Electrodeposition of Zn-V composite films was performed from non-suspension solutions containing VO2+ ions, and the effects of electrolytic factors such as current density, additive, solution temperature and agitation on the codeposition behavior of V compounds and the microstructure of the deposited films were investigated. The critical current density for Zn deposition from a Zn-V solution decreased with decreasing solution temperature and without agitation. The addition of polyethylene glycol (PEG) slightly decreased the current efficiency of Zn, and slightly increased the V content in the deposited films. The curve showing the relationship between current density and current efficiency of Zn shifted toward lower current densities with decreasing temperature, whereas it shifted toward higher current densities with agitation. The curve showing the relationship between current density and V content in the deposited films shifted toward lower current densities with decreasing temperature and toward higher current densities with agitation. V compounds were uniformly codeposited in the deposited films with decreasing solution temperature and the addition of PEG. A decrease in solution temperature and the addition of PEG increased the overpotential for deposition, resulting in smaller Zn platelet crystals. V compounds are co-deposited in the gaps between Zn platelet crystals, and it is thought that as the size of the platelet crystals decreases, the gaps between the crystals become smaller and their number increases, leading to the co-deposition of V compounds being dispersed. Furthermore, in electrolysis from a solution containing PEG, the number of hydrogen generation sites increases, which is expected to increase the number of hydrolysis sites for VO2+, and is thought to be the factors of the uniform co-deposition of V compounds.
Ruthenium, a platinum-group metal, is used in the form of a mixture of ruthenium and tantalum oxides in the catalytic layer of chlorine evolution electrodes owing to the unique catalytic properties and chemical stability of Ru. The recovery of Ru from end-of-life products is important because of its low production, uneven geographical distribution of Ru sources, and high supply risks. However, recovery of Ru requires the dissolution of Ru in an aqueous solution, a procedure which involves the use of a strong acid and is, therefore, dangerous and environmentally hazardous. Moreover, if metals other than Ru dissolve in the aqueous solution during the recovery of Ru, harmful effluents and gases would be generated and the separation of Ru from other metals would be difficult. In this study, we developed a method that involves the extraction of only Ru from the catalyst layer of a chlorine evolution electrode and simultaneous recovery of Ru as a Nd-Ru composite oxide, where the composite oxide is soluble in hydrochloric acid. Only ruthenium oxide was volatilized from the catalyst layer of the oxygen-generating electrode and brought into contact with Nd2O3 via the gas phase. The composite oxide obtained was dissolved in hydrochloric acid and analyzed; the analysis revealed that Ru was highly soluble in hydrochloric acid and that the composite oxide did not contain Ta. [doi:10.2320/jinstmet.J202606]
High-entropy alloys (HEAs) are promising for advanced structural applications because they can achieve a unique combination of strength, damage tolerance, and environmental resistance. In powder-metallurgy processing routes, mechanical alloying (MA) may introduce carbon contamination, which significantly influences phase evolution and microstructural development. Carbon uptake, phase evolution, and mechanical response in a CoCrFeNiTi HEAs processed by mechanical alloying followed by spark plasma sintering were found to be strongly dependent on MA time. The carbon content in milled powders was quantified by combustion analysis. Phase constitution and lattice parameters were analyzed using X-ray diffraction (XRD), with lattice constants determined by Nelson-Riley extrapolation and crystallite size and lattice strain evaluated by Williamson-Hall analysis. Dislocation density was estimated using a Burgers-vector-based formulation. The sintered compacts were characterized by XRD, scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), electron probe microanalysis (EPMA), and electron backscatter diffraction (EBSD). Mechanical properties were evaluated using micro-Vickers hardness and nanoindentation, from which the performance indices H/E and H3/E2 were derived. Carbon uptake increased monotonically with MA time and tended to saturate at longer milling durations. The milled powders formed a predominantly BCC solid solution after MA, accompanied by crystallite refinement and increased lattice strain/dislocation density. After SPS, the microstructure evolved into an FCC-dominant matrix with TiC-related regions and Cr-rich phases. Grain refinement and increased Geometrically Necessary Dislocations (GND) were observed with longer MA time. Mechanical properties showed a hardness drop at short MA time followed by recovery and stabilization at longer MA time, while nanoindentationbased performance indices suggested an optimal intermediate MA-time window. These results demonstrate that MA time controls not only alloying/defect states but also carbon-mediated precipitation and phase balance, providing a practical guideline for optimizing MA-SPS processing of Ti-containing HEAs.
The influence of cold rolling on hydrogen desorption behavior in Al-Cu-Mg and Al-Zn-Mg alloy plates was investigated. Solution-treated plates were cold-rolled with total reductions of 0, 50, 80 and 90%, and kept at room temperature for 168 h. Vickers hardness of the specimens increased with the rolling reduction. Thermal desorption analysis revealed that a desorption peak at about 350 degrees C in the specimen without cold rolling (0% reduction), attributable to hydrogen trapped by dislocations, changed markedly with rolling reduction: the desorption peak split into two peaks and the desorption amount of the peak at lower temperature increased notably with increasing cold reduction. To investigate the cause of this phenomenon, hardness measurement and electron backscattering diffraction analysis were carried out for the specimen 90% cold-rolled and then heated to 350 degrees C. The hardness was decreased by about 50% by the heating, and partially recrystallized microstructure containing some recrystallized grains in the recovered matrix was observed in the heated specimen. From these results, recovery and partial recrystallization were attributable to the appearance of the low-temperature peak. The change in hydrogen desorption behavior with holding time for up to 144 h at room-temperature was also examined in the 90% cold-rolled specimens. The desorption amount corresponding to the two peaks described above stemming from hydrogen atoms trapped by dislocations decreased with the holding time at room temperature, indicating that the hydrogen atoms trapped by dislocations can be released during room-temperature holding. The whole results obtained in this study have clarified the role of deformation microstructures on desorption behavior of the hydrogen atoms trapped by dislocations.[doi:10.2320/jinstmet.J202601]
Vacancy trapping is a key nonequilibrium phenomenon during rapid solidification, yet its behavior in alloy solid solutions has not been fully clarified. In this study, molecular dynamics (MD) simulations of isothermal solidification were performed for Al-Cu (FCC) and Fe-Cr (BCC) alloys to investigate the occurrence of vacancy trapping and the temperature and composition dependence of the nonequilibrium vacancy concentration cneq. Vacancy trapping was observed in both alloy systems. In Al-Cu alloys, cneq increased almost monotonically with decreasing temperature, whereas in Fe-Cr alloys, it exhibited a non-monotonic dependence, closely resembling that reported previously for pure BCC metals. In the high-temperature regime (T/T-m >= 0.8), cneq correlated strongly with the interface velocity Vint, indicating that vacancy trapping is governed by interface migration kinetics. Analysis based on the Wilson-Frenkel mode showed that solute additions increase the activation energy for diffusion across the interface in Al-Cu alloys, reducing Vint and suppressing vacancy trapping, while such effects were negligible in Fe-Cr alloys.
The shape of creep curve was quantified using the Strain Acceleration and Transition Objective-index, alpha, and the extrapolated life to failure were estimated from the creep curve near the minimum creep rate. In a two-phase Mg-Li-Al-Zn alloy, where the strain dependence of creep rate varies depending on stages, alpha varies in each stage. It indicates that the index alpha reflects the state of the microstructure. The relationship between the extrapolated life, the minimum creep rate and the index alpha was systematically clarified, and shows that the Monkman-Grant constant is inversely proportional to the square root of alpha and to the minimum creep rate. To improve the life to failure, in addition to reducing the minimum creep rate, reducing the alpha in primary and tertiary creep is effective.
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 alpha/beta 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.
The recovery of nickel from nickel sulfide (NiS) is an important process for the effective utilization of metal resources. In our previous work, the addition of metallic pieces, such as Fe and Sn, was found to enhance Ni leaching from NiS in acidic solutions containing a copper oxidant. This study investigates the promotional effect of metallic copper on this leaching process. The addition of metallic Cu was observed to significantly accelerate Ni leaching from NiS, even in the absence of a copper oxidant. Notably, when Cu was introduced as a powder, a complete Ni leach was achieved. Experimental results demonstrated that direct physical contact between the metallic Cu and NiS, as well as sufficient proton concentration, were essential factors for promoting the reaction. Furthermore, analysis of the residue by XRD confirmed the formation of Cu2S. These findings suggest that Ni leaching is enhanced by a solid-phase reaction between metallic Cu and NiS, leading to the formation of Cu2S. [doi:10.2320/jinstmet.J202524]
Titanium dioxide (TiO2), widely used as a white pigment, exhibits high hiding power due to its high refractive index. In our research group, the optical characteristics of the oxide layer formed on titanium (Ti) and its alloys at high temperature have been investigated, aiming to enhance the esthetic properties of Ti-based dental materials. Although the refractive index is theoretically determined by the material's dielectric constant and atomic volume, the visual appearance of oxide films can vary even among Ti alloys with identical compositions. These variations are influenced not only by changes in intrinsic refractive index due to alloying or impurities but also by the microstructural features of the oxide layer, such as layer thickness, particle size, and surface roughness, which affect light reflectance in the visible spectrum. In this study, commercially pure titanium (CP Ti) was subjected to high-temperature oxidation at various conditions. The effects of oxide layer thickness, particle size on the surface, and surface roughness on the resulting color tone of the oxide layer were systematically investigated. The oxide layers formed were identified as rutile-type TiO2 by X-ray diffraction (XRD). Color measurements using a spectrophotometer revealed that both layer thickness and particle size strongly influenced the L*a*b* color parameters. Particle size analysis suggested Mie scattering as the dominant light scattering mechanism and the size distribution affects reflectance in particular range of wavelength, consequently, correlates with changes in the b* value. Additionally, increased oxidation temperatures broadened the particle size distribution, and layer growth was associated with a transition in visible color from gray through yellow. These findings indicate that both the oxide layer thickness and particle size play critical roles in determining the color appearance of high-temperature oxidized CP Ti. Such insights can contribute the development of aesthetically improved Ti-based biomaterials.
The hot shortness caused by Cu and Sn contained in steel scrap represents a significant technical challenge for promoting carbon neutrality in the steel industry. Hot shortness induced by Cu is considered to occur when liquid Cu, formed at the oxide scale/substrate interface during steel oxidation, penetrates the grain boundaries; however, the detailed mechanism of this penetration remains unclear. In this study, Fe-0.08C-0.3Si-2Mn- 0.3Cu-0.01Sn-0.04Ni-0.2Cr steel was heat-treated under conditions that induce hot shortness, and the Cu concentration distribution at the grain boundaries of the substrate was analyzed in detail using Electron Probe Micro Analyzer (EPMA), Scanning Electron Microscope (SEM) equipped dynamics simulations were performed to evaluate the penetration behavior when liquid Cu contacts random grain boundaries of Fe. The results revealed that, in the early stage, Cu does not penetrate the grain boundaries as a liquid phase, but diffuses along the grain boundaries in the solid phase beyond its solubility limit. After this solid-state grain boundary diffusion of Cu, it is inferred that liquid Cu subsequently forms or infiltrates along the grain boundaries. These findings suggest that controlling the grain boundary diffusion of Cu is essential for mitigating hot shortness.
This study presents tensile properties of Al-Mg-Si alloys after processing by severe plastic deformation through high-pressure torsion (HPT). The alloys were fabricated so as to include excess Fe and Si with different additions of Cu as model alloys for recycling purpose. The tensile strength well exceeded 500 MPa with the total elongation more than 15% after HPT-processing under 2 GPa for 1 turn in all the model alloys. The strength further increases to more than 700 MPa with increasing addition of Cu while maintaining reasonable ductility (similar to 8%). Transmission electron microscopy confirmed that the grain size was reduced to 180 nm and further reduced to 160 nm with increasing Cu addition. Micros structural analyses using scanning transmission electron microscopy and atom probe tomography revealed that Cu was segregated at grain boundaries, contributing to the increase in the tensile strength. The high strength with enhanced ductility is discussed in terms of strain rate sensitivities measured from strain rate change tests.
Creep tests were carried out for the Mg-14.2 mass% Ca-2.9 mass% Al alloy (hereafter referred to as Mg-14Ca-3Al alloy) at temperatures between 498-548 K to elucidate the effect of Al addition on creep properties for the binary Mg-14Ca alloy. The Mg-14Ca-3Al alloy exhibits a fine lamellar structure with alpha-Mg and C14-Mg2Ca phase, together with a small amount of the primary alpha-Mg phase. It was confirmed that Al preferentially substitutes to C14-Mg2Ca phase rather than alpha-Mg phase. The minimum creep rate for the Mg-14Ca-3Al alloy is approximately one seventh of that for the binary Mg-14Ca alloy at 498 K. The stress exponent of minimum creep rate for the Mg-14Ca-3Al alloy, n, continuously decreases with increasing temperature and the activation energy for creep, Q(c), decreases with increasing applied stress. The formation of coarse lamellae during creep is limited around colony-boundaries at a low temperature, while it is pronounced typically at high temperature and low stress conditions. The change in creep parameters, n and Q(c), for the Mg-14Ca-3Al alloy results from the decreased creep strength driven by the formation of coarse lamellae during creep. The minimum creep rate and creep rupture life for the alloy follow the phenomenological Monkman-Grant relationship.
This study presents the tensile strength of 1010 MPa with the total elongation to fracture of 13% in an A2024 aluminum alloy. The alloy was solution-treated and processed by high-pressure torsion (HPT) under 6 GPa for 10 turns at room temperature to refine the grain size to 3130 nm. A micro tensile specimen with gauge dimensions of 50 & micro;m in length, 20 & micro;m in width and 15 & micro;m in thickness was fabricated by focused ion beam at a position 2 mm away from the center of the HPT-processed disk. The high-strength with ductility was achieved because (i) the micro tensile specimen minimized larger inclusions which may lead to a premature fracture due to stress concentration, (ii) the ultrafine-grained structure produced by HPT processing enhanced the strain rate sensitivity due to lower activation volume, and (iii) the reduction of pore density due to application of high pressure by HPT processing. This study thus demonstrates that the A2024 alloy has a potential to be highly strengthened with the tensile strength more than 1 GPa and with ductility when the alloys are processed by severe plastic deformation under high pressure.
Machine-learning interatomic potentials (MLIPs) are emerging as a practical route to bridge the accuracy-cost gap between empirical force fields and first-principles methods for atomistic modeling of structural materials. This article reviews two major families-descriptor-based models (e.g., BPNN, GAP/SOAP, SNAP, DeePMD) and graph neural network approaches (e.g., SchNet, NequIP, MACE, Allegro)-highlighting differences in symmetry handling, scalability, and data requirements. We outline dataset construction workflows, including active-learning loops, uncertainty estimation, and transfer learning, that reduce labeling cost while improving coverage of phases, defects, and compositions. Representative applications to metals and ceramics are summarized, such as screw-dislocation core energetics in bcc Fe, diffusion and chemical short-range order in CrCoNi medium-entropy alloys, and large-scale plasticity in functional ceramics. Practical guidelines are discussed for choosing between descriptor-based and equivariant GNN models, balancing accuracy and throughput, leveraging GPU acceleration, and validating models via thermo-mechanical properties and dynamical simulations
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 8x8 provided a better angular resolution than traditional indexing using the Hough transformation of EBSD patterns without binning (binning of 1x1). 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.
The corrosion resistance of hot-stamped zinc-coated steel sheet with a coating layer of the alpha-(Fe, Zn) phase is proposed based on the structural and electrochemical characterization of corrosion products. Goethite, lepidocrocite, akaganeite, and magnetite are the main corrosion products formed on the uncoated steel sheet. However, when the surface is coated with the alpha-(Fe, Zn) phase, zinc ferrite is formed instead of magnetite in the inner layer of corrosion products. The formation of zinc ferrite is considered to suppress the cathodic reduction reactions of lepidocrocite and akaganeite, thereby enhancing the corrosion resistance of the steel sheet. [doi:10.2320/matertrans.MT-M2026021]
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 an 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 highquality 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.
The causes of the differences of the graphite nodularity (ratio of graphite spheroidization) depending on the methods built on the Japanese Industrial Standards (JIS) in spheroidal graphite cast iron castings were investigated based on the factors influencing the roundness (roundness factor or roundness shape factor) and area (cross-sectional microstructure) of the graphite particles on the cross-sectional microstructure and the graphite nodularity. Although the effects of the sharpness and resolution of the image data and the binarization threshold in the image analysis on the roundness and the area of the mock graphite particles were generally small, the roundness of the hexagram or octagram increased beyond 0.6 with a decrease in the sharpness of the resolution. Meanwhile, the relationships between the graphite nodularity by JIS and ISO methods built on the JIS for various combinations of the roundness and area showed that the nodularity by the ISO method is often greater than that by the JIS method. This is because the graphite nodularity by the ISO method depends on whether the roundness is less than 0.6 or not. These suggest that the smaller graphite nodularity by the JIS method than that by the ISO method can be caused by many unsharp graphite particles, many small out-of-round particles in the low-resolution image, and/or by the manufacturing condition targeting the roundness of a little over 0.6.
In this study, adsorption behavior of oxygen on platinum surface in Pt/C-based catalysts used for oxygen reduction was investigated in terms of the surface plane and lattice distortion of platinum by a first-principles calculation. The calculations revealed that Pt(110) surface has higher oxygen adsorption stability than Pt(111) surface. Dissociative adsorption of the oxygen molecule was observed only in the model with a distortion of about-4% on the Pt(111) surface, whereas such reaction was observed on many Pt(110) surface even with and without distortions. In other words, both surface distortion and surface plane would play important roles for the oxygen adsorption behavior of ORR, suggesting that the Pt/C-based catalysts prepared with a large amount of Pt(110) surface with distortions exposed are more likely to proceed through a pathway involving dissociative adsorption of molecular oxygen.
