Sintered Ag nanoparticles display brittle fatigue crack propagation behavior at 298 K because of their submicron-size crystals. On the other hand, at elevated test temperatures above 413 K, ductile fatigue crack propagation characteristics similar to those of soft metals such as solder appear owing to viscous creep behavior at the grain boundaries, and no temperature dependence of the fatigue crack propagation properties was observed. The fatigue crack initiation lives observed experimentally and the fatigue lives derived by a pseudo-fracture mechanics approach using numerical fatigue tests with the fatigue crack propagation law mostly coincided with each other. However, the fatigue crack initiation life was calculated on the excessively safe side because of the long incubation period for crack initiation due to the influence of continued sintering during the tests performed near the sintering temperature. The application of the pseudo-fracture mechanics approach made it possible to derive the fatigue crack initiation law for smooth specimens of sintered Ag nanoparticles with satisfactory accuracy if the test temperature is lower than the sintering temperature.

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A model cathode interface for sulfide all-solid-state lithium-ion batteries consisting of a LiCoO₂(104) epitaxial film, LiNbO₃ buffer layer, and Li₃PS₄ film was fabricated using physical vapor deposition. In situ thin-film X-ray diffraction were applied to observe the crystal structure changes in the bulk and surface regions of LiCoO₂ during the initial lithium (de)intercalation. The Li₃PS₄/LiNbO₃/LiCoO₂ interface exhibited an irreversible capacity during the first charge-discharge cycle, followed by reversible lithium (de)intercalation in the second cycle. The bulk and surface structures of LiCoO₂ showed reversible structural changes during charging and discharging without significant degradation, suggesting that the initial irreversible capacity was due to the oxidation side reactions in the LiNbO₃ and/or Li₃PS₄ layers. The crystal structure of the LiCoO₂ surface differs from that of the bulk region and undergoes greater structural change than the bulk region. These results indicate that the surface structure of LiCoO₂ depends on structural changes at the electrolyte-side interface, where side reactions occur. Direct observation of the crystal structure changes is crucial for achieving a deeper understanding of the reactions occurring at the oxide cathode/sulfide electrolyte interface.

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A Li₁₀GeP₂S₁₂-type lithium-ion conductor Li₁₀P₃S₁₂Br was investigated as a potential solid electrolyte for composite anodes in all-solid-state lithium-ion batteries. Cyclic voltammetry measurements using an Au/Li₁₀P₃S₁₂Br/Li cell revealed that Li₁₀P₃S₁₂Br possesses a sufficiently wide electrochemical window, making it suitable for anode reactions at low potentials. Spherical graphite-Li₁₀P₃S₁₂Br composite anodes, fabricated via rotary mixing, exhibited lithium (de)intercalation activity, demonstrating the feasibility of Li₁₀P₃S₁₂Br as an electrolyte for all-solid-state battery anodes. Composite anodes with a higher proportion of Li₁₀P₃S₁₂Br relative to graphite exhibited improved cycle retention of charge-discharge capacities. A composite comprising graphite (d₅₀: 8 µm) and Li₁₀P₃S₁₂Br (d₅₀: 0.3 µm) in a 20:80 wt.% ratio achieved a discharge capacity of 365 mAh g^–1 at the 30th cycle. In contrast, the 50:50 wt.% composite exhibited a notable decrease in lithium intercalation capacity in the stage 2 (LiC₁₂) and stage 1 (LiC₆) regions. These results suggest that reducing the lithium diffusion distance within graphite particles is crucial for enhancing the intercalation properties of graphite/Li₁₀P₃S₁₂Br composite anodes.

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A theorem of creep strengthening was derived from two axioms of creep for the polycrystalline Ni–20 mass% Cr–X (X = Nb, Ta, Mo, W) solid solutions on the basis of internal stress concept. The general equation describing the minimum creep rate can be divided into two terms: one term is determined by the creep testing condition and the other term with no dimensions represents the creep strength. In the core-mantle model in dislocation creep, the central core region sustains the internal stress during creep and the peripheral mantle region along grain-boundaries is free from the internal stress. The creep strength for the polycrystalline solid solutions is improved by the enhancement of core intensity and core fraction. The strengthening techniques in high-temperature creep for the polycrystalline solid solutions rely on this simple principle: Enhancing core region renders a material stronger.

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In metastable β titanium alloys, superelasticity induced by martensitic transformation can be achieved by lowering the phase stability of the β phase. However, reducing the stability of the β phase also promotes the formation of the isothermal ω phase, which suppresses martensitic transformation and leads to embrittlement. The addition of Sn and Al effectively inhibits the formation of the isothermal ω phase; however, these elements also promote the formation of the isothermal α′′ phase in β-type titanium alloys. In this study, we conducted aging heat treatment on two Ti-Cr-Sn alloys exhibiting superelasticity at room temperature and investigated the resulting aging products and mechanical properties. In alloys with low Sn concentrations, aging at low temperatures led to the formation of the isothermal ω phase, whereas in alloys with high Sn concentrations, the isothermal α′′ phase formed instead of the isothermal ω phase. Both alloys in which the isothermal ω phase formed and those in which the isothermal α′′ phase formed exhibited a loss of superelasticity and significant embrittlement.

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Geopolymers are attracting attention as an environmentally friendly alternative to cement. In this study, compressive strength tests were conducted on geopolymer pastes using fly ash and blast furnace slag as active fillers. Sodium hydroxide solution and sodium silicate were used as alkaline activators. Raman spectroscopy was also employed to investigate its potential for analyzing Ca-enriched geopolymers. These results indicated that calcium aluminosilicate hydrate was formed by 7-day in the environment containing a certain amount of soluble Si in NaOH solution. This was reinforced by the formation of magnesium aluminosilicate hydrate and sodium aluminosilicate hydrate by 28-day, which may contribute to higher compressive strength. Moreover, the coexistence of high-polymerized silicates and relatively low-polymerized silicates is thought to enhance the physical entanglement of the silicates and to increase the compressive strength. These findings suggest that Raman spectroscopy is a useful tool for microstructural analysis of Ca-enriched geopolymers.

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High-strength joints used in timber structures are increasing to utilize the shear properties of wood. Thus, it is important to understand the long-term shear performance. Therefore, we proposed the tensile shear testing method to investigate the long-term shear performance of wood. This testing method is to apply stabilized axial load for a long-term and to be able to measure the shear deformation. In order to evaluate the method, the results were compared with results of JIS block shear test. As a result, the mean value of shear strength in the proposed method was 30% lower than the block shear test. The reason for the small results of the proposed method is that the specimen has two shear face and breaks at the weak side, and the shear face is affected by rotation due to the tensile deformation of the perpendicular to grain direction. Therefore, the coefficient of variation of 6.8% in the proposed method shows smaller than 11.1% in the block shear test. And the shear strength value of the proposed method was little bit higher than one of the four-point-bending type shear test methods, and all specimens were shown the shear failure. Based on these results, the proposed method was judged to be useful as a shear test method.

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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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