The various current conduction mechanisms of Ag/ZnO Schottky diodes were explored by measuring the current–voltage characteristics from 100 to 300 K. In terms of thermionic emission, a comparison of the Schottky barrier height (SBH) to the ideality factor revealed two linear regions within 100–160 K and 200–300 K. Thus, the forward current characteristics feature two SBH sets with Gaussian distributions. The experimental ideality factor was approximated using the tunneling-related characteristic energy (E₀₀) (31 meV). Locally enhanced electric fields were associated with local low-barrier regions that enhanced the tunneling probability. The reverse current characteristics revealed that Poole–Frenkel (not Schottky) emission predominated, attributable to Zn_i-associated defects. Localized electric fields affected both the forward and reverse current characteristics and enhanced the internal electric field about five-fold.

The hot-extruded bars of a Cu-Zn-Si alloy were subjected to groove rolling. Groove rolling was performed using rolls with grooves of different sizes so that the cross-sectional area of the bars after rolling decreased. The specimen bars were rotated by 90 degrees along the rolling direction after each rolling pass, and rolling was continued up to 68% reduction in cross-sectional area. With increasing rolling reduction, the initial coarse-equiaxed grains macroscopically elongated parallel to the rolling direction. Within the grains, ultrafine mechanical twins were high-densely introduced, which promptly and drastically fragmented the initial coarse grains to develop heterogeneous nanostructure consisting of micro- and nano-meter-ordered mechanical twins. The tensile strength of the as-hot-extruded bar of 464 MPa increased to 704 MPa after 42% reduction, and further increased up to 940 MPa after 68% reduction. The remarkable increase in strength is attributed to the evolution of the heterogeneous nanostructure developed by grain subdivision owing to dense mechanical twinning. It can be concluded, therefore, that the strength of the Cu-Zn-Si alloy bars was significantly increased by the evolution of the heterogeneous nanostructure even by relatively small area reduction of 68%, i.e., equivalent strain of 1.13.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 63 (2024) 14–19. The caption of Fig. 4 was slightly modified.

Hydrogen embrittlement affected by three types of plating (low-P and high-P types electroless Ni-P plating and electrolytic zinc plating) was investigated by means of slow-strain-rate three-point bending test on three aluminum alloys (2017-T3, 6061-T6 and 7075-T651). Hydrogen generated by the Ni-P and zinc plating was absorbed in the aluminum alloy substrates, and the trap sites in the aluminum alloy substrates for the absorbed hydrogen differed between Ni-P and zinc plating. Hydrogen embrittlement was able to be evaluated by the three-point bending tests on plated aluminum alloys. Zinc plating did not cause embrittlement for all the alloys, but Ni-P plating induced embrittlement only for the 6061-T6 aluminum alloy. The result of embrittlement of the Ni-P plated 6061-T6 aluminum alloy corresponds to the highest amount of hydrogen desorbed below 240°C than the other alloys.

This Paper was Originally Published in Japanese in J. JILM 73 (2023) 196–200.

The macroscopic mechanical fatigue properties of negative electrodes in lithium-ion batteries and their estimation methods have been investigated based on a simple mechanical model. Tensile and bending fatigue tests were conducted on a negative electrode made of carbon powder and polyvinylidene fluoride (PVDF) binder. The simple model proposed in this study was used to estimate the stress and strain in the PVDF binder supporting the structure of the negative electrode. This model approximates the orientation of the carbon particles as the body-centered cubic (bcc) or the face-centered cubic (fcc), referring to the crystal lattice of metallic materials. The carbon particles in the model are bonded by the PVDF binder. The tensile fatigue test results showed that the negative electrode dissipated energy under the repeated loading, and the stress–strain curve showed hysteresis loops. The total dissipated energy of the binder obtained from the tensile fatigue test and the proposed simple model were used to estimate the mechanical fatigue life of the negative electrode with different binder ratios. The estimated S–N curve agreed with the mechanical fatigue life of the negative electrode with low binder ratios in the bending fatigue test.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 73 (2024) 610–617.

Recently, metal bats have been widely used in high school and other baseball games, but owing to their improved performance, these bats have led to increased amount of accidents. Pitchers are often untimely hit the ball, resulting in serious injuries. However, the National Collegiate Athletic Association evaluates the repulsion performance of bats and balls using a standardized value called BBCOR (Bat-Ball Coefficient of Restitution). Thus, only bats with a value of 0.50 or less can be used. The BBCOR can quantitatively indicate the restitution performance of a bat, and several designs for controlling the BBCOR of metal bats have been proposed in previous studies. However, most of these require the bat to be actually manufactured; therefore, a simple method for predicting the BBCOR using dimensions and other factors during bat design is needed. In this study, the compressive load and BBCOR was first determined using simple compression and ball impact tests on aluminum alloy baseball bats with varying outside diameters and plate thicknesses. Subsequently, the relationship between the BBCOR and spring constant of the bats was examined, and the effects of the outside diameter and plate thickness on the spring constant were investigated. Based on these results, the effects of the outer diameter and plate thickness on the BBCOR were examined, and a simple equation that can determine the BBCOR from the shape (outer diameter and plate thickness) was proposed.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 73 (2024) 597–602.

Zn-Ni alloy plating from sulfuric acid baths has excellent hydrogen embrittlement resistance for high strength steels. In this study, we investigated the factors that contribute to the hydrogen embrittlement resistance of Zn-Ni alloy plating. In Zn-Ni alloy plating, microcracks are formed in the coating. Hydrogen embrittlement was accelerated by mechanical sealing of these microcracks, and the microcracks that form in the coating were a pathway for hydrogen release. Therefore, these microcracks are found to play an extremely important role in suppressing hydrogen embrittlement. It is suggested that a gap in the plating film that can release hydrogen-induced vacancies is important to suppress hydrogen embrittlement due to plating.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 87 (2023) 120–124.

The corrosion resistance of WC-Ni-Cr-Mo cemented carbides in aqueous NaCl solutions at various pH values has been investigated by electrochemical measurements, surface observation and solution analysis. In acidic environments, WC passivates and binder metals selectively dissolve. In neutral environments, Cr and Ni passivate at corrosion potential and lower potentials than 0.5 V and WC either passivate or dissolve at a slower rate, while transpassive dissolution of Cr in the binder and dissolution of W occurs at potentials higher than 0.5 V. In a basic environment, the dissolution behavior of the WC-Ni-Cr-Mo alloy is similar to that in a neutral environment, however, the dissolution of WC occurs significantly with increasing anodic potential from corrosion potential.

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 73 (2024) 234–243.

The keyhole behavior of low-power pulsed laser induced arc welding of magnesium alloys constitutes an essential factor in the formation of porosity defects. An in-depth exploration of the keyhole behavior represents a theoretical breakthrough for eliminating porosity and enhancing weld quality. This is a significant focus for investigating defect control approaches. A model of the gas-liquid interface during the keyhole formation process of low-power pulsed laser induced arc welding of magnesium alloys is established herein. The influence of welding parameters on the evolution of keyholes was investigated through experiments. This study aims to clarify the evolution of keyhole morphology and the delayed closing mechanism in pulsed laser induced arc welding. The results indicate that the laser excitation current and arc current are the primary factors influencing keyhole depth and delayed closing time, respectively. On this basis, the correlation system of process parameters, mechanical factors, and keyhole behavior parameters was established. By combining experiments and simulations, the process threshold for controlling porosity defects of the weld was obtained. The threshold can be determined by considering the following conditions: the laser excitation current is less than 190 A and the arc current is greater than 85 A. This method can effectively prevent the formation of weld porosity.

Recently, due to global climate change, extreme weather events have occurred frequently. While the majority of roads in China are constructed using asphalt pavement, the current unmodified asphalt has been unable to withstand the growing axle load and harsh weather conditions. Consequently, this situation significantly impacts the lifespan of asphalt pavement. This study proposes an improved asphalt performance based on organic vermiculite inorganic nano materials, and designs experiments for analysis. Then, it combines atomic force microscopy and nuclear magnetic resonance methods to analyze the microscopic molecular composition of asphalt materials. The grayscale correlation method is used to analyze the macroscopic physical rheological indicators and microscopic component changes, molecular structure and other indicators of asphalt. Experiments showed that compared with macroscopic physical and rheological aging indicators, the modulus growth rate was the highest and the residual roughness was the lowest. The rutting factor approached 0 as the temperature rose around 50°C. The deformation of ZnO was similar to that of the base asphalt, with the smallest degree of modification and the strongest modification ability of TiO₂. The softening points of 70# matrix asphalt, ZnO, TiO₂, and SiO₂ were 49.5, 51.2, 48.9, and 54.6, respectively. Furthermore, the modified asphalt exhibits enhanced stability at high temperatures, indicating the effectiveness of incorporating inorganic nano materials to improve the performance of matrix asphalt. This finding can significantly contribute to the wider adoption and engineering development of asphalt pavement.

In this study, we investigated the effect of a combination of deformation and aging after solution heat treatment of an Al-1%Cu-0.96%Mg-0.36%Si (mass%) alloy on the precipitation during subsequent artificial aging. The combination of microstructural studies and hardness tests allowed for a detailed characterization of the precipitation in the preformed material. The main phase in the deformed condition is the S′ phase. Aging time-hardness curves, DSC analysis, microstructural examination, and heat treatment optimization were performed to understand the precipitation process in more detail. The results showed that high hardness can be achieved in a short period of time. The aging process is also analyzed to compare the peak aging period and the hardness level of the material. We then compared the thermal aging process with three different cold-rolling conditions and concluded which condition has the most suitable properties for commercial purposes.

Differential thermal analysis (DTA) on quenched Mn₅₅Al₄₅ with hcp structure (ε-phase) was performed under magnetic fields up to 15 T in order to investigate the magnetic field effects on the transformation kinetics of ε-phase. So far, the annealing of ε-phase under magnetic field indicated the acceleration of the phase transformation from the ε-phase to the metastable ferromagnetic τ-phase with L1₀ structure and the suppression of the decomposition into the equilibrium phase (β-phase). In this study, as the magnetic field intensity increased, the transformation temperature from ε-phase gradually decreased to the lowest value in the range from 0 to 4 T. A single exothermic peak was observed on each DTA curve, and it was found that the peak contained plural exothermic ε–τ and τ–β transformations. Activation energy of the transformation also showed the lowest value in the magnetic field range from 4 to 10 T, suggesting that the activation energy of the ε–τ transformation decreases at low magnetic field region from 0 to 4 T and the activation energy of the τ–β transformation increases at high magnetic field region from 10 to 15 T. These changes in activation energy were discussed by contribution of Zeeman energy for nucleation of the τ-phase in the ε-matrix and that of β-phase from the τ-phase.

While duplex stainless steel has excellent mechanical properties and corrosion resistance, intermetallic compounds called σ phase easily precipitate. In this study, SSRT was performed using specimens with different amounts of σ phase precipitation. In corrosive solution, specimens with precipitated σ phase tended to have a more pronounced decrease in ductility. Moreover, SSRT was performed in a similar corrosive solution while continuously charging hydrogen by cathodic charging method. As a result, there was no correlation between the amounts of σ phase precipitation and mechanical properties. Therefore, the σ phase is considered to promote SCC while not promoting hydrogen embrittlement.

This study reports the synthesis of the Zr₃AlC₂ MAX phase from ZrH₂, Al, and ZrC as raw materials by means of spark plasma sintering (SPS). The crystal structure of the resulting product was analyzed by X-ray diffraction (XRD), and the microstructure was examined using scanning electron microscopy (SEM). We investigated the influence of sintering temperature and process parameters on the Zr₃AlC₂ content within the sintered product. We also introduce a novel two-layer powder filling approach that significantly enhances the purity of Zr₃AlC₂ in the final product. This method leverages a specific stacking mechanism to control phase distribution, achieving a Zr₃AlC₂ content as high as 93%.

The effect of B content was studied on the crystalline structures, magnetic properties, and microstructures of (Sm_0.80Zr_0.20)_8.6(Fe_0.71Co_0.20Ti_0.08Cu_0.01)_91.4−xB_x (x = 0.8, 2.0, 5.0, and 8.0) melt-spun alloys with a ThMn₁₂-type structure (1–12 phase) to achieve high saturation magnetization (μ₀M_s) and large intrinsic coercivity (H_cj). With increasing x, the amorphous forming ability improved in the as-quenched alloys, and the average crystallite size decreased in the annealed alloys. The x = 5.0 alloy annealed at 1173 K for 60 min exhibited the largest H_cj of 454 kA/m and the μ₀M_s was estimated to be 1.29 T. In addition, the x = 5.0 alloy exhibited demagnetization curve without a two-step shape, which indicates a low volume fraction of soft magnetic phases. The scanning transmission electron microscopy revealed that 1–12 phase grains have sizes in the range of 30–100 nm in the x = 5.0 alloy after annealing at 1173 K. Fine Ti-B precipitates were also observed. The reduction in the 1–12 phase grain size is attributed to the suppression of crystal nucleation and the crystal growth caused by the amorphous formation in the as-quenched alloy, and the grain boundary pinning by the Ti-B inhibiting the grain growth. The grain sizes in the x = 5.0 alloy were smaller than the estimated critical single-domain diameter of 190 nm, which contributes to the increase in H_cj.

A method for preparing micrometer-sized particles coated with amorphous calcium phosphate (ACP) was developed. The composite particles were synthesized using (Ca, Sr)CO₃ (aragonite) particles as a substrate. Immersion of these aragonite particles in a dilute phosphate aqueous solution at pH 4 led to the formation of strontium-containing ACP. This occurred through the reaction of Ca²⁺ and Sr²⁺ ions with phosphate ions. The incorporation of strontium into the aragonite effectively moderated the rapid dissolution of aragonite, facilitating the deposition of an ACP layer on the aragonite particles. Subsequent immersion of the composite particles in a tris-HCl buffer solution at pH 7.4 resulted in the slow release of therapeutic ions such as calcium, phosphate, and strontium for up to 72 h. Thereafter, a novel amorphous phase, distinct from the original composition and incorporating strontium and sodium, precipitated.