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

Deadline for manuscript submissions: closed (10 February 2024) | Viewed by 19727

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Prof. Dr. Petru Berce

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Manufacturing Engineering Department, Technical University of Cluj Napoca, 400641 Cluj-Napoca, Romania
Interests: additive manufacturing and their applications; rapid tooling; CNC manufacturing
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Special Issue Information

Dear Colleagues,

Additive manufacturing (AM) is a new type of manufacturing engineering, with less than 35 years of history. The real value of additive manufacturing is in identifying those applications where reductions in lead time, manufacturing cost, weight, tooling, and so on can lead to huge benefits across a part’s lifecycle in many applications from industry to medicine.

Additive manufacturing has evolved rapidly in last few years. It has been embraced by major industrial companies looking for ways to improve their products. The ability to deliver near-instant part production and fully custom designs that cannot be replicated with other manufacturing techniques has accelerated investment and research in additive engineering.

A number of different metals are now available in powdered form to suit exact processes and requirements. Titanium, steel, stainless steel, aluminum, and copper-, cobalt chrome-, titanium- and nickel-based alloys are available in powdered form, as are precious metals such as gold, platinum, palladium and silver.

This Special Issue will cover fundamental studies of additive manufacturing process, optimizations, new additive processes, rapid tooling, and applications from industry to medicine using metal powders as raw materials.

I hope that the present Special Issue will be an opportunity for creating a strong network between authors and users, working in some different sectors, for smart applications from industry to medicine.

Prof. Dr. Petru Berce
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 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 process
Optimization of AM process
Rapid tooling
Industrial applications
Medical applications

Related Special Issue

Advances in Additive Manufacturing and Their Applications (2nd Edition) in Metals

Published Papers (11 papers)

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Editorial

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4 pages, 158 KiB

Open AccessEditorial

Advances in Additive Manufacturing and Their Applications

by Petru Berce

Metals 2024, 14(2), 165; https://doi.org/10.3390/met14020165 - 29 Jan 2024

Viewed by 796

Abstract

Additive manufacturing (AM) has evolved rapidly in the last few years [...] Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing and Their Applications)

Research

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23 pages, 9267 KiB

Open AccessArticle

Investigation on Optical Absorption and Reflection of Carbon Nanotubes Mixed Copper Composites for Laser Sintering Process Improvement

by Hasan Ayub, Lehar Asip Khan, Eanna McCarthy, Inam Ul Ahad, Karsten Fleischer and Dermot Brabazon

Metals 2023, 13(12), 1984; https://doi.org/10.3390/met13121984 - 07 Dec 2023

Viewed by 882

Abstract

Selective laser sintering (SLS) of copper components manufactured via powder metallurgy is widely studied due to minimal material wastage. However, copper has poor optical absorption when exposed to infrared (IR) lasers, such as in laser-based additive manufacturing or laser surface processing. To address this issue, an innovative approach to enhance the optical absorption of copper powders during infrared laser sintering is presented in this study. Carbon nanotubes (CNTs) have several unique properties, including their high surface area, plasmonic response, excellent conductivity, and optical absorption properties. CNTs were mixed with copper powders at different weight percentages using an acoustic method. The resulting Cu-CNT compositions were fabricated into pellets. The Box-Behnken Design of Experiments methodology was used to optimize the IR laser processing conditions for sintering. Spectroscopic analysis was conducted to evaluate the reflection and thermal absorption of the IR wavelengths by the Cu-CNT composites. Density and hardness measurements were taken for the laser-sintered Cu-CNT pellets. The coating of copper powders with CNTs demonstrated enhanced optical absorption and correspondingly reduced reflection. Due to the enhanced optical absorption, increased control and sensitivity of the laser sintering process was achieved, which enabled improvement in the mechanical properties of strength, hardness, and density, while also enabling control over the composite thermal expansion coefficient. A maximum average hardness of 66.5 HV was observed. Indentation test results of the samples revealed maximum tangential and radial stresses of 0.148 MPa and 0.058 Mpa, respectively. Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing and Their Applications)

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19 pages, 10460 KiB

Open AccessArticle

Aging Behaviour of a 12.2Cr-10Ni-1Mo-1Ti-0.6Al Precipitation-Hardening Stainless Steel Manufactured via Laser Powder Bed Fusion

by Alessandro Morri, Mattia Zanni, Lorella Ceschini, Alessandro Fortunato and Massimo Pellizzari

Metals 2023, 13(9), 1552; https://doi.org/10.3390/met13091552 - 03 Sep 2023

Cited by 1 | Viewed by 1190

Abstract

The combination of precipitation-hardening stainless steels (PH-SS) and laser powder bed fusion (LPBF) enables the manufacturing of tools for plastic injection moulding with optimised geometry and conformal cooling channels, with potential benefits in terms of productivity, part quality, and tool duration. Moreover, the suitability of LPBF-manufactured PH-SS in the as-built (AB) condition to be age-hardened through a direct aging (DA) treatment enables a great heat treatment simplification with respect to the traditional solution annealing and aging treatment (SA). However, plastic injection moulding tools experience severe thermal cycles during their service, which can lead to over-aging of PH-SS and thus shorten tool life. Therefore, proper thermal stability is required to ensure adequate tool life and reliability. The aim of the present work is to investigate the aging and over-aging behaviour of a commercially available PH-SS (AMPO M789) manufactured by LPBF in the AB condition and after a solution-annealing treatment in order to evaluate the effect of the heat treatment condition on the microstructure and the aging and over-aging response, aiming at assessing its feasibility for plastic injection moulding applications. The AB microstructure features melt pool borders, oriented martensite grains, and a cellular solidification sub-structure, and was retained during aging and over-aging. On the other hand, a homogeneous and isotropic martensite structure was present after solution annealing and quenching, with no melt pool borders, cellular structure, or oriented grains. The results indicate no significant difference between AB and solution-annealed and quenched specimens in terms of aging and over-aging behaviour and peak hardness (in the range 580–600 HV), despite the considerably different microstructures. Over-aging was attributed to both the coarsening of strengthening precipitates and martensite-to-austenite reversion (up to ~11 vol.%) upon prolonged exposure to high temperature. Based on the results, guidelines to aid the selection of the most suitable heat treatment procedure are proposed. Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing and Their Applications)

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19 pages, 18064 KiB

Open AccessArticle

Modelling Crack Growth in Additively Manufactured Inconel 718 and Inconel 625

by Rhys Jones, Andrew Ang, Daren Peng, Victor K. Champagne, Alex Michelson and Aaron Birt

Metals 2023, 13(7), 1300; https://doi.org/10.3390/met13071300 - 20 Jul 2023

Cited by 2 | Viewed by 1189

Abstract

This paper first examines crack growth in a range of tests on additively manufactured (AM) and conventionally manufactured Inconel 718. It is shown that whereas when the crack growth rate (da/dN) is plotted as a function of the range of the stress intensity factor (ΔK), the crack growth curves exhibit considerable scatter/variability, when da/dN is expressed in terms of the Schwalbe crack driving force (Δκ), then each of the 33 different curves essentially collapse onto a single curve. This relationship appears to hold over approximately six orders of magnitude in da/dN. The same phenomenon also appears to hold for 20 room temperature tests on both conventionally and additively manufactured Inconel 625. Given that the 53 studies examined in this paper were taken from a wide cross section of research studies it would appear that the variability in the da/dN and ΔK curves can (to a first approximation) be accounted for by allowing for the variability in the fatigue threshold and the cyclic fracture toughness terms in the Schwalbe crack driving force. As such, the materials science community is challenged to address the fundamental science underpinning this observation. Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing and Their Applications)

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15 pages, 7853 KiB

Open AccessArticle

Microstructure and Mechanical Properties of High-Strength, Low-Alloy Steel Thin-Wall Fabricated with Wire and Arc Additive Manufacturing

by Kaijie Song, Zidong Lin, Yongzhe Fa, Xuefeng Zhao, Ziqian Zhu, Wei Ya, Zhen Sun and Xinghua Yu

Metals 2023, 13(4), 764; https://doi.org/10.3390/met13040764 - 14 Apr 2023

Cited by 7 | Viewed by 1881

Abstract

High-strength, low-alloy (HSLA) steel has attracted much attention in the manufacturing industry because of its good combination of high strength and toughness, low cost, and good formability. Wire and arc additive manufacturing (WAAM) technology can realize the rapid prototyping of HSLA steel parts. This study investigated a 26-layer HSLA steel component fabricated with the WAAM technique. The microstructure of the deposited wall of ER120S-G is mainly acicular ferrite, and there are longitudinal, preferentially growing dendrites along the deposition direction. With the deposition height accumulation, the top sample’s interlayer temperature increases and the amount of acicular ferrite in the microstructure decreases, while the amount of quasi-polygonal ferrite, Widmanstatten ferrite increases. The changes in microhardness were consistent with the corresponding microstructure gradients: the microhardness of the top sample showed a decreasing trend along the deposition direction, while the microhardness of the middle sample was uniform and stable. The present work shows that the mechanical properties of HSLA steel parts deposited using WAAM technology have good strength and toughness. The microstructure gradient of the sample along the deposition direction did not lead to a significant difference in the tensile strength of the sample at different heights. On the contrary, the ductility of the longitudinal sample is slightly lower than that of the transverse sample, indicating some anisotropy in the deposited sample, which is related to the directional growth of grains along the direction of heat flow. From the current work, the thin wall of HSLA steel prepared with the WAAM process has good mechanical properties, which indicates that it is feasible to replace the traditional processing method with the WAAM process to rapidly manufacture an HSLA steel structure meeting the performance requirements. Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing and Their Applications)

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20 pages, 3579 KiB

Open AccessFeature PaperArticle

Suitability of Eroded Particles from Die-Sink Electro Discharge Machining for Additive Manufacturing—Review, Characterization and Processing

by Oliver Voigt and Urs Alexander Peuker

Metals 2022, 12(9), 1447; https://doi.org/10.3390/met12091447 - 30 Aug 2022

Cited by 5 | Viewed by 1775

Abstract

In this bipartite study, waste products of die-sink electro discharge machining (die-sink EDM) are investigated. EDM is based on an erosive character of discharges leading to material removal and molten material congeals in the dielectric. The aim is to show a theoretical suitability of these particles for a further usage as a secondary, recycled material in additive manufacturing (AM). Due to the energy- and cost-intensive process of gas atomization for AM powders, there is a need for alternative concepts for particle generation. The first part deals with an intensive review of references from the literature regarding particle size and circularity using image analysis. Secondly, real waste streams were investigated after washing and cleaning processes for oil removal via laser diffraction, dynamic image analysis, SEM with energy dispersive X-ray spectroscopy (EDX) as well as optical emission spectroscopy (ICP OES), categorized within the literature and compared to commercial AM powders. In general, it could be shown that, in principle, recycled particles fulfill main requirements for an AM usage regarding size and shape. Reference powders show median particle sizes of 30 µm to 34 µm and circularities of 0.90 to 0.93, whereas eroded particles exhibit an x₅₀ value of 27 µm and circularity of 0.90, too. However, chemical purity, mainly caused by carbon contamination (5.4 wt% in eroded powder compared to 0.4 wt% in reference powder), must be improved before printing via AM machines. Additionally, several separation techniques have to be applied to remove undesired elements (alumina). Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing and Their Applications)

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16 pages, 7053 KiB

Open AccessArticle

Investigation of the Interface between Laser-Melted CoCr and a Stainless Steel Substrate

by Cosmin Cosma, Christina Teusan, Peter Gogola, Mihaela Simion, Zuzana Gabalcova, Adrian Trif, Petru Berce and Nicolae Balc

Metals 2022, 12(6), 965; https://doi.org/10.3390/met12060965 - 04 Jun 2022

Cited by 3 | Viewed by 1833

Abstract

Recent advances in laser technologies offer significant flexibility in the additive manufacturing domain. Extensive work was focused on material processing using laser-directed energy deposition for repairing parts. This pilot study investigated the use of selective laser melting (SLM) for depositing a superior material such as CoCr on an existing stainless steel base. The interface between these dissimilar materials was analyzed. During fabrication, both metals were gradually mixed in the liquid state as the first CoCr powder layer was melded on the steel base without obvious defects. According to SEM and EDAX, the heat-affected zone has a limited depth (<20 µm). XRD patterns recorded across the CoCr–304 interface show a homogenous mixture of γ(Fe) and α(Co) solid solutions. The microporosity calculated by CT was under 0.5%. Microhardness was measured at and near the interface region, showing that the intermixing zone has high hardness (470–480 HV1), which may be related to the fine-grained microstructure. Mechanical testing reveals that the adhesion strength at rupture is 35% higher compared with the ultimate tensile strength of 304 steel. This adhesion strength can be attributed to the complete melting of CoCr particles after laser irradiation and to the reduced thickness of the HAZ and the IZ. Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing and Their Applications)

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15 pages, 6089 KiB

Open AccessFeature PaperArticle

Effects of Electrode Negative Pulsing Ratio in Direct Energy Deposition via Variable-Polarity Cold Metal Transfer Process on the Deposition Behavior and Microstructural Characteristics

by Tae Hyun Lee, Cheolhee Kim and Minjung Kang

Metals 2022, 12(3), 475; https://doi.org/10.3390/met12030475 - 11 Mar 2022

Cited by 3 | Viewed by 1857

Abstract

Interest in research on the application of variable-polarity cold metal transfer mode in wire-based direct energy deposition has been growing; particularly popular are investigations into the respective influences of polarity, amplitude of the arc current, and polarity variation sequence on the quality of the final product manufactured via additive manufacturing. The application of the electrode-negative phase is more capable of yielding relatively large droplets and increasing the weight of the deposited material. However, the proportions of the electrode positive phase are typically larger than those of the electrode-negative phase because it maintains arc stability and droplet transfer. This discrepancy has prevented the accurate evaluation of the effects of the polarity mode and polarity sequences on the deposition characteristics associated with variable-polarity cold metal transfer. In this study, variable-polarity cold metal transfer was performed using a tuned waveform, and the effects of the electrode-negative pulsing ratio and pulse repetition on the geometrical features and deposition rate were assessed. The weight tended to increase with decreasing welding speed and increasing electrode-negative pulsing ratio. The number of repetitions influenced molten pool behavior, and when sufficiently high, induced ripple formation via droplet accumulation below the electrode. In addition, the effects of the electrode-negative pulsing ratio and repetition on the microstructure formation were analyzed. It was revealed that the average grain size was related to the amount of supplied energy and polarity switching during grain formation. Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing and Their Applications)

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11 pages, 5128 KiB

Open AccessArticle

Microstructure and Mechanical Properties of Al-Cu-Mg Alloy Fabricated by Double-Wire CMT Arc Additive Manufacturing

by Siyue Fan, Xinpeng Guo, Yan Tang and Xuming Guo

Metals 2022, 12(3), 416; https://doi.org/10.3390/met12030416 - 26 Feb 2022

Cited by 3 | Viewed by 2833

Abstract

The high cracking sensitivity of Al-Cu-Mg alloy limits its application in wire + arc additive manufacturing (WAAM). In this paper, a double-wire cold metal transfer (CMT) arc additive manufacturing system was applied. ER2319 and ER5183 wires were selected as feedstocks and a new type of high-strength, crack-free Al-Cu-Mg alloy was manufactured. T6 (solution and artificial aging) heat treatment was conducted to further improve the mechanical properties. The microstructure, the second phase, distribution of main alloy elements and fracture morphology of Al-Cu-Mg alloys in both as-deposited and T6 heat-treated conditions were analyzed by optical micrographs (OM), X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. The micro-hardness and tensile properties of WAAM Al-Cu-Mg alloy in both as-deposited and T6 heat-treated conditions were tested. The results demonstrated that the microstructure of the as-deposited Al-Cu-Mg alloy was composed of short rod-shaped columnar grains, equiaxed grains in the inter-layer region, and coarsen equiaxed grains in the inner-layer region; most of the second phases were continuously distributed along the grain boundaries. After the T6 heat treatment, α(Al) grains became coarsened, most of second phases were dissolved, and the Cu and Mg elements were distributed homogeneously in the aluminum matrix. The micro-hardness and strength were significantly improved but the elongation was reduced. Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing and Their Applications)

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Review

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38 pages, 9602 KiB

Open AccessReview

Non-Destructive Testing Inspection for Metal Components Produced Using Wire and Arc Additive Manufacturing

by Douglas S. M. Serrati, Miguel A. Machado, J. P. Oliveira and Telmo G. Santos

Metals 2023, 13(4), 648; https://doi.org/10.3390/met13040648 - 24 Mar 2023

Cited by 4 | Viewed by 2458

Abstract

The wire and arc additive manufacturing (WAAM) process enables the creation and repair of complex structures based on the successive deposition of fed metal in the form of a wire that is fused with an electric arc and then solidifies. The high number of depositions required to create or repair parts increases the likelihood of defect formation. If these are reliably detected during manufacturing, timely correction is possible. However, high temperatures and surface irregularity make inspection difficult. Furthermore, depending on the size, morphology, and location of the defect, the part can be rejected. Recent studies have shown that non-destructive testing (NDT) based on different physical phenomena for the timely, reliable, and customized detection of defects can significantly reduce the rejection rate and allow in-line repair, which consequently reduces waste and rework. This paper presents the latest developments in NDT for WAAM and its limitations and potential. Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing and Their Applications)

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15 pages, 3882 KiB

Open AccessReview

Adiabatic Shear Banding in Nickel and Nickel-Based Superalloys: A Review

by Russell A. Rowe, Paul G. Allison, Anthony N. Palazotto and Keivan Davami

Metals 2022, 12(11), 1879; https://doi.org/10.3390/met12111879 - 03 Nov 2022

Cited by 4 | Viewed by 1773

Abstract

This review paper discusses the formation and propagation of adiabatic shear bands in nickel-based superalloys. The formation of adiabatic shear bands (ASBs) is a unique dynamic phenomenon that typically precedes catastrophic, unpredicted failure in many metals under impact or ballistic loading. ASBs are thin regions that undergo substantial plastic shear strain and material softening due to the thermo-mechanical instability induced by the competitive work hardening and thermal softening processes. Dynamic recrystallization of the material’s microstructure in the shear region can occur and encourages shear localization and the formation of ASBs. Phase transformations are also often seen in ASBs of ferrous metals due to the elevated temperatures reached in the narrow shear region. ASBs ultimately lead to the local degradation of material properties within a narrow band wherein micro-voids can more easily nucleate and grow compared to the surrounding material. As the micro-voids grow, they will eventually coalesce leading to crack formation and eventual fracture. For elevated temperature applications, such as in the aerospace industry, nickel-based superalloys are used due to their high strength. Understanding the formation conditions of ASBs in nickel-based superalloys is also beneficial in extending the life of machining tools. The main goal of the review is to identify the formation mechanisms of ASBs, the microstructural evolutions associated with ASBs in nickel-based alloys, and their consequent effect on material properties. Under a shear strain rate of 80,000 s⁻¹, the critical shear strain at which an ASB forms is between 2.2 and 3.2 for aged Inconel 718 and 4.5 for solution-treated Inconel 718. Shear band widths are reported to range between 2 and 65 microns for nickel-based superalloys. The shear bands widths are narrower in samples that are aged compared to samples in the annealed or solution treated condition. Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing and Their Applications)

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