Nanocrystalline Ni₈₅W₁₅ alloys were computationally modeled as solid solutions with face-centered cubic (fcc) structures, incorporating random crystallographic orientations. Each alloy was enclosed within one of three hypothetical, space-filling polyhedral containers (crystallites): cubic (CB), truncated octahedron (TO), and rhombic dodecahedron (RD), in conjunction with a single-crystal (SC) configuration for comparison. The alloys were represented by 60 × 60 × 60 supercells containing 8.64 × 10⁵ atoms to model the initial Ni₈₅W₁₅ configurations. These initial alloys were equilibrated at 300 K for 10 ps via molecular dynamics (MD) simulations utilizing a large-scale atomic/molecular massive parallel simulator (LAMMPS). Computational X-ray diffraction confirmed the formation of nanocrystalline structures in the CB, TO, and RD alloys. Subsequently, the equilibrated alloys were subjected to mechanical testing at 300 K for 30 ps (engineering strain, ε, in the range of 0–0.3 principally) with varying engineering strain rate (ε̇) of 10⁻²/ps (10¹⁰/s) for the 60 × 60 × 60 supercells, 10⁻² and 10⁻³/ps (10¹⁰ and 10⁹/s) for the 40 × 40 × 40 supercells, and 10⁻², 10⁻³, and 10⁻⁴/ps (10¹⁰, 10⁹, and 10⁸/s) for the 20 × 20 × 20 supercells. At ε̇ and 10⁻³/ps, fractures were observed at the interfaces, where their normal vectors aligned with the tensile direction. Examples of fractures include alloys with a 40 × 40 × 40 supercell elongated along the z axis for the CB-type, diagonal of x, y, and z axes for the TO-type, and a 60 × 60 × 60 supercell along the diagonal of −x and y axes for the RD-type. The results demonstrated that morphological inhomogeneity owing to the presence of interfaces between crystallites can lead to fracture when subjected to a relatively high strain rates (ε̇ and 10⁻³/ps) in tensile MD simulations.

Due to the complex and nonlinear correlations between microstructures and mechanical properties in dual phase alloys, it is difficult to estimate their strength by conventional methods. This study attempts to model the relationship between microstructure and mechanical properties in sintered and hot-rolled α + β titanium-iron (Ti-Fe) alloys using machine learning. In the preparation of the models, 4–9 microstructural factors were investigated to identify the most important predictors of mechanical properties. A Random Forest (RF) model was found to have best predictive power, producing a good match with experimental data in samples which were outside of the training dataset. Moreover, the average α grain diameters, β phase widths (by intercept method), and β phase area fractions were found to be the strongest predictors of mechanical behavior.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 72 (2025) 73–78. Reference [8] has been corrected.

Reliable fracture simulations are expected to contribute to the longer life cycle of structures. The phase-field fracture (PFF) model is anticipated to be a robust approach to reproducing crack propagation and branching. Measurement techniques for detecting cracks and fractures have also advanced and are widely used for health monitoring. In the field of structural analysis, a data assimilation method using the full-field measurement data obtained by digital image correlation has been proposed. The data assimilation method is attracting attention as a method of improving the simulation accuracy by utilizing the time-series measurement data obtained from such measurement techniques. In this study, we apply for the first time the nonsequential data assimilation method minimizing the cost function using tree-structured Parzen estimator (DMC-TPE method) to assimilate full-field strain measurement data into PFF simulations. In this paper we validate the proposed data assimilation method through numerical experiments, where data assimilation is performed using the pseudo-measurement data obtained from PFF simulations conducted with parameters assumed as true values. The results demonstrate that the proposed method enables the simultaneous inverse estimation of multiple parameters included in the PFF model. The validation results revealed that, although the DMC-TPE depends on the initially estimated values, the parameters that significantly impact the simulation results were accurately estimated.

This Paper was Originally Published in Japanese in J. JSTP 66 (2025) 91–99.

ASTM grade 1 titanium sheets with the strong TD-split type basal texture and grain sizes ranging from 9 to 152 µm were subjected to tensile tests at tensile speeds ranging from 0.1 to 100 mm/min to investigate the strain rate dependency, while considering anisotropy. The yield and flow stresses at each strain level increased proportionally with the logarithm of the strain rate. The slope of these proportionalities, namely, the strain rate sensitivity index of m decreased with increasing grain size and tensile angle to rolling direction, θ. However, in the high-strain region, the larger the grain size, the higher the index m. Meanwhile, uniform elongation decreased with an increase in strain rate except for a θ value of 90°, where uniform elongation was roughly constant. However, the highest uniform elongation was observed in relatively larger grain-sized specimens when θ changed from 0° to 45°. There was an average reduction in local elongation with increasing strain rate and grain size; however, an inversed trend was observed with increasing grain size in specimens with a grain size of 9–36 µm when θ was 45°.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 89 (2025) 132–141.

In terms of safety and environmental impact, trivalent chromium plating is a potential surface treatment which alternates conventional hexavalent chromium plating. In order to improve the tribological properties, including friction characteristics, of the coating from trivalent baths, the authors attempted to incorporate silicon carbide (SiC) fine particles in the coating. Composite coating incorporating SiC particle deposited on a mild steel rod substrate successfully reduced the friction coefficient against alumina rod even while no significant increase in film hardness was achieved by particle incorporation. The effect of the coating hardness on the reduction in friction coefficient was limited. It was supposed that a possible reason for friction reduction was attributed to the reduction in the contact area by the incorporated particles. Coating surface texture modified by incorporating SiC particle should have contributed to the reduced friction because the texture allowed to bury wear debris and SiC particles detached from the film. Such a feature was supposed to promote reduced shear resistance as well as eliminate three-body abrasive wear.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 73 (2024) 853–860. The figure and caption of Fig. 6 are slightly modified.

In this study, the mechanism of pH decrease in an electrolytic solution containing ammonium thiocyanate (NH₄SCN) during electrolytic hydrogen charging was elucidated. The pH of an electrolytic solution containing NH₄SCN decreases during hydrogen charging, which is caused by the formation of sulfate ions from the oxidative decomposition reaction of thiocyanate ions (SCN⁻) on a Ti-Pt anode. The suppression of pH decrease using a cation-exchange-resin-coated IrO₂ electrode, which has a lower probability of decomposing NH₄SCN than a Ti-Pt anode, was investigated to develop a method for controlling the pH decrease in an electrolytic solution containing NH₄SCN during electrolytic hydrogen charging. Specifically, the use of a cation-exchange-resin-coated IrO₂ electrode suppresses the decrease in the pH of the electrolytic solution.

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 74 (2025) 26–32. All figures and captions are slightly modified. Also the chemical formula (5), (6) and unit are corrected.

The microstructure and chemical composition of iron phosphate conversion coatings were investigated by surface/cross-sectional observation using FE-SEM/STEM and chemical state analysis using XPS. As a result, it was suggested that the conversion reaction progressed while the surface oxide on the base material remained, and the fine particles of coatings components were deposited and agglomerated to cover the material surface. The upper layer of coatings was mainly composed of iron phosphate, while the interface between the coatings and base material was deposited iron oxide. The proportion of iron phosphate and iron oxide was almost equal at the initial stage, and the amount of iron phosphate increased as the coating thickness.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 87 (2023) 235–241. The units in Fig. 4, 5, 6, 7 and 8 have been corrected.

The occupancy sites of Mg in the corrosion products formed on the steel substrate at the cut-edge of the Zn–11Al–3Mg (mass%) coated steel was investigated by XAFS analysis at the initial corrosion stage. At the cut-edge, corrosion products containing Zn and Mg were formed in the early stages of corrosion. The XRD and XAFS analyses revealed that the corrosion products at the cut-edge of the Zn–11Al–3Mg coated steel were Mg-containing Zn₅(OH)₈Cl₂·H₂O. Based on the first-principles calculations, Mg in Zn₅(OH)₈Cl₂·H₂O was more likely to substitute two types of the crystallographic sites of Zn rather than intercalate between the ZnO₆ and ZnO₃Cl layers. Therefore, at the initial stage of corrosion, it is considered that Zn₅(OH)₈Cl₂·H₂O with Mg partially substituting two types of Zn crystallographic sites forms at the cut-edge of the Zn–11Al–3Mg coated steel.

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 74 (2025) 179–184. The abstract is slightly modified.

The alloy design of the equiatomic CuSnZn and CuSnAl alloys for the development of the Medium Entropy (ME) bronzes was performed by the empirical alloy parameters. The solidification microstructures of the metallic mold casting ingots in the equiatomic CuSnZn and CuSnAl alloys were investigated by X-ray diffraction, optical and electron microscopy. The repulsive tendency between Sn and other constituent elements was observed in the ingots of equiatomic CuSnZn and CuSnAl alloys, resulting in the Sn-rich liquid formation via the liquid phase separation in the equatomic CuSnAl alloys and the enrichment of Sn element at the inter-dendrite regions of the equiaxis dendrite structure in the equiatomic CuSnZn alloys. The significant segregation tendency of Sn element indicates the difficulty in the development of the equiatomic Cu-Sn-based ME bronzes with a single solid solution phase.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 62 (2023) 60–67.

The effect of Al addition on the pressure sintering (so-called spark plasma sintering, SPS) behavior of B₄C powder by transient liquid phase sintering (TLPS) was investigated. First, an accurate sample temperature evaluation in a closed graphite die was performed using elemental standard powders. It was found that as the sintering temperature increased, the measurable die surface temperature exponentially decreased compared to the die internal temperature (i.e., sample temperature) due to thermal radiation. Next, pressure sintering treatment of the mixed powder of B₄C containing 5 vol% Al was performed in vacuum at a constant compressive stress (50 MPa) and heating rate (2 K/s). Although densification due to Al melting was not observed at 933 K, it was found that densification began at temperatures above 1550 K, where the wettability of Al for B₄C is improved, and reached the final stage of sintering at approximately 2200 K. As a result, the densification temperature of B₄C with Al addition could be shifted to a lower temperature by approximately 250 K compared to B₄C without additives. It was suggested that the formation of Al₃BC₃ between Al and B₄C promoted the rearrangement and shape change of B₄C particles, resulting in densification at low temperatures.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 72 (2025) 173–180.

Copper and its alloys are well known to have bactericidal activity and applied to touch surface to suppress the transmission of pathogens via material surface. The touch surface is exposed to real life conditions, which are generally lower in humidity than that in laboratory testing conditions. The influence of humidity on the antibacterial activity of copper and other materials was reported as contradictory results due to different inoculation methods and contact periods. In this study, the antibacterial activity of copper (C1020) and its alloys (C7060, C7150, MONEL400, and antibacterial stainless steel) was systematically investigated by a method simulating droplet transmission under controlled humidity (60 and 35%RH) with Escherichia coli or Staphylococcus aureus. Corrosion rate of C1020 was estimated by electrochemical impedance spectroscopy under the controlled humidity. As a parameter of antibacterial activity, the contact time to reduce the viable bacteria to be 1% of the inoculated ones, T_0.01, was decided based on the test results. The all materials increased their T_0.01 with reduction in humidity, indicating the decrease in their antibacterial activity. In case of C1020, the smallest T_0.01 for E. coli was observed at 90% RH as 6.96 min, which increased to 67.4 min at 35%RH. At both high and low humidity, the materials with high copper contents (C1020, C7060, and C7150) had the smaller T_0.01 than those with lower copper contents. S. aureus, which has higher tolerance to the environment with low water activity than E. coli, resulted in greater increase in T_0.01 with reduction in humidity (In case of C1020, T_0.01 at 90 and 35%RH for S. aureus were 8.50 and 230 min, respectively). The corrosion rate of C1020 decreased with reduction in humidity, suggesting the importance of copper ion release at the surface for their antibacterial activity.

An electric double-layer capacitor-based heat flow switching device working with a bias voltage was developed as a key technology of thermal management. This device allows us to rapidly control the magnitude of heat flow passing through the device using variations in electronic thermal conductivity of component material induced by the bias voltage. We employed a thin film of Ag₂S_0.8Se_0.2 as the most important component material, because it possesses an exceptionally low lattice thermal conductivity and a semiconducting electronic structure. The thermal conductivity of the fabricated device was measured by means of a periodic heating method under various applied bias voltages. The thermal conductivity of Ag₂S_0.8Se_0.2 was found to increase linearly with increasing bias voltage V_B up to a factor of 1.9 at V_B = 2.4 V. The transient current response during the charging and discharging processes revealed that the response time for switching was fast enough to be less than 0.2 sec. By measuring the stored charge and comparing it with the electronic thermal conductivity, we confirmed that the observed variation in thermal conductivity of the component material is attributed to the accumulated charge in the material.

This Paper was Originally Published in Japanese in J. Thermoelec. Soc. Jpn. 22 (2025) 3–7.