Faculty Profiles - KOBASHI, Makoto

Papers - KOBASHI, Makoto

Division display 1 - 20 of about 286 ／ All the affair displays >>

Elucidating dominant flow channel size for capillary performance of open-cell porous wicks Reviewed

Shen, HF; Suzuki, A; Takata, N; Kobashi, M

INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER Vol. 223 page： 125217 2024.5

Laser-beam powder bed fusion of Al-Fe-Cu alloy to achieve high strength and thermal conductivity Reviewed

Cheng, Y; Miyawaki, T; Wang, WY; Takata, N; Suzuki, A; Kobashi, M; Kato, M

ADDITIVE MANUFACTURING LETTERS Vol. 8 page： 100191 2024.2

Evaluation of reactive wetting kinetics of carbon fibers by molten Al-Ti alloy and its application to the fabrication of Al/carbon fiber composites Reviewed

Suzuki, A; Ishiguro, R; Miwa, T; Takata, N; Kobashi, M; Furukawa, Y

JOURNAL OF ALLOYS AND COMPOUNDS Vol. 968 page： 172168 2023.12

Persistent Homology Analysis of the Microstructure of Laser-Powder-Bed-Fused Al–12Si Alloy Reviewed

Asuka Suzuki, Yusuke Sasa, Makoto Kobashi, Masaki Kato, Masahito Segawa, Yusuke Shimono, Sukeharu Nomoto

Materials Vol. 16 ( 22 ) page： 7228 2023.11

Language：English Publishing type：Research paper (scientific journal) Publisher：MDPI AG

The laser powder bed fusion (L-PBF) process provides the cellular microstructure (primary α phase surrounded by a eutectic Si network) inside hypo-eutectic Al–Si alloys. The microstructure changes to the particle-dispersed microstructure with heat treatments at around 500 °C. The microstructural change leads to a significant reduction in the tensile strength. However, the microstructural descriptors representing the cellular and particle-dispersed microstructures have not been established, resulting in difficulty in terms of discussion regarding the structure–property relationship. In this study, an attempt was made to analyze the microstructure in L-PBF-built and subsequently heat-treated Al–12Si (mass%) alloys using the persistent homology, which can analyze the spatial distributions and connections of secondary phases. The zero-dimensional persistent homology revealed that the spacing between adjacent Si particles was independent of Si particle size in the as-built alloy, whereas fewer Si particles existed near large Si particles in the heat-treated alloy. Furthermore, the first principal component of a one-dimensional persistent homology diagram would represent the microstructural characteristics from cellular to particle-dispersed morphology. These microstructural descriptors were strongly correlated with the tensile and yield strengths. This study provides a new insight into the microstructural indices describing unique microstructures in L-PBF-built alloys.

DOI： 10.3390/ma16227228

Web of Science

PubMed

researchmap

Machine learning surrogate modeling toward the design of lattice-structured heat sinks fabricated by additive manufacturing Reviewed

Asuka Suzuki, Hideto Nakatani, Makoto Kobashi

Materials & Design Vol. 230 page： 111969 2023.6

Mechanical coupling and tuned anisotropic elasticity: Numerical and experimental material design for shear-normal and shear-shear interactions Reviewed International coauthorship

Molavitabrizi, D; Suzuki, A; Kobashi, M; Mousavi, SM

MATERIALS & DESIGN Vol. 230 page： 111950 2023.6

Fabrication of Al-CNT composite with high hardness and electrical conductivity by controlling Al4C3 formation Reviewed

Kim, D; Hirayama, Y; Liu, Z; Takagi, K; Kobashi, M

JOURNAL OF ALLOYS AND COMPOUNDS Vol. 942 page： 169102 2023.5

B2-structured Fe<inf>3</inf>Al alloy manufactured by laser powder bed fusion: Processing, microstructure and mechanical performance Reviewed International coauthorship

A. M. Vilardell, L. Pelcastre, D. Nikas, P. Krakhmalev, M. Kato, N. Takata, M. Kobashi

Intermetallics Vol. 156 page： 107849 2023.5

Authorship：Last author Language：English Publishing type：Research paper (scientific journal)

Prealloyed Fe3Al was successfully manufactured by laser powder bed fusion. The best set of process parameters led to parts with a relative density of 99.5 %, a surface roughness, Sa, of 31.5 ± 5.6 μm and a hardness of 319 ± 14 HV0.1. Its microstructure as well as its mechanical properties at room and high temperatures were analyzed. The results of the chemical composition showed minor variations in aluminum content oscillating between 21 and 28 at.% along the melt pool. Additionally, elongated grains were observed to grow parallel to the building direction, as well as the development of a weak {001} texture along the building direction. The mechanical properties were influenced by the temperature. Compression tests showed a loss in strength with the increase in temperature, from a yield strength of 621 ± 40 MPa at room temperature to 89 ± 20 MPa at 650 °C. Reciprocating sliding wear tests showed that fragmentation of the intermetallic at room temperature occurs, whereas plastic deformation dominated at higher temperatures. For all temperatures, tribochemical wear was also present due to the oxidation of wear debris.

DOI： 10.1016/j.intermet.2023.107849

Web of Science

Scopus

researchmap

Ultra-high coercivity Sm-Co bulk magnets with remarkable thermal stability Reviewed

Park, K; Hirayama, Y; Wang, J; Kobashi, M

SCRIPTA MATERIALIA Vol. 218 2022.9

Iron aluminides as an alternative binder for cemented carbides: A review and perspective towards additive manufacturing Reviewed International coauthorship

Vilardell, AM; Cinca, N; Tarres, E; Kobashi, M

MATERIALS TODAY COMMUNICATIONS Vol. 31 2022.6

Laser powder bed fusion of polyamide-composite for antibacterial applications: Characterization and properties Reviewed International coauthorship

Vilardell, AM; Yadroitsava, I; Wolf, WKC; Du Plessis, A; Tshibalanganda, M; Kouprianoff, DP; Garcia-Giralt, N; Kobashi, M; Yadroitsev, I

MATERIALS TODAY COMMUNICATIONS Vol. 31 2022.6

Exchange-Coupled SmCo5/Fe Nanocomposite Magnet Prepared by Low Oxygen Powder Metallurgy Process Reviewed

Park K., Hirayama Y., Yamaguchi W., Kobashi M., Takagi K.

IEEE TRANSACTIONS ON MAGNETICS Vol. 58 ( 2 ) 2022.2

Anisotropic Sm-Co nanopowder prepared by induction thermal plasma Reviewed

Kwangjae Park, Yusuke Hirayama, Masaya Shigeta, Zheng Liu, Makoto Kobashi, Kenta Takagi

Journal of Alloys and Compounds Vol. 882 page： 160633 - 160633 2021.11

Effect of added stabilizing elements on thermal activation process of plastic deformation in 18Cr ferritic stainless steel Reviewed

Hongmei Li, Naoki Takata, Makoto Kobashi, Masataka Yoshino

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING Vol. 824 2021.9

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

The effects of a trace amount (similar to 0.1 at.%) of added stabilizing elements (Nb, Ti, and Zr) on the tensile properties of 18Cr ferritic stainless steel sheets at strain rates ranging from 10(-3)-10(2) s(-1) (from ordinary quasi-static deformation to dynamic deformation) were investigated. The additional Ti or Zr elements formed coarse carbide or nitride precipitates, which consumed interstitial solute elements (C and/or N) in the ferrite matrix. In the Nb-added steel, however, only fine NbN precipitates with a few hundred nanometers in size were observed locally, implying a small amount of solute Nb in the ferrite matrix. Ti or Zr additions had only a slight effect on the deformation resistance of 18Cr ferritic steel sheets and strain rate sensitivity (m) of the flow stress, however, the Nb addition increased the deformation resistance and significantly reduced the strain rate sensitivity. The measured activation volume (v*) values of the Ti- and Zr-added steels (62 b(3) and 66 b(3)) were almost equivalent to one of the 18Cr base steel (64 b(3)). This result suggested that a general thermally activated process for screw dislocation motion is controlled by double-kink nucleation, which is slightly affected by Ti or Zr additions. The high v* value (106 b(3)) of the Nb-added steel indicated that the thermally activated process of plastic deformation would be associated with the substitutional solute Nb atoms (act as short-range obstacles) interacting with the moving dislocations. These results showed that the Nb element played a distinct role in plastic deformation from the other stabilizing elements of Ti and Zr.

DOI： 10.1016/j.msea.2021.141866

Web of Science

researchmap

Dual plateau stress of C15-type topologically close-packed lattice structures additive-manufactured by laser powder bed fusion Reviewed

Xiaoyang Liu, Asuka Suzuki, Naoki Takata, Makoto Kobashi, Masaki Kato

SCRIPTA MATERIALIA Vol. 202 2021.9

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Imitating crystal structures offers new avenues to design lattice structures composed of unit cells with nodes (act as atoms) and struts (act as atomic bonds). We found out unique dual plateau regions in the stress-strain curves of lattice structures inspired by topologically close-packed (TCP) structure of C15 Laves phase (AB(2)-type intermetallic compounds) and manufactured via the laser powder bed fusion. X-ray computed tomography of compressively deformed lattice structures as well as finite element analysis revealed that the existence of two kinds of units with different relative density caused the dual plateau regions. In addition, the C15 lattice structures exhibited a hybrid deformation mode of bending- and stretch-dominated deformations and can absorb high total energy of 5.0 MJ.m(-3) in two stress levels. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2021.114003

Web of Science

researchmap

Thermal activation process of plastic deformation in Fe-18Cr single-crystal micropillars with high-density dislocations Reviewed

Hongmei Li, Tianqi Zhu, Naoki Takata, Makoto Kobashi, Masataka Yoshino

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING Vol. 819 2021.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

Micropillar compression testing was performed on bcc solid-solution single-crystal micropillars with two diameter (d) ranges (2-3 and 5-6 mu m) prepared on the surfaces of fully annealed and subsequently 10% coldrolled 18Cr ferritic steel specimens. This was done to investigate the effect of initial dislocations on the plastic deformation of micron-sized crystals. The 10% cold rolling process significantly increased the stress level (provided by an activated single slip system) required to initiate slip in the annealed micropillars with different diameter ranges. In the case of the annealed micropillars, the strain-rate sensitivity (m) of the yield stress becomes lower for larger specimens (the m value decreased from 0.12 to 0.04). However, the 10% cold-rolled micropillars exhibited a much lower strain-rate sensitivity regardless of the specimen size. The activation volume (v*) of the annealed micropillars showed a significant specimen size dependency (v*proportional to d1.47), consistent with published data on the micropillar compression experiments of single-crystals of the bcc metals and alloys. For the 10% cold-rolled micropillars, the high v* values (88b3 and 112b3) showed a slight dependency on the specimen size (v*proportional to d0.33). The v* values appeared somewhat higher but were equivalent to those of bulk-size specimens, suggesting that the initial high-density dislocations would provide sufficient sources for dislocation multiplication in the micron-sized specimens under compression. The observed high v* values might be associated with the strong dislocation interactions in the alpha-(Fe, Cr) solid-solution matrix.

DOI： 10.1016/j.msea.2021.141459

Web of Science

researchmap

Highly Conductive Al/Al Interfaces in Ultrafine Grained Al Compact Prepared by Low Oxygen Powder Metallurgy Technique Reviewed

Kim, D; Hirayama, Y; Liu, Z; Kwon, H; Kobashi, M; Takagi, K

NANOMATERIALS Vol. 11 ( 5 ) 2021.5

Processability and Optimization of Laser Parameters for Densification of Hypereutectic Al-Fe Binary Alloy Manufactured by Laser Powder Bed Fusion Reviewed

Wenyuan Wang, Naoki Takata, Asuka Suzuki, Makoto Kobashi, Masaki Kato

CRYSTALS Vol. 11 ( 3 ) 2021.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：MDPI

Centimeter-sized samples of hypereutectic Al-15 mass% Fe alloy were manufactured by a laser powder bed fusion (L-PBF) process while systematically varying laser power (P) and scan speed (v). The effects on relative density and melt pool depth of L-PBF-manufactured samples were investigated. In comparison with other Al alloys, a small laser process window of P = 77-128 W and v = 0.4-0.8 ms(-1) was found for manufacturing macroscopically crack-free samples. A higher v and P led to the creation of macroscopic cracks propagating parallel to the powder-bed plane. These cracks preferentially propagated along the melt pool boundaries decorated with brittle theta-Al13Fe4 phase, resulting in low L-PBF processability of Al-15%Fe alloy. The deposited energy density model (using P center dot v(-1)(/2)) would be useful for identifying the optimum L-PBF process conditions towards densification of Al-15%Fe alloy samples, in comparison with the volumetric energy density (using P center dot v(-1)), however, the validity of the model was reduced for this alloy in comparison with other alloys with high thermal conductivities. This is likely due to inhomogeneous microstructures having numerous coarsened theta-Al13Fe4 phases localized at melt pool boundaries. These results provide insights into achieving sufficient L-PBF processability for manufacturing dense Al-Fe binary alloy samples.

DOI： 10.3390/cryst11030320

Web of Science

researchmap

Managing both high strength and thermal conductivity of a laser powder bed fused Al-2.5Fe binary alloy: Effect of annealing on microstructure Reviewed

Xing Qi, Naoki Takata, Asuka Suzuki, Makoto Kobashi, Masaki Kato

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING Vol. 805 page： 140591 2021.2

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

The microstructure of Al-2.5Fe (wt%) binary alloy samples additively manufactured by laser powder bed fusion (L-PBF) was systematically characterized, and its change due to subsequent annealing at 300 degrees C and 500 degrees C was examined. The as-fabricated samples featured homogeneous distribution of numerous fine particles of the metastable Al6Fe phase in the solidification microstructure where melt pools formed, and a relatively coarsened cellular structure was observed around the boundaries between the melt pools formed at different locations (melt pool boundaries). After the annealing at 300 degrees C, a slight growth of the nano-sized Al6Fe phase occurred, and coarsened plate-like.-Al13Fe4 phases were locally formed in the cellular structure at melt pool boundaries. Annealing at 500 degrees C induced a pronounced transformation of the metastable Al6Fe phase to the stable.-Al13Fe4 phase in the microstructure where melt pools formed, although no significant change in the microstructure of the a-Al matrix was detected. The thermal conductivity and tensile properties of as-fabricated and subsequently annealed specimens were measured. The as-fabricated specimens exhibited a high tensile strength of similar to 320 MPa and a thermal conductivity of similar to 150 W m(-1) K-1. Annealing at 300 degrees C improved the thermal conductivity to similar to 185 W m(-1) K-1 without a loss of tensile strength, whereas annealing at 500 degrees C significantly decreased the tensile strength. These results are utilized to discuss a balance between mechanical properties and thermal conductivity, which provided novel insights for managing both high strength and thermal conductivity of L-PBFbuilt Al-Fe binary alloys by controlling microstructure.

DOI： 10.1016/j.msea.2020.140591

Web of Science

researchmap

Understanding and suppressing shear band formation in strut-based lattice structures manufactured by laser powder bed fusion

Liu Xiaoyang, Wada Takafumi, Suzuki Asuka, Takata Naoki, Kobashi Makoto, Kato Masaki

MATERIALS & DESIGN Vol. 199 2021.2

　 PREV - NEXT 　

<KOBASHI, Makoto>

Papers - KOBASHI, Makoto