研究者詳細 - 髙田　尚記

論文 - 髙田　尚記

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Metal-like ductility and high hardness in nitrogen-rich HfN thin films by point defect superstructuring 査読有り国際共著国際誌 Open Access

Lorentzon M., Sangiovanni D.G., Takata N., Zhu T., Hahn R., Palisaitis J., Hultman L., Birch J., Ghafoor N.

Communications Materials 6 巻 ( 1 ) 2025年12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：Communications Materials

The strength of refractory ceramics is much limited by their brittleness. Counterintuitively, we observe simultaneous high hardness and metallic-like ductility in highly overstoichiometric single-crystal HfN<inf>1.22</inf> and HfN<inf>1.33</inf> films grown by ion-assisted reactive magnetron sputtering. Here, we show by electron microscopy, diffraction methods, and ab-initio calculations the existence of a superstructure ordering of metal vacancies and nitrogen interstitials into sub-nanometer hyper-overstoichiometric and quasi-stoichiometric domains that self-organize into a checkerboard pattern superimposed onto the NaCl-structured lattice. A high intrinsic dislocation density and low dislocation nucleation barrier on {111} < 011> slip systems enable extraordinary ductility and strain hardening at >50% strain, in room temperature uniaxial compression of HfN<inf>1.22</inf> micropillars. The films simultaneously exhibit a high hardness – tunable up to 28 GPa via control of stoichiometry – and a remarkable fracture resistance due to dislocation-mediated stress dissipation. The presented findings provide a route for synthesizing nitride superstructured films with unique hardness/toughness combinations.

DOI： 10.1038/s43246-025-00768-5

Stabilization and destabilization of precipitation morphologies of T‐Al6Mg11Zn11 phase by trace element additions 査読有り国際誌 Open Access

Li R., Kondo M., Suzuki T., Hayasaka Y., Miyamoto G., Takata N.

Journal of Materials Science and Technology 235 巻頁： 261 - 273 2025年11月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Materials Science and Technology

This study was undertaken to understand the effects of incorporating a trace amount (0.1 at.%) of Ti and/or Mn with low diffusivities on the thermal stability of the precipitation morphologies of the T-Al<inf>6</inf>Mg<inf>11</inf>Zn<inf>11</inf> phase in a heat-resistant Al-Mg-Zn-Cu-Ni quinary alloy in terms of the locations of the added solute elements. In the Ti-added alloy, solute Ti was concentrated in the center of the dendritic α-Al phase via a peritectic reaction during solidification. The Ti distribution was retained even after solution treatment at 480 °C. In contrast, in the Mn-added alloy, Mn appeared localized around granular intermetallic phases (or formed Mn-rich phases), resulting in a slight amount of solute Mn in the α-Al matrix. Solute Mn slightly affected the precipitation morphology of the T-phase at 200 or 300 °C. Nevertheless, much finer precipitates were observed in the α-Al matrix (resulting in finer precipitation morphology) with higher solute Ti concentration, indicating suppressed growth and coarsening of the T-phase precipitates by solute Ti. Introducing both Ti and Mn enhanced local coarsening of the precipitates inside the dendritic α-Al phases with higher Ti solute concentrations. The coexistence of solute Ti and Mn promoted the formation of a significantly coarsened stable Al<inf>18</inf>Mg<inf>3</inf>(Ti, Mn)<inf>2</inf> phase accompanied by the decomposition of initial fine T-phase precipitates, leading to mechanical degradation of the alloy in a high-temperature environment for a long period. These results provide new insights into element selection for the design of heat-resistant Al alloys with superior high-temperature creep performances.

DOI： 10.1016/j.jmst.2025.02.043

Effect of aging temperature after solution treatment on the wear behavior of maraging 18Ni-300 steel manufactured by laser powder bed fusion 査読有り国際共著国際誌

Lim S., Gong S., Takata N., Kobashi M., Shin S.E.

Wear 576-577 巻 2025年8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：Wear

Maraging steel was fabricated using laser powder bed fusion (LPBF), followed by solution treatment and aging at various temperatures. Hardness increased with aging temperature, but aging at 590 °C led to reduced hardness enhancement due to over-aging and the formation of reverted austenite. Nevertheless, the specimen aged at 590 °C showed comparable or even superior wear resistance, attributed to the formation of a tribo-film and strain-induced martensite during sliding. This tribo-film played a significant role in enhancing wear protection. Surface and subsurface analyses confirmed localized martensitic transformation induced by plastic deformation, further contributing to the enhancement of wear resistance. These results indicate that the wear resistance of LPBF-produced maraging steel is influenced not only by hardness but also by sliding-induced microstructural changes, including tribo-film formation and strain-induced phase transformation.

DOI： 10.1016/j.wear.2025.206117

レーザ積層造形技術が創出するアルミニウム合金の新奇力学機能とその制御招待有り査読有り

高田　尚記，足立　大樹，宮嶋　陽司

軽金属 75 巻 ( 4 ) 頁： 199 - 208 2025年5月

Effect of hydrogen on dynamic precipitation in additively manufactured aluminum alloys: Evidence for HEENT mechanism 査読有り国際共著国際誌 Open Access

Safyari M., Takata N., Kim D., Khonsari M.M., Moshtaghi M.

Journal of Alloys and Compounds 1027 巻 2025年5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：Journal of Alloys and Compounds

The influence of hydrogen on the dynamic precipitation and morphology of Si particles in additively manufactured Al-12Si alloys was experimentally and numerically investigated. For the first time, hydrogen was observed to transform Si precipitates from globular to plate-like morphologies, with an increase in yield strength when the hydrogen content exceeds a critical value. Computational analysis indicated that the interface of Si particles could act as potential hydrogen traps, as suggested by density functional theory (DFT) calculations. Thermodynamic insights revealed that hydrogen likely increases interfacial entropy, stabilizes coherent interfaces, and reduces interfacial energy. These findings are consistent with the HEENT mechanism, which explains how hydrogen-enhanced entropy contributes to microstructural changes and alters the mechanical properties of metals. These findings suggest that hydrogen can influence precipitate morphology through its combined effects on thermodynamic stability and kinetic processes, offering new insights into the behavior of additively manufactured aluminum alloys under hydrogen exposure.

DOI： 10.1016/j.jallcom.2025.180395

Formation Behavior of Fe–Zn Intermetallic Layers at the Interface between Fe–Mn and Pure Zn Melt at 460°C 査読有り Open Access

Yoneda S., Takata N.

Tetsu to Hagane Journal of the Iron and Steel Institute of Japan 111 巻 ( 6 ) 頁： 297 - 304 2025年4月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Tetsu to Hagane Journal of the Iron and Steel Institute of Japan

The effect of Mn on the alloying reaction during hot-dip galvanization was investigated. The microstructure of the Fe–Zn intermetallic layers consisted of ζ, δ, and Γ phases for both pure Fe and Fe–2Mn (wt.%) alloy. The intermetallic layers grew thicker with increasing dipping time, and the growth rate of each layer was similar for both substrates. In the case of Fe–2Mn, the formation of the δ<inf>1p</inf> phase was observed after dipping for 2 s. However, δ<inf>1p</inf> formation was delayed for pure Fe, indicating that Mn may promote nucleation of the δ<inf>1p</inf> phase. It is known that the δ<inf>1p</inf> phase nucleates in the Fe-saturated ζ phase. The Fe content at the ζ/δ<inf>1p</inf> interface was found to be lower for the Fe–2Mn alloy by electron probe microanalysis, suggesting that the supersaturation of Fe for the nucleation of δ<inf>1p</inf> is decreased by Mn addition and Mn may stabilize the δ<inf>1p</inf> phase. Once δ<inf>1p</inf> became a continuous layer, the growth rates of the δ<inf>1p</inf> layer on pure Fe and Fe–2Mn were similar. Mn could affect only the nucleation of δ<inf>1p</inf> during the initial stage of the alloying reaction.

DOI： 10.2355/tetsutohagane.TETSU-2024-116

Role of Si Addition in Interfacial Reactions of Steel Sheets Hot-dipped in Zn–55%Al Alloy Melt 査読有り Open Access

Omi Y., Kim D., Takata N., Suzuki A., Kobashi M., Yoneda S.

Tetsu to Hagane Journal of the Iron and Steel Institute of Japan 111 巻 ( 6 ) 頁： 315 - 325 2025年4月

担当区分：責任著者記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Tetsu to Hagane Journal of the Iron and Steel Institute of Japan

This study was set to fundamentally understand the effect of Si addition on the interfacial reaction between Zn–55%Al alloy liquid (corresponding to a nominal composition of Al–25Zn (at%)) and Fe solid in the production process of GALVALUME steel sheets. The pure Fe sheets were hot-dipped in Al–25Zn and Al–25Zn–2Si (at%) alloy melts at 600, 650, and 700°C for 2~3600 s. Significantly thick coatings were formed on Fe sheets hot-dipped in the Al–25Zn binary alloy melt for a longer time than 10 s. The coating thickness became several millimeters after 30 s, resulting in a delamination of the coating. The significant Fe dissolution occurred in the Al–Zn binary alloy melt, accompanied by a significant growth of η phase (Fe<inf>2</inf>Al<inf>5</inf>) toward the solid Fe. The growth could be promoted by the Zn-rich liquid phase with a lower melting temperature. However, in the case of hot-dipping in the Al–25Zn–2Si ternary alloy melt, uniform coatings were formed on the hot-dipped Fe sheets due to the suppressed interfacial reactions. The Fe dissolution slightly occurred, and a continuous layer of Si-rich T<inf>5</inf> (Fe<inf>2</inf>Al<inf>7.4</inf>Si) phase was formed at the interface of solid Fe with the Al–25Zn–2Si alloy melt. The continuous T<inf>5</inf> phase layer would play a role in a diffusion barrier at the interface of solid Fe with liquid Al–Zn alloy, resulting in the suppressed interfacial reaction. These interfacial reaction processes are discussed based on thermodynamic calculations of the Fe–Al–Zn ternary and Fe–Al–Zn–Si quaternary systems.

DOI： 10.2355/tetsutohagane.TETSU-2024-097

Preface to the Special Issue “Fundamentals and Application Technologies for Microstructural Control of Hot-dip Galvanized Coatings for Creating New Functionalities” 招待有り査読有り Open Access

Takata N., Ueda M.

Tetsu to Hagane Journal of the Iron and Steel Institute of Japan 111 巻 ( 6 ) 頁： 273 - 274 2025年4月

Liquid Phase Sintering of Al Powder Using Al-X (X=Cu, Ca, Mg) Eutectic Alloy Powders: Effect of Alloy Elements and Oxide Film Thickness 査読有り国際誌 Open Access

Kusunoki, R; Hayashi, H; Matsumoto, E; Suzuki, A; Takata, N; Kobashi, M; Yoshida, A; Hamada, T; Mekata, M

MATERIALS 18 巻 ( 8 ) 2025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：Materials

Sinter-based additive manufacturing (AM) requires sintering for the densification of green bodies. Al powder is difficult to sinter due to the dense oxide film on the surface, and it is difficult to apply to sinter-based AM. Liquid phase sintering using Al-based eutectic alloy powder is promising for sintering Al powder without external pressure. In this study, Al powders with various oxide film thicknesses were sintered using Al-X eutectic alloy powders (X=Cu, Ca, and Mg) to clarify suitable alloy elements in the sintering aids for the liquid phase sintering. When an as-supplied Al powder with an oxide film thickness of approximately 2 nm (presumably amorphous Al<inf>2</inf>O<inf>3</inf> film) was used, Al-Cu and Al-Ca aids promoted the densification, whereas numerous pores were observed in the sample sintered using Al-Mg aid. The pores would be formed during the cooling after sintering, along with the homogenization of Mg distribution. When Al powder with an oxide film thickness of around 4 nm was used, a high relative density of over 95% was maintained using Al-Cu aid, whereas the relative density of the sample sintered using Al-Ca aid significantly degraded, presumably due to the formation of Ca-based oxide. These results indicate that the Al-Cu eutectic alloy powder is a promising sintering aid for the liquid phase sintering of Al powder.

DOI： 10.3390/ma18081755

Inhomogeneous α-Al/Mg2Si two-phase microstructures with chemical fluctuation produced by laser-beam powder bed fusion 査読有り国際誌 Open Access

Otani Y., Takata N., Suzuki A., Kobashi M., Umeda J.

Materials and Design 252 巻 2025年4月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials and Design

This study investigated the additive manufacturing of high-strength Al–Mg–Si ternary alloy with refined α-Al/Mg<inf>2</inf>Si two-phase microstructures by laser-beam powder bed fusion (PBF-LB). Although PBF-LB processing produced crack-free samples with high relative densities (>99.5 %), the scanning laser irradiation caused significant Mg vaporization, reducing the Mg content of the sample from 11.3 to 7.6 %. Laser-induced vaporization caused micron-scale chemical fluctuations in the melt-pool structure, resulting in the development of inhomogeneous microstructures. Refined cellular microstructures with many columnar α-Al phases surrounded by numerous Mg<inf>2</inf>Si nano-particles were observed in most parts of the melt-pool structure, corresponding to hypo-eutectic compositions in the Al–Mg–Si ternary system. However, primary solidified Mg<inf>2</inf>Si phases were observed in some parts of the melt-pool boundaries with local Mg-rich compositions (hyper-eutectic compositions). The PBF-LB manufactured alloy specimens with a total composition of Al–7.6Mg–5.4Si (wt%) exhibited a high tensile strength, which reduced significantly with increasing testing temperature, and low ductility (529 MPa and < 2 %, respectively) at room temperature. Moreover, the specimens underwent mechanical deterioration at elevated temperatures, owing to a significant coarsening of metastable microstructural factors (nanoscale Mg<inf>2</inf>Si precipitates or their related metastable phases and atomistic clusters) that contribute towards the high room-temperature strength.

DOI： 10.1016/j.matdes.2025.113787

Capillary Performance of Bi-porous Al Fabricated Using Space Holders with Different Sizes 査読有り Open Access

Shen H., Suzuki A., Takata N., Kobashi M.

Funtai Oyobi Fummatsu Yakin Journal of the Japan Society of Powder and Powder Metallurgy 72 巻頁： S1629 - S1633 2025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：Funtai Oyobi Fummatsu Yakin Journal of the Japan Society of Powder and Powder Metallurgy

Capillary pressure (∆Pcap) and fluid permeability (K) of porous media are important for heat transfer devices including loop heat pipes. In general, smaller pore sizes enhance capillary pressure but decrease permeability. To solve this trade-off relationship, introducing bi-modal pore size distributions is promising. In the present study, the capillary performance of bi-porous Al fabricated using NaCl space holder particles with two different sizes (approximately 400 μm and 40 μm) was evaluated and compared with that of mono-porous Al. Increasing the porosity (from 60% to 80%) of mono-porous Al with large pores around 400 μm enhanced the permeability but decreased the capillary pressure. By contrast, increasing the fraction (from 0% to 20%) of small pores (around 40 μm) led to the enhancement of both permeability and capillary pressure in bi-porous Al with a constant large-pore fraction of 60%.

DOI： 10.2497/jjspm.17C-T4-04

Pressure-less Mg Melt Infiltration into Ti Powder Preform with Various Flow Channel Structures toward the Application to Binder Jetting Additive Manufacturing 査読有り Open Access

Li Z., Suzuki A., Takata N., Kobashi M.

Funtai Oyobi Fummatsu Yakin Journal of the Japan Society of Powder and Powder Metallurgy 72 巻頁： S389 - S393 2025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：Funtai Oyobi Fummatsu Yakin Journal of the Japan Society of Powder and Powder Metallurgy

Binder jetting (BJT), an additive manufacturing process, injects a binder into the powder bed to build up the green body. The green body undergoes sintering to obtain a dense product. However, the shrinkage during sintering makes it difficult to achieve a high dimensional accuracy. Pressure-less melt infiltration (PMI) is an alternative process that fills the pores of a preform with a metal melt spontaneously infiltrating by the capillary force. It becomes important to clarify how molten metal infiltrates and how defects form. This study investigates the mechanism of defect forming inside PMIed Mg/Ti composites by controlling the structure of Ti powder preforms. Different-sized (20-2300 μm) Ti powders were pressed under various pressures (76-153 MPa) to fabricate preforms with various structures. It was found that gravity and gas pressure were key resistant forces for the capillary infiltration.

DOI： 10.2497/jjspm.15A-T7-09

AM技術が創出する非平衡組織・準安定相の制御に基づくアルミニウム合金の設計招待有り査読有り

高田尚記

AMフューチャー 1 巻頁： 65 - 68 2025年2月

Comparative study of thermodynamic calculations with solidification microstructures of Al-Si-Fe and Al-Si-Mn ternary eutectic alloys 査読有り Open Access

Kita S., Takata N., Suzuki A., Kobashi M., Furukawa Y., Tomita T.

Keikinzoku Journal of Japan Institute of Light Metals 75 巻 ( 4 ) 頁： 190 - 198 2025年

担当区分：責任著者記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Keikinzoku Journal of Japan Institute of Light Metals

This study systematically investigated the solidification microstructures of Al-Si-Fe and Al-Si-Mn ternary alloys solidified at various cooling rates ranging from 0.3 to 145°C・s<sup>-1</sup>. The thermodynamic calculations assessed three alloy compositions of Al-5%Si-1.5%Fe, Al-8%Si-1%Fe, and Al-5%Si-1.5%Mn exhibiting two-phase eutectic reactions of α-Al and intermetallics (β-Al<inf>5</inf>FeSi, α<inf>h</inf>-Al<inf>7</inf>Fe<inf>2</inf>Si or α<inf>c</inf>-Al<inf>15</inf>Mn<inf>3</inf>Si<inf>2</inf>) phases in solidification. The needle-shaped β phase was formed in the Al-Si-Fe ternary alloy. The microstructural characterizations revealed that the α<inf>c</inf> phase (rather than α<inf>h</inf> phase) and Si phase were dominantly formed in eutectic reactions. The α<inf>c</inf> phase with Chinese-script morphology was formed in the Al-5%Si-1.5%Mn ternary alloy. The dendritic α-Al phase was dominantly formed as the primary solidified phase, and the intermetallic phases were subsequently solidified at lower temperatures, which was independent of the cooling rate in solidification. The observed microstructures can provide insights into the solidification sequences, which were consistent with exothermal reactions detected by differential scanning calorimetry measurements at controlled cooling rates in solidification. The solidification sequence may not follow the calculated liquidus projections and its associated Scheil solidification simulations. The difference between experiments and calculations would be associated with the thermodynamic stability of the constitute phases below the solidus temperatures of Al-Si-Fe and Al-Si-Mn ternary systems.

DOI： 10.2464/jilm.75.190

Anomalous temperature-dependent strength of copper alloy manufactured by laser-beam powder bed fusion 査読有り国際誌 Open Access

Kim D., Takata N., Umeda J., Shimizu T., Kobashi M.

Additive Manufacturing Letters 11 巻 2024年12月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Additive Manufacturing Letters

This study reports an anomalous temperature-dependent tensile behavior of laser-beam powder bed fusion (PBF-LB) processed Cu–Cr–Zr alloy. The yield strength of the alloy initially decreases as the temperature increases to 200±5 MPa and then increases to 350±11 MPa at 500°C before reducing to 234±6 MPa at 600°C. The microstructure consists of elongated Cu grains with a high concentration of Cr solute (∼1 mass%), resulting from rapid solidification during the PBF-LB process. Transmission electron microscopy for the specimens deformed at 500°C revealed the presence of numerous nanoscale Cr-rich particles embedded inside the supersaturated solid solution of the Cu matrix. Nanoscale particles can act as barriers to dislocation motion, leading to an increase in internal stress during plastic deformation at elevated temperatures. This work provides the high potential of post heat treatments for achieving superior mechanical performance using high solute supersaturation formed by the PBF-LB process.

DOI： 10.1016/j.addlet.2024.100236

Fe/polymer joining via Fe/TiB2 composite structures via in-situ laser-induced reaction of Fe-Ti-B system: Effect of powder composition 査読有り国際誌 Open Access

Zhou S., Omiya K., Ueda Y., Suzuki A., Takata N., Kobashi M.

Journal of Advanced Joining Processes 10 巻 2024年11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：Journal of Advanced Joining Processes

Achieving strong direct joining between steel and polymers through mechanical interlocking is crucial for developing multi-material structures, particularly in the automotive and aerospace industries. This study synthesized micro-scale structures on a pure Fe substrate (simulating interstitial-free (IF) steel) for mechanical interlocking with thermoplastic parts. Numerous submillimeter-scale Fe/TiB<inf>2</inf> composite particles were in-situ synthesized by laser scanning on the Fe-Ti-B powder mixture and well-bonded with the Fe substrate. The effects of powder composition (TiB<inf>2</inf> volume fraction) on the morphology, microstructure, and joint strength with PA6 were investigated. A TiB<inf>2</inf> volume fraction over 60 % was essential for the formation of the composite particles promoted by a TiB<inf>2</inf> skeletal structure. Higher TiB<inf>2</inf> volume fractions increased the area fraction of the composite particles and decreased the bonding ratio (adhesive) of the particles with the substrate due to poor adhesiveness at the edge of the laser-scanning line. A wider high-temperature region was generated at a higher TiB<inf>2</inf> volume fraction, suggesting that the reaction heat to form TiB<inf>2</inf> assisted the bonding of the particles with the substrate at the edge of the laser scanning line. The Fe/PA6 joint strength increased to approximately 30 MPa with increasing the TiB<inf>2</inf> volume fraction to 100 % and showed a linear correlation with the product of particle area fraction and bonding ratio. A higher TiB<inf>2</inf> volume fraction was preferable for enhancing the joint strength via the micro-scale structures synthesized by laser scanning on the Fe-Ti-B powder mixture. A combination of the micro-structuring process using a high fraction of TiB<inf>2</inf> with advanced joining technologies will contribute to manufacturing high-strength Fe/polymer hybrid parts.

DOI： 10.1016/j.jajp.2024.100249

Pressure-less melt infiltration characteristics of Mg melt into Ti powder preforms with various pore structures: Toward the application to the binder jetting additive manufacturing 査読有り国際誌 Open Access

Li Z., Suzuki A., Takata N., Kobashi M.

Journal of Materials Processing Technology 331 巻 2024年10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：Journal of Materials Processing Technology

Binder jetting (BJT) additive manufacturing enables the fabrication of complex-shaped metallic parts but requires sintering as post-processing to obtain dense parts. The sintering inevitably causes the shrinkage from green body to dense products, resulting in low dimensional accuracy. In contrast, pressure-less melt infiltration (PMI) fills pores in the green body with a liquid metal driven by capillary pressure and fabricates a dense metal matrix composite without severe shrinkage. To consider the applicability of pressure-less melt infiltration to the post-processing of binder jetting additive manufacturing, it is required to clarify the relationship between pressure-less melt infiltration process conditions and the relative density of the composites. In this study, the liquid Mg/solid Ti system was selected because of good wettability and absence of Mg-Ti intermetallic, and the conditions of Ti powder preforms (corresponding to the green body) were focused on. Ti powder preforms with various powder sizes (2300, 410, 140, and 20 μm) and different shapes (irregular and spherical) were cold-pressed at 76, 102, 127, 153, and 178 MPa to fabricate preforms with various relative densities, pore sizes, and pore morphologies to response the similar characteristics in BJT preforms. Mg melt infiltrated into the preforms under constant conditions to fabricate Mg/Ti composites. The structures of the preforms and composites were characterized by sample size measurement, optical and scanning electron microscopy, and X-ray computed tomography. It was revealed that the relative density of the composite increased with decreasing Ti powder size and using spherical Ti powder, whereas the compact pressure exhibited a slight effect. Furthermore, defect volume increased with increasing infiltration height but decreased around the top surface of the sample. Minute observations around defects in the composites revealed that defects were formed at larger pores, and Mg melt was infiltrated into pores above the defects. These results indicated that infiltration velocity varied depending on the flow channel structure, and gas was trapped at larger pores (far from the outside of the sample) where infiltration velocity was low. Using smaller Ti powder decreased the variation in pore size in the preform, resulting in improving the relative density of the composites by suppressing the gas trapping. This study provides a new insight into the pressure-less melt infiltration process as a post-processing of binder jetting additive manufacturing.

DOI： 10.1016/j.jmatprotec.2024.118509

Achieving exceptional strain-hardening ability in nanocrystalline Ni–W coatings through compositionally modulated multilayer approach 査読有り国際共著国際誌

Padmaganesan H.T., Lavakumar B., Choshi A., Takata N., Wasekar N.P., Prasad M.J.N.V.

Materials Science and Engineering A 912 巻 2024年10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：Materials Science and Engineering A

Nanocrystalline Ni–W coatings show exceptional strength; however, they exhibit poor toughness due to limited ductility and high residual stresses which impede their use in practical applications as a potential hard chrome replacement. In the present study, compositionally modulated multilayer (CMM) coatings with alternate layers of Ni-1 at% W (soft) and Ni-15 at% W (hard) of three different layer thicknesses of 1, 0.5, and 0.1 μm are developed by pulse reverse electrodeposition to achieve the strength-ductility synergy, thereby enhanced wear resistance. Microcompression test results reveal that all the CMM coatings exhibit remarkably higher strain-hardening ability than the homogenous coatings. Significant fluctuations in the strain-hardening rate and a positive shift in the onset stress for the work-hardening stages were observed with the layer thickness. This suggests a strong interplay between the hard and soft layers on the deformation characteristics of multilayer coatings. Detailed electron microscopy of the cross-section of the deformed micropillars shows substantial evidence of co-deformation of both layers. A mechanism is proposed to explain the enhanced strain-hardening in multilayers involving the strength incompatibility arising in the layers leading to lateral constraints, resulting in strain gradient plasticity, stabilizing of local shear by the soft layers, and the barrier effect of the interfaces.

DOI： 10.1016/j.msea.2024.146971

Enhancing Capillary Pressure of Porous Aluminum Wicks by Controlling Bi-Porous Structure Using Different-Sized NaCl Space Holders 査読有り国際誌

Shen H., Suzuki A., Takata N., Kobashi M.

Materials 17 巻 ( 19 ) 2024年10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：Materials

Capillary pressure and permeability of porous media are important for heat transfer devices, including loop heat pipes. In general, smaller pore sizes enhance capillary pressure but decrease permeability. Introducing a bi-porous structure is promising for solving this trade-off relation. In this study, the bi-porous aluminum was fabricated by the space holder method using two different-sized NaCl particles (approximately 400 and 40 μm). The capillary pressure and permeability of the bi-porous Al were evaluated and compared with those of mono-porous Al fabricated by the space holder method. Increasing the porosity of the mono-porous Al improved the permeability but reduced the capillary pressure because of better-connected pores and increased effective pore size. The fraction of large and small pores in the bi-porous Al was successfully controlled under a constant porosity of 70%. The capillary pressure of the bi-porous Al with 40% large and 30% small pores was higher than the mono-porous Al with 70% porosity without sacrificing the permeability. However, the bi-porous Al with other fractions of large and small pores did not exhibit properties superior to the mono-porous Al. Thus, accurately controlling the fractions of large and small pores is required to enhance the capillary performance by introducing the bi-porous structure.

DOI： 10.3390/ma17194729

Design of Al-Fe based alloys strengthened by Al6Fe metastable phase formed in laser powder bed fusion 査読有り

N. Takata, W. Wang, Y. Cheng, T. Miyawaki, A. Suzuki, M. Kobashi, M. Kato

Proceedings of the 44th Risø International Symposium on Materials Science 頁： 369 - 374 2024年9月

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