研究者詳細 - 小橋　眞

論文 - 小橋　眞

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Austenite Reversion Behavior of Maraging Steel Additivemanufactured by Laser Powder Bed Fusion 査読有り

Takata, N; Ito, Y; Nishida, R; Suzuki, A; Kobashi, M; Kato, M

ISIJ INTERNATIONAL 64 巻 ( 2 ) 頁： 303 - 315 2024年

Combustion Foaming of Porous (Al, Fe)3Ti with L12 Ordered Structure

Suzuki, A; Fujishiro, T; Takata, N; Kobashi, M

MATERIALS TRANSACTIONS 65 巻 ( 4 ) 頁： 414 - 421 2024年

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

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

JOURNAL OF ALLOYS AND COMPOUNDS 968 巻頁： 172168 2023年12月

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

Suzuki, Asuka, Ishiguro, Renkichi, Miwa, Takumi, Takata, Naoki, Kobashi, Makoto, Furukawa, Yuichi

Journal of Alloys and Compounds 968 巻頁： 172168 2023年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

Wetting and interfacial reactions between molten Al and carbon fibers (CFs) are crucial for the fabrication of high-thermal conductive Al/CF composites through liquid-state processes including casting. The formation of Al4C3 which has a low thermal conductivity and high reactivity with water needs to be suppressed while improving wettability. The addition of Ti into molten Al forms TiC and contributes to significant improvement in wettability. To control a thin morphology of TiC, the kinetics of reactive wetting need to be clarified. In the present study, the reactive wetting kinetics between molten Al or Al-Ti alloy and pitch-based CF were investigated using the dipping coverage method combined with microstructural observations. The addition of Ti into molten Al drastically accelerated the wetting and reduced the apparent activation barrier for reactive wetting, which was related to the change in the interfacial products from the Al4C3 phase to the TiC phase. The Al4C3 phase grew while eroding the CFs, whereas the TiC phase formed in a thin-layered morphology around CFs and suppressed the diameter reduction of CF. The reduction in the apparent activation barrier and the morphology of carbides indicated a change in the dominant phenomena for reactive wetting from Al4C3 growth to TiC formation (controlled by diffusion in liquid Al). Based on the kinetics evaluations, CF were hybridized with pure Al and Al-Ti alloy through a casting process, and their thermal conductivities were evaluated. The addition of CF into pure Al degraded the thermal conductivity due to the eroded CF and coarsened Al4C3 phase, whereas the addition of CF into Al-Ti alloy enhanced the thermal conductivity. This study provides new insights into reactive wetting phenomena related to the fabrication of high-thermal conductive metal matrix composites.

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単結晶マイクロピラー圧縮試験を用いたAl-Fe合金積層造形体の高強度支配因子の検討査読有り

長子明弘, 朱天斉, 高田尚記, 鈴木飛鳥, 小橋眞

軽金属 73 巻 ( 11 ) 頁： 523 - 529 2023年11月

Wear properties of aluminum alloys fabricated by laser powder bed fusion 査読有り国際共著

Gong, S; Takata, N; Kobashi, M; Shin, SE

TRIBOLOGY INTERNATIONAL 187 巻頁： 108769 2023年9月

Design of Al-Fe-Mn alloy for both high-temperature strength and sufficient processability of laser powder bed fusion 査読有り

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

ADDITIVE MANUFACTURING 68 巻頁： 103524 2023年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER

This paper presents a novel design concept for Al alloys with both sufficient laser powder bed fusion (L-PBF) processability and high-temperature mechanical performance using an Al-Fe-Mn ternary alloy with a refined alpha-Al/Al6M (M = Fe, Mn) two-phase microstructure. The near-eutectic (liquid -> alpha-Al(fcc) + Al6M) composition of Al-2.5Fe-2Mn (mass%) was designed to avoid the formation of coarse primary intermetallics (having a detrimental effect on the PBF processability for densification) based on non-equilibrium liquidus projection thermodynamic calculations. The designed Al-2.5Fe-2Mn alloy powder exhibited sufficient L-PBF processability, and fully dense centimeter-sized samples (relative densities of above 99%) were successfully prepared. The L-PBF Al-2.5Fe-2Mn alloy samples exhibited a significantly refined solidification microstructure consisting of Al6M and alpha-Al phases in the melt-pool regions. Fe and Mn alloying elements contributed to the formation of nanoscale Al6M-phase particles and a high solid solution concentration in the alpha-Al matrix. The strength of the L-PBF Al-2.5Fe-2Mn alloy was slightly reduced at higher temperatures, but remained above 240 MPa at an elevated temperature of 300 degrees C. This superior high-temperature mechanical performance was attributed to the high thermal stability of the refined alpha-Al/Al6M two-phase microstructure and the formation of nanosized Al6M-phase precipitates.

DOI： 10.1016/j.addma.2023.103524

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Microstructural origin of anisotropic tensile ductility of Al-Si alloy manufactured by laser powder bed fusion 査読有り

Otani, Y; Takata, N; Suzuki, A; Kobashi, M; Kato, M

SCRIPTA MATERIALIA 226 巻 2023年3月

Austenite Reversion Behavior of Maraging Steel Additive-manufactured by Laser Powder Bed Fusion 査読有り

Naoki Takata, Yuya Ito, Ryoya Nishida, Asuka Suzuki, Makoto Kobashi, Masaki Kato

TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN 109 巻 ( 3 ) 頁： 201 - 214 2023年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IRON STEEL INST JAPAN KEIDANREN KAIKAN

This study was set to fundamentally investigate the characteristics of austenite reversion occurring in maraging steels additive-manufactured by laser powder bed fusion (L-PBF). The maraging steel samples manufactured under different L-PBF process conditions (laser power P and scan speed v) were subjected to heat treatments at 550 degrees C for various durations, compared with the results of the austenitized and water-quenched sample with fully martensite structure. The L-PBF manufactured samples exhibited the martensite structure (including localized austenite (gamma) phases) containing submicron-sized cellular structures. Enriched alloy elements were detected along the cell boundaries, whereas such cellar structure was not found in the water-quenched sample. The localized alloy elements can be rationalized by the continuous variations in the gamma-phase composition in solidification during the L-PBF process. The precipitation of nanoscale intermetallic phases and the following austenitic reversion occurred in all of the experimental samples. The L-PBF manufactured samples exhibited faster kinetics of the precipitation and austenite reversion than the water-quenched sample at elevated temperatures. The kinetics changed depending on the L-PBF process condition. The enriched Ni element (for stabilizing gamma phase) localized at cell boundaries would play a role in the nucleation site for the formation of gamma phase at 550 degrees C, resulting in the enhanced austenite reversion in the L-PBF manufactured samples. The variation in the reaction kinetics depending on the L-PBF condition would be due to the varied thermal profiles of the manufactured samples by consecutive scanning laser irradiation operated under different P and v values.

DOI： 10.2355/tetsutohagane.TETSU-2022-066

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Effects of Mn and Cu Additions on Solidification Microstructure and High-Temperature Strength of Cast AlFe Binary Alloy 査読有り

Naoki Okano, Naoki Takata, Asuka Suzuki, Makoto Kobashi

Materials Transactions 64 巻 ( 2 ) 頁： 492 - 499 2023年

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）

In order to investigate the effects of Mn and Cu additions on solidification microstructure and high-temperature strength of cast AlFe alloys, we have fabricated various AlFe-based alloys with compositions of Al1%Fe, Al1%Fe1%Mn, Al1%Fe1%Cu, and Al1%Fe1%Cu1%Mn (mol%) solidified at different cooling rates (0.3 K·s11 and 145 K·s11). In the Al1%Fe binary alloy, the coarsened ª-Al13Fe4 phase with a needle-shaped morphology was often observed in the furnace-cooled sample (0.3 K·s11), whereas the cast sample (145 K·s11) exhibited several elongated ¡ phases surrounded by fine ¡/Al6Fe eutectic microstructure. Such a solidification microstructure was observed in the cast Al1%Fe1%Cu alloy, whereas the Al23CuFe4 phase was locally formed in the finally solidified zone in the furnace-cooled sample. In the Al1%Fe1%Mn alloy, the Al6(Fe, Mn) phase was formed regardless of the cooling rate. Finer ¡/Al6(Fe, Mn) two-phase eutectic microstructure was almost entirely occupied in the cast sample. The fine eutectic microstructure was observed in the cast Al1%Fe1%Cu1%Mn alloy as well. Compression tests for cast alloy specimens revealed that the Al1%Fe1%Cu1%Mn alloy exhibited the highest strength level among the studied alloy specimens, indicating the combined addition of Mn and Cu elements could be effective in improving the high-temperature strength of the cast AlFe alloys.

DOI： 10.2320/matertrans.MT-LA2022010

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Influence of Dislocation Substructure on Size-Dependent Strength of High-Purity Aluminum Single-Crystal Micro pillars 査読有り

Naoki Takata, Shintaro Uesugi, Tianqi Zhu, Socihiro Takeyasu, Asuka Suzuki, Makoto Kobashi

MATERIALS TRANSACTIONS 64 巻 ( 8 ) 頁： 1952 - 1958 2023年

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：JAPAN INST METALS & MATERIALS

In order to understand the influence of dislocation substructures on the size-dependent strength (smaller is stronger) of micron-sized metals, we have fabricated single-crystal cylindrical micropillars with various diameters approximately ranging from 1 to 10 mu m, which were prepared on the surface of the fully annealed sample and the subsequently cold-rolled samples of high-purity aluminum (Al). The annealed micropillars exhibited a size dependence of the resolved shear stress required for slip. The shear stress (tau(i)) normalized by shear modulus (G) and the specimen diameter (d) normalized by Burgers vector (b) followed the correlation of tau(i)/G=0.33(d/b)(-0.63). The size-dependent strength was reduced by cold-rolling, resulting in lower power-law exponents (0.26 similar to 0.31) for the correlation in the cold-rolled specimens. The fine dislocation substructures introduced by the cold-rolling could be associated with the reduced size-dependent strength, which can be rationalized using the stochastic model of the dislocation source length in an assumption of homogenously distributed dislocations existing in the experimental micropillars. The inhomogeneous dislocation substructure with various dislocation cell sizes would contribute to a variation in the measured strength depending on the location, likely due to the probability of exiting the dislocation cell walls (local variation in dislocation density) in the micropillars fabricated on the cold-rolled Al samples<bold>.</bold>

DOI： 10.2320/matertrans.MT-L2023004

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Introducing Hatch Spacing into Deposited Energy Density toward Efficient Optimization of Laser Powder Bed Fusion Process Parameters 査読有り

Mai Kunieda, Asuka Suzuki, Naoki Takata, Masaki Kato, Makoto Kobashi

Materials Transactions 64 巻 ( 6 ) 頁： 1099 - 1106 2023年

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）

The optimization of processing parameters is indispensable for the laser powder bed fusion (L-PBF) process. The deposited energy density (DED) is one of the process indexes for the L-PBF process and has a simplified formula of P v 0.5, where P is the laser power, and v is the scan speed. This parameter describes the change in the relative density and the melt pool morphology with laser power and scan speed well, whereas it does not include the effect of other processing parameters, e.g., hatch spacing (S). In the present study, an attempt was made to incorporate the effect of S into DED. Al12Si (mass%) alloy cube samples were fabricated by L-PBF under various P, v, and S, for evaluating the relative density and the melt pool morphology. The melt pool depth and width of L-PBF-manufactured Al12Si alloy increased linearly with P v 0.5 and did not exhibit a clear correlation with S. Based on the experimental observation, the effect of hatch spacing on DED was estimated to be S 0.5, and a new index of P v 0.5 S 0.5 was proposed. This index described the change in the relative density of the L-PBF-manufactured Al12Si alloy with laser conditions (P, v, and S) well when the thermal conduction mode melting was dominant. This study also indicated the limitation of the applicability of P v 0.5 S 0.5 under the keyhole or transition mode melting.

DOI： 10.2320/matertrans.MT-ME2022002

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Effect of solute Ni on thermal activation process of plastic deformation in Fe-18Cr single-crystal micropillars 査読有り

Zhu, TQ; Li, HM; Takata, N; Kobashi, M; Yoshino, M

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 857 巻 2022年11月