Publisher：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

Open Access

Web of Science

Scopus

Language：Japanese   Publisher：The Iron and Steel Institute of Japan  

<p>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 (Fe₂Al₅) 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 T₅ (Fe₂Al_7.4Si) phase was formed at the interface of solid Fe with the Al–25Zn–2Si alloy melt. The continuous T₅ 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.</p>

DOI： 10.2355/tetsutohagane.tetsu-2024-097

Open Access

Web of Science

Scopus

CiNii Research

Language：Japanese   Publisher：The Iron and Steel Institute of Japan  

<p>An attempt was made to apply the laser powder bed fusion (L-PBF) process to Fe–Ni–Nb ternary alloys as a major composition of heat-resistant Fe-based alloys strengthened by the Fe₂Nb intermetallic phase. This study focused on a composition of Fe–40Ni–15Nb (at%) near a eutectic composition of austenite (γ-Fe) and Fe₂Nb in the Fe–Ni–Nb ternary system for the pre-alloy powder with an average particle size of approximately 17 μm, which was produced by the gas-atomizing process. The Fe–40Ni–15Nb pre-alloy powder exhibited insufficient L-PBF processability for fabricating fully dense centimeter-sized samples, whereas several alloy samples with relative densities above 90 % were manufactured. The L-PBF manufactured alloy samples exhibited a representative melt-pool structure in which regions had locally melted and rapidly solidified by scanning laser irradiation in the L-PBF process. The L-PBF sample exhibited a high hardness of approximately 900 HV compared to the slowly solidified alloy sample (about 550 HV). The high hardness could be attributed to the formation of nanoscale γ-Fe/Fe₂Nb eutectic microstructure by the L-PBF process. Intriguingly, the observed melt-pool boundary had several tens of micrometers in width, which significantly varied depending on the applied laser condition. Nanoindentation tests demonstrated the melt-pool boundary region exhibited a relatively lower hardness than inside the melt pools. It was assumed that the unique melt-pool boundary region would consist of a relatively coarsened solidification microstructure formed at the interface of liquid with the solid and a locally coarsened microstructure affected by laser local heating, which can be controlled by manipulating the laser conditions.</p>

DOI： 10.2355/tetsutohagane.tetsu-2025-077

Open Access

CiNii Research

Publisher：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

Open Access

Web of Science

Scopus

Publisher：Corrosion Science  

Four-dimensional (4D) electrochemical impedance spectroscopy was applied to clarify the role of microstructures on the corrosion behaviour of Al-Si alloys additively manufactured by laser powder bed fusion in the immersion of NaCl solution. 3D complex impedance plots, comprising real, imaginary, and time axes, indicate that the impedance increases gradually at initial stage and then does not show apparent time variation. These behaviours, following surface morphology analysis, are strongly related to the remaining fine silicon particles on the surface due to the preferential Al dissolution, which suppress the further dissolution from underlying along with the protective oxide film formation.

DOI： 10.1016/j.corsci.2024.112018

Open Access

Web of Science

Scopus

Publisher：Applied Physics Letters  

High-entropy alloys (HEAs) are a class of materials known for their unique properties, including high strength, excellent wear resistance, and good corrosion resistance. Sub-micron- and nanosized HEA particles were fabricated via pulsed laser ablation in liquid using a Cantor alloy target. The Cr<inf>20</inf>Mn<inf>20</inf>Fe<inf>20</inf>Co<inf>20</inf>Ni<inf>20</inf> target was immersed in pure water and ablated using a focused nanosecond-pulsed Nd: YAG laser. A dark solution containing HEA particles was obtained which was stable for about one week before agglomeration and precipitation was observed. The diameters of the obtained particles ranged from several tens of nanometers to several hundred nanometers. Increasing the laser power resulted in higher particle concentration and an increase in the intensity of UV-vis absorption spectra. Electron diffraction was used to confirm that the composition of the particles was close to that of the Cantor alloy, although the concentrations of Cr and Mn were slightly deficient. There was also a weak dependence of the composition on laser power, and all the particles also contained oxygen. Selected area electron diffraction revealed that the composition varied spatially within some particles and that they are mainly polycrystalline. This work shows that HEA particles can be quickly, safely, and effectively manufactured using liquid-based laser ablation, opening the pathway for mass manufacture and disruptive applications in, e.g., catalysis or tribology.

DOI： 10.1063/5.0200341

Web of Science

Scopus

Publisher：Materials Science and Engineering A  

This study identifies the role of solute Cr in the thermal activation process in the plastic deformation of α-(Fe, Cr) ferrite (BCC solid solutions) using micropillar compression tests for micron-sized single-crystals fabricated on various Fe–Cr binary alloys that were solution-treated at 1573 K. Fe–18%Cr single-crystal micropillars with a mean diameter d of ∼2 μm exhibited a relatively higher strain rate sensitivity (m) of 0.12 for the stress required for slip initiation. Larger Fe–18%Cr micropillars (d = 5 μm) exhibited a lower m value of 0.04. The corresponding activation volume of 50 b³ was equivalent to the millimeter-sized pure Fe and Fe–18%Cr alloy specimens (60–70 b³), indicating the prevalence of a general mechanism involving dislocation motion (kink-pair nucleation of screw dislocations). This mechanism controls the thermal activation process of plastic deformation in the Fe–18%Cr alloy, which has sufficient sources for dislocation multiplication. In the Fe–25%Cr and Fe–40%Cr single crystal micropillars, a less pronounced size-dependent m value (0.01–0.03) was determined, almost independent of specimen size. The corresponding activation volumes of large micropillars (74–77 b³) were similar to those of millimeter-sized specimens, which indicates a mild effect of solute Cr atoms on the thermal activation process of dislocation motion in Fe–Cr binary alloys at ambient temperature. Initial dislocations, rather than Cr content in Fe–Cr binary alloys, led to the low changes in size-dependent activation volume of Fe–Cr alloys with higher Cr content. Planar faults (Cr-enriched regions) were observed in Fe–40%Cr alloys, which may become sufficient sources for dislocation nucleation. However, the influence of Cr-enriched regions on dislocation motion remains unclear.

DOI： 10.1016/j.msea.2024.146499

Open Access

Web of Science

Scopus

Publisher：Corrosion Science and Technology  

An attempt was made to apply digital image correlation (DIC) strain analysis to in-situ scanning electron microscopy (SEM) observations of bending deformation to quantify local strain distribution inside a ZnMgAl-alloy coating in deformation. Interstitial-free steel sheets were hot-dipped in a Zn-3Mg-6Al (mass%) alloy melt at 400 ^oC for 2 s. The specimens were deformed using a miniature-sized 4-point bending test machine inside the SEM chamber. The observed in situ SEM images were used for DIC strain analysis. The hot-dip ZnMgAl-alloy coating exhibited a solidification microstructure composed of a three-phase eutectic of fine Al (fcc), Zn (hcp), and Zn<inf>2</inf>Mg phases surrounding the primary solidified Al phases. The relatively coarsened Zn<inf>2</inf>Mg phases were locally observed inside the ZnMgAl-alloy coating. The DIC strain analysis revealed that the strain was localized in the primary solidified Al phases and fine eutectic microstructure around the Zn<inf>2</inf>Mg phase. The results indicated high deformability of the multi-phase microstructure of the ZnMgAl-alloy coating.

DOI： 10.14773/cst.2024.23.2.113

Open Access

Web of Science

Scopus

Publisher：Journal of Alloys and Compounds  

Al-12mass%Si binary alloy was fabricated by laser-powder bed fusion (L-PBF). The effect of low temperature annealing (LTA) less than 573 K on electrical and mechanical properties, microstructure, and residual stress of L-PBF Al-12mass%Si was investigated. Due to LTA, electrical resistivity at 77 K and 293 K changed from 34 nΩm down to 10 nΩm and from 68 nΩm down to 45 nΩm, respectively. The lattice constant of α-Al phase increased around 0.0005 nm by LTA according to X-ray diffraction. The change was associated with the decrease in the concentration of solid-solution Si of around 3.4 mass% by electrical resistivity measurement and 3 mass% by X-ray diffraction, when the annealing temperature was 473 K. Whereas, Vickers hardness increases around 145 HV compared with that for the as-built value of 141 HV, and then, decreases down to 126 HV and saturates. TEM/EDS observations confirmed the precipitation of fine Si within the α-Al phase. The decrease in annealing temperature increases the time to reach the Vickers hardness peak. 0.2% proof stress obtained by compression tests shows anisotropy, which can be attributed to the anisotropy on residual stress, which still exists after LTA.

DOI： 10.1016/j.jallcom.2024.173737

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

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

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

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

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

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

Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (scientific journal)  

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

Authorship：Lead author  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publisher：Kwangjae Park, Dasom Kim, Jehong Park, Seungchan Cho, Miyazaki Takamichi, Hansang Kwon  

DOI： https://doi.org/10.1002/adem.201800312

Event date： 2022.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Toyama, Japan   Country：Korea, Republic of  

Event date： 2021.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Online  

Event date： 2018.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Changwon, Korea   Country：Korea, Republic of