Early-stage dislocation structures inside dislocation channels of rapid-cooled and tensile-deformed aluminum single crystals were investigated by using the bright field imaging mode in a scanning transmission electron microscope (STEM-BF). Inside dislocation channels, arrays of the prismatic dislocation loops originated from dislocations of the primary slip system, i.e., (1 1 1)[1 0 1], were mainly formed. Dislocations of the primary coplanar slip systems such as (1 1 1)[0 1 1] and (1 1 1)[1 1 0] were activated owing to internal stresses caused by the primary dislocations pile-up inside the cleared channels. The activated primary coplanar dislocations left the dislocation loops elongating along the edge dislocation directions behind them. Inter-dislocation-loop interactions occur especially at the arrays of the prismatic dislocation loops originated from dislocations of the primary slip systems and produce “butterfly shape” dislocation loops. As the “butterfly shape” dislocation loops have “sessile” junctions, they should act as “obstacles” against the following multiplications and glides of the dislocations. When the interactions proceed, “tangled structures” would be formed around the arrays of the prismatic dislocation loops originated from dislocations of the primary slip system.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 87 (2023) 67–80.

Since Cu exhibits the highest electrical conductivity among base metals and common metals, pure Cu and dilute Cu alloys are widely used as functional materials for electrical components and power transmission materials. It is also expected that in the future, conductive pure Cu and Cu alloys will continue to be used according to the desired properties by understanding inherent characteristics of pure Cu and Cu alloys. This paper reviews factors such as the contribution of lattice defects and solute elements to the electrical conductivity of pure copper, and factors affecting strengthening processes such as precipitation hardening, solid solution hardening, and work hardening in dilute Cu alloys. In precipitation hardening, the type and amount of alloying elements added and the precipitation treatment are adjusted, but softening of the Cu alloy due to overaging must be avoided. In solid solution hardening, the type and amount of alloying elements are also optimized, often in combination with work hardening. Although work hardening generally results in changes in elongation and strength after processing, the decrease in electrical conductivity due to dislocations is small. Therefore, it is effective to combine work hardening with solid solution hardening and other processes. Microstructural characterization using analytical techniques have been conducted to elucidate the electrical conductivity and strengthening mechanisms of these alloys. Their findings are useful in controlling the conductive and mechanical properties of advance Cu alloys. This review also demonstrates the usefulness of these characterization methods.

This paper reviews recent studies on the relationships between local electrochemical properties at the steel/inclusion boundary and pitting corrosion resistance of stainless steels. The effect of Mo addition to the steel matrix on the local dissolution behavior at the steel/inclusion boundary is explained. The inhibition of inclusion dissolution is beneficial for improving the pitting corrosion resistance of stainless steels. The importance of spark plasma sintering and microelectrochemical techniques in the research on localized corrosion processes are briefly discussed. We also discuss novel methods for improving the pitting corrosion resistance of stainless steels, such as the addition of corrosion inhibitors.

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 71 (2022) 401–408. The title and abstract were slightly modified.

Flash sintering was first reported in 2010 by a research group of Raj et al. at Colorado University. Since then, flash sintering has attracted attention as an innovative sintering method that uses the steep power spike, generated when ceramic green compact is heated while an electric field, is applied to densify ceramic green compact in an instant. However, there are several technical challenges that must be overcome before flash sintering can be used as a practical sintering method. This paper outlines the problems and improvements related to flash sintering from a viewpoint of sintering method and introduces the improved flash sintering noted as shrinkage-rate controlled flash sintering developed by the author.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 70 (2023) 18–29.

We have investigated the hydrogen-annealing influence on the crystalline and electronic structures, and magnetic properties of La_2/3Ca_1/3MnO₃ (LCMO). The results have indicated that the annealing at 700 and 900°C (labeled as LCMO-700 and LCMO-900, respectively) readily reduced single-phase LCMO, resulting in a complex phase composition of several isostructural oxygen-deficient perovskite-type phases coexisting with the Ruddlesden-Popper (La/Ca)₂MnO₄-type phase. While a Mn³⁺/Mn⁴⁺ mixed valence is present in LCMO, the hydrogen-annealed samples mainly have Mn²⁺ and Mn³⁺ ions. Under such circumstance, large changes in magnetic parameters have been recorded, such as remarkable decreases in values of the magnetization, the Curie temperature (from 251 K for the as-prepared LCMO through 240 K for LCMO-700 to ∼221 K for LCMO-900), and the magnetic-entropy change. Particularly, the crystal and electronic-structure changes also enhance the magnetic inhomogeneity, resulting in a strong development of the Griffiths phase, and cause the first-to-second-order phase transformation. These results reflect the instability of the LCMO perovskite-type manganite versus hydrogenation.

A novel oxide YCu₃Rh₄O₁₂ has been obtained using high-pressure and high-temperature conditions of 12 GPa and 1573 K. Electron diffraction and synchrotron X-ray powder diffraction data demonstrates that YCu₃Rh₄O₁₂ crystallizes in a cubic AA′₃B₄O₁₂-type quadruple perovskite structure. The valence state is estimated to be Y³⁺Cu³⁺₃Rh³⁺₄O₁₂ by X-ray absorption spectroscopy. The electric resistivity and magnetization data prove that YCu₃Rh₄O₁₂ is a diamagnetic insulator, which is expected from the electron configurations of Cu³⁺ (3d⁸, low spin, S = 0) and Rh³⁺ (4d⁶, low spin, S = 0) ions. The first-principle calculation displays the insulating band structure for YCu₃Rh₄O₁₂. The valence state transition from Ca²⁺Cu^2.8+₃Rh^3.4+₄O₁₂ to Y³⁺Cu³⁺₃Rh³⁺₄O₁₂ indicates that the doped electrons by the substitution of Y³⁺ for Ca²⁺ are not simply injected to Cu and/or Rh ions, realizing unusual charge redistributions consisting of the simultaneous Cu oxidation (Cu^2.8+ → Cu³⁺) and Rh reduction (Rh^3.4+ → Rh³⁺).

Perovskite-structured transition metal oxides, AMO₃, demonstrate catalytic activities for oxygen evolution reaction (OER), which can be enhanced by chemical substitutions for both A- and M-sites. Considerable efforts are needed to realize the optimum composition with high OER activity because of the huge composition space for doped perovskites of A_1−xA′_xM_1−yM′_yO₃, where A and M ions can be respectively replaced by A′ and M′ ions at arbitrary ratios. Combinatorial synthesis methods were extensively utilized to examine the properties of overall compositions of transition metal oxides. However, perovskite oxides requiring high-temperature treatments were not eligible for the above methods because of the low heat resistance of the conductive substrate, such as indium tin oxide glass and carbon. In this study, we propose an efficient method using the high-temperature synthesis of polycrystalline thin films of perovskite oxides on quartz glasses and Pt films to systematically investigate the OER catalytic activities of perovskite oxides of La_1−xSr_xFe_1−yCo_yO₃ with 100 distinct chemical compositions in 0 ≤ x ≤ 0.9 and 0 ≤ y ≤ 0.9. X-ray diffractometry confirmed that all the samples loaded on the quartz glass crystallized in perovskite structures, whereas the electrochemical study unveiled a continuous landscape depending on both x and y for La_1−xSr_xFe_1−yCo_yO₃. The present method proposes the high-throughput screening for highly active OER perovskite oxide catalysts.

A novel complex transition metal oxide AgCu₃Cr₄O₁₂ has been obtained using high-pressure and high-temperature conditions of 12 GPa and 1223 K. The crystal structure is refined to be a cubic AA′₃B₄O₁₂-type quadruple perovskite structure based on the Rietveld refinement of the synchrotron X-ray powder diffraction data. The density-functional theory calculation obtains a metallic band structure. The valence state is estimated to be Ag^∼1.3+Cu^∼2.2+₃Cr⁴⁺₄O₁₂ by bond valence sum and X-ray absorption spectroscopy analyses. The valence state on ACu₃Cr₄O₁₂ series (A = Ag, Ca, La, Ce) sequentially transforms from Ag^∼1.3+Cu^∼2.2+₃Cr⁴⁺₄O₁₂, Ca²⁺Cu²⁺₃Cr⁴⁺₄O₁₂, La³⁺Cu^(2+δ)+₃Cr^{(3.75−0.75δ)+}₄O₁₂, to Ce⁴⁺Cu²⁺₃Cr^3.5+₄O₁₂, where the electrons are doped into the A′-site (Cu^∼2.2+ → Cu²⁺), followed by predominant doping into the B-site (Cr⁴⁺ → Cr^{(3.75−0.75δ)+} → Cr^3.5+). Their electron doping sequence is distinguished from those reported in other quadruple perovskite oxides, proposing characteristic features of the ACu₃Cr₄O₁₂ family.

We investigated pressure-induced order-disorder transition in the B-site-ordered double perovskite oxide La₂CoRuO₆. La₂CoRuO₆ crystallized in a double perovskite structure with rock-salt-type B-site ordering of Co²⁺ and Ru⁴⁺ ions in the sample synthesized under ambient-pressure and high-temperature (1373 K) conditions. The ambient-pressure B-site-ordered phase of La₂CoRuO₆ underwent phase transition from monoclinic to orthorhombic structure by treating high-pressure and high-temperature conditions of 8 GPa and 1373 K. Structure refinement based on the synchrotron X-ray powder diffraction data demonstrates that the B-site cationic ordering was completely destroyed in the high-pressure phase of La₂CoRuO₆, accompanied by a slight reduction in lattice volume (ΔV = −0.25%). X-ray absorption spectroscopy revealed that the valence states of Co²⁺ and Ru⁴⁺ were retained in the high-pressure phase, indicating that the primary driving force for the pressure-induced order-disorder transition in La₂CoRuO₆ is the negative PΔV term in the Gibbs free energy. The order-disorder transition pressure in La₂CoRuO₆ (8 GPa) was lower than that in isoelectronic oxide Y₂CoRuO₆ (15 GPa), suggesting that the compressibilities of A-site metal ions play a crucial role in the transition. The high-pressure disordered phase of La₂CoRuO₆ exhibited a short-range magnetic ordering below 22 K because of the absence of the cationic ordering, whereas the ambient-pressure ordered phase exhibited an antiferromagnetic long-range ordering below 25 K.

Chemical substitution is an effective way to improve electrocatalytic properties in transition metal oxides. We investigate the synergistic effect between Fe⁴⁺ and Co⁴⁺ ions on the catalytic activity for oxygen evolution reaction (OER) in the Fe–Co-mixed perovskite oxide CaFe_1−xCo_xO₃. The OER activity of CaFe_1−xCo_xO₃ is substantially increased by small amounts of Co (Fe) doping into CaFeO₃ (CaCoO₃), leading to the superiority compared to the pure Fe and Co perovskite oxides. The x dependences of the OER overpotential and specific activity for CaFe_1−xCo_xO₃ (0.05 ≦ x ≦ 0.95) are expressed by constant offset from the weighted average between CaFeO₃ and CaCoO₃, which can be interpreted to be the synergistic effect between Fe⁴⁺ and Co⁴⁺ ions on OER activity. The absence of the optimum x for the highest activity for CaFe_1−xCo_xO₃ contrasts with the volcano-like plots reported in various mixed-metal oxides. First-principle calculations using the special quasirandom structure models on CaFe_1−xCo_xO₃ (x = 0.03–0.5) demonstrate that about half the amount of Fe⁴⁺ is electronically activated to possess smaller charge-transfer energies, corroborating the enhancement of catalytic activity in CaFe_1−xCo_xO₃. These findings provide new insight into the synergistic effects in complex transition metal oxide catalysts.

A novel quadruple perovskite oxide YMn₃Co₄O₁₂ has been synthesized in high-pressure and high-temperature conditions of 16 GPa and 1473 K, respectively. Rietveld refinement of synchrotron X-ray powder diffraction data reveals that this oxide crystallizes in a cubic quadruple perovskite structure in a space group of Im3 (No. 204) with a 1:3-type atomic ordering of Y and Mn at A-sites, and the bond valence analysis suggests the valence state of YMn³⁺₃Co³⁺₄O₁₂. A ferromagnetic-like transition is observed at ∼125 K and the magnetization value reaches up to ∼3 μ_B per formula unit at 5 K. The low-temperature magnetic state can be interpreted as ferrimagnetism with antiparallel alignment of A′-site Mn³⁺ (S = 2) and B-site Co³⁺ (high-spin, S = 2), which is in contrast to the antiferromagnetism in other A′-Mn-containing quadruple perovskite oxides. This finding proposes that the coexistence of A′-Mn³⁺ and B-Co³⁺ leading to ferrimagnetic state is realized in the specific structure with distinct crystallographic sites.

We performed first-principles calculations to investigate the effect of Cu or Fe partial substitution in MnCoGe on the stabilization of the hexagonal structure. In the case of Cu partial substitution at x = 0.125, a substitution for one site is more effective than that for both sites. In the case of Fe partial substitution at x = 0.125, there is no difference between two types of substitution for both sites and the Mn site. The result of Fe partial substitution at x = 0.25 indicates that Fe partial substitution for both sites is more effective than that for the Mn or the Co site.

To investigate the magnetic field effect on the synthesis reaction and phase growth in a Mn–Bi–Sn composite pellet, in-field heat treatments were performed in 5 T at 573 K for 1 to 48 hours. X-ray diffraction measurements and electron probe micro analysis revealed that MnBi phase did not appear but Mn₃Sn, Mn₃Sn₂ and MnSn₂ phases were detected in the pellet. In zero-field heat treatment, the phase fraction of Mn₃Sn₂ increased and that of MnSn₂ decreased as the heat treatment time increased. In contrast, no significant change in the phase fractions of Mn₃Sn₂ and MnSn₂ phase was observed in 5 T even if the heat treatment time was increased to 48 h. The obtained results suggested that the application of magnetic field suppressed the diffusion of Mn atoms between Mn–Sn phases.

The magnetization process of the AA-stacked bilayer honeycomb spin lattice in the out-of-plane applied field is examined in the framework of the Ising model and mean field approximation. Competition between different kinds (antiferromagnetic: AF, or ferromagnetic: FM) of intra-layer and inter-layer spin exchange couplings could lead to the first order magnetization process, characterized by sharp jumps in magnetization curves occurring in critical external fields (spin-flop and spin-flip fields). There is only the spin-flip field at very low temperature and its magnitude depends not only on the intra-layer frustration level but also exchange coupling between spin layers. During the magnetization process, the initial AF bilayer honeycomb spin lattice may undergo ferrimagnetic or week-ferromagnetic states before reaching full ferromagnetic saturation state by the spin-flip field. The results of this work can be applied for an explanation of the spin-flip phenomenon registered in the AF bilayer CrI₃.

In this research, we have analyzed the electrical resistance of Co/Pd and Co/Pt thin multilayered films with perpendicular magnetic anisotropy (PMA) deposited by magnetron sputtering to determine and compare their magnetoresistance (MR) mechanisms. The studies were carried out depending on the magnitude and direction of the applied magnetic field in a wide temperature range T = 3–300 K. It is shown that both the isotropic and angle-dependent MR mechanisms are different for these two films studied. Magnon and anisotropic MR mechanisms (MMR and AMR) are found to be characteristic of the Co/Pd film, while Lorentz and spin Hall MR mechanisms (LMR and SMR) determine the magnetotransport in the Co/Pt film. The revealed differences in the MR mechanisms are discussed in terms of the quality of interfaces and properties of 5d (4d) metals.

Ultrasensitive magnetic field sensors at low frequencies envisaged for applications on biosensors require the detection of superparamagnetic nanoparticles as biomarkers and weak biomagnetic fields. However, superparamagnetic nanoparticles can be magnetized and detected in the presence of a relatively large external magnetic field in which other low field sensors and flux concentrators cannot be used since those are saturated in the bias field. To overcome this problem, we made submicron-sized orthogonal magnetic tunnel junctions with an appropriate perpendicular anisotropy free layer. By applying a perpendicular external magnetic field, the magnetization in the magnetic free layer is brought into an unstable state. As a result, relatively high field sensitivity of 1.3%/Oe is achieved in the external field of about 975 Oe for the 300 nm magnetic tunnel junction. By tilting the angle of the bias field of 10 degrees from film normal, the maximum sensitivity of 4.5%/Oe was obtained at 295 Oe. We also investigated the low-frequency noise generated by the sensor for their capability to detect weak low-frequency magnetic signals. Noise equivalent signal of the device is estimated to be about 235 nT/√Hz from 1/f noise measurements which is suitable for single superparamagnetic nanoparticles detection.

Binary copper oxides with different copper ion oxidation states including cuprous Cu₂O and cupric CuO have already been successfully synthesized by the simple and highly repeatable grow-up technique from the modified copper Cu sheet. By controlling the annealing time and temperature, the copper oxide (CuO, Cu₂O) composites were hierarchically formed on Cu surface. All obtained samples were characterized using X-ray diffraction (XRD) spectroscopy and scanning electron microscopy (SEM). The results showed that the modified Cu sheets after annealing in air yielded the mixture of CuO and Cu₂O phases. The obtained Cu₂O/CuO composites have been used as active photocatalysts to decolourize the 10 ppm dyes rose bengal solution with the degradation efficiency of 73% over a period of 3 h under UV-A irradiation after three uses. These results make them attractive as reusable photocatalytic materials in form of flat sheet. The other testing conditions as pH values and oxidant agent (H₂O₂) was carried out. It was observed that the photodegradation achieved up to 96% with the presence of H₂O₂.

Sorting and trapping cells play an important role in fundamental cellular and biology research that enables the study of single-cell behaviors, which are different in comparison with a cluster of cells. Contactless handling techniques using different optical, mechanical, or magnetic phenomena have been studied for single-cell trapping. Among them, the diamagnetic force created by magnetic structures on cells is significant and stable both in time and in space. In this work, arrays of hard magnetic clusters in the PDMS background (hereafter called magnetic structure) were successfully fabricated using the magnetic imprinting method. The magnetic structure shows a proper magnetic property and the possibility to sort and trap T47D single cells via the diamagnetic levitation phenomenon at defined positions, which are both experimentally observed and theoretically calculated. The obtained results show the promise of developing a simple way to separate directly living cells.

Hydrogen adsorption in WO₃ thin films is known to cause the change of color of the films. Due to its high sensitivity, chemical stability as well as biocompatibility, the WO₃ offers itself as an efficient hydrogen sensor, especially for detection of hydrogen in humid environments. In this paper we report the preparation and characterization of WO₃ electrochoromic thin films prepared on ITO substrates by thermal evaporation synthesis. These films show significant decreases in transparency from over 92% to as low as 2% at an applied bias of −0.7 V. Structure as well as the effect of annealing temperature on the structure and properties of the films are also studied. The changes of optical band gap and the role of hydrogen in coloration process are also discussed.

Cupric-oxide-based thin films with various amounts of 0, 1, 2, 3, and 4 wt.% Ni doping were, in turn, deposited on ITO/glass substrates via a solution process. The 0.25 M concentrated solutions of copper (II) acetate monohydrate and nickel acetate tetrahydrate were used as starting materials mixed in ethanol solvent, in order to form the precursors. We obtained that the crystalline structure was not affected by the increase in Ni doping concentration as evidenced by X-ray diffraction patterns. The surface morphology observed by scanning electron microscope pointed out the presence of linked-structure nanoparticles. The influence of Ni doping on the optical bandgap width was evaluated by using ultraviolet-visible spectrometry. We found that the optical bandgap should be direct, and it decreased from 2.69 to 2.38 eV for the range doped. Interestingly, we determined the relaxation time of the Ni-doped CuO/ITO/glass structure from measuring the electrochemical impedance spectroscopy, and it was 0.36 s for the undoped film, then gradually decreased to be 0.31, 0.11, 0.1, and 0.04 s with increasing the Ni doping concentration. This achievement result will serve as a foundation for the future photonic researches.

Bifunctional magneto–plasmonic nanoparticles Fe₃O₄@SiO₂–Au (FSA) were successfully synthesized by an ultrasound-assisted chemical method with high pH conditions. Gold ions were absorbed on the surface of silica-coated magnetic nanoparticles and then reduced by sodium borohydride (NaBH₄) under the influence of a 200 W ultrasonic wave for 45 min. The magneto–plasmonic FSA exhibits superparamagnetism with a high saturation magnetization and simultaneously absorbs visible blue light with the surface plasmon resonant (SPR) peak at around 545 nm. When the amount of precursor gold ions increased from 16 µmol to 40 µmol, the relative atomic ratio of gold/iron increased from 0.84 to 3.35. In the consequence, the peak absorption positions increased from 540 nm to 550 nm, which can be explained by the increase in the Au crystal size. The controllable optical and magnetic properties of the nanoparticles show that they have high potential in biomedical applications, such as MR imaging, SERS-enhanced, computed tomography imaging, photothermal therapy, etc.

Silver nanoparticles (Ag NPs) were quick synthesized by electrochemical method combined with heat treatment using silver electrodes and trisodiumcitrate (TSC) as reducing agent. This method is highly productive, with simple equipment, which is easily deployed on an industrial scale. The size of the Ag NPs is controlled through the amperage and the concentration of TSC. The effect of the synthesis’ conditions on optical properties of Ag NPs was surveyed. The Ag NPs were used to fabricate the Ag NPs-coated nonwoven fabrics. The bactericidal testing showed that Ag NPs-coated nonwoven fabrics were able to kill over 80% of E. coli and 96.9% of B. subtilis bacteria. These results can be considered as a new choice to prevent the spread of diseases caused by bacteria and viruses, thereby contributing to the protection of human health.

Recently, two-dimensional (2D) layered organic-inorganic perovskites have been a hot topic not only in photovoltaics but also in optoelectronic applications due to their remarkable optical and electronic properties. In this study, the multiferroic property of the 2D layered (C₆H₅CH₂CH₂NH₃)₂NiCl₄, abbreviated PEA-NiCl₄, perovskite single crystals has been first reported. The crystals were synthesized by anti-solvent evaporation method by a layer-by-layer mode with relative smooth surface that confirmed by SEM image. The XRD patterns reveal the high crystalline quality with (n00) dominant plane (n = 2, 4, 6, …). The 180° reproducible hysteresis phase loop, butterfly-like amplitude curve, and an effective piezoelectric coefficient of 327 pm/V was evaluated using Piezoelectric Force Microscopy (PFM) measurement. The multiferroic properties has been confirmed by P-E hysteresis loops with P_S = 16.3 µC/cm² P_r = 14.8 µC/cm², and E_C = 6.7 kV/cm and M-H hysteresis loops with H_C = 151 G. The 80-nm-width ferroelectric domains orienting along the crystal surface have been observed by the PFM images. This study offers an opportunity to develop new multiferroics material based on 2D layered hybrid perovskite single crystals.

Computational materials design (CMD) based on the first-principles electronic structure calculations is demonstrated for two topics related to the design of high-entropy alloys (HEAs). The first one is a construction of prediction model of elastic constants. By applying machine learning technique with the use of the linearly independent descriptor generation method to the database of elastic constants of 2555 BCC HEAs generated by the full potential Korringa-Kohn-Rostoker coherent potential approximation (FPKKR-CPA) method. The obtained model is used to predict new HEAs with high Young’s modulus. The second topic is a simulation of atomic arrangement in HEAs at finite temperature. In this simulation, HEAs are described by using the Potts-like model and the interaction parameters are determined based on the generalized perturbation method combined with the KKR-CPA method. Monte Carlo simulations for the models of CrMnFeCoNi and CrMnFeCoCu predict atomic arrangements which are consistent to the experimental observations.

In this work, we constructed machine learning models to predict structural descriptors that numerically represent the atomic structures in three dimensions from x-ray absorption near-edge structure (XANES) spectra. The neural network models that predict radial distribution functions (RDF) and orbital-field matrix (OFM), a descriptor that deals with the anisotropy of the local structure, the valence electron number of the ligand, and orbital information, were constructed. We used more than 120,000 O K-edge XAS spectra data from the Materials Project database as the training data set. We successfully constructed models that roughly predicted RDFs with 74% of the test data. Furthermore, the model that predicted OFM also captured an overview of OFM in 97% of the test data. These results demonstrate that the atomic structural information can be directly extracted from XANES spectra using neural network models.

Cr⁴⁺-doped crystals are promising materials for infrared solid laser applications. In order to choose proper host materials of Cr⁴⁺ from the wide variety of crystals, multiplet energy levels of Cr⁴⁺ should be evaluated without experimental information. A newly developed first-principles method for determining the mean-field Hamiltonian of the localized luminescent center based on quasiparticle self-consistent GW was applied to 3d² transition metal ions (Cr⁴⁺ and V³⁺) in α-Al₂O₃. Our method gave good agreement with the effective Coulomb parameters and crystal-field parameters estimated from experimental data. Multiplet energy structures were therefore well reproduced by our method. These results show the possibility of designing new laser host materials within the framework of the first-principles calculations.

In the present study, we investigate the use of convolutional neural network (CNN) models for classifying the characteristics of surface fractures in plastics, which are affected by environmental stress cracking agents. Nineteen CNN models with different architectures are adopted with 4,012 crack images, and they are evaluated based on the classification accuracy. Four models with a relatively higher accuracy are selected and compared with each performance metric obtained from a confusion matrix. The model with the Inception-ResNet-v2 architecture showed the highest performance metrics value of over 0.96. Although the model with the ResNet-18 architecture showed slightly lower levels of performance metrics, its training time was more than 10 times faster.

This study proposes a machine learning model to predict the martensite start temperature (M_s) of alloy steels. We collected 219 usable data from the literature, and adjusted the hyperparameters to propose an accurate machine learning model. Artificial neural networks (ANN) exhibited the best performance compared with existing empirical equation. The prediction mechanisms and feature importance of the ANN with regards to the whole system were discussed via the Shapley additive explanation (SHAP).

In the present study, we investigated a finite element simulation considering the martensite transformation and transformation-induced plasticity (TRIP) to predict the quench distortion of a cut-cylinder 4340 steel. The distortion predicted by the finite element simulation considering both the martensite transformation and TRIP showed good quantitative agreement with the measured results. We analyzed the effects of the martensite transformation and TRIP on the quench distortion separately and concluded that TRIP has a very critical impact on the quench distortion of cut-cylinder 4340 steel. In addition, the chemical composition and quenching condition were confirmed to be important factors influencing the quench distortion even though the same cut-cylinder sample was used.

The parameters affecting the hydrophilicity and its aging effect on the polymer surface treated with atmospheric pressure plasma were investigated. A series of experimental procedures were performed according to various parameter combinations using the DoE method. The main factors having the most impact were found by quantifying the effect of each process parameter in plasma treatment. In addition, based on the results, multiple regression analysis was conducted to optimize the parameters of the experiment under conditions that maximize the hydrophilicity of the polymer surface. Finally, process capability analysis showed the superiority of optimized conditions statistically, physically, and chemically. A series of experiments and analytical procedures were characterized with the Minitab 20 program, X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM).

The random forest regression (RFR) model was proposed to predict the bainite start temperature (B_s) using alloying elements, such as C, Mn, Si, Ni, Cr, and Mo, as well as the prior austenite average grain size (AGS). RFR demonstrated a performance improvement of approximately 1.2% over the empirical equation. Cr, C, Mo, Mn, Si, AGS, and Ni were assigned importance, in that order, in the RFR using Shapley additive explanation (SHAP) analysis. The detailed prediction mechanisms of the RFR are discussed using the SHAP dependence plot.

The current study utilized a two-step laser power bed fusion (LPBF) method to create a heterostructured material (HSM) composed of STS316L and Inconel 718. STS316L enhances ductility, while Inconel 718 improves strength. We examined the tensile deformation behavior of HSMs and found that stress is mainly localized in the cell or grain boundary area. The volumetric ratio of Inconel 718 to STS316L in the HSM affects the tensile properties, although the structural design is crucial for improving tensile strength. Fractographic analysis revealed that fracture occurred and propagated at the STS316L and Inconel 718 interface, with evident unmelted powders due to insufficient energy density. Achieving an optimized process parameter is necessary to ensure a reliable chemical joining which increases the mechanical properties of HSM.

This study investigates the effect of Mg content on precipitation behavior and resulting mechanical properties of Al–Mg–Si(–Cu) alloy plates manufactured by gravity casting and cold rolling. An alloy with a relatively low Mg content (0.3 wt%) remains after baking hardening without sufficient transformation of Mg–Si clusters or stable Mg2Si in the low temperature phase, whereas, alloys with relatively high Mg content mainly form major strengthening contributors such as β′- and β′′ phases. DSC analysis combined by thermodynamic modeling demonstrates that the formation of β′- or β′′-phases in the 0.3 Mg samples requires much high pre-aging (P.A.) temperatures, which limits improvement of strength by bake hardening (B.H.). This new observation provides the guideline to design the content of Mg and pre-aging condition to obtain optimal bake-hardening characteristics for Al–Mg–Si(–Cu) alloys.

We performed 1.5 MeV electron-irradiation at 333 K and 533 K for Cu–4.2 at% Ti alloy with a single phase of super-saturated solid solution, and investigated the irradiation-induced changes in Vickers hardness and electrical conductivity. With increasing the electron fluence, both of the hardness and the electrical conductivity increase. Such phenomena can be ascribed to the formation of Ti-rich precipitates that are caused by irradiation-enhanced diffusion of Ti atoms. The increase in electrical conductivity is caused by the reduction of Ti content in Cu matrix because of the formation of Ti-rich precipitates. The increase in hardness is also caused by Ti-rich precipitates that are effective obstacles against the motions of dislocations. We found a clear correlation between the irradiation-induced change in the hardness, ΔHv and change in electrical resistivity, Δρ, or that in electrical conductivity, Δσ, as ΔHv ∝ √-Δρ, or ΔHv ∝ √Δσ/σ, irrespective of irradiation temperatures. This correlation suggests that the precipitate-cutting mechanism governs the irradiation-induced increase in hardness; that is, 1.5 MeV electron-irradiation at relatively low temperatures of 333 K to 533 K should promote the nucleation of fine Ti-rich precipitates preferentially rather than the growth of them. The present result shows that energetic electron irradiation is a good tool to improve the mechanical and electrical properties of Cu–Ti alloys.

A damping alloy with a nominal composition of 50Al–49.9Zn–0.1Ce (at%) was tested in hot compression (60% depression) using a Gleeble-3800 thermomechanical simulator at deformation temperatures and strain rates ranging from 573 to 648 K and 0.01 to 10 s⁻¹, respectively. According to the true stress-strain curves, two constitutive equation models based on peak stress and strain compensation were constructed. The microstructure of the alloy after deformation was characterized and analyzed by means of X-ray diffractometer (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results show that the flow stress increases with decreasing deformation temperature and increasing strain rate. The theoretical predictions of the constitutive equation model at low temperature and high strain rate are well fitted to the measured values with low average absolute relative errors. At low strain rates and high temperatures, the α + η eutectoid structure tends to transform from lamellar to granular morphologies, which is accompanied by the increased sizes of α and η phases. Also, the obvious dissolution of η into α phase has been occurred and some tiny holes induced by thermal-force coupling have been formed during compression. In this work, the Al–Zn–Ce damping alloy is more suitable for thermomechanical processing at relatively lower temperatures and meanwhile higher strain rates (such as at 573 K/0.1 s⁻¹, 573 K/10 s⁻¹ and 623 K/10 s⁻¹).

In this study, the effect of the initial phases of the Si-bearing near-α titanium alloy Ti–6Al–2.75Sn–4Zr–0.4Mo–0.45Si (Ti-1100) on Vickers microhardness during aging at 600°C from 5 min to 42 days was investigated by transmission electron microscopy. The initial phases included α′ martensite and α phases. The variation in the hardness of the specimen with the initial α′ martensite phase occurred in the following order: the decrease caused by dislocation recovery, the increase caused by silicide precipitation, the decrease caused by silicide coarsening, and the increase caused by α₂ precipitation. As for the initial α phase, hardness initially decreased and then increased because of dislocation recovery and silicide/α₂ precipitation, respectively. The difference in age-hardening behavior resulted from the difference between the dislocation amounts in the two initial phases. Silicide precipitation was promoted by dislocations, whereas α₂ precipitation occurred via homogeneous nucleation irrespective of the dislocations.

Extended X-ray absorption fine structure (EXAFS) and neutron diffraction experiments were carried out to clarify the typical features of the local structure of a family of medium-entropy alloys (CrCoNi, MnCoNi, and FeCoNi). A simple random cluster model was constructed for analyzing EXAFS spectra, and static and dynamic components of the mean-square relative displacement (MSRD) were separately extracted. In our analysis, the static MSRD of the MnCoNi sample was slightly larger than those of the CrCoNi and FeCoNi samples, whereas the dynamic MSRDs of these samples were almost identical. Based on the complementary neutron diffraction data, we argued that the origin of the large static displacement in the MnCoNi alloy can be associated with a short-range structural transformation through long-term structural relaxation.

This study conducts dislocation-based modeling and numerical analysis for kink deformation using the theory of nonlinear continuum mechanics based on differential geometry. The kinematics of the continuum is represented by the reference, intermediate, and current states, which are related to the multiplicative decomposition of the deformation gradient into plasticity and elasticity. The intermediate state is determined by the Cartan first structure equation, whereas the current state is obtained from the stress equilibrium equation. Kink deformation is modeled by a planar array of edge dislocations, and the governing equations are solved numerically using the finite element method. Quantitative verification of the model is conducted by comparing the bending angle at a kink interface and the theoretical prediction given for the tilt grain boundary. We construct two types of ortho-type kink models for several interface lengths to understand the energetics and mechanics of the kink growth process. The present numerical analysis demonstrates the significant stress concentration at the growth front due to the formation of wedge disclination. We also discuss the material strengthening mechanism from elastic strain energy, nonsingular stress fields, and nonlinear elastic interaction between the disclinations.

Press hardened steel (PHS) has been applied to many automotive body parts to reduce the weight of the white body, and high corrosive properties are required in PHS. Al–Si coated steel sheets are widely used for protection against scaling and decarburization. Although Al–Si coated steel sheets have better corrosion resistance than bare steels due to the barrier effect, the corrosive protection performance of Al–Si coated steel sheets is not sufficient for use in wet under-body areas compared with galvanized or galvannealed steel sheets. Zn coated PHS is appropriate for hot stamped parts in which corrosive protection is required because of its sacrificial protection property. However, micro-cracks occur in severely deformed areas of Zn-coated parts under some hot stamping conditions, and deep micro-cracks can affect the fatigue property. In this study, several hat-shaped samples were prepared, and the depth of micro-cracks was changed by altering hot stamping conditions. The effects of the micro-crack depth on the fatigue property of Zn–Ni coated PHS were investigated by a plane bending fatigue test. At the average depth of 20 µm, the fatigue life of the Zn–Ni coated samples was almost equal to that of the Al–Si coated sample which was taken from the wall side of the hat-shaped sample after crash forming. Considering the standard deviation of the micro-crack depth in practical use, the Zn–Ni coated steel sheets can be used equally with the Al–Si coated steel sheets in fatigue property when the micro-crack depth was restricted to under 10 µm. Moreover, the impacts of hot deformation conditions on the micro-crack depth were investigated. It was found that the reduction of equivalent plastic strain is effective in lowering the micro-crack depth.

Fracture at sheared edges upon stretch flanging is a severe problem for ultrahigh-strength steel (UHSS). This study was focused on the improvement of stretch flangeability by heat treatment of the sheared edge of UHSS samples. The materials studied were dual-phase steel and full martensite steel. The steel samples were pierced with 10 mmΦ holes and then heat-treated by whole-area or partial-area heating. The heated materials were tested by the hole expansion test to determine the hole expansion ratio (λ). The mechanical properties and microstructural transformation depending on the heat-treatment temperature were also investigated. The experimental results of whole-area heating showed that λ of the steels improved with heat-treatment temperature up to Ac1 (the temperature at which ferrite starts to transform to austenite). The λ significantly decreased with heat treatment between Ac1 and Ac3 (the temperature at which ferrite has transformed completely to austenite). The λ increased again with heat treatment over Ac3. The λ dependence on the heat-treatment temperature was explained by the recovery of work hardening and microstructural transformation. The experimental results of partial-area heating showed that short-time and partial-area heat treatment was sufficient to improve λ.

This Paper was Originally Published in Japanese in J. JSTP 63 (2022) 65–71.

An Al₈Co₁₉Cr₂₃Fe₃₂Ni₁₈ high-entropy alloy with a solid solution of Al was prepared, and its pitting corrosion resistance in 0.1 M NaCl and high-temperature oxidation resistance at 1273 K were assessed. The pitting potential of this alloy is lower than that of the Al-free Co₁₉Cr₂₃Fe₄₀Ni₁₈ alloy, although its oxidation resistance is higher. The decrease in the pitting potential owing to Al addition was attributed to Al in the surface oxide film and Al nitride inclusions in the metal matrix. For the Al₈Co₁₉Cr₂₃Fe₃₂Ni₁₈ alloy, potentiodynamic polarization in 1 M H₂SO₄ improved the pitting corrosion resistance without decreasing the high-temperature oxidation resistance.

A primary melted mark (PMM) on copper wire has been expected to identify the fire origin. However, the solidification microstructure under various cooling conditions has not been extensively studied. In this research, the effects of cooling conditions on PMM microstructure before and after heat treatment were investigated. The results represent dendrite growth direction to the surface of the melted mark with copper dendrites surrounded by (Cu+Cu₂O) eutectic structure for air and water-cooling specimens. Moreover, the melted mark cooled in the air has more than twice of secondary dendrite arm spacing (SDAS) than the water-cooling sample in the case of pre-heat treatment. After heat treatment and cooled down in the furnace, air, and water: the dendritic structure disappears and Cu₂O precipitates on the copper matrix. The smaller crystallite size and oxide layer cracking could be found in a higher cooling rate case. Therefore, by connecting thermal history with solidification structure and surface oxidation morphology, the change in microstructures and physical parameters of PMM could be expected to be helpful for fire investigation.

A technique, which can explain the behavior of fires by using microstructural and oxide examinations of melted marks on copper wire, has been required for fire investigators. However, a study on the microstructural and oxide evolution after a fire is insufficient due to various and complicated fire conditions. In this research, changes in surface morphology, oxide layer thickness, oxidation kinetics, and microstructure were investigated at various annealing temperatures and times on the melted mark on the copper wire. The results show that the copper dendrites surrounded by (Cu+Cu₂O) eutectic structure under Cu₂O and CuO surface is the fingerprint of melted mark on copper wire annealed between 220°C and 600°C. At an annealing temperature of 800°C to 1000°C, the characteristic microstructure of the melted mark is Cu₂O precipitates without dendrites in grains under a single layer of Cu₂O. Moreover, the diffusion processes contributed to Cu₂O growth could be as follows: lattice diffusion at 220°C to 400°C and grain boundary diffusion at 400°C to 1000°C.

The effects of casting speed on macrosegregation and grain structure during the direct-chill casting of an Al–Mg–Si alloy are experimentally investigated. Results show that increasing the casting speed yields a more pronounced negative centerline segregation. Regard this mechanism, apart from the increased contribution of solidification shrinkage, the variation in floating grains is newly observed. The increased casting speed significantly increases the size and fraction of floating grains at the central portion of the billet, thus resulting in a more severe negative segregation. To clarify the experimentally observed phenomena, the solidification and distribution of floating grains in billets cast at different casting speeds are numerically simulated. The increased casting speed deepens the slurry zone significantly, thus providing more time for the floating grains to freely float and develop before settling into the mushy zone. Additionally, the greater slope of the coherency isotherm resulting from the increased casting speed promotes the movement and sedimentation of the floating grains toward the central portion of the billet. Consequently, more floating grains are detected at the billet center.

The apparent activation energy of sintering for 8-mol%-Y₂O₃-doped ZrO₂ during shrinkage-rate-controlled flash sintering was determined using a master sintering curve. The activation energy during SCF sintering was found to decrease from approximately 700 to 430 kJ/mol with density. The activation energy in a high-density region is approximately similar value of lattice diffusion, 460 kJ/mol. The relative density range over which the decrease in activation energy occurred during SCF sintering was smaller than during thermal sintering and further moved to a lower temperature range. The increase in shrinkage rate at lower temperatures that occurs during SCF sintering could be considered to be related to this decrease in activation energy.

The Mg_0.1In_0.9 phase with FCC structure was formed in Mg–In and Mg–Al–In alloys. The LCR (Limiting Cold-Rolling ratio) at room temperature tended to increase with increasing area fraction of the Mg_0.1In_0.9 phase, and the LCR achieved 80% for the single Mg_0.1In_0.9 phase in both alloys. The hardness value of the Mg_0.1In_0.9 phase in the Mg–In binary alloys increased after rolling originated from grain-refinement by recrystallization and precipitation hardening due to processing heat generated by rolling at room temperature. On the other hand, the Mg_0.1In_0.9 phase formed in the Mg–Al–In ternary alloys was stable at room temperature and work hardened after rolling. Since the Mg_0.1In_0.9 phase dissolves about 5 mol% of Al, substituting Al for In in the Mg–In alloy was effective in reducing density. The density of the Mg₈₀Al₇In₁₃ (mol%) alloy is 2.60 Mg/m³, which is lower than that of Al, and the LCR showed 49%. In Mg–In alloys, the substitution of Al is effective in developing alloys that are easy to process at room temperature and have low density, because the Mg_0.1In_0.9 phase has a solid solution of Al and contributes to phase stabilization at room temperature.

This Paper was Originally Published in Japanese in J. JILM 73 (2023) 152–157.

T6-tempered A6061 aluminum alloy sheets were edge joined using electrodeposited copper. Anodic oxidation of the aluminum alloy substrates improved the resulting join strength. This observation is attributed to the nanoanchor effect—mechanical interlocking between the nanoporous structure of anodic aluminum oxides (AAOs) and the electrodeposited copper. A tensile join strength of 214 MPa was obtained when the sheets were joined in an electroplating bath containing thiourea. The microstructures at the AAOs/copper interface were observed using scanning and transmission electron microscopies to elucidate the underlying mechanism of the high join strength. Mechanical strengthening of the electrodeposited copper is necessary for further strengthening of the joint.

We investigated the alloy composition of Mg–Ca–Zn alloys suitable for rapidly solidified powder metallurgy (RS PM) processing and tried to develop biomedical Mg–Ca–Zn RS PM alloys with high strength, high ductility, and high corrosion resistance. The alloy composition suitable for RS PM processing was Mg–1.0Ca–0.5Zn (at%) in ternary Mg–Ca–Zn alloys. An Mg–1.0Ca–0.5Zn RS PM alloy with combined additions of 0.1 at% Y and 0.03 at% Mn exhibited excellent performance with a tensile yield strength of 376 ± 17 MPa, an elongation of 14.1 ± 3.1%, and a corrosion rate of 0.46 ± 0.04 mm·year⁻¹ when immersed in HBSS, resulting in the achievement of our target properties. Especially the yield strength of the Mg–1.0Ca–0.5Zn–0.1Y–0.03Mn RS PM alloy developed in this study was higher than that of previously reported Mg–Zn–Ca(–Mn–Zr) or Mg–Ca–Zn(–Mn–Zr) ingot metallurgy (IM) alloys, which were produced by single extrusion, double extrusion or severe plastic deformation (SPD) of cast ingots.