, the aim of this study was to investigate the effect of the size of features on the density, hardness, microstructural evolution, and mechanical properties of Ti-6Al-4V parts fabricated using a fixed set of parameters. It was found that there is an acceptable range of sizes that can be produced using a fixed set of parameters. Beyond a specific window, the relative density decreased. Upon decreasing the size of a cuboid from (5 × 5 × 5 mm) to (1 × 1 × 5 mm), porosity increased from 0.3% to 4.8%. Within a suitable size range, the microstructure was not significantly affected by size; however, a major change was observed outside the acceptable size window. The size of features played a significant role in the variation of mechanical properties. Under tensile loading, decreasing the gauge size, the ultimate and yield strengths deteriorated. This investigation, therefore, presents an understanding of the correlation between the feature size and process parameters in terms of the microscopic and macroscopic properties of Ti-6Al-4V parts manufactured using SLM. This study also highlights the fact that any set of optimized process parameters will only be valid within a specific size window. Full article
(This article belongs to the Special Issue New Materials and Understandings in Selective Laser Melting (SLM))
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Open AccessArticle
Processability of Atypical WC-Co Composite Feedstock by Laser Powder-Bed Fusion
Materials 2020, 13(1), 50; https://doi.org/10.3390/ma13010050 - 20 Dec 2019
Abstract
Processing of tool materials for cutting applications presents challenges in additive manufacturing (AM). Processes must be carefully managed in order to promote the formation of favourable high-integrity ‘builds’. In this study, for the first time, a satelliting process is used to prepare a [...] Read more.
Processing of tool materials for cutting applications presents challenges in additive manufacturing (AM). Processes must be carefully managed in order to promote the formation of favourable high-integrity ‘builds’. In this study, for the first time, a satelliting process is used to prepare a WCM-Co (12 wt.% Co) composite. Melting trials were undertaken to evaluate the consolidation behaviour of single tracks within a single layer. Tracks with continuous and relatively uniform surface morphology were obtained. These features are essential for high-quality AM builds in order to encourage good bonding between subsequent tracks within a layer which may reduce porosity within a 3D deposition. This study elucidates the formation of track irregularities, melting modes, crack sensitivity, and balling as a function of laser scanning speed and provides guidelines for future production of WCM-Co by laser powder-bed fusion. Full article
(This article belongs to the Special Issue New Materials and Understandings in Selective Laser Melting (SLM))
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Open AccessFeature PaperArticle
Defect Prevention in Selective Laser Melting Components: Compositional and Process Effects
Materials 2019, 12(22), 3791; https://doi.org/10.3390/ma12223791 - 18 Nov 2019
Abstract
A model to predict the conditions for printability is presented. The model focuses on crack prevention, as well as on avoiding the formation of defects such as keyholes, balls and lack of fusion. Crack prevention is ensured by controlling the solidification temperature range [...] Read more.
A model to predict the conditions for printability is presented. The model focuses on crack prevention, as well as on avoiding the formation of defects such as keyholes, balls and lack of fusion. Crack prevention is ensured by controlling the solidification temperature range and path, as well as via quantifying its ability to resist thermal stresses upon solidification. Defect formation prevention is ensured by controlling the melt pool geometry and by taking into consideration the melting properties. The model’s core relies on thermodynamics and physical analysis to ensure optimal printability, and in turn offers key information for alloy design and selective laser melting process control. The model is shown to describe accurately defect formation of 316L austenitic stainless steels reported in the literature. Full article
(This article belongs to the Special Issue New Materials and Understandings in Selective Laser Melting (SLM))
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Authors: Christopher Tuck, Nesma Aboulkhair
Afffiliation: University of Nottingham, UK

Authors: Moataz Attallah 
Afffiliation:University of Birmingham, UK

Authors: Leonhard Hiltzer, Ewald A. Werner*
Afffiliation: Technical University of Munich, Germany 

Authors: Pedro Eduardo
Afffiliation:Lancaster University, UK

Authors: Manyalibo Matthews
Afffiliation:Lawrence Livermore National Laboratory, USA

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