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18 pages, 7347 KiB

Open AccessArticle

Selective Laser Melting of Pre-Alloyed NiTi Powder: Single-Track Study and FE Modeling with Heat Source Calibration

by Stanislav V. Chernyshikhin, Denis G. Firsov and Igor V. Shishkovsky

Materials 2021, 14(23), 7486; https://doi.org/10.3390/ma14237486 - 6 Dec 2021

Cited by 22 | Viewed by 3313

Abstract

Unique functional properties such as the low stiffness, superelasticity, and biocompatibility of nickel–titanium shape-memory alloys provide many applications for such materials. Selective laser melting of NiTi enables low-cost customization of devices and the manufacturing of highly complex geometries without subsequent machining. However, the [...] Read more.

Unique functional properties such as the low stiffness, superelasticity, and biocompatibility of nickel–titanium shape-memory alloys provide many applications for such materials. Selective laser melting of NiTi enables low-cost customization of devices and the manufacturing of highly complex geometries without subsequent machining. However, the technology requires optimization of process parameters in order to guarantee high mass density and to avoid deterioration of functional properties. In this work, the melt pool geometry, surface morphology, formation mode, and thermal behavior were studied. Multiple combinations of laser power and scanning speed were used for single-track preparation from pre-alloyed NiTi powder on a nitinol substrate. The experimental results show the influence of laser power and scanning speed on the depth, width, and depth-to-width aspect ratio. Additionally, a transient 3D FE model was employed to predict thermal behavior in the melt pool for different regimes. In this paper, the coefficients for a volumetric double-ellipsoid heat source were calibrated with bound optimization by a quadratic approximation algorithm, the design of experiments technique, and experimentally obtained data. The results of the simulation reveal the necessary conditions of transition from conduction to keyhole mode welding. Finally, by combining experimental and FE modeling results, the optimal SLM process parameters were evaluated as P = 77 W, V = 400 mm/s, h = 70 μm, and t = 50 μm, without printing of 3D samples. Full article

(This article belongs to the Special Issue Recent Advances in Additive Manufacturing Technologies)

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17 pages, 5660 KiB

Open AccessArticle

Electron Beam Melting of Niobium Alloys from Blended Powders

by Jameson P. Hankwitz, Christopher Ledford, Christopher Rock, Scott O’Dell and Timothy J. Horn

Materials 2021, 14(19), 5536; https://doi.org/10.3390/ma14195536 - 24 Sep 2021

Cited by 12 | Viewed by 3356

Abstract

Niobium-based tungsten alloys are desirable for high-temperature structural applications yet are restricted in practice by limited room-temperature ductility and fabricability. Powder bed fusion additive manufacturing is one technology that could be leveraged to process alloys with limited ductility, without the need for pre-alloying. [...] Read more.

Niobium-based tungsten alloys are desirable for high-temperature structural applications yet are restricted in practice by limited room-temperature ductility and fabricability. Powder bed fusion additive manufacturing is one technology that could be leveraged to process alloys with limited ductility, without the need for pre-alloying. A custom electron beam powder bed fusion machine was used to demonstrate the processability of blended Nb-1Zr, Nb-10W-1Zr-0.1C, and Nb-20W-1Zr-0.1C powders, with resulting solid optical densities of 99+%. Ultimately, post-processing heat treatments were required to increase tungsten diffusion in niobium, as well as to attain satisfactory mechanical properties. Full article

(This article belongs to the Special Issue Recent Advances in Additive Manufacturing Technologies)

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12 pages, 2896 KiB

Open AccessArticle

Adhesion Studies during Generative Hybridization of Textile-Reinforced Thermoplastic Composites via Additive Manufacturing

by Johanna Maier, Christian Vogel, Tobias Lebelt, Vinzenz Geske, Thomas Behnisch, Niels Modler and Maik Gude

Materials 2021, 14(14), 3888; https://doi.org/10.3390/ma14143888 - 12 Jul 2021

Cited by 7 | Viewed by 2417

Abstract

Generative hybridization enables the efficient production of lightweight structures by combining classic manufacturing processes with additive manufacturing technologies. This type of functionalization process allows components with high geometric complexity and high mechanical properties to be produced efficiently in small series without the need [...] Read more.

Generative hybridization enables the efficient production of lightweight structures by combining classic manufacturing processes with additive manufacturing technologies. This type of functionalization process allows components with high geometric complexity and high mechanical properties to be produced efficiently in small series without the need for additional molds. In this study, hybrid specimens were generated by additively depositing PA6 (polyamide 6) via fused layer modeling (FLM) onto continuous woven fiber GF/PA6 (glass fiber/polyamide 6) flat preforms. Specifically, the effects of surface pre-treatment and process-induced surface interactions were investigated using optical microscopy for contact angle measurements as well as laser profilometry and thermal analytics. The bonding characteristic at the interface was evaluated via quasi-static tensile pull-off tests. Results indicate that both the bond strength and corresponding failure type vary with pre-treatment settings and process parameters during generative hybridization. It is shown that both the base substrate temperature and the FLM nozzle distance have a significant influence on the adhesive tensile strength. In particular, it can be seen that surface activation by plasma can significantly improve the specific adhesion in generative hybridization. Full article

(This article belongs to the Special Issue Recent Advances in Additive Manufacturing Technologies)

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18 pages, 8782 KiB

Open AccessArticle

Effect of Fillets on Mechanical Properties of Lattice Structures Fabricated Using Multi-Jet Fusion Technology

by Aamer Nazir, Ahmad-Bin Arshad, Chi-Pin Hsu and Jeng-Ywan Jeng

Materials 2021, 14(9), 2194; https://doi.org/10.3390/ma14092194 - 24 Apr 2021

Cited by 19 | Viewed by 3780

Abstract

Cellular structures with tailored topologies can be fabricated using additive manufacturing (AM) processes to obtain the desired global and local mechanical properties, such as stiffness and energy absorption. Lattice structures usually fail from the sharp edges owing to the high stress concentration and [...] Read more.

Cellular structures with tailored topologies can be fabricated using additive manufacturing (AM) processes to obtain the desired global and local mechanical properties, such as stiffness and energy absorption. Lattice structures usually fail from the sharp edges owing to the high stress concentration and residual stress. Therefore, it is crucial to analyze the failure mechanism of lattice structures to improve the mechanical properties. In this study, several lattice topologies with fillets were designed, and the effects of the fillets on the stiffness, energy absorption, energy return, and energy loss of an open-cell lattice structure were investigated at a constant relative density. A recently developed high-speed AM multi-jet fusion technology was employed to fabricate lattice samples with two different unit cell sizes. Nonlinear simulations using ANSYS software were performed to investigate the mechanical properties of the samples. Experimental compression and loading–unloading tests were conducted to validate the simulation results. The results showed that the stiffness and energy absorption of the lattice structures can be improved significantly by the addition of fillets and/or vertical struts, which also influence other properties such as the failure mechanism and compliance. By adding the fillets, the failure location can be shifted from the sharp edges or joints to other regions of the lattice structure, as observed by comparing the failure mechanisms of type B and C structures with that of the type A structure (without fillets). The results of this study suggest that AM software designers should consider filleted corners when developing algorithms for generating various types of lattice structures automatically. Additionally, it was found that the accumulation of unsintered powder in the sharp corners of lattice geometries can also be minimized by the addition of fillets to convert the sharp corners to curved edges. Full article

(This article belongs to the Special Issue Recent Advances in Additive Manufacturing Technologies)

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19 pages, 8657 KiB

Open AccessArticle

CMT Additive Manufacturing Parameters Defining Aluminium Alloy Object Geometry and Mechanical Properties

by Gyula Ferenc Vasvári, Dávid Csonka, Tamás Zsebe, Ádám Schiffer, Ivan Samardžić, Roland Told, Attila Péntek and Péter Maróti

Materials 2021, 14(6), 1545; https://doi.org/10.3390/ma14061545 - 22 Mar 2021

Cited by 6 | Viewed by 3472

Abstract

Additive manufacturing technologies based on metal melting use materials mainly in powder or wire form. This study focuses on developing a metal 3D printing process based on cold metal transfer (CMT) welding technology, in order to achieve enhanced productivity. Aluminium alloy test specimens [...] Read more.

Additive manufacturing technologies based on metal melting use materials mainly in powder or wire form. This study focuses on developing a metal 3D printing process based on cold metal transfer (CMT) welding technology, in order to achieve enhanced productivity. Aluminium alloy test specimens have been fabricated using a special 3D printing technology. The probes were investigated to find correlation between the welding parameters and geometric quality. Geometric measurements and tensile strength experiments were performed to determine the appropriate welding parameters for reliable printing. The tensile strength of the product does not differ significantly from the raw material. Above 60 mm height, the wall thickness is relatively constant due to the thermal balance of the welding environment. The results suggest that there might be a connection between the welding parameters and the printing accuracy. It is demonstrated that the deviation of ideal geometry will be the smallest at the maximum reliable welding torch movement speed, while printing larger specimens. As a conclusion, it can be stated that CMT-based additive manufacturing can be a reliable, cost-effective and rapid 3D printing technology with enhanced productivity, but without significant decrease in mechanical stability. Full article

(This article belongs to the Special Issue Recent Advances in Additive Manufacturing Technologies)

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17 pages, 6895 KiB

Open AccessArticle

Properties of Additively Manufactured Electric Steel Powder Cores with Increased Si Content

by Giulia Stornelli, Antonio Faba, Andrea Di Schino, Paolo Folgarait, Maria Rita Ridolfi, Ermanno Cardelli and Roberto Montanari

Materials 2021, 14(6), 1489; https://doi.org/10.3390/ma14061489 - 18 Mar 2021

Cited by 65 | Viewed by 4665

Abstract

In this paper, the best laser powder bed fusion (L-PBF) printing conditions for FeSi steels with two different Si content (3.0% and 6.5%) are defined. Results show very strict processing window parameters, following a lack of fusion porosity at low specific energy values [...] Read more.

In this paper, the best laser powder bed fusion (L-PBF) printing conditions for FeSi steels with two different Si content (3.0% and 6.5%) are defined. Results show very strict processing window parameters, following a lack of fusion porosity at low specific energy values and keyhole porosity in correspondence with high specific energy values. The obtained microstructure consists of grains with epitaxial growth starting from the grains already solidified in the underling layer. This allows the continuous growth of the columnar grains, directed parallel to the built direction of the component. The magnetic behaviour of FeSi6.5 samples, although the performances found do not still fully reach those of the best commercial electrical steels (used to manufacture magnetic cores of electrical machines and other similar magnetic components), appears to be quite promising. An improvement of the printing process to obtain thin sheets with increased Si content, less than 0.5 mm thick, with accurate geometry and robust structures, can result to an interesting technology for specific application where complex geometries and sophisticated shapes are required, avoiding mechanical machining processes for electrical steel with high silicon content. Full article

(This article belongs to the Special Issue Recent Advances in Additive Manufacturing Technologies)

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Review

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17 pages, 1588 KiB

Open AccessEditor’s ChoiceReview

Selective Laser Melting of Al-Based Matrix Composites with Al₂O₃ Reinforcement: Features and Advantages

by Ivan A. Pelevin, Anton Yu. Nalivaiko, Dmitriy Yu. Ozherelkov, Alexander S. Shinkaryov, Stanislav V. Chernyshikhin, Alexey N. Arnautov, Sergey V. Zmanovsky and Alexander A. Gromov

Materials 2021, 14(10), 2648; https://doi.org/10.3390/ma14102648 - 18 May 2021

Cited by 22 | Viewed by 3752

Abstract

Aluminum matrix composites (AMC) are of great interest and importance as high-performance materials with enhanced mechanical properties. Al₂O₃ is a commonly used reinforcement in AMCs fabricated by means of various technological methods, including casting and sintering. Selective laser melting (SLM) [...] Read more.

Aluminum matrix composites (AMC) are of great interest and importance as high-performance materials with enhanced mechanical properties. Al₂O₃ is a commonly used reinforcement in AMCs fabricated by means of various technological methods, including casting and sintering. Selective laser melting (SLM) is a suitable modern method of the fabrication of net-shape fully dense parts from AMC with alumina. The main results, achievements, and difficulties of SLM applied to AMCs with alumina are discussed in this review and compared with conventional methods. It was shown that the initial powder preparation, namely the particle size distribution, sphericity, and thorough mixing, affected the final microstructure and properties of SLMed materials drastically. The distribution of reinforcing particles tends to consolidate the near-melting pool-edges process because of pushing by the liquid–solid interface during the solidification process that is a common problem of various fabrication methods. The achievement of an homogeneous distribution was shown to be possible through both the thorough mixing of the initial powders and the precise optimization of SLM parameters. The strength of the AMCs fabricated by the SLM method was relatively low compared with materials produced by conventional methods, while for superior relative densities of more than 99%, hardness and tribological properties were obtained, making SLM a promising method for the Al-based matrix composites with Al₂O₃. Full article

(This article belongs to the Special Issue Recent Advances in Additive Manufacturing Technologies)

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37 pages, 8928 KiB

Open AccessReview

Recent Trends in Three-Dimensional Bioinks Based on Alginate for Biomedical Applications

by Farnoosh Pahlevanzadeh, Hamidreza Mokhtari, Hamid Reza Bakhsheshi-Rad, Rahmatollah Emadi, Mahshid Kharaziha, Ali Valiani, S. Ali Poursamar, Ahmad Fauzi Ismail, Seeram RamaKrishna and Filippo Berto

Materials 2020, 13(18), 3980; https://doi.org/10.3390/ma13183980 - 8 Sep 2020

Cited by 62 | Viewed by 6352

Abstract

Three-dimensional (3D) bioprinting is an appealing and revolutionary manufacturing approach for the accurate placement of biologics, such as living cells and extracellular matrix (ECM) components, in the form of a 3D hierarchical structure to fabricate synthetic multicellular tissues. Many synthetic and natural polymers [...] Read more.

Three-dimensional (3D) bioprinting is an appealing and revolutionary manufacturing approach for the accurate placement of biologics, such as living cells and extracellular matrix (ECM) components, in the form of a 3D hierarchical structure to fabricate synthetic multicellular tissues. Many synthetic and natural polymers are applied as cell printing bioinks. One of them, alginate (Alg), is an inexpensive biomaterial that is among the most examined hydrogel materials intended for vascular, cartilage, and bone tissue printing. It has also been studied pertaining to the liver, kidney, and skin, due to its excellent cell response and flexible gelation preparation through divalent ions including calcium. Nevertheless, Alg hydrogels possess certain negative aspects, including weak mechanical characteristics, poor printability, poor structural stability, and poor cell attachment, which may restrict its usage along with the 3D printing approach to prepare artificial tissue. In this review paper, we prepare the accessible materials to be able to encourage and boost new Alg-based bioink formulations with superior characteristics for upcoming purposes in drug delivery systems. Moreover, the major outcomes are discussed, and the outstanding concerns regarding this area and the scope for upcoming examination are outlined. Full article

(This article belongs to the Special Issue Recent Advances in Additive Manufacturing Technologies)

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