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Special Issue "Selective Laser Sintering (SLS) of Materials"

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 March 2019)

Special Issue Editors

Guest Editor
Prof. Ioanna Zergioti

Physics Department, National Technical University of Athens, Zografou, Athens, Greece
Website | E-Mail
Interests: microfluidics; Laser Materials Processing, Laser Induced Forward Transfer,Laser sintering, Laser printing of biomaterials, biosensors, metallic nanoparticles, flexible/stretchable electronics; wearable electronics
Guest Editor
Prof. Costas P. Grigoropoulos

Department of Mechanical Engineering, 6129 Etcheverry Hall, University of California, Berkeley CA 94720-1740, U.S.A.
Website | E-Mail
Phone: +1-510-642-2525
Fax: +1-510-642-5539

Special Issue Information

Dear Colleagues,

Selective Laser Sintering (SLS) has been effectively utilized over the past 15 years as a microcuring process for the fabrication of solid patterns with supreme electrical and mechanical properties. Unlike conventional sintering in an oven, which affects the entirety of a sample, SLS is a digital process offering a high resolution, as the laser irradiated heat-affected zone is extremely short and, therefore, associated thermal damage to the substrate or adjacent layers is substantially reduced.

There are many SLS processes and applications. The field is rapidly expanding to novel areas: The advent of printed and flexible electronics has brought SLS into focus once more, as a process capable of providing high resolution micropatterns of electronic components and circuits without incurring serious damage on the sensitive substrates involved in this technology. This new application of SLS dictated the modification of several key-features of the conventional SLS process; lower power and ultra-short pulsed lasers have emerged as the best option for producing high resolution features with minimized heat affected zones and maximal selectivity. In line with this manufacturing trend, novel nanomaterials with very low sintering temperatures have been developed in ink or paste form, including metal (Ag, Cu), metal oxide (ZnO, ITO, CuO), composites (AZO, solder paste) and other materials (graphene oxide, CNTs).

Flexible electronics and overall the additive manufacturing of microelectronics rely on the efficiency of laser sintering. It is substantial for the field to clarify important issues such as laser matter interaction for pulse widths at the fs to ns regime, understand the underlying mechanisms of sintering and melting owing to the accumulative heating of high repetition rate pulses and to construct time- dependent theoretical models. The focus of this Special Issue will be on advancements in the SLS process itself for primarily flexible electronics and other emerging relevant applications (e.g. printed sensors), without excluding reports on SLS for additive manufacturing and novel materials developed specifically for laser sintering.

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

Prof. Ioanna Zergioti
Prof. Costas P. Grigoropoulos
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 1800 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

  • lases sintering
  • flexible electronics
  • nanoinks
  • nanopastes
  • micropatterns
  • electronic circuits

Published Papers (8 papers)

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Research

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Open AccessArticle
Prediction and Sensitivity Analysis of Bubble Dissolution Time in 3D Selective Laser Sintering Using Ensemble Decision Trees
Materials 2019, 12(9), 1544; https://doi.org/10.3390/ma12091544
Received: 31 March 2019 / Revised: 22 April 2019 / Accepted: 6 May 2019 / Published: 10 May 2019
Cited by 2 | PDF Full-text (3702 KB) | HTML Full-text | XML Full-text
Abstract
The presence of defects like gas bubble in fabricated parts is inherent in the selective laser sintering process and the prediction of bubble shrinkage dynamics is crucial. In this paper, two artificial intelligence (AI) models based on Decision Trees algorithm were constructed in [...] Read more.
The presence of defects like gas bubble in fabricated parts is inherent in the selective laser sintering process and the prediction of bubble shrinkage dynamics is crucial. In this paper, two artificial intelligence (AI) models based on Decision Trees algorithm were constructed in order to predict bubble dissolution time, namely the Ensemble Bagged Trees (EDT Bagged) and Ensemble Boosted Trees (EDT Boosted). A metadata including 68644 data were generated with the help of our previously developed numerical tool. The AI models used the initial bubble size, external domain size, diffusion coefficient, surface tension, viscosity, initial concentration, and chamber pressure as input parameters, whereas bubble dissolution time was considered as output variable. Evaluation of the models’ performance was achieved by criteria such as Mean Absolute Error (MAE), Root Mean Squared Error (RMSE) and coefficient of determination (R2). The results showed that EDT Bagged outperformed EDT Boosted. Sensitivity analysis was then conducted thanks to the Monte Carlo approach and it was found that three most important inputs for the problem were the diffusion coefficient, initial concentration, and bubble initial size. This study might help in quick prediction of bubble dissolution time to improve the production quality from industry. Full article
(This article belongs to the Special Issue Selective Laser Sintering (SLS) of Materials)
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Open AccessArticle
Selective Laser Sintering of Laser Printed Ag Nanoparticle Micropatterns at High Repetition Rates
Materials 2018, 11(11), 2142; https://doi.org/10.3390/ma11112142
Received: 29 September 2018 / Revised: 24 October 2018 / Accepted: 25 October 2018 / Published: 31 October 2018
Cited by 1 | PDF Full-text (38217 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The increasing development of flexible and printed electronics has fueled substantial advancements in selective laser sintering, which has been attracting interest over the past decade. Laser sintering of metal nanoparticle dispersions in particular (from low viscous inks to high viscous pastes) offers significant [...] Read more.
The increasing development of flexible and printed electronics has fueled substantial advancements in selective laser sintering, which has been attracting interest over the past decade. Laser sintering of metal nanoparticle dispersions in particular (from low viscous inks to high viscous pastes) offers significant advantages with respect to more conventional thermal sintering or curing techniques. Apart from the obvious lateral selectivity, the use of short-pulsed and high repetition rate lasers minimizes the heat affected zone and offers unparalleled control over a digital process, enabling the processing of stacked and pre-structured layers on very sensitive polymeric substrates. In this work, the authors have conducted a systematic investigation of the laser sintering of micro-patterns comprising Ag nanoparticle high viscous inks: The effect of laser pulse width within the range of 20–200 nanoseconds (ns), a regime which many commercially available, high repetition rate lasers operate in, has been thoroughly investigated experimentally in order to define the optimal processing parameters for the fabrication of highly conductive Ag patterns on polymeric substrates. The in-depth temperature profiles resulting from the effect of laser pulses of varying pulse widths have been calculated using a numerical model relying on the finite element method, which has been fed with physical parameters extracted from optical and structural characterization. Electrical characterization of the resulting sintered micro-patterns has been benchmarked against the calculated temperature profiles, so that the resistivity can be associated with the maximal temperature value. This quantitative correlation offers the possibility to predict the optimal process window in future laser sintering experiments. The reported computational and experimental findings will foster the wider adoption of laser micro-sintering technology for laboratory and industrial use. Full article
(This article belongs to the Special Issue Selective Laser Sintering (SLS) of Materials)
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Open AccessArticle
Numerical Simulation of Thermal Processes in a Domain of Thin Metal Film Subjected to an Ultrashort Laser Pulse
Materials 2018, 11(11), 2116; https://doi.org/10.3390/ma11112116
Received: 29 September 2018 / Revised: 21 October 2018 / Accepted: 26 October 2018 / Published: 28 October 2018
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Abstract
A thin metal film subjected to an ultrashort laser pulse is considered. With a sufficiently high laser intensity the process of the film heating may cause metal melting and even ablation. In this work, the numerical model of the melting and resolidification processes [...] Read more.
A thin metal film subjected to an ultrashort laser pulse is considered. With a sufficiently high laser intensity the process of the film heating may cause metal melting and even ablation. In this work, the numerical model of the melting and resolidification processes is presented. The mathematical model is based on the dual phase lag equation in which two positive constants appear, this means the relaxation and thermalization times. The considered equation contains a second-order time derivative and higher order mixed derivative in both time and space and should be supplemented by the appropriate boundary and initial conditions. The model of the melting and resolidification is presented in two versions. The first can be called ‘the introduction of the artificial mushy zone sub-domain’, while the second ‘the two forms of the basic energy equation’. At the stage of numerical computations, the implicit scheme of the finite difference method is used. The numerical algorithm is tested for the two proposed models which are applied to the computations concerning the thermal processes occurring in the cylindrical micro-domain (chromium, gold) subjected to an ultrashort laser pulse. Full article
(This article belongs to the Special Issue Selective Laser Sintering (SLS) of Materials)
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Open AccessArticle
Development of SiC/PVB Composite Powders for Selective Laser Sintering Additive Manufacturing of SiC
Materials 2018, 11(10), 2012; https://doi.org/10.3390/ma11102012
Received: 26 September 2018 / Revised: 15 October 2018 / Accepted: 16 October 2018 / Published: 17 October 2018
Cited by 1 | PDF Full-text (10498 KB) | HTML Full-text | XML Full-text
Abstract
Subsphaeroidal SiC/polymer composite granules with good flowability for additive manufacturing/3D printing of SiC were prepared by ball milling with surface modification using polyvinyl butyral (PVB). PVB adheres to the particle surface of SiC to form a crosslinked network structure and keeps them combined [...] Read more.
Subsphaeroidal SiC/polymer composite granules with good flowability for additive manufacturing/3D printing of SiC were prepared by ball milling with surface modification using polyvinyl butyral (PVB). PVB adheres to the particle surface of SiC to form a crosslinked network structure and keeps them combined with each other into light aggregates. The effects of PVB on the shape, size, phase composition, distribution and flowability of the polymer-ceramic composite powder were investigated in detail. Results show that the composite powder material has good laser absorptivity at wavelengths of lower than 500 nm. Full article
(This article belongs to the Special Issue Selective Laser Sintering (SLS) of Materials)
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Open AccessArticle
Laser-Induced Silver Seeding on Filter Paper for Selective Electroless Copper Plating
Materials 2018, 11(8), 1348; https://doi.org/10.3390/ma11081348
Received: 9 July 2018 / Revised: 28 July 2018 / Accepted: 31 July 2018 / Published: 3 August 2018
Cited by 1 | PDF Full-text (4232 KB) | HTML Full-text | XML Full-text
Abstract
The generation of a flexible printed circuit board on polymer fabrics has been a challenge over the last decade. In this work, a copper pattern was obtained on a soft substrate of filter paper/polyacrylonitrile (FP/PAN) film, where the filter paper was commercially available. [...] Read more.
The generation of a flexible printed circuit board on polymer fabrics has been a challenge over the last decade. In this work, a copper pattern was obtained on a soft substrate of filter paper/polyacrylonitrile (FP/PAN) film, where the filter paper was commercially available. The pattern of Ag particles was first produced on an Ag+-doped FP/PAN composite film, followed by electroless plating of copper using the metal silver particles as seeds. The in situ reduction of silver particles and the formation of the silver agglomeration pattern were induced by laser irradiation technology on the FP/PAN/AgNO3 composite film. A variety of characterizations indicated that the resultant copper deposition was uniform, with good conductivity properties. Full article
(This article belongs to the Special Issue Selective Laser Sintering (SLS) of Materials)
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Open AccessFeature PaperArticle
Single Step Laser Transfer and Laser Curing of Ag NanoWires: A Digital Process for the Fabrication of Flexible and Transparent Microelectrodes
Materials 2018, 11(6), 1036; https://doi.org/10.3390/ma11061036
Received: 2 May 2018 / Revised: 4 June 2018 / Accepted: 16 June 2018 / Published: 19 June 2018
Cited by 3 | PDF Full-text (4921 KB) | HTML Full-text | XML Full-text
Abstract
Ag nanowire (NW) networks have exquisite optical and electrical properties which make them ideal candidate materials for flexible transparent conductive electrodes. Despite the compatibility of Ag NW networks with laser processing, few demonstrations of laser fabricated Ag NW based components currently exist. In [...] Read more.
Ag nanowire (NW) networks have exquisite optical and electrical properties which make them ideal candidate materials for flexible transparent conductive electrodes. Despite the compatibility of Ag NW networks with laser processing, few demonstrations of laser fabricated Ag NW based components currently exist. In this work, we report on a novel single step laser transferring and laser curing process of micrometer sized pixels of Ag NW networks on flexible substrates. This process relies on the selective laser heating of the Ag NWs induced by the laser pulse energy and the subsequent localized melting of the polymeric substrate. We demonstrate that a single laser pulse can induce both transfer and curing of the Ag NW network. The feasibility of the process is confirmed experimentally and validated by Finite Element Analysis simulations, which indicate that selective heating is carried out within a submicron-sized heat affected zone. The resulting structures can be utilized as fully functional flexible transparent electrodes with figures of merit even higher than 100. Low sheet resistance (<50 Ohm/sq) and high visible light transparency (>90%) make the reported process highly desirable for a variety of applications, including selective heating or annealing of nanocomposite materials and laser processing of nanostructured materials on a large variety of optically transparent substrates, such as Polydimethylsiloxane (PDMS). Full article
(This article belongs to the Special Issue Selective Laser Sintering (SLS) of Materials)
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Open AccessArticle
The Effect of Post-Processes on the Microstructure and Creep Properties of Alloy718 Built Up by Selective Laser Melting
Materials 2018, 11(6), 996; https://doi.org/10.3390/ma11060996
Received: 11 April 2018 / Revised: 7 June 2018 / Accepted: 8 June 2018 / Published: 12 June 2018
Cited by 2 | PDF Full-text (11288 KB) | HTML Full-text | XML Full-text
Abstract
The selective laser melting (SLM) process was used to fabricate an Alloy718 specimen. The microstructure and creep properties were characterized in both the as-built and post-processed SLM materials. Post-processing involved several heat treatments and a combination of hot isostatic pressing (HIP) and solution [...] Read more.
The selective laser melting (SLM) process was used to fabricate an Alloy718 specimen. The microstructure and creep properties were characterized in both the as-built and post-processed SLM materials. Post-processing involved several heat treatments and a combination of hot isostatic pressing (HIP) and solution treatment and aging (STA) to homogenize the microstructure. The experimental results showed that the originally recommended heat treatment process, STA-980 °C, for cast and wrought materials was not effective for SLM-processed specimens. Obvious grain growth structures were obtained in the STA-1180 °C/1 h and STA-1180 °C/4 h specimens. However, the grain size was uneven since heavy distortion or high-density dislocation formed during the SLM process, which would be harmful for the mechanical properties of SLM-fabricated materials. The HIP+ direct aging process was the most effective method among the post-processes to improve the creep behavior at 650 °C. The creep rupture life of the HIP+ direct aging condition approached 800 h since the HIP process had the benefit of being free of pores, thus preventing microcrack nucleation and the formation of a serrated grain boundary. Full article
(This article belongs to the Special Issue Selective Laser Sintering (SLS) of Materials)
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Other

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Open AccessLetter
Study on the Selective Laser Melting of CuSn10 Powder
Materials 2018, 11(4), 614; https://doi.org/10.3390/ma11040614
Received: 14 March 2018 / Revised: 9 April 2018 / Accepted: 13 April 2018 / Published: 17 April 2018
Cited by 4 | PDF Full-text (9782 KB) | HTML Full-text | XML Full-text
Abstract
The selective laser melting of tin bronze (CuSn10) powder was performed with a laser energy density intensity level at 210, 220, and 230 J/mm2. The composition was homogeneous with almost all tin dissolved into the matrix. The grain size [...] Read more.
The selective laser melting of tin bronze (CuSn10) powder was performed with a laser energy density intensity level at 210, 220, and 230 J/mm2. The composition was homogeneous with almost all tin dissolved into the matrix. The grain size of the obtained alpha copper phase was around 5 μm. The best properties were achieved at 220 J/mm2 laser energy density with a density of 8.82 g/cm3, hardness of 78.2 HRB (Rockwell Hardness measured on the B scale), yield strength of 399 MPa, tensile strength of 490 MPa, and an elongation that reached 19%. “Balling effect” appeared and resulted into a decrease of properties when the laser energy density increased to 230 J/mm2. Full article
(This article belongs to the Special Issue Selective Laser Sintering (SLS) of Materials)
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