This paper reviews recent progress in understanding the relationship between microstructure and localized corrosion behavior in Mg–Al–Zn alloys, as well as the formation of corrosion-resistant coatings. The importance of microelectrochemical techniques and in situ optical microscopy for elucidating localized corrosion processes is highlighted. Additionally, spark plasma sintering is introduced as an effective method for fabricating model specimens with α/β phase boundaries to systematically evaluate micro-galvanic corrosion. Recent advancements in pulse electrolysis for the formation of corrosion-resistant coatings on Mg alloys are also discussed. This review provides insights into localized corrosion mechanisms and offers guidance for alloy design and surface modification strategies aimed at improving the corrosion resistance of Mg–Al–Zn alloys.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 90 (2026) 73–82.

Multilayer structures for improving both the strength and ductility of electroformed multilayer nanocrystalline iron-nickel alloy composed of alternately stacked nickel-rich (fcc) alloy and iron-rich (bcc) alloy layers were explored. Multilayer structures were produced from single electrolyte mainly composed of nickel sulfamate and iron chloride using a sequence-controlled DC power supply. Nanocrystalline Fe-Ni alloy specimens with multilayer structures ranging from 3 to 75 layers were produced. The strength and elongation increase gradually in specimens with layers ranging from 25 to 45. When the number of layers was in the range of 45 to 51, both the tensile strength and elongation increased significantly. The specimen with 51 layers showed the ultimate tensile strength of 2.12 GPa and elongation of 12.5%. As the number of layers further increased, the tensile strength and elongation decreased, and the 75-layered specimen fractured with almost no plastic deformation. Interphase boundaries contribute to the strengthening and deformation of multilayer alloys; however, as the interfacial spacing decreases, the bcc alloy layer with a low thickness hardens and loses its ability to deform, resulting in brittle fracture. It was shown that the optimum number of layers for enhancing both strength and ductility is governed by the interfacial spacing, namely, the thickness of the bcc alloy layer in the multilayer material.

The effects of Ag addition and aging treatment on the phase stability, microstructure, element partitioning, and mechanical properties of Ti–2Cr–9Sn–1.7Ag (mol%) alloy were systematically investigated. Ag addition promoted β phase stability in the solution-treated condition and suppressed α′′-martensite formation at room temperature. Aging treatment of the Ti–2Cr–9Sn–1.7Ag alloy induced distinct precipitation behavior depending on aging temperature, including the formation of fine α precipitates at lower temperatures and Sn-rich α₂ (Ti₃Sn) precipitates at higher temperatures. The formation of fine α precipitates caused severe embrittlement, while high-temperature aging restored superelasticity. A clear correlation was established between precipitation behavior, solute redistribution in the β matrix, and deformation mode. Under optimized aging conditions, a maximum recoverable strain of 2.5% was achieved, demonstrating that appropriate aging treatment can effectively induce superelasticity even in alloy compositions that exhibit predominantly plastic deformation in the solution-treated condition.

Single-crystalline (SC) Ni-Mn-Ga particles/silicone rubber composites exhibiting large magnetic field-induced strain (MFIS) are promising candidates for high-speed actuator applications. Nevertheless, a key challenge for practical use is lowering the magnetic field (H-field) required to activate shape deformation. To achieve this, soft magnetic Fe- and FeNi-added SC Ni-Mn-Ga particles/silicone composites have been developed; however, the investigations of the magnetic property and the dimensional issues are not well discussed. In this study, Fe-Si-Al (Sendust) particles were introduced into SC Ni-Mn-Ga particles/silicone rubber composites to investigate their influence on MFIS behavior of the composite. Sendust particles possess a higher initial magnetic permeability and larger particle dimensions compared to Fe and FeNi particles used in previous studies. The magnetic, mechanical, and MFIS behaviors of four composites containing Sendust and/or SC Ni-Mn-Ga particles fabricated under different curing conditions were examined. The results show that tailoring Sendust particles decreased the necessary H-field for the commencement of shape deformation. A comparison of MFIS behavior among Fe-, FeNi-, and Sendust-tailored composites revealed that higher magnetization and larger dimensions could be advantageous for enhancing MFIS response. Furthermore, magnetic finite element simulations were conducted to elucidate the roles of magnetic properties and particle dimensions of tailoring materials in governing magnetic interactions with Ni-Mn-Ga particles. These results indicate that tailoring materials with higher magnetization and larger particle dimensions effectively reduce the necessary H-field for actuation. These findings provide design guidelines for advanced smart composites.

Periodic atomistic simulations of incommensurate grain boundaries (GBs) require an appropriate rational approximation of lattice matching across the interface. In a previous study, the {100} || {110}[001] GB in MgO was successfully modeled using a 5:7 rational approximation of the interplanar spacing ratio, providing important insight into the atomic structure of this incommensurate interface. Building upon this work, the present study examines the same GB within a framework based on rational approximation and the Farey hierarchy. The irrational spacing ratio d(110)/d(100) = √2 /2 is systematically approximated using continued-fraction expansion, yielding a sequence of rational approximants. Periodic GB models corresponding to selected low-order approximants are constructed and optimized using first-principles calculations. The resulting structures reveal that higher-order approximants are composed of structural units already present in lower-order models, reflecting the hierarchical structure of the Farey diagram. The calculated GB energies do not exhibit a monotonic dependence on the global misfit parameter. The relatively small energy differences among several approximants indicate that interfacial stability is not determined solely by lattice mismatch. Instead, the arrangement and relative abundance of local structural units play an important role in determining interfacial energetics. Atomic-resolution ABF-STEM observations further confirm the presence of similar structural units at the GB. These results suggest that rational approximation in modeling incommensurate GBs serves not only to reduce lattice mismatch but also to reveal the structural hierarchy underlying the interface. The present approach provides a systematic framework for interpreting periodic approximations of incommensurate GBs and may be applicable to other interfaces with irrational lattice relationships.

Mg₂(Si,Sn) solid-solution thermoelectric materials were synthesized by Spark Plasma Sintering to investigate their temperature-dependent transport properties. Both n-type and p-type samples exhibit behavior characteristic of heavily doped semiconductors, with increased power factor and reduced lattice thermal conductivity up to the intermediate-temperature range. As a result, zT peaks at around 623–673 K, reaching ≈1.2 for n-type and ≈0.5 for p-type. At higher temperatures, intrinsic excitation induces minority carriers and bipolar thermal conduction, leading to reduced Seebeck coefficient and increased thermal conductivity, thus lowering zT. A prototype thermoelectric module consisting of 32 p–n couples was fabricated using the developed materials. The module exhibits a nearly linear increase in output voltage with ΔT and maintains stable internal resistance, although assembly-related losses increased the total resistance. The module provided 7.8 W of output power and an efficiency of ∼7.5% at ΔT = 470 K. These results confirm the suitability of Mg₂(Si,Sn) for medium-temperature power generation and highlight pathways for further optimization.

Dislocation structures in the {0112}/⟨2110⟩ low-angle tilt grain boundary of α-Al₂O₃ were characterized by transmission electron microscopy. It was found that the grain boundary consists of dislocations with the Burgers vector of ⟨0110⟩, 1/3⟨1011⟩, and 1/3⟨0221⟩. These dislocations are dissociated into partial dislocations with stacking faults on the (0001) and/or {0110} planes. While the dissociation structures of the ⟨0110⟩ and 1/3⟨1011⟩ dislocations were consistent with previous reports, the 1/3⟨0221⟩ dislocation showed a characteristic V-shaped structure that had not been reported. This paper discusses the accommodation mechanism of the misorientation by the three types of dislocations and the dissociation structure of 1/3⟨0221⟩ in detail.

Kink-band formation in Ti₂AlC was investigated in a multiphase Ti-Al-C alloy consisting of Ti₂AlC, TiAl, and Ti₃Al phases. The influence of the TiAl/Ti₂AlC interface during nanoindentation was examined. Nanoindentation tests were performed on multiphase polycrystalline alloy specimens, in which Ti₂AlC grains with surface normals nearly parallel to [3362] were selected for examination. Nanoindentation behavior in the grain interior was compared with that adjacent to the TiAl/Ti₂AlC interface. In the grain interior, deformation was dominated by basal dislocation slip, and kink-band formation was accompanied by basal plane delamination. In contrast, indentation immediately adjacent to the TiAl interface resulted in the formation of ridge-type kink structures without basal plane delamination. The presence of TiAl grains modifies the local mechanical boundary condition during nanoindentation, thereby enabling kink-band formation in Ti₂AlC without basal plane delamination.

Microstructure strongly governs the macroscopic mechanical response of Mo–Si–B–TiC (MoSiBTiC) alloys, yet the local constitutive and fracture properties of the constituent phases and interfaces remain insufficiently quantified. Here, we determine the room-temperature elastoplastic parameters of individual phases in a MoSiBTiC alloy by combining nanoindentation with an inverse analysis of load–displacement curves. In addition, pop-in events observed during nanoindentation into brittle phases and across interfaces are analyzed using an energy-based approach to estimate a nanoindentation-derived local fracture resistance. The Mo solid-solution phase exhibits a yield stress of ∼0.63 GPa, consistent with strengthening associated with grain refinement and solid-solution hardening effects. The pop-in-based fracture resistance of the T₂, TiC, and Mo₂C phases falls within literature ranges reported for the corresponding monolithic materials, supporting the applicability of the method to this alloy system. Notably, TiC shows the highest fracture resistance among the brittle phases, whereas ductile–brittle interfaces exhibit markedly lower interfacial fracture resistance than brittle–brittle interfaces, consistent with severe mechanical incompatibility and stress concentration that promote interfacial debonding.

The process of high-pressure sliding (HPS) was used to investigate the phase transformation from α phase to ω phase in pure Zr and Hf. The samples were illuminated by high-energy X-rays and in situ analysis was undertaken during high-pressure loading, heating up to 180°C, and straining by the HPS process for samples which were annealed and/or severely strained by high-pressure torsion (HPT). It was shown for Zr that the α→ω transformation is promoted by concurrent straining under high pressures and it is more pronounced in the HPT-processed samples than in the annealed samples. The heating was also effective for the phase transformation and it was suggested that the α→ω transformation was assisted by thermal activation. For Hf, it was failed to confirm the phase transformation because the pressure was insufficient to reach the critical pressure for the α→ω transformation even in a severely strained state.

The influence of the surface-affected layer formed by mechanical polishing of a metal single crystal specimen on fluorescence X-ray holography was investigated. When a affected layer remains on the surface of the single crystal, the intensity of the fluorescence X-ray emitted from the specimen decreases due to absorption of the incident X-ray by the affected layer. Furthermore, the intensity of the high-quality hologram generated in the undistorted lattice region beneath the affected layer also decreases while passing through the affected layer before exiting the specimen. These effects caused by the affected layer obscure the standing waves used to determine the crystal orientation in the holograms, and strong artifact images are observed in the reconstructed atomic images. By removing the affected layer through sufficiently long electropolishing, high-quality reconstructed atomic images with reduced artifact intensity can be obtained.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 90 (2026) 1–9.

To clarify how Y-Ti-O nano-oxides mitigate radiation damage, this study presents a depth-resolved comparison between fully recrystallized 12Cr oxide-dispersion-strengthened (ODS) steels and an Fe-12Cr model alloy. By normalizing the microstructures through heat treatment before irradiation, the intrinsic influence of nano-oxides was isolated from other defect sinks. Both materials were irradiated with Fe²⁺ ions to 2 dpa at 400°C, enabling direct evaluation of defect evolution under identical conditions. Transmission electron microscopy (TEM) revealed that the ODS steels developed substantially lower dislocation-loop densities and smaller, more uniform loop sizes than the Fe-12Cr alloy. The ODS steels also exhibited a dominant population of 1/2〈111〉 interstitial loops, whereas the model alloy formed both 〈100〉 and 1/2〈111〉 loops with large depth-dependent fluctuations. Nano-indentation testing further demonstrated that irradiation-induced hardening in the ODS steels was significantly reduced, consistent with dispersed barrier hardening calculations based on the observed microstructure. These results provide direct experimental evidence that nano-oxides destabilize defect evolution, suppress loop growth, and mitigate hardening, offering mechanistic insight for the design of advanced radiation-tolerant materials.

Hydrogen penetration into PC steel bars in utility poles occurs in narrow environments such as inside concrete cracks. However, hydrogen penetration phenomena are generally evaluated under a uniform environment, such as immersion tests in alkaline solutions. In this study, we constructed a system for evaluating hydrogen penetration into pure iron in an environment that simulates cracks in the concrete of a utility pole. It was found that a non-uniform hydrogen penetration phenomenon occurred in this narrow environment.

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 74 (2025) 198–203. The citation for Fig. 2(d) in the main text is corrected.

To meet the growing demand for copper (Cu), the higher impurity levels commonly associated with secondary raw materials have increased the demand for cleaner copper concentrates derived from primary ores in Cu production. Under such conditions, effective separation of Cu from impurities, including zinc (Zn), in mineral processing—particularly flotation—has become increasingly important and is expected to be even more critical in the future to ensure stable downstream metallurgical processing. Selective flotation of Cu sulfides, including chalcopyrite (CuFeS₂), from Cu sulfide ores is often hindered by unwanted activation of sphalerite (ZnS). Pyrite (FeS₂) enhances the release of Cu ions via the galvanic dissolution of CuFeS₂, thereby promoting Cu activation of ZnS. Although zinc sulfate (ZnSO₄) is commonly used to depress ZnS, extensive flotation testing is still required in practice to determine the appropriate ZnSO₄ dosage for ores varying mineral compositions. To address this issue, the present study proposes a mineral composition–based conceptual approach for predicting ZnS depression in flotation. First, the degree of Cu activation of ZnS at pH 9 was evaluated by quantifying the amount of Zn released from ZnS after conditioning with different mineral compositions, represented by the CuFeS₂/ZnS and FeS₂/CuFeS₂ ratios. Second, an empirical model was established to estimate the degree of Cu activation of ZnS based on these mineral composition parameters. Finally, by combining the empirical model with flotation results, a concept was proposed to predict the appropriate ZnSO₄ dosage as a guideline for ZnS depression. The proposed approach can provide a systematic basis for reducing trial-and-error flotation testing and may support more robust Cu/Zn separation across Cu sulfide flotation systems with variable mineral compositions.

Copper tubes are widely used as heat transfer tubes for air conditioners and heat exchangers due to their excellent corrosion resistance, heat transfer, and workability. However, carbon film is formed on an inner surface of copper tube by the burning of the lubricating oil used in the annealing after drawing process during copper tube manufacturing. This causes pitting corrosion of copper tubes and increases the risk of leakage accidents. General method to quantify the amount of residual carbon includes collecting the amount of residual carbon by acid treatment and measuring the amount of residual carbon by infrared absorption method. In this study, as a simpler method to measure the amount of residual carbon, we used a gel electrolyte whose shape can be easily controlled and measured the potential difference (hereafter ΔE) between pure copper and carbon-attached copper. As a result, an increasing trend of ΔE value with increasing residual carbon was the most observed in the 0.5 mol L⁻¹ Na₂SO₄ gel electrolyte adjusted to pH 6.5.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 64 (2025) 214–218.

Ti and its alloys are expensive materials because of the complexities involved in their extraction from the ore, melting, and machining processes. In this study, an energy-effective approach to induction melting of commercially pure Ti using ceramic crucibles was investigated. Crucibles composed of yttrium oxyfluorides were prepared, and pure Ti was melted in a high-frequency induction furnace using the oxyfluoride crucibles. Ti with silver-like luster was obtained when a YOF/Y₇O₆F₉ crucible was used. The Vickers hardness of the thus-obtained Ti was comparable to that of Ti before melting and the concentration of O in the Ti was 0.2%, which is within the acceptable range for pure Ti. There were no cracks in the crucible after melting Ti. When Ti was melted using Y₅O₄F₇ or Y₅O₄F₇/YF₃ crucible, the concentration of O in melted Ti was 0.15%, while the crucible cracked after melting Ti. Consequently, YOF/Y₇O₆F₉ is a promising refractory material for handling molten Ti.

Amorphous electrical steel sheets were subjected to shearing using a tungsten carbide–cobalt (WC–Co) punch. To suppress crack formation on the surface of the piercing holes, the punch was ion-sharpened and subsequently laser-processed to introduce a nanometer-periodic surface structure. A diamond-like carbon coating was applied to increase surface hardness, and the shearing characteristics were compared.

The crack width on the piercing hole surface was measured at two stages, namely the half-piercing stage and the full-piercing stage. The fracture propagation mechanism was analyzed by correlating the crack behavior with the load–stroke diagrams and their characteristics. It was found that the introduction of the nanometer-periodic structure is the dominant factor in improving the shearing characteristics.

Platinum group metals (PGMs) are vital in catalysis and electronic materials, yet their supply remains unstable due to concentrated primary production and limited substitutability. Conventional powder synthesis methods struggle to produce submicron PGM alloy powders with both controlled morphology and high thermal durability, creating demand for alternative approaches.

Molten salt offer high reactivity and accelerate solid-state processes, but integrated methods that directly yield PGM alloy powders with tailored particle characteristics are still limited. This study examines PGM alloy powders synthesized via a molten-salt-based chlorination–reduction route and compares them with powders produced by chemical reduction. The results highlight molten-salt-mediated synthesis as a promising pathway for generating thermally durable PGM alloy powders with industrial applicability.

This study investigated the influence of media material on the fracture behavior and morphology of glass particles in binary grinding systems using carbon steel and stainless steel of nearly identical sizes and densities. Dry grinding experiments were conducted in an attritor-type stirred mill, and the products were analyzed using particle size classification, population balance modeling, X-ray fluorescence, microscopy, surface analysis, and discrete element method (DEM) simulation. In both systems, glass breakage primarily occurred through surface-related fracturing. The glass–carbon steel system exhibited faster grinding at 10 and 40 min, whereas both systems showed temporary stagnation at 20 min, followed by renewed grinding at 40 min. The carbon steel system produced glass particles with slightly higher circularity, whereas the stainless-steel system produced particles with higher aspect ratios. Surface analysis indicated greater roughening and stronger adhesion of the glass-derived species on stainless steel. The DEM results showed a higher collision frequency and lower collision energy in the carbon steel system, but a lower frequency and higher energy in the stainless-steel system, indicating that more frequent low-energy collisions are more effective for promoting glass breakage than less frequent high-energy impacts. These results demonstrate that the media material significantly affects the grinding kinetics and particle morphology in binary-grinding systems.

This study prepared ZnO@FCIP composite electromagnetic absorbing materials via an in-situ loading combined with thermal conversion strategy, systematically investigating their microstructure, electromagnetic parameters, absorption performance and RCS characteristics by regulating ZnO loading (10–40 wt.%). XRD, SEM and EDS characterizations showed ZnO nanoparticles were uniformly loaded on FCIP surface, forming stable heterogeneous interfaces while maintaining FCIP crystalline stability. Electromagnetic tests indicated appropriate ZnO enhanced interfacial polarization loss and modulated conductive networks, optimizing dielectric-magnetic loss synergy. The 20 wt.% ZnO composite exhibited optimal performance: at 10 mm thickness, it achieved a minimum reflection loss of −37.8 dB and an effective absorption bandwidth (RL ≤ −10 dB) of 4.2 GHz. RCS tests showed good wide-frequency scattering suppression. The excellent performance originated from synergistic impedance matching, multiple scattering, interfacial polarization and conductive loss, providing a new design approach for high-performance absorbing/stealth materials.

Hierarchical nanoporous metals have nanometer-scale pores on the surface of a larger-scale structure. The hierarchy of the porous structure combines both a high specific surface area and good fluid permeability, enhancing catalytic performance. In this study, laser powder bed fusion (L-PBF) of a hypereutectic Al-Cu alloy is explored as a route to manufacture hierarchical nanoporous Cu. The L-PBF process enables the fabrication of the lattice structure, and the subsequent dealloying process imparts nanometer-scale pores on the surface of the lattice structure (nano/millimeter-scale hierarchy). In addition, rapid solidification in the L-PBF process introduces a refined microstructure with high interfacial energy, enabling the control of microstructural morphology through annealing. Dealloying from the annealed microstructures enables the formation of micrometer-scale pores, on which the nanometer-scale pores are formed. As a result, the microstructure of the L-PBF-processed Al-27 mol%Cu alloy was controlled through annealing, and subsequent dealloying formed a nano/micrometer-scale hierarchical porous structure not only on its cross-section but also on its surface. This study provides a novel process concept for manufacturing hierarchical nanoporous metals with nano/micro/millimeter-scale hierarchy.