Creep strength and material degradation of heat-resistant steel were discussed, focusing on microstructural changes during long-term creep exposure. The materials and creep rupture data were obtained from Creep Data Sheet Project by National Institute for Materials Science. For determining the allowable stress, the 100,000 h creep rupture strength should be evaluated based on creep rupture data. The selection of TTP and dividing the creep rupture data set are important to evaluate long-term creep strength when creep strength degradation occurs in the long term. In order to establish the allowable stress, minimum creep strength must also be evaluated. The minimum creep strength depends on the standard error of estimate (SEE) for creep rupture data. If the heat-to-heat variation of creep strength is large even for the same material specification, the value of SEE is estimated to be large. Therefore, it is important to clarify the reason for the heat-to-heat variation of creep strength in terms of microstructural changes and chemical compositions. Microstructural degradations were reported for carbon steels, low alloy steels, 9–12%Cr ferritic steels and austenitic heat-resistant steels, focusing on precipitates and dislocation structures. The reason for the heat-to-heat variation of creep rupture strength was discussed in term of the difference of solute atoms, segregation and grain size.

Precipitates formed during the hot-rolling process of Al-1%Mn alloy were quantitatively characterized by 3-dimensional (3-D) evaluation. The 3-D image was reconstructed using a serial sectioning technique by combining the focused ion beam and scanning electron microscopy (SEM). In the reconstructed 3-D volume, more than 10000 precipitates were extracted, and the log-normal distribution explained the size distribution well. We also quantitatively evaluated the precipitates from the 2-dimensional (2-D) SEM image taken during the serial-sectioning and from the scanning transmission electron microscopy (STEM) observation that the specimen was fabricated from the serial-sectioned sample. According to the data evaluated from the 2-D and the 3-D images, the average size of the precipitation measured by the 3-D image was larger than that of the 2-D images of SEM and STEM. That is presumed by the morphological anisotropy owing to hot rolling. We also discussed the effect of the number of the analyzed precipitates on the average size and distribution. The average size significantly depends on the number of analyzed precipitates. Besides, we evaluated the normality of the logarithmic distribution of the size by the Quantile-Quantile plot.

This Paper was Originally Published in Japanese in J. JILM 75 (2025) 144–150.

Age–hardenable Cu–Ti alloys, which combine high strength and high electrical conductivity, are widely used as conductive materials and have attracted significant interest due to the miniaturization and performance enhancement of electronic devices. The addition of trace amounts of third elements, such as Al and Fe, has been found to effectively improve alloy properties. However, accurately evaluating the effects of these minor additions remains challenging. In this study, a detailed microstructural analysis of fine precipitates and secondary phases in Cu–Ti alloys with trace additions of Al and Fe was conducted using TEM observation with replica specimens. In a Cu–3.2Ti–1.1Al–0.1Fe (mass%) alloy, solid–solution treatment resulted in the formation of Cu₃Ti₂ with a tetragonal, 50–100 nm in size, incorporating approximately 11 at% Fe. After subsequent aging treatment, a metastable β′–Cu₄Ti (tetragonal) phase was observed within the Cu matrix grains, similar to conventional Cu–Ti alloys. However, unlike in binary Cu–Ti alloys, a lamellar structure containing β–Cu₄Ti did not form at the grain boundaries; instead, Cu₂TiAl (cubic) precipitates, 0.5–1 µm in size, were identified. These findings demonstrate that the replica method is a highly effective technique for the precise analysis of the composition and structure of fine precipitates in Cu–Ti alloys. The results provide valuable insights for optimizing the microstructure of Cu–Ti alloys and advancing their material design.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 64 (2025) 49–53. The abstract and figure captions are slightly modified.

NiCr and NiCr/10WC coatings were fabricated by high-velocity oxy-fuel (HVOF) spraying to investigate the effect of WC incorporation on cavitation and cavitation–corrosion behavior in deionized water and 3.5 mass% NaCl solution. The NiCr/10WC coating exhibited a significantly lower cavitation erosion rate than the NiCr coating in both media. The improvement was attributed to a pronounced reduction in porosity (from 5.7% to 0.5%) and a 46% increase in the microhardness of the Ni(Cr) solid-solution. Microstructural observations revealed that semi-molten WC particles exerted a peening effect during spraying, suppressing the formation of pores and oxide films and enhancing coating densification and strain hardening. In deionized water, the NiCr/10WC coating primarily failed by localized WC spallation, while the Ni(Cr) solid-solution remained largely intact. In 3.5 mass% NaCl solution, electrochemical analysis showed that NiCr/10WC coating exhibited a more noble corrosion potential (−0.352 V) and a lower corrosion current density (1.68 × 10⁻⁶ A cm⁻²) than NiCr, confirming its superior corrosion resistance. The improved cavitation–corrosion resistance originated from a synergistic effect between the enhanced impact resistance and the chemical stability of WC and the Ni(Cr) solid-solution. The incorporation of WC thus transforms the failure mode from defect-driven large-area degradation to localized, WC-controlled damage, establishing a beneficial coupling between mechanical robustness and corrosion resistance.

Achieving a synergistic improvement in strength and ductility remains a fundamental challenge in metallic materials. Here, large-particle ultrasonic shot peening is employed to induce an intralayer bimodal heterogeneous microstructure in an SPS-sintered AlSi10 alloy. EBSD analyses reveal that highly localized plastic deformation occurs adjacent to the Si phase, whereas regions farther away experience much weaker deformation, leading to the coexistence of micrometer-scale fine-grained and relatively coarse-grained regions within the same peening-affected layer. Meanwhile, the Si phase undergoes in situ fragmentation and redistribution into the Al matrix, further enhancing intralayer heterogeneity. As a result, the USP-treated alloy exhibits simultaneous improvements in strength and ductility, with the ultimate tensile strength increasing from ∼120 MPa to ∼145 MPa and the fracture strain extending from ∼15% to ∼25%.

Aluminum (Al) matrix composites (AMCs) reinforced with boron carbide (B₄C) particles were produced using a combination of wet shear pulverization (WSP) and spark plasma sintering (SPS). The WSP process, which generates high shear stress in an ethanol medium, enabled uniform dispersion of B₄C particles and effectively reduced agglomeration compared to traditional hand mixing. However, oxygen analysis showed a slight increase in oxidation after WSP processing, a nanoscale Al–Al₂O₃ interfacial layer, known as the marble pattern, formed and contributed to improved particle–matrix bonding. Microstructural studies revealed that WSP-treated composites exhibited a uniform distribution of B₄C particles and a dense microstructure, while hand-mixed samples displayed uneven dispersion and localized oxide formation. The Al–10 vol% B₄C composite produced by WSP achieved an ultimate tensile strength of 201 MPa and a fracture elongation of 19.4%, both surpassing the values reported for previous Al–B₄C composites. These findings confirm that WSP is an effective powder-processing method for enhancing the interfacial structure and mechanical properties of Al–B₄C composites.

Work hardening in metals has traditionally been interpreted mainly in terms of dislocation-based mechanisms. In polycrystals, however, deformation incompatibility inevitably develops between neighboring grains, generating mesoscale elastic stresses that can significantly influence hardening. In this study, such stresses are termed elastic incompatibility stresses (EI stresses), which are defined as elastic stresses arising from the requirement of intergranular deformation compatibility, although their origin differs from that of back stress associated with dislocation accumulation. We first show that EI stress has an effective-stress form analogous to that of back stress at the grain scale. Using bicrystal models, the role of EI stress in work hardening is then investigated for HCP, FCC, and BCC metals. The analyses reveal that EI stress contributes to work hardening in all three crystal structures, with the largest effect observed in HCP crystals. EI stress decreases as the number of active slip systems increases, leading to a reduction in the work-hardening rate. Furthermore, when both Taylor-type dislocation-based hardening and EI stress are considered, both contribute to work hardening, although their relative contributions vary depending on the deformation conditions. These findings demonstrate that a comprehensive understanding of work-hardening mechanisms requires consideration of EI stress in addition to conventional dislocation-based mechanisms.

Molten sulfide electrolysis, which produces metals and sulfur gas by electrolyzing sulfides, is expected to be a sustainable metal production technology due to its extremely low CO₂ emissions. A mixture of BaS and La₂S₃ is used as the electrolyte for molten sulfide electrolysis. In this study, the kinetics of the carbosulfidation reaction of BaSO₄–La₂O₃ mixtures were investigated to develop an electrolyte manufacturing process for molten sulfide electrolysis. Sulfidation of the mixture was performed at 1423 K in the presence of carbon under a sulfur partial pressure of 0.10 atm, confirming CO gas generation from the carbosulfidation reaction. The fraction of oxygen removal from the BaSO₄–La₂O₃ mixture reached 99%, yielding a mixture of BaS and BaLa₂S₄. Under these experimental conditions, the rate-controlling step was the chemical reaction. The apparent activation energy of the reaction was estimated as 140 ± 34 kJ·mol⁻¹ based on the experiments at 1323–1473 K. Furthermore, the analysis based on the Langmuir adsorption model indicated that the reaction rate was governed by the chemical adsorption of sulfur molecules on the adsorption site. The findings from this study are expected to contribute to the optimization and industrialization of the electrolyte manufacturing process for molten sulfide electrolysis.

The influence of co-deposited hydrogen on microstructure of electrodeposited platinum (Pt) films was investigated using thermal desorption spectroscopy, X-ray diffraction and transmission electron microscopy. The Pt films were potentiostatically electrodeposited on a gold foil from a tetrachloroplatinate(II) solution at 0.1∼−0.3 V vs. Ag/AgCl. From the thermal desorption spectra of hydrogen, a broad desorption peak at around 650 K was observed in the Pt films deposited at 0.1∼−0.2 V vs. Ag/AgCl, and a pronounced desorption peak at around 500 K was observed in the Pt films deposited at −0.3 V vs. Ag/AgCl. As the deposition potential was more negative, the current efficiency of Pt deposition was lower and the hydrogen concentration of Pt films was higher. These electrodeposited Pt films were consisted of fine grains of 9–17 nm, and the lattice parameter decreased with increasing hydrogen concentration. After heat treatment at 500 K, reduction of lattice contraction and increase in grain size were observed in the Pt films with higher hydrogen concentrations. The increase in grain size by the heat treatment was larger as the hydrogen concentration of Pt films was higher. Thus, it is clear that such grain growth observed in the electrodeposited Pt films was enhanced by hydrogen–induced superabundant vacancies.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 88 (2024) 233–238. The main text has been slightly modified.

The quality classification of recycled aggregate is based on the water absorption rate and the density of the adhered mortar. However, the quality of recycled aggregate is affected by the adhesion characteristics between the original aggregate and mortar (Interfacial Transition Zone: ITZ). It has been reported that carbonation of recycled aggregate improves mortar quality, but the effect on the above adhesion interface is not clearly evaluated. In this study, laser-induced vibration method is conducted on recycled aggregate before and after carbonation to evaluate the quality of the adhesion interface between the aggregate and mortar. A simple spring model, in which the adhesion strength of the interface is expressed as a spring constant, is applied to the quality evaluation of the recycled aggregate. As a result, it is found that there is a correlation with Vickers hardness, which can measure the strength of the interface.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 74 (2025) 316–323.

In situ observation was employed to elucidate shear-induced cracking in semisolid Cu–0.1 mass% Fe–P ternary alloys and to clarify the role of phosphorus content in crack formation. During shear deformation, crack formation in Cu–0.1 mass% Fe–P alloys with estimated solid fractions ranging from 0.94 to 0.99 depended strongly on the phosphorus content. Cracking occurred at the phosphorus content range of 0.09–0.15 mass%, whereas no cracking occurred at the range of 0.03–0.06 mass%. Semisolid deformation is generally governed by either grain deformation or grain rearrangement. Phosphorus addition shifts this balance toward grain rearrangement rather than grain deformation, leading to cracking due to insufficient melt flow between solid grains. Because the solid fractions during shear deformation were comparable, the effect of phosphorus is attributed to its dissolution into the solid grains, which modifies their mechanical properties and promotes grain rearrangement.

The furan no-bake process is widely used because of its applicability to a variety of casting materials. In recent years, it has been applied to additive manufacturing systems. The furan AM process has advantages in the production of complex or long thin cores. Those cores deformed more due to their own weight than in the conventional furan no-bake process. The objective of this study is to determine the deflection characteristics of the mold at room temperature under the application of equally distributed loads. The transverse strength and the deflection of molds were measured under various stress conditions, curing time and humidity conditions. The deflection of molds increases as stress increases or curing time decreases. On the other hand, there is no correlation between transverse strength and deflection. It is suggested that the progressive curing leads to an increase in the degree of polymerization, increase in resin viscosity, and increase in deformation resistance. The deflection characteristics of the mold at ambient temperature are similar to the creep behavior of chemically cross-linked polymers, and it is influenced by the viscoelastic properties of furan resins. Under high humidity, extremely large deflections of molds are observed, which is due to the softening of the furan resin as it absorbs moisture.

This Paper was Originally Published in Japanese in J. JFS 97 (2025) 679–684.

Immersion heaters are increasingly used for heating aluminum alloys, but conventional heaters struggle to achieve the high-power density required for aluminum melting. For high-power operation, filler must provide chemical stability, high thermal conductivity, and low electrical conductivity at over 1273 K in oxidization atmosphere. Owing to their low cost, Al₂O₃ particles are promising candidates. In this study, molded specimens were fabricated using Al₂O₃ particles with different particle-size distributions, aspect ratios, and circularities, and their thermal and electrical conductivity were evaluated. Specimens composed solely of fine particles (<50 µm) exhibited relative density of 65% and the thermal conductivity of 2.5 W/m·K at 867 K (25% of bulk Al₂O₃) due to thermal resistance from porosity. In contrast, their electrical conductivity reached 6.8 µS/cm at 1473 K, (370% of bulk Al₂O₃) attributed to discharge phenomena within pores. When coarse particles (<1.7 mm) and fine particles were mixed at 7:3 ratio, the relative density varied from 65% to 83% depending on coarse particle morphology. Thermal conductivity increased with relative density, reaching 6.0 W/m/K at 867 K (60% of bulk Al₂O₃). Electrical conductivity decreased with increasing coarse particle mass fraction. LN2D analysis revealed that random dispersion caused by broad size distribution, low circularity, and low aspect ratio disrupted conductive paths, reducing conductivity to 1.7 µS/cm at 1473 K (94% of bulk Al₂O₃). Conversely, ordering structures formed by high circularity, and high aspect ratio caused linear electrical conductivity and limited reduction effect. Based on these insights, a filler consisting of coarse particles with broad size distribution, low circularity, and low aspect ratio mixed with fine particles at 7.5:2.5 was designed. The prototype immersion heater demonstrated 20% higher power density than conventional heaters, confirming that high-power heaters can be fabricated using Al₂O₃ fillers that are over 50% cheaper than nitride-based materials.

Since die casting simulations need to calculate complex multi-physics simulations, such as the coupling between solid and the flow of molten metal, a calculation method which can handle a wide range of calculation conditions is required. The MPH (Moving Particle Hydrodynamics) method, which is a particle method based on analytical mechanics, is expected to be effective for the die casting simulations as it has high numerical stability. In this paper, the applicability of the MPH method to the die casting simulation was investigated. The fundamental models of heat transfer, phase change, and variable volume were introduced to the MPH method, and the calculations which simulate the die casting process with simple geometries were conducted. It was shown that the proposed method has the potential to simulate various phenomena in the die casting process in a unified manner.

This Paper was Originally Published in Japanese in J. JFS 97 (2025) 742–749. The abstract and Table 1 are slightly modified.

Composite Ca–Mn oxide catalysts with distinct crystal structures—orthorhombic perovskite CaMnO₃, delafossite-related layered Ca₂Mn₃O₈, and marokite-type CaMn₂O₄—were synthesized via a coprecipitation method and evaluated for CO oxidation. Among these oxides, Ca₂Mn₃O₈ exhibited the highest low-temperature activity, achieving significant CO conversion above 120°C, comparable to that of Pd/Al₂O₃. Repeated reaction tests confirmed the structural robustness of Ca₂Mn₃O₈. CO-TPD measurements revealed that CO oxidation on Ca–Mn oxides proceed predominantly via the Mars–van Krevelen (MvK) mechanism. It is considered that the structural feature of Ca₂Mn₃O₈, layered framework containing ordered Mn vacancies, enhances lattice-oxygen mobility, thereby accelerating the MvK-type CO oxidation pathway. These results demonstrate that Ca₂Mn₃O₈ is a structurally stable, non-noble-metal catalyst capable of efficient low-temperature CO oxidation, offering a promising alternative to conventional metal nanoparticle catalysts.

Wood exhibits high anisotropy and is mainly composed of highly biocompatible cellulose. This work explores the potential of delignified wood to serve as anisotropic scaffolds for regenerative medicine. Samples of cedar and cypress wood were treated via two-step delignification (alcoholysis and Wise method) to remove lignin while maintaining their anisotropic structures. The lignin removal was confirmed by the whitening of the samples. The chemical structures of the samples measured using attenuated total reflection-Fourier transform infrared spectroscopy showed a significant decrease in lignin-related peaks. Mouse-derived osteoblast-like cells (MC3T3-E1) were cultured on the samples. Fluorescence microscopy images showed that the MC3T3-E1 cells were elongated and aligned along the longitudinal axis of the wood lumina. Thus, the delignified wood architecture effectively guides the MC3T3-E1 cell orientation. These observations suggest that delignified wood skeletons can be used as anisotropic scaffolds in tissue engineering.

Surface-softened clad steel (SCS) was developed to achieve both high strength and high resistance to liquid ammonia stress corrosion cracking (SCC), and SCS plates with tensile strength (TS) of 600 MPa were applied to two ammonia tanks more than 30 years ago. In order to grasp the long-term SCC resistance, the open inspection results were analyzed. During 30 years of service, one of the SCS plate tanks had no crack, and only six crack incidents were detected cumulatively in the other tank. Compared with the conventional TS 600 MPa steel plate tank, SCC of the SCS plate tanks was remarkably suppressed, suggesting that the SCS plate tank has excellent long-term SCC resistance. The cracks in the SCS plates tanks were only in the welded parts, as in the same case of TS440 MPa SLA325A commonly applied to liquid ammonia tanks. It can be said that the TS 600 MPa SCS plate tank has high resistance to liquid ammonia SCC equivalent to the TS440 MPa SLA325A plate tank.

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 74 (2025) 216–221.

Self-bonding coated electrical steel sheets enable the laminations to be bonded through induction heating and pressure curing without the use of mechanical interlocks, thereby avoiding magnetic property degradation caused by stress concentration and plastic deformation associated with conventional interlocking processes. This paper presents an inductive heating method based on a magnetically closed-loop, intended for ring-shaped electrically conductive structures such as motor stator cores. The eddy-current-induced ohmic heating process can be modeled as a transformer with a short-circuited secondary winding. Compared with conventional open-loop induction heating configurations, the proposed closed-loop method exhibits superior performance in terms of magnetic flux coupling, dimensional tolerance, and effective heating power. Experimental measurements were conducted to validate these advantages. In addition, a partial differential equation (PDE)-based electromagnetic field analysis was performed to characterize the current density distribution along the radial direction of the ring core.

Using current–voltage (I–V) and capacitance–voltage (C–V) measurements, the current transport and interface characteristics properties of Pt/n-GaN Schottky barrier diodes (SBDs) were investigated. The forward I–V analysis (300–425 K) showed barrier inhomogeneity, consisted of a double Gaussian distribution of barrier heights. C–V characteristics revealed significant frequency dispersion and negative capacitance, indicating a high interface state density (D_it). The distribution of D_it was quantified using four different methods such as Hill-Coleman, Terman, conductance, and forward I–V, which displayed the D_it values in the range of low-10¹² to high-10¹³ eV⁻¹ cm⁻². In addition, C–V hysteresis analysis showed the presence of negatively charged traps at the Pt/n-GaN interface. These results indicate the non-ideal current transport in GaN SBDs by emphasizing the coupled effects of barrier inhomogeneity and interface states.

Electric arc furnace (EAF) slag, a by-product generated during the refining of steel scrap in electric furnaces, is produced in large quantities and should be effectively used as a recycled resource. When EAF slag is considered for use as a cement raw material, the chromium compounds in EAF slag may pose environmental and regulatory concerns, necessitating effective removal strategies. In this study, the presence of chromium (Cr) compounds in carbon steel (CS) slag was investigated, and alkaline roasting followed by water leaching experiments were conducted to reduce the Cr concentration to a level suitable for use as a raw material in cement production. Cr in CS slag was mainly present in spinel phases bonded to other metals such as Fe and Mg. The Cr removal efficiency was influenced more strongly by the amount of NaOH added than by the roasting time. When the weight ratio of NaOH to CS slag 1 was roasted for 30 min, the Cr concentration in the leaching residue was reduced by more than 95%, whereas the Ca concentration showed relatively little change. Thermodynamic calculations and XRD analysis of the NaOH-roasted products indicated that the insoluble Cr in the CS slag was converted into soluble compounds. These results suggest that the application of the present process to CS slag may enable the development of applications beyond its conventional uses.

Various scorodite synthesis processes have attracted attention as stable arsenic immobilization methods for non-ferrous smelting plants. The hematite method, which uses hematite as the iron source, produces scorodite from As(V), Fe₂O₃, and Fe²⁺ in solution. Compared with other scorodite synthesis routes, this method does not involve large changes in the solution pH and/or the Fe²⁺ concentration. In this study, we developed a recirculating process to reuse the post-reaction solution, and its feasibility was experimentally verified. Storage and reuse of the post-reaction solution will allow for an industrially favorable operation with simplified solution management and reduced wastewater generation. A laboratory-scale apparatus was constructed consisting of a reactor, filtration unit, and post-reaction solution reservoir. Scorodite formation behavior and changes in solution composition were compared between fresh reagent-based solutions and repeatedly recirculated solutions. Under recirculation conditions, slight differences in particle growth behavior were observed; however, scorodite formation proceeded stably. Without adjustment of the pH and Fe²⁺ concentration, arsenic was successfully immobilized as scorodite through repeated batch operations by simply adding stoichiometric amounts of hematite relative to the supplied arsenic. By combining this hematite-based recirculation process with downstream low-concentration arsenic removal technologies, an efficient and flexible arsenic treatment flow can be constructed while minimizing reagent consumption and wastewater generation.

The effects of the lattice parameter of the simulated master pattern and the EBSD pattern resolution for indexing of EBSD patterns via pattern matching (Spherical Indexing) were investigated using annealed austenitic steel. A larger deviation from the accurate lattice parameter in the master pattern resulted in a larger deviation from the true crystallographic orientation. Poorer EBSD pattern resolution resulted in a lower angular resolution, especially near the grain boundary, and increased kernel average misorientation (KAM) values. These results suggest that accurate lattice parameter and higher pattern resolution are required for Spherical Indexing to achieve a better angular resolution. Nevertheless, Spherical Indexing using a master pattern with a 15% deviation from the accurate lattice parameter and EBSD patterns with a binning of 8 × 8 provided a better angular resolution than traditional indexing using the Hough transformation of EBSD patterns without binning (binning of 1 × 1). This indicates that Spherical Indexing is an excellent indexing procedure in terms of angular resolution, which is robust for the lattice parameter of the master pattern and EBSD pattern resolution.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 90 (2026) 17–26.

The present study developed a novel solderable polymer composite (SPC) system incorporating a low-melting-point solder (LMS) filler, in which copper nanoparticles (Cu-NPs) were introduced as nano-reinforcements to improve mechanical performance. To investigate the effect of Cu-NPs content on the mechanical interconnection behavior of SPC joints, four SPCs formulations containing different Cu-NPs concentrations (0, 0.2, 0.5, and 0.8 vol%) were synthesized. The mechanical interconnection properties of the resulting SPC joints were evaluated using ball shear and microhardness tests. The results indicated that excessive Cu-NP addition deteriorated the solderability of the SPC joints. However, below a critical concentration, the SPCs produced uniform and proper spherical solder ball joints due to appropriate flow, coalescence, and wetting behavior of the molten LMS fillers. Under these conditions, the mechanical interconnection properties improved with increasing Cu-NP content. This enhancement was attributed to the reinforcing effect of the incorporated Cu-NPs as well as to microstructural grain refinement within the joint region.