What's New
2023（July－December）
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2023.12.19
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2023.11.23
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2023.11.18
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2023.11.17
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2023.11.17
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2023.10.25
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2023.8.3
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2023.7.14
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2023.7.13
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2023.7.7
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2023.12.19
Metals and Materials International (IF=3.5) has published a study of beta-containing TiAl alloys as an OA paper.
Sung-Hyun Park, Ozkan Gokcekaya, Ryosuke Ozasa, Myung-Hoon Oh, Young-Won Kim, Hyoung Seop Kim, Takayoshi Nakano:
Microstructure and crystallographic texture evolution of β-solidifying γ-TiAl alloy during single- and multi-track exposure via laser powder bed fusion,
Metals and Materials International, (2023), 1-15
https://doi.org/10.1007/s12540-023-01579-4
click here for this paper.
Abstract
The microstructural evolution and crystallographic texture formation of β-solidifying Ti-44Al-6Nb-1.2Cr alloy were identified under single- and multi-track exposures via laser powder bed fusion (L-PBF) for various process parameters. Under single-track exposure, the microstructure of the melt pool was divided into the band-like α2 phase in the melt pool boundary and β phase in the melt pool center. Numerical and thermodynamic simulations revealed that the underlying mechanism of phase separation was related to the variation in the cooling rate in the melt pool, whereas microsegregation induced a shift in the solidification path. Meanwhile, the crystallographic texture of the α2 phase region was identical to that of the substrate owing to the epitaxial growth of the β phase and subsequent α phase nucleation. In contrast, the β phase exhibited a ± 45° inclined <100> alignment in the melt pool, which was tilted to align along the build direction toward the center of the melt pool corresponding to the simulated thermal gradient direction. Furthermore, the narrow hatch space condition maintained the crystallographic texture to the subsequent scan, forming a continuous band-like α2 phase with a strong selection. However, the crystallographic texture in a wide hatch space condition manifested a random distribution and constituted a fine mixture of the β and α2 phases. For the first time, these results will offer an understanding of an anisotropic microstructure control via the L-PBF process and ensure the tailoring of the mechanical properties in the β-solidifying γ-TiAl-based alloys by approaching hatch spacing control.
Keywords
γ-TiAl alloy, Microstructural evolution, Crystallographic texture, Laser powder bed fusion
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2023.11.23
A study on microstructural changes after heat treatment of beta TiAl powder for AM has been published as an OA article in Crystals (IF=2.7).
Sung-Hyun Park, Ozkan Gokcekaya, Ryosuke Ozasa, Ken Cho, Hiroyuki Y. Yasuda, Myung-Hoon Oh, Takayoshi Nakano*:
Microstructure evolution of gas-atomized β-solidifying γ-TiAl alloy powder during subsequent heat treatment,
Crystals, 13, (2023), 1629; 1-10.
https://doi.org/10.3390/cryst13121629click here for this paper.
Abstract
To promote the use of γ-TiAl alloys in various domains, such as the aerospace industry, it is pivotal to investigate the unusual phase transformation from rapidly solidified and metastable γ-TiAl toward the equilibrium state. In this study, the microstructure characteristics of gas-atomized β-solidifying Ti-44Al-6Nb-1.2Cr alloy powder, in terms of the effect of rapid solidification on microstructure evolution, were explored in comparison with cast materials. The phase constitution, morphology, and crystallographic orientation between phases were noted to be distinct. Furthermore, subsequent heat treatment was conducted at different temperatures using gas-atomized powder. The transition from the metastable to equilibrium state was observed, wherein firstly, the γ phase precipitated from the retained α2 phase, forming an α2/γ lamellar microstructure. In intensified heat-treatment conditions adequate for cellular reaction, β/γ cells were formed at the grain boundaries of α2/γ lamellar colonies. The findings highlight the overall phase transformation during rapid solidification and continuous microstructural evolution from the nonequilibrium to the equilibrium state. This research can bridge the gap in understanding the effect of the solidification rate on microstructural evolution and contribute to enhanced comprehension of the microstructure in other domains involving rapid solidification, such as the additive manufacturing of γ-TiAl alloys.Keywords
gas atomization; rapid solidification; nonequilibrium state; β-solidifying γ-TiAl alloy; recrystallization -
2023.11.18
Journal of Materials Research and Technology (IF=6.4) published an OA paper on the unique properties of double arrowhead structures fabricated by electron beam additive manufacturing.
Zana Eren*, Ozkan Gokcekaya*, Takayoshi Nakano, Zahit Mecitoğlu:
In-plane quasi-static compression deformation of Ti6Al4V double arrow-headed lattices fabricated by electron beam powder bed fusion process: Build orientation, scan speed and failure mechanism,
Journal of Materials Research and Technology, 27, (2023), 6192-6210.
https://doi.org/10.1016/j.jmrt.2023.11.027click here for this paper.
Abstract
The 2D double arrow-headed (DAH) lattice structures, which are promising cellular structures for impact mitigation, remain relatively unexplored in terms of their compression response when manufactured using the powder bed fusion process with Ti6Al4V (Ti64) alloy. This study aims to investigate the effects of build orientation and beam scan speed of Electron Beam Powder Bed Fusion (PBF-EB) process on the energy absorption of 2D Ti64 DAH lattice structures. Additionally, potential microstructural variations due to adjusted process parameters can be linked to different levels of energy absorption. For the compressions, the lattice structures were manufactured at two build orientations (0° and 45°), using three different beam scan speeds: speed function (SF), low speed (LS), high speed (HS). In micro-characterizations, the unit cells of 0deg-LS exhibited the lowest micro-porosity level at 0.12 . Based on KAM values, thin struts at unit cells had higher residual stresses than thick struts, contributing to the initiation of failure locations. The compressions revealed that the 0deg-LS group absorbed 21.6 and 24 more energy than 0deg-SF and 0deg-HS groups, respectively, at compressions of 33 . 45° samples absorbed approximately 10 % more energy than 0° samples except HS groups. The lowest micro-porosity of 0deg-LS contributed to having the highest energy absorption among 0deg samples. As the residual stresses in KAM values did not differ strongly with varying beam speed, varied energy absorptions were not linked to them. An optimization of the numerical compressions helped obtain designs with higher energy absorption and less relative volume. This study provides valuable insights into Ti64 cellular applications constrained with 2D-type designs.Keywords
Mechanical metamaterials
Electron beam powder bed fusion process
Double arrow-headed lattice
Compression deformation
Microstructure -
2023.11.17
Our paper on lightweight MEA Fe47Mn25Al13Cr7Ni5C3 in collaboration with Prof. Hyoung Seop Kim's group at POSTECH has been published in Materials Science and Engineering A (IF=6.4).
Gang Hee Gu, Hyeonseok Kwon, Jae Heung Lee, Takayoshi Nakano, Hyoung Seop Kim*:
Lightweight Fe47Mn25Al13Cr7Ni5C3 medium-entropy alloy with enhanced mechanical properties,
Materials Science and Engineering A, 890, (2024), 145924: 1-8.
https://doi.org/10.1016/j.msea.2023.145924
click here for this paper.
Abstract
In this study, we designed a lightweight Fe47Mn25Al13Cr7Ni5C3 medium-entropy alloy (MEA) (calculated density of 6.803 g/cm3) with enhanced mechanical properties. The MEA samples were produced in three conditions with varying microstructures via thermomechanical processing. They achieved excellent tensile properties through strengthening mechanisms such as partial recrystallization, ultrafine grains, and M23C6 and B2 precipitates. Different strengthening mechanisms were applied depending on the annealing heat treatment conditions, resulting in three different strength-elongation combinations. Furthermore, the MEA, under all designed conditions, exhibited superior specific yield strength-uniform elongation and specific ultimate tensile strength-uniform elongation combinations compared to previously studied lightweight high-entropy alloys (HEAs) and lightweight steel. This was primarily attributed to the combination of benefits obtained from the low proportion of iron (47 at%) as a principal element and the large amount of aluminum addition (13 at%). The proposed MEA and its design strategy can satisfy the requirements for lightweight, cost-effective, strong, and ductile metallic materials, making a great contribution to the automotive industry in terms of crash resistance and fuel efficiency. -
2023.11.17
A paper demonstrating that bone matrix orientation has strong resistance to bacterial infection has been published in Biomaterials Advances.
Ryota Watanabe, Aira Matsugaki, Ozkan Gokcekaya, Ryosuke Ozasa, Takuya Matsumoto, Hiroyuki Takahashi, Hidekazu Yasui, Takayoshi Nakano:
Host bone microstructure for enhanced resistance to bacterial infections,
Biomaterials Advances, 154, (2023), 213633, 1-9
https://doi.org/10.1016/j.bioadv.2023.213633Abstract
Postoperative bacterial infection is a serious complication of orthopedic surgery. Not only infections that develop in the first few weeks after surgery but also late infections that develop years after surgery are serious problems. However, the relationship between host bone and infection activation has not yet been explored. Here, we report a novel association between host bone collagen/apatite microstructure and bacterial infection. The bone-mimetic-oriented micro-organized matrix structure was obtained by prolonged controlled cell alignment using a grooved-structured biomedical titanium alloy. Surprisingly, we have discovered that highly aligned osteoblasts have a potent inhibitory effect on Escherichia coli adhesion. Additionally, the oriented collagen/apatite micro-organization of the bone matrix showed excellent antibacterial resistance against Escherichia coli. The proposed mechanism for realizing the antimicrobial activity of the micro-organized bone matrix is by the controlled secretion of the antimicrobial peptides, including β-defensin 2 and β-defensin 3, from the highly aligned osteoblasts. Our findings contribute to the development of anti-infective strategies for orthopedic surgeries. The recovery of the intrinsically ordered bone matrix organization provides superior antibacterial resistance after surgery.Keywords
Postoperative infection; Laser powder bed fusion; Titanium alloy; Surface topography; Bone matrix anisotropy; Antimicrobial activity -
2023.10.25
ACS Applied Materials & Interfaces (IF=10.4) published online a study on a proposed metal catalytic flow reactor made of MOF-based metal 3D printers.
Kohsuke Mori*, Tatsuya Fujita, Hiroto Hata, Hyo-Jin Kim, Takayoshi Nakano, Hiromi Yamashita:
Surface Chemical Engineering of a Metal 3D-Printed Flow Reactor Using a Metal-Organic Framework for Liquid-Phase Catalytic H2 Production from Hydrogen Storage Materials,
ACS Applied Materials & Interfaces, (2023), online.
https://doi.org/10.1021/acsami.3c10945click here for this paper.
Abstract
The accurate positioning of metal-organic frameworks (MOFs) on the surface of other materials has opened up new possibilities for the development of multifunctional devices. We propose here a postfunctionalization approach for three-dimensional (3D)-printed metallic catalytic flow reactors based on MOFs. The Cu-based reactors were immersed into an acid solution containing an organic linker for the synthesis of MOFs, where Cu2+ ions dissolved in situ were assembled to form MOF crystals on the surface of the reactor. The resultant MOF layer served as a promising interface that enabled the deposition of catalytically active metal nanoparticles (NPs). It also acted as an efficient platform to provide carbonous layers via simple pyrolysis under inert gas conditions, which further enabled functionalization with organic modifiers and metal NPs. Cylindrical-shaped catalytic flow reactors with four different cell densities were used to investigate the effect of the structure of the reactors on the catalytic production of H2 from a liquid-phase hydrogen storage material. The activity increased with an increasing internal surface area but decreased in the reactor with the smallest cell size despite its high internal surface area. The results of fluid dynamics studies indicated that the effect of pressure loss becomes more pronounced as the pore size decreases.KEYWORDS:
metal 3D printing, flow reactor, metal−organic framework, postfunctionalization, hydrogen -
2023.8.3
Materials (IF=3.4) published a paper on the creation of shape memory alloys by electron beam coating.
Lei Wang, Masayuki Okugawa*, Hirokazu Konishi, Yuheng Liu, Yuichiro Koizumi*, Takayoshi Nakano:
Fusion of Ni Plating on CP-Titanium by Electron Beam Single-Track Scanning: Toward a New Approach for Fabricating TiNi Self-Healing Shape Memory Coating,
Materials, 16(15), (2023), 5449; 1-15.
https://doi.org/10.3390/ma16155449click here for this paper.
Abstract
The limited wear resistance of commercially pure titanium (CP-Ti) hinders its use in abrasive and erosive environments, despite its good strength-weight ratio and corrosion resistance. This paper reports the first study proposing a novel method for wear-resistant TiNi coating through Ni plating and electron beam (EB) irradiation in an in situ synthetic approach. Single-track melting experiments were conducted using the EB to investigate the feasibility of forming a TiNi phase by fusing the Ni plate with the CP-Ti substrate. Varying beam powers were employed at a fixed scanning speed to determine the optimal conditions for TiNi phase formation. The concentration of the melt region was found to be approximate as estimated from the ratio of the Ni-plate thickness to the depth of the melt region, and the region with Ni-48.7 at.% Ti was successfully formed by EB irradiation. The study suggests that the mixing of Ti atoms and Ni atoms was facilitated by fluid flow induced by Marangoni and thermal convections. It is proposed that a more uniform TiNi layer can be achieved through multi-track melting under appropriate conditions. This research demonstrates the feasibility of utilizing EB additive manufacturing as a coating method and the potential for developing TiNi coatings with shape memory effects and pseudoelasticity.Keywords: commercially pure Ti; TiNi coating; shape memory alloy; pseudoelasticity; wear resistance; electron beam melting
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2023.7.14
Additive Manufacturing Letters published an OA paper on that the presence of Mo prevents the freezing of thermal equilibrium vacancies in a beta Ti-15Mo-5Zr-3Al alloy fabricated via laser lithography by positron annihilation and computer simulation.
Masataka Mizuno*, Kazuki Sugita, Kousuke Do, Takuya Ishimoto, Takayoshi Nakano, Hideki Araki:
Stability of vacancies in β-type Ti-15Mo-5Zr-3Al alloy fabricated via laser powder bed fusion,
Additive Manufacturing Letters, 7, (2023), 100162; 1-7.
https://doi.org/10.1016/j.addlet.2023.100162
click here for this paper.
Abstract
The structural instability in the β-type titanium alloys could affect the stability of vacancies. The stability of vacancies in a β-type Ti-15Mo-5Zr-3Al alloy, fabricated via laser powder bed fusion (LPBF), was investigated using positron annihilation spectroscopy and first-principles calculations. The observed positron lifetimes were close to the experimental and calculated bulk lifetime of Ti-15Mo-5Zr-3Al, which indicates that vacancies were not detected in Ti-15Mo-5Zr-3Al by positron lifetime measurements. Therefore, for the first time, it has been confirmed that quenched-in vacancies are not introduced in the LPBF-manufactured β-type Ti-15Mo-5Zr-3Al despite the fast cooling rate in LPBF process. This feature is preferable for the structural stability in biomedical and industrial applications. The calculated atomic displacement from the ideal bcc lattice positions decreased in β-type Ti-Mo alloys with increasing Mo concentration, indicating that the bcc structure was stabilized by the added Mo. The calculated vacancy formation energies of Ti atoms in β-type Ti-14.5Mo and Ti-27.0Mo alloys exhibited an increasing trend with an increasing number of neighboring Mo atoms. Mo atoms also increased the migration energies of the neighboring paths of vacancies. The calculated results for Ti-15Mo-5Zr-3Al suggest that, while the bcc structure was stabilized by the Mo atoms in Ti-15Mo-5Zr-3Al, the migration and formation energies were still low enough for the diffusion of vacancies. -
2023.7.13
A paper determining the quantification of thresholds for auditory brainstem responses has been published as an OA article in the International Journal of Molecular Sciences (IF=5.6).
Kenji Tanaka, Shuma Ohara, Tadaaki Matsuzaka, Aira Matsugaki*, Takuya Ishimoto, Ryosuke Ozasa, Yukiko Kuroda, Koichi Matsuo, Takayoshi Nakano*:
Quantitative threshold determination of auditory brainstem responses in mouse models,
International Journal of Molecular Sciences, 24(14), (2023), 11393; 1-12.
https://doi.org/10.3390/ijms241411393
click here for this paper.
Abstract
The auditory brainstem response (ABR) is a scalp recording of potentials produced by sound stimulation, and is commonly used as an indicator of auditory function. However, the ABR threshold, which is the lowest audible sound pressure, cannot be objectively determined since it is determined visually using a measurer, and this has been a problem for several decades. Although various algorithms have been developed to objectively determine ABR thresholds, they remain lacking in terms of accuracy, efficiency, and convenience. Accordingly, we proposed an improved algorithm based on the mutual covariance at adjacent sound pressure levels. An ideal ABR waveform with clearly defined waves I-V was created; moreover, using this waveform as a standard template, the experimentally obtained ABR waveform was inspected for disturbances based on mutual covariance. The ABR testing was repeated if the value was below the established cross-covariance reference value. Our proposed method allowed more efficient objective determination of ABR thresholds and a smaller burden on experimental animals.
Keywords:
auditory brainstem responses (ABR); auditory function; ABR threshold; correlation coefficient; cross-covariance -
2023.7.7
A collaborate research paper with Tokyo Dental College on alveolar bone microstructure around orthodontic anchor screws was published as an OA article in Journal of Functional Biomaterials (IF=4.901).
Keisuke Okawa, Satoru Matsunaga*, Norio Kasahara, Masaaki Kasahara, Chie Tachiki, Takayoshi Nakano, Shinichi Abe, Yasushi Nishii:
Alveolar Bone Microstructure Surrounding Orthodontic Anchor Screws with Plasma Surface Treatment in Rats,
Journal of Functional Biomaterials, 14(7), (2023), 356: 1-12.
https://doi.org/10.3390/jfb14070356click here for this paper.
Abstract
A lateral load was applied to anchor screws that had undergone surface treatment, and the structure, cellular dynamics, and quality of the bone surrounding anchor screws were analyzed to investigate the effect of this surface treatment on the peri-implant jawbone. In addition, bone microstructural characteristics were quantitatively evaluated for each site of loading on the bone around the anchor screw. Rats were euthanized after observation on days 3, 5, or 7, and bone quality analyses were performed. Bone-implant contact rate increased more rapidly at an early stage in the treated surface group than in the untreated surface group. Bone lacuna morphometry showed that the measured values adjacent to the screw at the screw neck on the compressed side (A) and at the screw tip on the uncompressed side (D) were significantly lower than those at the screw tip on the compressed side (B) and at the screw neck on the uncompressed side ©. Collagen fiber bundle diameter showed that the measured values adjacent to regions A and D were significantly higher than those at regions B and C. Anchor screw surface activation facilitates initial bone contact of the screw, suggesting that early loading may be possible in clinical practice.
Keywords
bone quality; biological apatite orientation; collagen fiber; miniscrews; horizontal loading