Structural metallic materials used in hydrogen gas or corrosive environments may suffer from loss of ductility owing to hydrogen atoms (hydrogen embrittlement). To design hydrogen-resistant metallic materials, it is crucial to elucidate the mechanism of hydrogen entry and diffusion. However, visualization of corrosion-induced hydrogen entry and microstructure-dependent hydrogen diffusion requires a highly sensitive hydrogen detection technique with high spatial and temporal resolutions. Hydrogen visualization techniques using polyaniline (PANI), which is a hydrogenochromic sensor, have recently been developed. The PANI layer reacts with atomic state hydrogen in a metal, changing its color from blue to yellow. Thus, the hydrogen distribution in the metal can be analyzed by observing the color distribution of the PANI layer using a digital camera. Owing to the high sensitivity and spatial resolution of hydrogenochromic sensors, corrosion-induced hydrogen entry and microstructure-dependent hydrogen diffusion have been successfully visualized in real time. In this paper, the principles of the sensor and representative application examples are introduced.

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In this study, we developed a method for reproducibly fabricating high-performance nano-grained bulk Si-Ge thermoelectric materials free from severe oxidization. In our previous work, the oxidization of Si-Ge during mechanical alloying and sintering processes had led to poor reproducibility of the value of electrical resistivity. We found that co-sintering with Ti, which is more easily oxidized than Si and Ge near the sintering temperature, effectively reduces the oxygen concentration in the nano-grained bulk Si-Ge samples. The oxygen concentration in the sample co-sintered with Ti was found to be less than 2.4 at%, and electrical resistivity was found to be less than 3.9 mΩ cm at 922 K with good reproducibility. High Seebeck coefficient (more than 400 µV K⁻¹) and low thermal conductivity (less than 1 Wm⁻¹K⁻¹) were simultaneously achieved by constructive electronic structure modification via iron doping and nano-crystallization, respectively. As a consequence, we succeeded in obtaining a surprisingly large value of dimensionless figure of merit, ZT = 4 at 922 K, and the temperature range of ZT exceeding 1 extended at high temperatures above 700 K.

 

This Paper was Originally Published in Japanese in J. Thermoelec. Soc. Jpn. 21 (2025) 141–146.

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We studied the suppression of pitting corrosion in copper tubes used for heat transfer in cooling water systems with absorption chillers. The corrosion was caused by the relation between the carbon film on the copper tube surface and the water quality flowing through the tube. Phosphonic acid and benzotriazole (BTA) were used as water treatment chemicals to suppress pitting corrosion. Silicate and calcium ions are effective for corrosion resistance of copper in the presence of phosphonic acid and BTA. In addition, we also studied the effects of chloride ions, known to have a corrosive effect, on copper pitting corrosion. In this study, hydrogen carbonate ions were added to these factors including phosphonic acid, BTA, silicate ions, calcium ions, and chloride ions, and the effects of hydrogen carbonate ions on copper pitting corrosion were investigated. As the hydrogen carbonate ion concentration increased, the number of sites of pitting corrosion decreased, and the potential decreased in the immersion test. Anode polarization curve measurements showed a tendency toward a parallel shift toward the cathode side. These results suggested that increasing hydrogen carbonate ion concentration resulted in greater inhibition of corrosion.

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Based on electronic structure calculations and the strategic selection of commonly available transition metal elements, this study proposes Co-Ni-Al shape memory alloys (SMAs) with transformation temperatures exceeding 373 K, guided by two electronic parameters derived from fundamental electronic concepts. Nine Co-Ni-Al alloys with γ+β dual-phase structures were synthesized via cold crucible levitation melting: Co-40Ni-18Al, Co-23Ni-18Al, Co-6Ni-18Al, Co-40Ni-23Al, Co-23Ni-23Al, Co-6Ni-23Al, Co-40Ni-28Al, Co-23Ni-28Al and Co-6Ni-28Al. They showed γ+β dual phase and volume fraction of each phase could be evaluated by two electronic parameters bond order and d-orbital. Alloys exhibiting both high shape recovery rates and high phase transformation temperatures were concentrated within specific regions of the Bo–Md diagram. Furthermore, manganese (Mn) was selected as a fourth element taking into consideration the effect on the enhancement of the mechanical properties and phase transition temperature. The Co-29Ni-27Al-3Mn alloy emerged as a promising quaternary alloy, demonstrating excellent shape memory behavior characterized by high recovery strain and transformation temperatures. The promising alloy showed an excellent shape memory behavior. This provides a theoretical basis for composition optimization and enhancement of shape memory properties in Co-Ni-Al alloys.

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The strength, deformation, and hydraulic properties of geomaterials, which constitute embankments, vary with fine fraction content. Therefore, numerous research studies have been conducted regarding the effects of fine fraction content on the engineering properties of geomaterials. However, there have only been a few studies in which the effects of fine fraction content on the soil skeletal structure have been quantitatively evaluated and related to compaction and mechanical properties. In this study, mechanical tests were conducted on geomaterials with various fine fraction contents to evaluate their compaction and mechanical properties focusing on the soil skeletal structure and void distribution. Furthermore, an internal structural analysis of specimens using X-ray computed tomography (CT) images was conducted to interpret the results of mechanical tests. As a result, it was discovered that the uniaxial compressive strength increased with fine fraction content, and the maximum uniaxial compressive strength was observed at a low water content, not at the optimum water content. Additionally, the obtained CT images revealed that large voids, which could serve as weak points for maintaining strength, decreased in volume, and small voids were evenly distributed within the specimens, resulting in a more stable soil skeletal structure.

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The corrosion behavior of the inner surface of commercially available pineapple cans (unlacquered tinplate cans) were investigated using accelerated pack test and electrochemical measurements. In the accelerated pack test, the tin concentration in the contents increased over time. The increase was greater as the tin-iron alloy layer became exposed, and the internal pressure also increased. Electrochemical measurements showed that the corrosion potentials of tin, iron, and the tin-iron alloy layer were increasingly noble, in that order, supporting the corrosion behavior of tin in the accelerated pack test. Based on these results, it is suggested that corrosion of the inner surface of the can is represented by five stages.

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The reduction reaction and slag-metal separation behavior are important factors influencing metal recovery rates during copper slag cleaning. In this study, theoretical calculations combined with experiments were carried out to investigate the effects of temperature, reductant dosage and CaO on the recovery of Cu and Fe, while revealing the separation behavior of metal particles from slag. Theoretically, the Fe₃O₄ reduction is cascaded and prioritized over Fe₂SiO₄ reduction. Increase of temperature and reductant dosage effectively promotes the recycling of Cu and Fe, and the appropriate amount of CaO promotes the depolymerization of complex silicate structure of slag and the aggregation of metal particles. The temperature was increased from 1623 K to 1698 K, the recoveries of Cu and Fe were increased from 88.46% and 73.68% to 96.78% and 95.88%, respectively. During initial stage of copper slag cleaning, Fe₃O₄ is reduced, and metal particles aggregate and settle in the middle and lower layers. Subsequently, Fe₂SiO₄ is reduced to metallic Fe, which combines with matte to form alloy and settle to bottom slag. The optimal recovery rates for Cu and Fe are 96.78% and 95.88%, respectively. The results of this study provide a reliable reference for strengthening the slag-metal separation, recovering Cu-Fe binary liquid alloy and improving the utilization rate of copper slag in the copper slag cleaning.

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Employing the first-principles approach grounded in density functional theory, the interfacial properties of the Al (111)/HfB₂ (0001) were investigated to provide a basis for understanding the reinforcement mechanism in HfB₂ ceramic nanoparticle-strengthened aluminum alloys. Our comprehensive investigation demonstrates that among six structurally distinct Al (111)/HfB₂ (0001) interfaces, the B-terminated H stacking(H-B) interface characterized by the aluminum atoms occupying positions above the second-layer atoms of the HfB₂ substrate exhibits superior interfacial stability, as evidenced by its maximal work of adhesion (4.74 J/m²) and minimal interfacial energy (-0.54 J/m²).The disparity in charge density and partial density of states further elucidate that H-B interface display pronounced covalent bonding characteristics, while the Hf-terminated H stacked (H-Hf) interface is dominated by metallic interactions. The exceptional stability of the H-B interface promotes coherent epitaxial growth of α-Al on the HfB₂ substrate, while simultaneously inducing grain refinement in primary α-Al phases, thereby mechanical properties of metal matrix.

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The present study examines the influence of sputtering power from 90 W to 110 W on the structural, morphological, optical, electrical, and thermoelectric characteristics of Indium-doped ZnO thin films that are produced on glass substrates via radio frequency-magnetron reactive sputtering. The In-doped ZnO thin films show a highly oriented hexagonal wurtzite structure with preferential development along the (002) plane after being doped with 2 at.% In. The surface morphology of In-doped ZnO thin films becomes rougher with increased sputtering power, which correlates with improved crystallinity. UV-Vis spectroscopy demonstrates a high average transmittance (> 80%) within the visible spectrum and a variable optical band gap ranging from 3.38 to 3.44 eV. Hall measurements indicate increased carrier concentrations (>10²¹ cm⁻³), enhanced electron mobility (up to 6.22 cm²/V·s), and minimal resistance (~10⁻⁴ Ω·cm). The Seebeck coefficient of In-doped ZnO thin films increases with sputtering power, achieving 48.04 µV/K, while the power factor maximizes at 261.07 µW·m⁻¹·K⁻². These findings highlight the potential of In-doped ZnO thin films for application in transparent electronics and thermoelectric devices.

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The ten best papers for young scientists were awarded by The Japan Institute of Light Metals (JILM) and The Japan Institute of Metals and Materials (JIMM) in Materials Transactions. Here, the awarded papers are briefly summarized as current trends in research of Materials Transactions. Among the ten best papers, six were from JILM for young scientists whose ages are 30 or below and four from JIMM for those with ages of 35 or below. A total of six best papers were originally published in Japanese in Journal of the Japan Institute of Light Metals and Journal of The Japan Institute of Metals and Materials as cutting-edge research in JILM and JIMM. In association with all the awarded papers, special issues edited in Materials Transactions are also briefly introduced to show the recent activities of Materials Transactions.

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The √area parameter model is widely used for predicting the fatigue limit of materials containing small defects based on the assumption that a small defect can be regarded as a crack. Although the model was successfully applied to various materials, its applicability to high-strength steel requires further validation. In this study, the fatigue limit was evaluated using specimens of vacuum-quenched and tempered martensitic steel in which a drill hole, an electric discharge machined (EDM) notch, and a pre-crack were introduced. The fatigue limit of the specimen with the pre-crack was consistent with the prediction of the √area parameter model, whereas the specimens with the drilled hole and EDM notch exhibited higher fatigue limits, indicating that these defects could not be regarded as cracks in the fatigue limit evaluation. Fracture surface observations confirmed that the fatigue limits were determined by the crack non-propagation limit rather than the crack initiation limit. Furthermore, finite element analysis indicated that differences in defect-induced stress fields influenced the fatigue crack propagation, leading to deviations in the fatigue limits. These findings contribute to an accurate estimation of the fatigue limit of high-strength steels.

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Internal friction in magnesium alloys with a varying volume fraction of the long-period stacking-ordered (LPSO) phase was investigated using polycrystalline Mg-Zn-Y alloys with the aim of elucidating the initial dislocation dynamics. The phase composition and microstructure were characterised via electron microscopy and X-ray diffraction. Results show that Young’s modulus and the temperature-dependent modulus softening scale nearly proportionally with LPSO content, highlighting its strong influence on both elastic and damping properties. The most pronounced softening occurs the single-phase fully LPSO alloys, likely due to their intrinsic characteristics and impact on mobile dislocation density. Internal friction measurements reveal that amplitude-independent damping increases with LPSO content, while the critical strain amplitude for amplitude-dependent damping decreases. Notably, the critical stress for dislocation motion is significantly lower than the characteristic CRSS for basal slip, emphasising the crucial role of thermal activation in dislocation liberation at very low applied cyclic stresses/strains.

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Electromagnetic crimping is a crimping method for applying uniform crimping force to metal parts in a shorter forming time than conventional press crimping. It is difficult to measure and determine the crimping force acting on metal parts because the crimping force affected by the magnetic field and Lorentz force induced by current in a forming coil is invisible. Additionally, current is affected by the circuit characteristics of an electromagnetic forming instrument and the shape of a forming coil. Hence, it is difficult to design a forming coil. In this study, simulation procedures were developed for designing a forming coil. First, the circuit characteristics of an electromagnetic forming instrument were identified to predict current in a forming coil accurately. Second, electromagnetic crimping was simulated by the coupled analysis of a circuit simulation to consider the effects of circuit characteristics and the finite element method to consider shape of a forming coil. Finally, a forming coil for electromagnetic crimping was designed by using the developed simulation procedures. Required current in the designed coil was determined. The shape of the crimped workpiece in the simulation was similar to an experimentally crimped sample. These results indicate that the developed simulation procedures are useful for designing the shape of a forming coil.

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High-strength joints used in timber structures are increasing to utilize the shear properties of wood. Thus, it is important to understand the long-term shear performance. Therefore, we proposed the tensile shear testing method to investigate the long-term shear performance of wood. This testing method is to apply stabilized axial load for a long-term and to be able to measure the shear deformation. In order to evaluate the method, the results were compared with results of JIS block shear test. As a result, the mean value of shear strength in the proposed method was 30% lower than the block shear test. The reason for the small results of the proposed method is that the specimen has two shear face and breaks at the weak side, and the shear face is affected by rotation due to the tensile deformation of the perpendicular to grain direction. Therefore, the coefficient of variation of 6.8% in the proposed method shows smaller than 11.1% in the block shear test. And the shear strength value of the proposed method was little bit higher than one of the four-point-bending type shear test methods, and all specimens were shown the shear failure. Based on these results, the proposed method was judged to be useful as a shear test method.

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Announcement Concerning Article Retraction
The following paper has been withdrawn from the database of Mater. Trans., because a description based on a misinterpretation of the experimental results was found by the authors in advance of publication after acceptance.
Mater.Trans. 52(2011) Advance view.
Improvement in Fatigue Strength of Biomedical β-Type Ti-Nb-Ta-Zr Alloy while Maintaining Low Young’s Modulus through Optimizing ω-Phase Precipitation

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