Ammonia is increasingly recognized as a clean fuel, and large tanks are required to store substantial amounts of ammonia for use as fuel. However, these large tanks, which are made of high-strength carbon steel to withstand their own weight, raise concerns about stress corrosion cracking (SCC), particularly in the presence of impurities. Accurate electrochemical measurements are essential to understand SCC mechanisms, and they require a reference electrode showing a stable potential in liquid ammonia environments. This study aimed to evaluate the potential stability of platinum (Pt) electrodes, commonly used as pseudo-reference electrodes in Japan, under the low-temperature liquid ammonia condition that simulate the actual liquid ammonia stored in the large tanks. Cyclic voltammetry (CV) and corrosion potential measurements were conducted to examine the effects of electrode polarization, cumulative cathodic charge, and air addition to the liquids on electrode potential stability. The results demonstrated that polarization process caused negative shifts in corrosion potential for both the working and the reference electrodes. This potential shift was considered to be attributed to the formation of reduced species during cathodic polarization and their oxidation under potential-free conditions. The negative shift in the corrosion potential in the liquid ammonia without air became significant when a cumulative cathodic charge exceeded approximately 100 C. Introducing air to the liquid increased a cathodic current and helped to stabilize the electrode potential. These findings highlight that minimizing the cathodic charge and adding an adequate amount of air into the liquid are important for suppressing the potential shift of Pt pseudo-reference electrodes in low-temperature liquid ammonia during electrochemical measurements. A reference electrode with a reliable potential facilitates accurate assessment of SCC risk in ammonia storage tanks.

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This study aims to elucidate the hydrogen entry behavior into partially Ni-coated steel sheet in a 0.1 M NaCl aqueous solution. Electrochemical hydrogen permeation tests and hydrogen visualization tests using a polyaniline-based hydrogenochromic sensor were conducted to investigate corrosion-induced hydrogen entry. While the hydrogen permeation current was not detected during the electrochemical hydrogen permeation test, the hydrogenochromic sensor successfully visualized the hydrogen entry in situ. It was revealed that hydrogen entry is accelerated in the pits formed in the area where the steel substrate is exposed. Hydrogen entry was not confirmed in the Ni-coated area. The visualization tests also demonstrated time-lag between the corrosion initiation and the detection of hydrogen entry. The highly sensitive hydrogenochromic sensor provides insight into the spatial distribution of hydrogen entry sites, which is not readily detectable by conventional electrochemical hydrogen permeation methods. The findings clarified that the critical role of solution chemistry on the corroded area in hydrogen entry into Ni-coated steel.

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As for the alloying additions of carbon (C) and nitrogen (N), the involvement of solute hydrogen (H) in face–centered–cubic (FCC) Fe–Cr–Ni–based austenitic steels causes considerable magnitude of solid solution–hardening. Notably, the strengthening ability of these three interstitial elements is almost comparable to each other, although H is significantly smaller than C and N in its atomic size. The present paper overviews the phenomenology of such H–induced solid solution–hardening and its underlying rationales in commercial 300–series Fe–Cr–Ni austenitic steels after uniform H–charging in pressurized gaseous H₂ environment at elevated temperatures. The effects of H concentration, deformation temperature, strain rate, and chemical composition of the alloy, as well as the thermal activation process of deformation, are extensively reviewed based mainly on the authors’ recent works. Potential roles of three key factors: 1) solute drag of H atmosphere around a dislocation; 2) H–diffusion–controlled glide of dislocation core; and 3) the presence of H–substitutional complex, are discussed in light of the conventionally established theories of dislocation dynamics and plasticity. The H–induced solid solution–hardening is maximized when the factors 1) and 2) (i.e., dynamic interactions between diffusible H and mobile dislocation) exert primary contributions to the flow stress. This fact is attributed to the exclusively high mobility of H atoms in austenite lattice even at around an ambient temperature, which is not the case for C and N that remain immobile during the deformation.

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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 ~130 nm. A micro tensile specimen with gauge dimensions of 50 μm in length, 20 μm in width and 15 μm 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.

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The Ta–Te dodecagonal quasicrystal (dd-QC) is the only known van der Waals (vdW) layered quasicrystal and exhibits bulk superconductivity at ∼1 K. In this study, ternary and quaternary compounds were synthesized by adding a third element (X = Cu, In, Sb, Ag, Au, Ti, Nb) to the Ta–Te dd-QC system. Powder X-ray diffraction (XRD) revealed that single-phase dd-QCs were obtained for several compositions, with improved quasicrystallinity indicated by a reduced full width at half maximum (FWHM) of the quasiperiodic peaks. Electrical resistivity measurements demonstrated superconducting transitions at approximately 1 K, with T_c varying systematically depending on the added element. The Ta–Ti–Nb–Te quaternary system exhibited the highest T_c of 1.14 K. These results demonstrate that compositional modification effectively tunes both the structural and superconducting properties of vdW layered quasicrystals.

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Low-k (low dielectric constant) films, which are used as insulators to prevent signal delays in multi-layer connection of integrated circuits (ICs), are very weak and brittle. Therefore, mechanical machining using electroformed blades is avoided in wafer cutting, as the diamonds protruding from the blades catch the low-k film and peel it off. This paper describes the use of a newly developed polycrystalline diamond (PCD) blade to groove a low-k film on a Si substrate. The continuous high-density cutting edges of the PCD blade formed by electrical discharge machining result in smooth grooving without side chipping or crack generation. Using a PCD blade to groove Si substrates with low-k films greatly reduced side chipping. It proved possible to machine the low-k film with almost no film breakage. A patterned wafer including a low-k film could be machined without chipping or film peeling.

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The effects of organic additives and Sb(III) addition to the Zn electrowinning solutions on the current efficiency and crystal structure of zinc deposition were investigated. When only 1 mg/L of sodium lauryl sulfate (SLS), polyethylene glycol (PEG), or gelatin was added, the current efficiency for Zn deposition increased slightly regardless of the type of organic additives. The current efficiency was highest when the gelatin was added, indicating that the gelatin suppresses the hydrogen evolution more effectively than Zn deposition. When only Sb(III) was added into the solution, the current efficiency of Zn increased slightly at 5 μg/L, but decreased at above 10 μg/L. When both organic additives and 5 μg/L of Sb(III) were added, the current efficiency of Zn was similar to that when the organic additive alone was added, showing no synergistic effect of organic additive and Sb. The large holes resulting from the foam mark of hydrogen evolution clearly decreased when PEG and gelatin were added. This is probably attributed to hydrogen gas being more easily desorbed from the cathode by addition of gelatin and PEG. The presence of 10 μg/L Sb(III) in addition to gelatin and PEG further reduced the number of the holes on Zn deposits. The crystal orientation of Zn deposited from solutions containing both organic additives and Sb(III) showed a similar tendency to that deposited from solutions containing organic additive alone. However, the preferred orientation of a specific plane decreased when PEG and Sb(III) were added simultaneously. The crystal grain size of Zn decreased with the addition of Sb(III), despite the decrease in overpotential. Upon simultaneous addition of SLS or PEG with Sb(III), the grain size of Zn was clearly smaller than that deposited from the solutions added only with organic additive, indicating a synergistic effect of the addition of organic additives and Sb(III).

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All composite materials with Al₂O₃ as the matrix, TiC as the reinforcing phase, and Ti₃SiC₂ as the lubricating phase were synthesized in this study. The composites were prepared by using the in-situ reaction of the raw powders of Ti, Si, graphite, Al and Al₂O₃ through spark sintering technology. Three peaks for both Al₂O₃-TiC-10 and 20 vol% Ti₃SiC₂, in densification rate curves corresponded to plastic deformation and power law creep deformation of Al₂O₃, Ti₃SiC₂ and TiC, respectively. The Al₂O₃-TiC-10, 20 vol%Ti₃SiC₂ compacts showed homogeneously localized Ti₃SiC₂ as a lubricating phase between the TiC and Al₂O₃ hard phases. Pin-on-disc friction and wear tests on Al₂O₃-TiC-0, 10, 20 vol%Ti₃SiC₂/ Ti-6Al-4V combinations revealed that the introduction of Ti₃SiC₂ phase could effectively improve the damage morphology of the worn surface, and the optimal wear resistance was exhibited when the content was 20 vol%. Al₂O₃-TiC-20 vol%Ti₃SiC₂ tool exhibited superior intermittent cutting performance to WC-7Co tools, particularly in terms of wear resistance and tool life. Judging from the Hv, K_IC, cutting and friction-wear properties, it may be believed that Al₂O₃-TiC-20 vol%Ti₃SiC₂ compact is replace candidate for the WC-7Co under the rare metal element strategy.

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To investigate the starting points and progression directions of ant nest corrosion, semi-immersion test was conducted using oxygen-free copper. A formic acid solution was used as the test solution. The results revealed that the starting point of pores was primarily formed at grain boundary triple junctions. Furthermore, EBSD was used to measure the crystallographic misorientation in the areas around the pits induced by ant nest corrosion. The average of crystallographic misorientation at grain boundary triple junctions was most frequently observed at 53°, followed by a peak at 45°. On the other hand, ant nest corrosion occurred most frequently at approximately 33°, which is considered to have the highest grain boundary energy. Therefore, it was clarified that the starting point of ant nest corrosion is grain boundary triple junctions with high grain boundary energy.

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FeB-Ni hard materials were promising alternatives to conventional cemented carbides due to their high hardness, low cost and environmental benefits. In order to optimize the densification and mechanical properties, Al was selected as a functional alloying addition. In this study, 86FeB-10Ni-4Al hard materials were prepared by ball milling and spark plasma sintering under uniaxial applied pressures of 30, 50 and 70 MPa. The effects of uniaxial applied pressures on densification, microstructures and mechanical properties were also investigated. This study demonstrated that at 1373 K for holding 0.9 ks, both apparent relative density and densification rate increased with uniaxial applied pressures. The values of apparent relative density corresponding to the maximum densification rate of the 86FeB-10Ni-4Al hard materials sintered at 30, 50 and 70 MPa were 0.67, 0.74 and 0.78, respectively, falling between those of pure FeB of 0.53 and 71Ni-29Al of 0.88. With increasing uniaxial applied pressures, the equivalent diameter of binder-binder voids decreased from 0.16 to 0.08 μm, and their spheroidization rate increased from 0.44 to 0.64. At the same time, the binder-hard voids exhibited the same trend as the binder-binder voids. The changes in equivalent void diameter and spheroidization rate further promoted densification and fracture toughness. Among them, 86FeB-10Ni-4Al hard materials sintered at 70 MPa demonstrated outstanding mechanical properties, with a hardness of 14.7 GPa and a fracture toughness of 14.5 MPa·m^1/2.

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During the recovery of nickel from laterite ores, scandium is recovered from sulfuric acid leachates as a byproduct using an ion-exchange resin method. The efficient recovery of scandium requires the kinetic and thermodynamic behaviors of the scandium adsorption reaction to be elucidated. In general, the calculation of the standard Gibbs free energy change (ΔG°) for the adsorption of metal ions from solution onto ion exchange resins is complex. Therefore, the use of the Langmuir model to derive the equilibrium constant has been widely discussed. Calculation of the equilibrium constant, which represents the ratio of the activities of the reactants to those of the products at equilibrium, requires the determination of the activity coefficients. In this study, we performed a thermodynamic analysis of the adsorption isotherms to investigate in detail the adsorption reaction of Sc³⁺ from the sulfuric acid solution onto the chelating resin. As a portion of Sc³⁺ forms complexes with sulfate ions, we calculated the concentration and activity coefficient of uncomplexed Sc³⁺ using chemical equilibrium calculations and constructed adsorption isotherms. In this study, we fitted the Sc³⁺ adsorption isotherms using both the Langmuir model, which assumes a homogeneous surface, and several modified models that account for surface heterogeneity. Our analysis indicates that the Langmuir model accurately describes the adsorption behavior of Sc³⁺ under the experimental conditions. Based on the equilibrium constant obtained from the Langmuir adsorption isotherm and on the standard enthalpy change (ΔH°) value of approximately 30 kJ mol^–1 determined by using the van’t Hoff equation, we concluded that the adsorption of Sc³⁺ onto the chelating resin is an endothermic process. Our findings are expected to contribute to improving the efficiency of the recovery of scandium from leachates.

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Nickel electrodeposited films with a black appearance were produced by adding nitrate ions to a nickel sulfate (Watt’s) bath. The blackening of the deposited films was attributed to both the formation of a Ni₂O₃ layer on their surface and the refinement of their structure. The addition of nitrate ions increased the pH in the vicinity of the cathode through their reduction reaction, thereby promoting the formation of nickel hydroxide. This hydroxide suppressed Ni²⁺ diffusion during Ni deposition and induced refinement of the deposited films.

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Alloys formed by laser power bed fusion (LPBF) contain high residual stress and strain due to the cyclic heating process, which decreases ductility. Therefore, many researchers have investigated heat treatments to improve ductility by removing residual stress and forming α + β phase structures. However, in this study the ductility of some heat-treated samples was found to decrease below that of as-built samples. This study investigated the heat treatment of LPBF at different temperatures to decompose α′ grains to α grains and understand the resulting microstructure and mechanical properties. Specifically, the influence of microstructural factors on ductility was examined. In the samples heat treated at 500°C, α′ was found to decompose into α with elevated strain and finer β grains, which increased yield strength at the cost of ductility. Meanwhile, in the samples heat treated at 700°C, coarser β phase was precipitated, and greater ductility was supported by the transfer of the slip deformation between α phase grains.

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The process of severe plastic deformation under high pressure through high-pressure torsion (HPT) was applied to an Al-Mg-Si alloy containing excess Fe and Si, which was designed as a model alloy for aluminum recycling. It was shown that the tensile strength exceeded 500 MPa with a total elongation to failure more than 20% after HPT processing under 2 GPa for 1 revolution. Microstructure observation was carried out using transmission electron microscopy for grain size and dislocations. Three dimensional image analyses were also carried out using high-energy X-rays in SPring 8 of JASRI for pores and intermetallic particles. Strain rate change tests were further performed for the evaluation of strain rate sensitivity (m). It was found that the m value increases with the imposed strain (the number of HPT revolution). This increase in the m value is attributed to a significant decrease in the activation volume through a reduction in mobile dislocation segments and/or their gliding distances along with the reduction in the grain size to the submicrometer range.

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B20-type structure was predominantly formed as the main phase in FeGe_1-xSi_x alloys (x = 0.01–0.07) via conventional alloying and annealing processes without high-pressure and high-temperature synthesis. The obtained phases were characterised by X-ray diffraction measurements, scanning electron microscopy, and scanning transmission electron microscopy, which infer that the B20 phase has high crystallinity and dilute Si content. A single phase B20-type structure was formed by annealing the FeGe_0.97Si_0.03 alloy ingot at 873 K for 10 days. The substitution effects on magnetic properties were also investigated, which showed that the Curie temperature of the B20 phases decreased just slightly with the increasing solute Si content. The facile synthesis method is expected to be applicable to further research on the physical properties of B20-type alloys, including the latest subject of magnetic skyrmions.

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Announcement Concerning Article Retraction
The following paper has been withdrawn from the database of Mater. Trans., because a description based on a misinterpretation of the experimental results was found by the authors in advance of publication after acceptance.
Mater.Trans. 52(2011) Advance view.
Improvement in Fatigue Strength of Biomedical β-Type Ti-Nb-Ta-Zr Alloy while Maintaining Low Young’s Modulus through Optimizing ω-Phase Precipitation

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