The magnetic properties of Nd–Fe–B sintered magnets depend on the secondary phase and its microstructure, which in turn depend on the post-sintering annealing conditions. Therefore, clarifying the correlation between magnetic properties, secondary phases, and annealing conditions is crucial. In this study, we examined the dependence of the formation/decomposition of crystalline phases during the cooling process of Nd–Fe–B sintered magnets containing Ga and C on the heat-treatment temperature using synchrotron radiation high-temperature in situ X-ray diffraction (HT in situ XRD). We also analyzed the correlation between the secondary phase formation/decomposition and magnetic properties. As a result, the existence of a secondary phase that correlated with the magnetic properties was clarified. An exhaustive search was conducted to determine the optimum heat-treatment conditions for the formation of secondary phase correlated with coercivity, thereby demonstrating the usefulness of the HT in situ XRD method in the development of high-performance permanent magnets.

In this study, titanium (Ti) alloy with carbon (C) solid solution was fabricated by laser powder bed fusion (LPBF) from Ti-TiC mixture powder to investigate the effect of C solid solution on microstructure and tensile properties of LPBF Ti alloy. XRD and TEM analysis showed that part of TiC particles was decomposed from the surface during melting process of LPBF and C was solid soluted in α-Ti for Ti-(0.09∼0.4 wt%) C. The solid solution of carbon changed the microstructure of the LPBF Ti alloy to fine acicular microstructure due to the martensitic phase transformation. This was also observed in Ti-0.4 wt% C, where solid solution of carbon was not confirmed, suggesting that in Ti-0.4 wt% C, C was once solid solution and precipitated as TiC after phase transformation. LPBF Ti-C alloys showed good strength-ductility, UTS and elongation at break for Ti-0.2 wt% C were 746 MPa and 26.3%, respectively.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 517–523, https://doi.org/10.2497/jjspm.23-00079. The citation in reference 22 is corrected.

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.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 72 (2025) 129–136.

We investigated the punch damage in the piercing of a 1470-MPa-class ultrahigh-strength steel sheet and discussed the effects of PVD coating properties on the punch damage behavior. Sequential piercing experiments were conducted using SKD11 punches with various types of PVD coating. A maximum of 240 shots of piercing were performed with a small clearance (5% of the pierced material thickness). The friction coefficient μ between the coatings and 1470 MPa steel was evaluated using a plate drawing tester at a high contact load without lubrication. For 120 shots of piercing, the higher the μ of coatings, the larger the damage area. For 240 shots, the effects of the heat resistance and adhesion of coatings additionally appeared. For the coatings with lower heat resistance, such as TiN and TiCN, the damage was greater and the effect of μ was more significant than for the coatings with high heat resistance, such as CrN, TiAlN, and TiCrAlN. In addition, among the low-heat-resistance coatings, the damage was smaller for the high-adhesion type. It was concluded that the frictional property, heat resistance, and coating adhesion are the major factors affecting punch damage in the piercing of ultrahigh-strength steel sheets.

This Paper was Originally Published in Japanese in J. JSTP 64 (2023) 57–64.

Copper is an antibacterial material. The surface of copper exposed to the atmosphere is covered with copper oxides (Cu₂O and CuO), and copper oxides exhibit photocatalytic activity under visible light irradiation. In this study, we investigated the effect of the light irradiation on the antibacterial activity of Cu₂O and CuO surface layer. Antibacterial tests were carried out on the basis of ISO 22196 using Escherichia coli (NBRC 3972) under the silica lamp irradiation or in the dark. Photocatalytic activities of Cu₂O and CuO were measured by methyl orange decomposition tests and electrochemical open-circuit potential measurements. CuO exhibited photocatalytic activity under the light irradiation, while Cu₂O was less active. Photocatalytic activity activated by the light irradiation increased the amount of hydrogen peroxide, super oxide radical and hydroxyl radical, and as the result, the antibacterial activity of CuO increased.

WC-Ti(C,N)-Cr₃C₂-Co ultrafine-grained cemented carbides with different contents of C, N and Co binder phases were fabricated. Their microstructures and mechanical properties were examined, and the relationship between the existing form of Ti(C,N) and various conditions was mainly discussed. The hardness of the samples increased, and their fracture toughness decreased with decreasing C content. The average T.R.S. peaked at 4.8 GPa on the low-C side. Their microstructures significantly changed when the N₂ partial pressure changed. At a N₂ partial pressure of 2.6 kPa, the microstructure became finer and the average T.R.S. was the highest. Meanwhile, at N₂ partial pressures of 0 and 11.7 kPa, the microstructure became coarser and the average T.R.S. decreased. As the content of Co binder phase decreased, the number of WC/WC interfaces increased. The average T.R.S. was maximum at 16.4 vol% Co, and decreases with the Co content, but was higher than those of conventional cemented carbides. The existing form of Ti(C,N) changed depending on the N content. Herein, a N₂ partial pressure of 2.6 kPa and low C contents were deemed optimal.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 391–399.

An electrochemical impedance spectroscopy was applied to the analysis of dezincification corrosion behavior of Cu-30 mass%Zn alloy. The impedance characteristics of Cu-30 mass%Zn alloy were different from those of Cu-30 mass%Zn alloy after dezincification corrosion susceptibility test (DCST). The impedance spectrum of Cu-30 mass%Zn alloy after DCST at arbitrary time showed the transmission line model type impedance in the high frequency range, indicating the current distribution on the copper rich layer formed on the alloy surface due to the selective dissolution of Zn. The maximum erosion depth of each sample after DCST was estimated from the cross-sectional images, demonstrating that these values were correlated to the low frequency impedance. These results imply that the selective dissolution rate of Zn from Cu-30 mass%Zn alloy can be evaluated by impedance measurement of Cu-30 mass%Zn alloy after DCST.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 63 (2024) 166–170.

Oxygen is one of the principal impurities in off-grade Ti sponges and Ti scraps. To promote the effective use of these low-cost materials, developing reliable technologies for removing oxygen from Ti is essential. This study investigated the removal of oxygen from commercially pure Ti (CP Ti, Gr. 2) with an initial oxygen content of 0.127 mass% using a two-step plasma-arc melting process consisting of hydrogen plasma-arc melting and subsequent Ar plasma-arc melting. In the first step, plasma-arc melting under an Ar-H₂ atmosphere with an H₂ partial pressure of 0.5 atm resulted in dissolved hydrogen content of 2 mass% in the subsurface region of the Ti melt. This high hydrogen content could be attributed to the high hydrogen potential of the atomic hydrogen (H) gas generated in the plasma. Second, Ar plasma-arc melting at a plasma current of 300 A reduced the oxygen content in the subsurface region of the Ti melt to 0.034 mass%. When the plasma current was increased to 600 A, the oxygen content decreased to approximately 0.05 mass%. Although the reduction was less pronounced than that observed at 300 A, the oxygen content decreased more uniformly over a deeper region of the melt. Thermodynamic considerations suggest that the dissolved hydrogen introduced during the first step functioned as a deoxidizer, with the deoxidation driven by the different water vapor partial pressures between the first and second steps. This study clarifies the underlying deoxidation mechanism and the influence of melting conditions on oxygen removal.

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.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 88 (2024) 106–111.

Aluminum bonding wire alloyed with a small amount of scandium (Al-Sc wire) has a potential to improve the reliability of power device. In this study, the failure mechanism of Al-Sc wire bond in active power cycle (APC) test at high temperature was investigated in comparison with conventional pure Al wire. EBSD and nanoindentation analyses were carried out to analyze the grain size and hardness evolution at bond interface during APC test. In addition to SEM microstructural analysis, TEM analysis was also conducted to reveal the detailed microstructure of Al-Sc wire bond. Our analysis demonstrated that the Al-Sc wire is able to retain its hardness very well by suppressing the grain coarsening by the presence of Al₃Sc nanoparticles even under high temperature, however the softening on the metallization side by grain coarsening coupled with the void formation just below the bond interface leads to a rapid growth of fatigue crack on the metallization side of bond interface.

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.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 72 (2025) 142–149.