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Crystals
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Additive Manufacturing: Materials, Processing, Characterization and Applications
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Additive Manufacturing: Materials, Processing, Characterization and Applications

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 53928

Special Issue Editors

Dr. Pan Wang

E-Mail Website
Guest Editor
Singapore Institute of Manufacturing Technology, 73 Nanyang Drive, Singapore 637662, Singapore
Interests: metal additive manufacturing; high-performance metallic powder; design and optimization of new structures; high-throughput microstructure analysis; phase transformation and deformation behavior
Prof. Dr. Takayoshi Nakano

E-Mail Website
Co-Guest Editor
Distinguished Professor in Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
Interests: additive manufacturing; matal 3d printing; biomaterials; bone substitute; crystallographic texture; deformation mechanism; regenerative medicine; biomimetic materials; implantology
Special Issues, Collections and Topics in MDPI journals
Dr. Jiaming Bai

E-Mail Website
Co-Guest Editor
Assistant Professor in Department of Mechanical and Energy Engineering, Southern University of Science and Technology, Shenzhen 518055, China
Interests: additive manufacturing, nanocomposites, ceramics, functional structures

Special Issue Information

Dear Colleagues,

Additive manufacturing (AM), as opposed to subtractive manufacturing methodologies, is a process of joining materials to make objects from three dimensional (3D) model data, usually layer upon layer, which is also called 3D printing, freeform fabrication, etc. With the advantage of considerable reduction of the production cost of parts or components with complex or intricate geometrical features creating a lot of interest in this technology, the number of applications from different industrial sectors, such as aerospace, biomedical, automobile, etc. has also been growing. Many efforts have been invested in evolving it from a prototyping process to a real industrial manufacturing process.

AM is revolutionizing the science and engineering fields. AM, with its inherent layer-by-layer feature, would create extraordinary properties of metals, polymer, ceramic, etc. compared to conventional manufacturing technologies. Hence, revealing the distinguished AM material properties and exploring the application of AM materials are of most interest to researchers. A large number of projects have been initiated or have tproceeded to study the properties, microstructural features, and potential application of AM materials.

This Special Issue intends to address the latest progress in the AM field. Original contributions related to current AM materials and processing for applications are welcome in the form of short communications, full-length articles, and reviews. Potential topics include but are not limited to:

  • AM material characterization;
  • New materials for AM;
  • AM process development;
  • Material and microstrucural properties evaluation during the AM process;
  • Post-processing of AM materials;
  • Hybrid AM processes and materials;
  • Modeling and simulation of AM processing;
  • AM applications;
  • Standardization of AM material performance.

Dr. Pan Wang
Guest Editors
Dr. Takayoshi Nakano
Dr. Jiaming Bai
Co-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 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. Crystals 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
  • 3D printing
  • materials
  • applications
  • microstructure and crystallographic texture
  • mechanical and functional properties

Published Papers (20 papers)

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Editorial

Jump to: Research

3 pages, 176 KiB  
Editorial
Additive Manufacturing: Materials, Processing, Characterization and Applications
by Pan Wang, Takayoshi Nakano and Jiaming Bai
Crystals 2022, 12(5), 747; https://doi.org/10.3390/cryst12050747 - 23 May 2022
Cited by 3 | Viewed by 1554
Abstract
The current Special Issue collected 19 original articles reporting the results of theoretical and experimental studies that provide new insights into this fascinating new generation manufacturing process, additive manufacturing (AM) [...] Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)

Research

Jump to: Editorial

16 pages, 10258 KiB  
Article
Thermoplastic Extrusion Additive Manufacturing of High-Performance Carbon Fiber PEEK Lattices
by Carolyn Carradero Santiago, Bharat Yelamanchi, Jose Angel Diosdado De la Peña, Jeffrey Lamb, Krzysztof Roguski, Filip Turzyński, Ron Faruqui, Kyosung Choo, Anton Du Plessis, Francesco Sillani, Eric MacDonald and Pedro Cortes
Crystals 2021, 11(12), 1453; https://doi.org/10.3390/cryst11121453 - 25 Nov 2021
Cited by 10 | Viewed by 2909
Abstract
Polyetheretherketone (PEEK) has been the focus of substantial additive manufacturing research for two principal reasons: (a) the mechanical performance approaches that of aluminum at relatively high temperatures for thermoplastics and (b) the potential for qualification in both the aerospace and biomedical industries. Although [...] Read more.
Polyetheretherketone (PEEK) has been the focus of substantial additive manufacturing research for two principal reasons: (a) the mechanical performance approaches that of aluminum at relatively high temperatures for thermoplastics and (b) the potential for qualification in both the aerospace and biomedical industries. Although PEEK provides outstanding strength and thermal stability, printing can be difficult due to the high melting point. Recently, high-temperature soluble support has enabled the printing of lattices and stochastic foams with overhanging features in these high-performance carbon fiber thermoplastics, in which density can be optimized to strike a balance between weight and strength to enhance performance in applications such as custom implants or aerospace structures. Although polymer powder bed fusion has long been capable of the combination of these geometries and materials, material extrusion with high-temperature sacrificial support is dramatically less expensive. This research provides a comprehensive mechanical analysis and CT-scan-based dimensional study of carbon fiber PEEK lattice structures enabled with high-temperature support and including model validation. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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13 pages, 4065 KiB  
Article
Mathematical Model for Metal Transfer Study in Additive Manufacturing with Electron Beam Oscillation
by Alexey Shcherbakov, Daria Gaponova, Andrey Sliva, Alexey Goncharov, Alexander Gudenko, Regina Rodyakina and Viktor Dragunov
Crystals 2021, 11(12), 1441; https://doi.org/10.3390/cryst11121441 - 23 Nov 2021
Cited by 2 | Viewed by 1435
Abstract
A computer model has been developed to investigate the processes of heat and mass transfer under the influence of concentrated energy sources on materials with specified thermophysical characteristics, including temperature-dependent ones. The model is based on the application of the volume of fluid [...] Read more.
A computer model has been developed to investigate the processes of heat and mass transfer under the influence of concentrated energy sources on materials with specified thermophysical characteristics, including temperature-dependent ones. The model is based on the application of the volume of fluid (VOF) method and finite-difference approximation of the Navier–Stokes differential equations formulated for a viscous incompressible medium. The “predictor-corrector” method has been used for the coordinated determination of the pressure field which corresponds to the continuity condition and the velocity field. The modeling technique of the free liquid surface and boundary conditions has been described. The method of calculating surface tension forces and vapor recoil pressure has been presented. The algorithm structure is given, the individual modules of which are currently implemented in the Microsoft Visual Studio environment. The model can be applied for studying the metal transfer during the deposition processes, including the processes with electron beam spatial oscillation. The model was validated by comparing the results of computational experiments and images obtained by a high-speed camera. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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11 pages, 4484 KiB  
Article
Microstructure and Corrosion Resistance in Bimetal Materials of Q345 and 308 Steel Wire-Arc Additive Manufacturing
by Qingxian Hu, Xiaoli Wang, Xinwang Shen and Zemin Tan
Crystals 2021, 11(11), 1401; https://doi.org/10.3390/cryst11111401 - 17 Nov 2021
Cited by 11 | Viewed by 1667
Abstract
The microstructure and corrosion resistance of samples fabricated by Q345 and 308 bimetallic feedings using two kinds of processes of wire-arc additive manufacturing (WAAM) was observed and compared with that of sample manufactured by a single feeding wire of Q345 or 308. The [...] Read more.
The microstructure and corrosion resistance of samples fabricated by Q345 and 308 bimetallic feedings using two kinds of processes of wire-arc additive manufacturing (WAAM) was observed and compared with that of sample manufactured by a single feeding wire of Q345 or 308. The results show that the interface between the Q345 and 308 had no defects and metallurgical bonding. The hardness of bimetal Q345/308 additive manufacturing samples was higher than that of Q345 or 308 single wire additive manufacturing. The sample made of Q345 single wire had serious electrochemical corrosion, while the sample made of 308 single wire had pitting corrosion. The pitting corrosion of the sample reinforced by bimetal Q345/308 feeding wires was improved. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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12 pages, 7065 KiB  
Article
Molecular Dynamics Simulations of the Tensile Mechanical Responses of Selective Laser-Melted Aluminum with Different Crystalline Forms
by Qiang Zeng, Lijuan Wang and Wugui Jiang
Crystals 2021, 11(11), 1388; https://doi.org/10.3390/cryst11111388 - 14 Nov 2021
Cited by 10 | Viewed by 2413
Abstract
The mechanical deformation of cellular structures in the selective laser melting (SLM) of aluminum was investigated by performing a series of molecular dynamics (MD) simulations of uniaxial tension tests. The effects of crystalline form, temperature, and grain orientation of columnar grains on the [...] Read more.
The mechanical deformation of cellular structures in the selective laser melting (SLM) of aluminum was investigated by performing a series of molecular dynamics (MD) simulations of uniaxial tension tests. The effects of crystalline form, temperature, and grain orientation of columnar grains on the mechanical properties of SLM aluminum were examined. The MD results showed that the tensile strength of SLM aluminum with columnar grains at different temperatures was lower than that of single-crystal aluminum, but greater than that of aluminum with equiaxed grains. The tensile strength and Young’s modulus both decreased approximately linearly upon increasing the temperature. The deformation mechanisms of equiaxed and columnar grains included dislocation slip, grain boundary migration, and torsion, while the deformation mechanisms of single crystals included stacking fault formation and amorphization. Finally, the influence of the columnar grain orientation on the mechanical properties was studied, and it was found that the Young’s modulus was almost independent of the grain orientation. The tensile strength was greatly affected by the columnar grain orientation. Reasonable control of the grain orientation can improve the tensile strength of SLM aluminum. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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15 pages, 3462 KiB  
Article
Analytical Study of Powder Stream Geometry in Laser-Based Direct Energy Deposition Process with a Continuous Coaxial Nozzle
by Qipeng Liu, Kun Yang, Yuehua Gao, Fencheng Liu, Chunping Huang and Liming Ke
Crystals 2021, 11(11), 1306; https://doi.org/10.3390/cryst11111306 - 27 Oct 2021
Cited by 7 | Viewed by 1415
Abstract
In the process of laser-based direct energy deposition, the particle concentration distribution and geometric characteristics of powder flow play an important role in laser–powder interaction and powder utilization, and they affect the forming quality and accuracy. In the current study, based on the [...] Read more.
In the process of laser-based direct energy deposition, the particle concentration distribution and geometric characteristics of powder flow play an important role in laser–powder interaction and powder utilization, and they affect the forming quality and accuracy. In the current study, based on the geometry information of a powder nozzle and the divergence angles of a powder jet at the nozzle outlet, the geometric profile of a powder stream is analyzed. A set of formulas for calculating the geometric characteristics of the powder stream is derived based on an analytic geometry method. The influence of each parameter on the geometric characteristics of the powder stream is further studied using single-factor and sensitivity analyses. Validation is performed by comparing the results from the presented analytical expressions with those from experiments and/or simulations in published papers. The analytical formulas provided in this paper are simple and practical, providing a theoretical foundation for the control of powder flow and related processes in the forming process. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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23 pages, 9280 KiB  
Article
Analysis of Microstructure and Mechanical Properties in As-Built/As-Cast and Heat-Treated Conditions for IN718 Alloy Obtained by Selective Laser Melting and Investment Casting Processes
by Juan Carlos Pereira, Jon Aranzabe, Mari Carmen Taboada, Noelia Ruiz and Pedro Pablo Rodriguez
Crystals 2021, 11(10), 1196; https://doi.org/10.3390/cryst11101196 - 02 Oct 2021
Cited by 13 | Viewed by 2866
Abstract
In this work, new customized heat treatments for selective laser melted (SLM) parts in IN718 alloy were analyzed. This was done through the evaluation of the mechanical properties and advanced characterization of the phases and microstructure obtained in as-built condition and after the [...] Read more.
In this work, new customized heat treatments for selective laser melted (SLM) parts in IN718 alloy were analyzed. This was done through the evaluation of the mechanical properties and advanced characterization of the phases and microstructure obtained in as-built condition and after the application of standard and tailored heat treatments. The microstructure and mechanical properties were compared and discussed with results reported in the literature. Finally, strengthening mechanisms of IN718 alloy processed by SLM and its differences with mechanisms that occur in investment casting were analyzed. Both processes generate quite different microstructures, investment casting is composed mainly by a dendritic structure, and SLM is characterized by columnar and cellular structures with very thin cells. Due to the fine and homogeneous microstructure obtained from SLM processing and its specific strengthening mechanisms, it is not necessary to apply homogenization and solution stages as in standard heat treatment used for this type of alloy in casting or wrought. The pre-heating and process parameters selected, in combination with a direct stepped aging (at 720 °C/620 °C), provide the material with its best mechanical properties, which are superior to those obtained by standard heat treatment (AMS 5383F) applied to investment casting of IN718 alloy. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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11 pages, 6289 KiB  
Article
Fabrication of Ti-Alloy Powder/Solid Composite with Uniaxial Anisotropy by Introducing Unidirectional Honeycomb Structure via Electron Beam Powder Bed Fusion
by Naoko Ikeo, Tatsuya Matsumi, Takuya Ishimoto, Ryosuke Ozasa, Aira Matsugaki, Tadaaki Matsuzaka, Ozkan Gokcekaya, Yorinobu Takigawa and Takayoshi Nakano
Crystals 2021, 11(9), 1074; https://doi.org/10.3390/cryst11091074 - 05 Sep 2021
Cited by 11 | Viewed by 2482
Abstract
In this study, a Ti–6Al–4V alloy composite with uniaxial anisotropy and a hierarchical structure is fabricated using electron beam powder bed fusion, one of the additive manufacturing techniques that enable arbitrary fabrication, and subsequent heat treatment. The uniaxial anisotropic deformation behavior and mechanical [...] Read more.
In this study, a Ti–6Al–4V alloy composite with uniaxial anisotropy and a hierarchical structure is fabricated using electron beam powder bed fusion, one of the additive manufacturing techniques that enable arbitrary fabrication, and subsequent heat treatment. The uniaxial anisotropic deformation behavior and mechanical properties such as Young’s modulus are obtained by introducing a unidirectional honeycomb structure. The main feature of this structure is that the unmelted powder retained in the pores of the honeycomb structure. After appropriate heat treatment at 1020 °C, necks are formed between the powder particles and between the powder particles and the honeycomb wall, enabling a stress transmission through the necks when the composite is loaded. This means that the powder part has been mechanically functionalized by the neck formation. As a result, a plateau region appears in the stress–strain curve. The stress transfer among the powder particles leads to the cooperative deformation of the composites, contributing to the excellent energy absorption capacity. Therefore, it is expected that the composite can be applied to bone plates on uniaxially oriented microstructures such as long bones owing to its excellent energy absorption capacity and low elasticity to unidirectionally suppress stress shielding. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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12 pages, 4047 KiB  
Article
Control of Crystallographic Texture and Mechanical Properties of Hastelloy-X via Laser Powder Bed Fusion
by Shinya Hibino, Tsubasa Todo, Takuya Ishimoto, Ozkan Gokcekaya, Yuichiro Koizumi, Kenichiroh Igashira and Takayoshi Nakano
Crystals 2021, 11(9), 1064; https://doi.org/10.3390/cryst11091064 - 03 Sep 2021
Cited by 22 | Viewed by 3751
Abstract
The influence of various laser powder bed fusion (LPBF) process parameters on the crystallographic textures and mechanical properties of a typical Ni-based solid-solution strengthened alloy, Hastelloy-X, was examined. Samples were classified into four groups based on the type of crystallographic texture: single crystalline-like [...] Read more.
The influence of various laser powder bed fusion (LPBF) process parameters on the crystallographic textures and mechanical properties of a typical Ni-based solid-solution strengthened alloy, Hastelloy-X, was examined. Samples were classified into four groups based on the type of crystallographic texture: single crystalline-like microstructure with <100>//build direction (BD) (<100>-SCM), single crystalline-like microstructure with <110>//BD (<110>-SCM), crystallographic lamellar microstructure (CLM), or polycrystalline microstructure (PCM). These four crystallographic textures were realized in Hastelloy-X for the first time here to the best of our knowledge. The mechanical properties of the samples varied depending on their texture. The tensile properties were affected not only by the Schmid factor but also by the grain size and the presence of lamellar boundaries (grain boundaries). The lamellar boundaries at the interface between the <110>//BD oriented main layers and the <100>//BD-oriented sub-layers of CLM contributed to the resistance to slip transmission and the increased proof stress. It was possible to control a wide range of crystallographic microstructures via the LPBF process parameters, which determines the melt pool morphology and solidification behavior. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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10 pages, 20537 KiB  
Article
3D Puzzle in Cube Pattern for Anisotropic/Isotropic Mechanical Control of Structure Fabricated by Metal Additive Manufacturing
by Naoko Ikeo, Hidetsugu Fukuda, Aira Matsugaki, Toru Inoue, Ai Serizawa, Tadaaki Matsuzaka, Takuya Ishimoto, Ryosuke Ozasa, Ozkan Gokcekaya and Takayoshi Nakano
Crystals 2021, 11(8), 959; https://doi.org/10.3390/cryst11080959 - 16 Aug 2021
Cited by 16 | Viewed by 2684
Abstract
Metal additive manufacturing is a powerful tool for providing the desired functional performance through a three-dimensional (3D) structural design. Among the material functions, anisotropic mechanical properties are indispensable for enabling the capabilities of structural materials for living tissues. For biomedical materials to replace [...] Read more.
Metal additive manufacturing is a powerful tool for providing the desired functional performance through a three-dimensional (3D) structural design. Among the material functions, anisotropic mechanical properties are indispensable for enabling the capabilities of structural materials for living tissues. For biomedical materials to replace bone function, it is necessary to provide an anisotropic mechanical property that mimics that of bones. For desired control of the mechanical performance of the materials, we propose a novel 3D puzzle structure with cube-shaped parts comprising 27 (3 × 3 × 3) unit compartments. We designed and fabricated a Co–Cr–Mo composite structure through spatial control of the positional arrangement of powder/solid parts using the laser powder bed fusion (L-PBF) method. The mechanical function of the fabricated structure can be predicted using the rule of mixtures based on the arrangement pattern of each part. The solid parts in the cubic structure were obtained by melting and solidifying the metal powder with a laser, while the powder parts were obtained through the remaining nonmelted powders inside the structure. This is the first report to achieve an innovative material design that can provide an anisotropic Young’s modulus by arranging the powder and solid parts using additive manufacturing technology. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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13 pages, 10218 KiB  
Article
Inverse Columnar-Equiaxed Transition (CET) in 304 and 316L Stainless Steels Melt by Electron Beam for Additive Manufacturing (AM)
by Yuichiro Miyata, Masayuki Okugawa, Yuichiro Koizumi and Takayoshi Nakano
Crystals 2021, 11(8), 856; https://doi.org/10.3390/cryst11080856 - 23 Jul 2021
Cited by 21 | Viewed by 3253
Abstract
According to Hunt’s columnar-to-equiaxed transition (CET) criterion, which is generally accepted, a high-temperature gradient (G) in the solidification front is preferable to a low G for forming columnar grains. Here, we report the opposite tendency found in the solidification microstructure of [...] Read more.
According to Hunt’s columnar-to-equiaxed transition (CET) criterion, which is generally accepted, a high-temperature gradient (G) in the solidification front is preferable to a low G for forming columnar grains. Here, we report the opposite tendency found in the solidification microstructure of stainless steels partially melted by scanning electron beam for powder bed fusion (PBF)-type additive manufacturing. Equiaxed grains were observed more frequently in the region of high G rather than in the region of low G, contrary to the trend of the CET criterion. Computational thermal-fluid dynamics (CtFD) simulation has revealed that the fluid velocity is significantly higher in the case of smaller melt regions. The G on the solidification front of a small melt pool tends to be high, but at the same, the temperature gradient along the melt pool surface also tends to be high. The high melt surface temperature gradient can enhance Marangoni flow, which can apparently reverse the trend of equiaxed grain formation. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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13 pages, 6934 KiB  
Article
Improving the Tensile Properties of Additively Manufactured β-Containing TiAl Alloys via Microstructure Control Focusing on Cellular Precipitation Reaction
by Ken Cho, Hirotaka Odo, Keisuke Okamoto, Hiroyuki Y. Yasuda, Hirotoyo Nakashima, Masao Takeyama and Takayoshi Nakano
Crystals 2021, 11(7), 809; https://doi.org/10.3390/cryst11070809 - 12 Jul 2021
Cited by 8 | Viewed by 2210
Abstract
The effect of a two-step heat treatment on the microstructure and high-temperature tensile properties of β-containing Ti-44Al-4Cr (at%) alloys fabricated by electron beam powder bed fusion were examined by focusing on the morphology of α2/γ lamellar grains and β/γ cells precipitated [...] Read more.
The effect of a two-step heat treatment on the microstructure and high-temperature tensile properties of β-containing Ti-44Al-4Cr (at%) alloys fabricated by electron beam powder bed fusion were examined by focusing on the morphology of α2/γ lamellar grains and β/γ cells precipitated at the lamellar grain boundaries by a cellular precipitation reaction. The alloys subjected to the first heat treatment step at 1573 K in the α + β two-phase region exhibit a non-equilibrium microstructure consisting of the α2/γ lamellar grains with a fine lamellar spacing and a β/γ duplex structure located at the grain boundaries. In the second step of heat treatment, i.e., aging at 1273 K in the β + γ two-phase region, the β/γ cells are discontinuously precipitated from the lamellar grain boundaries due to excess Cr supersaturation in the lamellae. The volume fraction of the cells and lamellar spacing increase with increasing aging time and affect the tensile properties of the alloys. The aged alloys exhibit higher strength and comparable elongation at 1023 K when compared to the as-built alloys. The strength of these alloys is strongly dependent on the volume fraction and lamellar spacing of the α2/γ lamellae. In addition, the morphology of the β/γ cells is also an important factor controlling the fracture mode and ductility of these alloys. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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17 pages, 4807 KiB  
Article
Comparison of Phase Characteristics and Residual Stresses in Ti-6Al-4V Alloy Manufactured by Laser Powder Bed Fusion (L-PBF) and Electron Beam Powder Bed Fusion (EB-PBF) Techniques
by Aya Takase, Takuya Ishimoto, Naotaka Morita, Naoko Ikeo and Takayoshi Nakano
Crystals 2021, 11(7), 796; https://doi.org/10.3390/cryst11070796 - 08 Jul 2021
Cited by 13 | Viewed by 3466
Abstract
Ti-6Al-4V alloy fabricated by laser powder bed fusion (L-PBF) and electron beam powder bed fusion (EB-PBF) techniques have been studied for applications ranging from medicine to aviation. The fabrication technique is often selected based on the part size and fabrication speed, while less [...] Read more.
Ti-6Al-4V alloy fabricated by laser powder bed fusion (L-PBF) and electron beam powder bed fusion (EB-PBF) techniques have been studied for applications ranging from medicine to aviation. The fabrication technique is often selected based on the part size and fabrication speed, while less attention is paid to the differences in the physicochemical properties. Especially, the relationship between the evolution of α, α’, and β phases in as-grown parts and the fabrication techniques is unclear. This work systematically and quantitatively investigates how L-PBF and EB-PBF and their process parameters affect the phase evolution of Ti-6Al-4V and residual stresses in the final parts. This is the first report demonstrating the correlations among measured parameters, indicating the lattice strain reduces, and c/a increases, shifting from an α’ to α+β or α structure as the crystallite size of the α or α’ phase increases. The experimental results combined with heat-transfer simulation indicate the cooling rate near the β transus temperature dictates the resulting phase characteristics, whereas the residual stress depends on the cooling rate immediately below the solidification temperature. This study provides new insights into the previously unknown differences in the α, α’, and β phase evolution between L-PBF and EB-PBF and their process parameters. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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10 pages, 61605 KiB  
Article
In-Situ Reduction of Mo-Based Composite Particles during Laser Powder Bed Fusion
by Suxia Guo, Weiwei Zhou, Zhenxing Zhou, Yuchi Fan, Wei Luo and Naoyuki Nomura
Crystals 2021, 11(6), 702; https://doi.org/10.3390/cryst11060702 - 18 Jun 2021
Cited by 4 | Viewed by 2259
Abstract
Raw powders are processed in water during the freeze-dry pulsated orifice ejection method (FD-POEM), leading to the inclusion of oxygen impurities. This study proposes a strategy for removing the oxygen content and enhancing the mechanical performance of laser powder bed fusion (L-PBF) builds [...] Read more.
Raw powders are processed in water during the freeze-dry pulsated orifice ejection method (FD-POEM), leading to the inclusion of oxygen impurities. This study proposes a strategy for removing the oxygen content and enhancing the mechanical performance of laser powder bed fusion (L-PBF) builds from powders using carbon nanotubes (CNTs) and H2 reduction. Spherical 1.5 wt.% CNT/Mo composite powders with uniform dispersion were fabricated via FD-POEM. The quantity of MoO2 decreased significantly, and a hexagonally structured Mo2C phase was simultaneously formed in the L-PBF build. The Mo2C with network structure was distributed along the boundaries of equiaxed Mo grains, leading to an increased Vickers hardness of the matrix. This study demonstrates the feasibility of fabricating oxygen-free and high-strength refractory parts during L-PBF for ultrahigh-temperature applications. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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15 pages, 20245 KiB  
Article
Analysis of In Situ Optical Signals during Laser Metal Deposition of Aluminum Alloys
by Liqun Li, Xian Wang and Yichen Huang
Crystals 2021, 11(6), 589; https://doi.org/10.3390/cryst11060589 - 24 May 2021
Cited by 8 | Viewed by 2230
Abstract
During laser metal deposition (LMD) of thin-walled aluminum alloy structures, the deposition height and width is hard to keep stable because of the special properties of aluminum alloys, such as high reflectivity to laser beams, low viscosity, and high thermal conductivity. Monitoring the [...] Read more.
During laser metal deposition (LMD) of thin-walled aluminum alloy structures, the deposition height and width is hard to keep stable because of the special properties of aluminum alloys, such as high reflectivity to laser beams, low viscosity, and high thermal conductivity. Monitoring the LMD process allows for a better comprehension and control of this process. To investigate the characteristics of the aluminum alloy LMD process, three real-time coaxial optical sensors sensitive to visible light, infrared light, and back-reflected lasers ere used to monitor the aluminum alloy LMD process. Thin-walled parts were deposited with different laser power, and the characteristics of the three in situ signals are analyzed. The results show that there exists high linear correlation between reflected laser and accumulated deposition height. A laser reflection model was built to explain the correlation. Besides, the infrared light is linearly correlated with deposition width. Overall, the results of this study show that the optical signals are able to reflect the deposition height and width simultaneously. Infrared light signals and reflected laser signals have the potential to serve as the input of online feedback geometry control systems and real-time defect alarm systems of the LMD process. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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15 pages, 4674 KiB  
Article
Process Parameter Optimization Framework for the Selective Laser Melting of Hastelloy X Alloy Considering Defects and Solidification Crack Occurrence
by Houichi Kitano, Masahiro Kusano, Masakazu Tsujii, Atsushi Yumoto and Makoto Watanabe
Crystals 2021, 11(6), 578; https://doi.org/10.3390/cryst11060578 - 21 May 2021
Cited by 13 | Viewed by 2463
Abstract
Recent years have witnessed increasing demand for selective laser melting (SLM) in practical applications; however, determining the appropriate process parameter range remains challenging. In this study, a framework was developed to determine the appropriate process parameter range considering the occurrence of defects and [...] Read more.
Recent years have witnessed increasing demand for selective laser melting (SLM) in practical applications; however, determining the appropriate process parameter range remains challenging. In this study, a framework was developed to determine the appropriate process parameter range considering the occurrence of defects and cracks by conducting a single-track test and thermal elastoplastic analysis. Keyholing, balling, and the residual unmelted regions were considered defects. The occurrence of solidification cracking, which is predominant in the SLM of solution-strengthened Ni-based alloys, was considered. Using the proposed framework, we could fabricate a part with largely no defects or cracks, except for the edges, under the determined optimal process parameters. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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18 pages, 7060 KiB  
Article
Influences of Process Parameters on the Microstructure and Mechanical Properties of CoCrFeNiTi Based High-Entropy Alloy in a Laser Powder Bed Fusion Process
by Takafumi Ikeda, Makiko Yonehara, Toshi-Taka Ikeshoji, Tohru Nobuki, Minoru Hatate, Kosuke Kuwabara, Yasuhiko Otsubo and Hideki Kyogoku
Crystals 2021, 11(5), 549; https://doi.org/10.3390/cryst11050549 - 14 May 2021
Cited by 16 | Viewed by 2994
Abstract
Recently, high-entropy alloys (HEAs) have attracted much attention because of their superior properties, such as high strength and corrosion resistance. This study aimed to investigate the influences of process parameters on the microstructure and mechanical properties of CoCrFe NiTiMo HEAs using a laser-based [...] Read more.
Recently, high-entropy alloys (HEAs) have attracted much attention because of their superior properties, such as high strength and corrosion resistance. This study aimed to investigate the influences of process parameters on the microstructure and mechanical properties of CoCrFe NiTiMo HEAs using a laser-based powder bed fusion (LPBF) process. In terms of laser power and scan speed, a process map was constructed by evaluating the density and surface roughness of the as-built specimen to optimize the process parameters of the products. The mechanical properties of the as-built specimens fabricated at the optimum fabrication condition derived from the process map were evaluated. Consequently, the optimum laser power and scan speed could be obtained using the process map evaluated by density and surface roughness. The as-built specimen fabricated at the optimum fabrication condition presented a relative density of more than 99.8%. The microstructure of the as-built specimen exhibited anisotropy along the build direction. The tensile strength and elongation of the as-built specimen were around 1150 MPa and more than 20%, respectively. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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13 pages, 6366 KiB  
Article
Numerical Study on Powder Stream Characteristics of Coaxial Laser Metal Deposition Nozzle
by Liqun Li, Yichen Huang, Chunyu Zou and Wang Tao
Crystals 2021, 11(3), 282; https://doi.org/10.3390/cryst11030282 - 12 Mar 2021
Cited by 21 | Viewed by 2806
Abstract
A 3D model was established to accurately simulate the internal and external powder stream characteristics of the coaxial discrete three-beam nozzle for laser metal deposition. A k-ε turbulence model was applied in the gas flow phase, and powder flow was coupled to the [...] Read more.
A 3D model was established to accurately simulate the internal and external powder stream characteristics of the coaxial discrete three-beam nozzle for laser metal deposition. A k-ε turbulence model was applied in the gas flow phase, and powder flow was coupled to the gas flow by a Euler-Lagrange approach as a discrete phase model. The simulated powder stream morphology was in good agreement with the experimental results of CCD and high-speed camera imaging. The simulation results showed that the length, diameter and shrinkage angle of the powder passage in the nozzle have different effects on the velocity and convergence characteristics of the powder stream. The influence of different particle size distribution and the inner laser shielding gas on the powder stream were also discussed in this study. By analyzing the powder stream caused by different incident directions of powder passage, and the collision process between powder and the inner wall, the basic principle of controlling powder stream convergence was obtained. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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14 pages, 7543 KiB  
Article
Effect of Scan Length on Densification and Crystallographic Texture Formation of Pure Chromium Fabricated by Laser Powder Bed Fusion
by Ozkan Gokcekaya, Takuya Ishimoto, Tsubasa Todo, Ryoya Suganuma, Ryo Fukushima, Takayuki Narushima and Takayoshi Nakano
Crystals 2021, 11(1), 9; https://doi.org/10.3390/cryst11010009 - 24 Dec 2020
Cited by 18 | Viewed by 2822
Abstract
Processing of pure chromium (Cr) encounters substantial challenges due to its high melting point and intrinsic brittleness. Although laser powder bed fusion processing (LPBF) offers a novel processing approach by reaching the temperature required to melt pure Cr, the high ductile-to-brittle transformation temperature [...] Read more.
Processing of pure chromium (Cr) encounters substantial challenges due to its high melting point and intrinsic brittleness. Although laser powder bed fusion processing (LPBF) offers a novel processing approach by reaching the temperature required to melt pure Cr, the high ductile-to-brittle transformation temperature (DBTT) of pure Cr prevents the density of the as-built Cr component from reaching the level of industrial acceptance. This study focuses on raising the quality of the as-built pure Cr components to the industrial level while considering the effect of scan length on densification and crystallographic texture. It was found that short scan length induced by feature size improved the density of as-built specimens while strengthening the texture suggesting uniform heat distribution and lower thermal gradients as a result of short time intervals in scanning tracks and layers. It was discovered that cracking caused by residual stress was detrimental to densification due to the DBTT characteristic of pure Cr, which was localized at high-angle grain boundaries (HAGBs) with high misorientation. The decrease in density and misorientation of HAGBs owing to the increase in grain size and texture strength, respectively, improved the density of as-built Cr up to 97.6% and altered its mechanical properties. Therefore, these findings offer new insight into the LPBF processing of metals with high DBTT characteristics. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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14 pages, 5474 KiB  
Article
Effect of Annealing on Anisotropic Tensile Properties of Al–12%Si Alloy Fabricated by Laser Powder Bed Fusion
by Mulin Liu, Takafumi Wada, Asuka Suzuki, Naoki Takata, Makoto Kobashi and Masaki Kato
Crystals 2020, 10(11), 1007; https://doi.org/10.3390/cryst10111007 - 05 Nov 2020
Cited by 34 | Viewed by 3273
Abstract
In this study, we systematically investigated microstructures and tensile properties of an Al–12mass%Si alloy additive-manufactured by laser powder bed fusion (LPBF) process and subsequently annealed at various temperatures. Microstructure of the as-fabricated sample was characterized by a number of melt pools consisting of [...] Read more.
In this study, we systematically investigated microstructures and tensile properties of an Al–12mass%Si alloy additive-manufactured by laser powder bed fusion (LPBF) process and subsequently annealed at various temperatures. Microstructure of the as-fabricated sample was characterized by a number of melt pools consisting of α-Al phases surrounded by Si eutectic phases. Fine Si precipitates were observed in the α-Al phase in the sample annealed at 200 °C. The eutectic Si phase appears to agglutinate, resulting in a coarsened Si phase formed at high temperatures above 300 °C. The initial cellular microstructure completely disappears and a number of coarsened Si phases and plate-shaped intermetallic phases (β-AlFeSi) were formed in the sample annealed at 530 °C. However, the grain morphology of the α-Al matrix slightly changed after the annealing at high temperatures. The as-fabricated specimen showed a high strength above 400 MPa and a low ductility of below 10% in total elongation. The tensile ductility varied depending on the tensile direction. The annealed specimens exhibited a lower tensile strength and larger elongation, whereas the direction dependence of the tensile properties was less pronounced in the specimens annealed at higher temperatures. The anisotropic tensile ductility can be rationalized by preferential fractures occurred around melt pool boundaries. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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