Quantum communication, memory, and computing show potential as next-generation information technologies. Controllable, stable, and repeatable single-photon emitters for off-chip applications are essential components of quantum information systems. In this study, one-dimensional photonic crystals (PhCs), based on Er,O-codoped GaAs (GaAs:Er,O) as the active component, are employed to enhance Er luminescence extraction efficiency, aiming to advance off-chip applications. Numerical simulations of these PhCs demonstrate an enhancement in light extraction efficiency. The two types of PhC cavities, bridge-type and nanobeam PhCs, are fabricated based on the simulation results. For objective lenses with different numerical apertures (NAs), numerical simulations show that both of the bridge-type and nanobeam PhCs enhance the Er luminescence extraction efficiency, which is consistent with the experimental results. Moreover, the bridge-type and nanobeam PhCs exhibited cavity quality factors of approximately 12000 and 7000, respectively, indicating significant potential for enhancing Er luminescence using cavity modes.

The deformation behavior, processing maps and microstructure evolution of AA7050 aluminum alloy were investigated using plane strain compression at temperatures of 300∼450°C and various strain rates ranging from 0.01 to 10 s⁻¹. Based on the flow stress and processing maps, the optimum hot working domains were established in the temperatures range of 420∼450°C and strain rates from 0.01 to 0.06 s⁻¹. The microstructure characterization of the deformed sample with the maximal power dissipation efficiency indicated that the deformation mechanism is the combined effect of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). At low strain, dynamic recrystallization (DRX) nucleation start preferentially at triple junctions. With increasing strain, continuous dynamic recrystallization grains are developed by the progressive rotation of sub-grains and the transformation from low angle boundaries to high angle boundaries within deformed grains. At the same time, discontinuous dynamic recrystallization grains spread along grain boundaries, which is related to the local grain boundary bulging.

Generally, age-hardenable aluminum alloys are quenched in water to obtain the required strength. However, recent studies have revealed that furnace cooling (FC) of an Al-Zn-Mg alloy can provide strength comparable to that of water quenched (WQed) material. The reason why higher strength can be obtained by FC has not been clarified. Furthermore, since hardness after artificial aging is also affected by the heating rate up to the aging temperature, in this study, electrical conductivity and TEM microstructure investigations were conducted to elucidate the effects of quenching rate and heating rate up to the aging temperature on changes in hardness. As a result, it was confirmed that the hardness of an Al-6Zn-0.8Mg (mass%) alloy could be obtained by FC to be equivalent to that by WQ. This may be due to the formation of solute clusters and GP zones during FC. Furthermore, in the effect of heating rate up to the aging temperature treatment, the hardness of WQed material decreased when the heating rate was rapid, especially after aging treatment at high temperature such as 473 K. At slower heating rates, higher hardness was obtained in WQed material. On the other hand, high hardness was obtained for FCed material regardless of the heating rate, suggesting that rapid heating of WQed material resulted in rapid decomposition of GP(I), which made the formation of GP(II) difficult and caused the precipitation only of the coarse η phase, resulting in a significant decrease in hardness. In FCed material, GP(I) was partially decomposed during rapid heating, but the clusters and GP zones formed during FC remained even at temperatures above 160°C, which is considered to have resulted in high hardness even after aging.

To explore the impact of solution treatment temperature on the interface microstructure and morphology of SiCp/Al-4.2Cu-4.0Mg composite, this study subjected the SiCp/Al-4.2Cu-4.0Mg composite to heat treatment at 505°C, 510°C, 515°C, 520°C, and 525°C for 2 hours, respectively. The results indicated that the precipitated phase in the sintered composite matrix is Al₂Cu. With increasing solution treatment temperature, the Al₂Cu content gradually decreases, and it is nearly eliminated at 515°C. At this temperature, the compressive strength of the composite reaches 834 MPa, representing a 40% increase compared to the compressive strength of the sintered composite. On the other hand, the interfacial reaction in the composite continues, leading to an increase in the thickness of the interfacial layer from 300 nm to over 450 nm. The Al₂Cu phase diffuses into the interfacial layer through solid-state diffusion, undergoing a phase transformation to form Al₂CuMg.

The effects of the normalized stress intensity factor gradient, C, on the relationship between crack propagation rate, da/dN, and stress intensity factor range, ΔK, in the near-threshold regime were investigated. When the force shedding rate at each crack extension step was less than 2%, and the force shedding interval for crack extension was 50 µm, the value of C exceeded −0.4 mm⁻¹ and a unique da/dN–ΔK relationship independent of the value of C was observed at the same force ratio.

Additionally, a method for the automatic evaluation of crack closure was proposed. In the evaluation of crack closure by the compliance method, compliance measurement were utilized to average strains during loading and unloading. In the relationship between the averaged nonlinear strain and applied force, where the averaged nonlinear strain was normalized by being divided by the linear strain at the same applied force, the crack opening/closing point was clearly identified. This approach allowed for the effective stress intensity factor range (ΔK_eff) to be evaluated automatically.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 73 (2024) 889–895. Abstract and Captions are slightly modified.

FeB-10 vol% Ni compacts were prepared by spark plasma sintering of FeB and Ni powders ball-milled at different durations. The density of the compacts consistently increased with the temperature regardless of the ball-milling time. The sintered compact of powders ball-milled for 21.6 ks exhibited the highest apparent relative density (D) of 0.92. The maximum densification rates of 0.66, 0.68, and 0.71 obtained for powders ball-milled for 7.2, 14.4 and 21.6 ks, respectively, are close to that of pure Ni (0.74). This suggests that good sinter-ability was achieved by ball milling. The grain size of FeB was more effective than the Ni content in increasing the D value of the sintered compacts. The FeB-10 vol% Ni compact prepared using the powders ball-milled for 21.6 ks exhibited the highest relative density of 0.92 and excellent mechanical properties (hardness of 11.9 GPa and fracture toughness of 9.8 MPa·m^1/2). This compact exhibited the decrease in grain size and increase of reacted (Fe,Ni)B phase.

High-entropy alloys (HEAs) are multicomponent alloys composed of five or more than five elements with near equimolar concentrations. In this study, molecular dynamics (MD) simulations of grain boundary (GB) migration in HEAs were performed in order to systematically investigate the concentration dependence of the constituent elements on its migration behavior. We found that the driving force required for GB migration in the model HEAs reaches the maximum when the GB migration becomes intermittent or the velocity reduces. The maximum driving force is achieved at the maximum degree of GB segregation, showing that GB segregation, which can be controlled by the element composition in the HEAs, strongly affects the GB migration behavior such as the required force for the migration and the velocity. Our study indicates that the element composition in HEAs plays an important role in determining the GB migration behavior and the obtained results contribute to designing the HEAs with superior mechanical properties.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 73 (2024) 101–108. The caption of Fig. 4 was slightly modified.

Fatigue fracture process of extruded and heat-treated Al-Zn-Mg alloys, i.e., 7075- and 7150-alloys, under uniaxial cyclic loading with positive stress ratio, i.e., R = 0.25, has been investigated. Several tens’ micrometers wide preexisting “pits” on surfaces have been confirmed as the preferential fatigue crack initiation sites of the original 7000 series alloys. And, after secondary surface treatment, i.e., surface layer removal, metallic compounds or scratches induced during specimen machining have become possible fatigue crack initiation sites. Cycles to failure of the surface-layer-removed specimens were much longer than the specimens before the surface removal. We have classified the entire fatigue process of the original extruded and heat-treated 7000 series alloys as follows. Crack Initiation Stage: Cleavage crack starts from the interface between several tens’ micrometers wide preexisting “pit” and matrix. Striation Incubation Stage: Cleavage crack without remarkable striation propagates into the specimen. Striation Stage: Striations propagate and create the several millimeters wide semicircle “Fatigue Crack Zone”. Final Fracture Stage: Ductile dimple fracture stage with the final one cycle follows the “Fatigue Crack Zone” and leads the specimen to failure. We have quantitatively estimated the period of each stage and revealed that the lengthiest stage is the combined stage of the crack initiation and the striation incubation. When the cycle to failure reaches six digits number, the period of the combined stage becomes around 90% of the cycle to failure.

Developing a new and energy-saving production process for high-purity terbium that combines molten salt electrolysis, liquid metal extraction, and distillation is necessary. Therefore, we experimentally determined the optimal conditions for the selective extraction of Tb from a Tb–Fe alloy using molten magnesium, which can be obtained via molten salt electrolysis. A eutectic alloy composition of 88 mass%Tb–12 mass%Fe and Mg was maintained at 973 or 1273 K under an Ar atmosphere. The sample was separated into an Fe-based solid phase with a Tb content lower than the eutectic composition and a Tb–Mg-based liquid phase with a small amount of Fe. The obtained results indicate that Tb alloys containing approximately 0.2 mass% Fe can be recovered by liquid Mg extraction at 973 K and subsequent distillation, assuming that only the Mg in the liquid phase is fully volatilized. This concentration of Fe was approximately 2 mass% at 1273 K. Therefore, increasing the extraction temperature significantly increased the concentration of Fe in the Tb obtained by the new process.

The use of COSMO-RS (COnductor-like Screening MOdel for Realistic Solvation) method was adopted in this study to efficiently identify substances that exhibit selective adsorption on chalcopyrite (CuFeS₂) and enargite (Cu₃AsS₄). For each mineral, the changes in concentration for approximately 20 substances were examined through experiment, and their adsorption capacities were quantified using Henry’s law constants. Multiple linear regression analyses were conducted using the Henry’s law constant data as the objective variables and the σ-moments acquired from COSMOtherm as the explanatory variables. This established adsorption prediction equations specific to each mineral. Equations for both minerals exhibited a high predictive accuracy with R² values of >0.9. Quantitative adsorption amounts were obtained by incorporating the σ-moments for 11,577 substances obtained from COSMOtherm into these equations. Further investigation was also executed by a novel concept of “Contributions,” representing the extent of contribution to adsorption, based on adsorption prediction equations and σ-moment definitions. In addition, for several selected chemicals, bubble pickup tests were performed as a fundamental evaluation of the reagents for flotation separation. It was found that PEG-8 increased the amount of chalcopyrite collected by 62% selectively and dodecane decreased the amount of enargite collected by 48%, demonstrating the effectiveness of screening based on this method. This study proposes a new screening method for flotation agent candidates based on a simple adsorption prediction formula obtained by combining adsorption experiments and numerical analysis, and demonstrates its validity.

The bending strength of ultrafine-grained cemented carbides exceeds that of medium-grained cemented carbides. This was thought to be due to the smaller size of defects within the ultrafine-grained cemented carbides. However, this attribution had not been verified because the specimens broke into numerous small pieces during bending tests. In addition, previous studies on the bending strength of medium-grained cemented carbides reported that there is limiting strength which is a region of not increasing bending strength by reducing the defect size. Therefore, in this study, we conducted the tensile test, which is unlikely to produce many small pieces, and the bending test to determine the cause of the high strength in ultrafine-grained cemented carbides. The ratio of bending strength to tensile strength was comparable between the medium- and ultrafine-grained cemented carbides. The number of fragments produced by fractures were almost same between the medium- and ultrafine-grained cemented carbides in case of the almost same strength. It was clear that the tensile strength of both medium- and ultrafine-grained cemented carbides increased as the defect size decreased with no sign of limiting strength. These results suggest that further strength improvements can be achieved by controlling defect size in ultrafine-grained cemented carbides.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 409–415.

A Cu/carbon steel multilayered sheet was quenched, and its tensile properties and electrical conductivity were evaluated. A full martensite structure was developed in the carbon steel layers in the multilayered sheet after quenching at 1063 K. The obtained Cu/martensite steel multilayered sheet exhibited a much higher ultimate tensile stress and approximately identical electrical conductivity compared to those in the Cu/carbon steel multilayered sheet without a quenching process. The decrease in the electrical conductivity during the quenching process in the multilayered sheet can be predicted from the decrease in the conductivity of the Cu layers owing to the diffusion of Fe atoms into the Cu layer. The ultimate tensile stress-electrical conductivity balance in the Cu/martensite steel multilayered sheet was 5.0 × 10⁴ MPa%IACS, which is higher than that in conventional commercial Cu alloys. The ultimate tensile stress-total strain balance in the Cu/martensite steel multilayered sheet was significantly lower than that in each phase in the sheet. The measured ultimate tensile stress and electrical conductivity in the Cu/martensite steel multilayered sheet were approximately identical to the values estimated from the rule of mixture, using the tensile stress, electrical conductivity, and volume fraction of each component phase. This result indicates that the ultimate tensile stress and electrical conductivity of multilayered sheets can be easily controlled based on the rule of mixture.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 63 (2024) 109–114. Several captions and sentences are slightly changed.

Magnetic and structural properties of MnCo_1−xFe_xGe_1−ySi_y (x, y = 0, 0.5) were investigated using X-ray powder diffraction and magnetization measurements in the temperature (T) range from 5 to 370 K and in magnetic fields up to μ₀H = 5 T. At room temperature, MnCoGe and MnCoGe_0.5Si_0.5 were the orthorhombic crystal structure (M-phase), MnCo_0.5Fe_0.5Ge was the hexagonal crystal structure (P-phase), and MnCo_0.5Fe_0.5Ge_0.5Si_0.5 had two-phase coexistence of the M- and P-phases. MnCoGe and MnCo_0.5Fe_0.5Ge were a simple ferromagnetic and their Curie temperatures (T_C) were determined to be 340 K and 200 K, respectively. MnCoGe_0.5Si_0.5 and MnCo_0.5Fe_0.5Ge_0.5Si_0.5 in μ₀H ≤ 1 T showed a gentle dip in thermomagnetic curves at 10 ≤ T ≤ 100 K below T_C which disappears when a magnetic field of μ₀H > 3 T was applied. The magnetization curves of MnCoGe_0.5Si_0.5 and MnCo_0.5Fe_0.5Ge_0.5Si_0.5 at 5 K exhibited that a metamagnetic transition with the magnetic hysteresis in 0 < μ₀H < 3 T. Our results suggest that substituting Fe for Co in MnCoGe system weakens the ferromagnetic interaction, whereas substituting Si for Ge strengthens the antiferromagnetic interaction.

Recently, direct recycling has gained attention as an environmentally friendly and cost-effective lithium-ion battery (LIB) recycling process. This technology focuses on recycling cathode active materials (CAMs) from spent LIBs or manufacturing scrap. In this study, we investigated the direct recycling of CAMs recovered from manufacturing scrap using a dry grinding and classification process, with dried cathode composite materials used as experimental material. In the grinding process, a jaw crusher was used for primary grinding, followed by a stirred media mill for secondary grinding. Particles under 32 µm were classified into three fraction size groups (coarse, medium, and fine) using an elbow-jet air classifier. Thermogravimetry differential thermal analysis and scanning electron microscopy confirmed the concentration of polyvinylidene difluoride and carbon powder in the fine-sized fraction. X-ray diffraction showed no degradation of crystallinity during the process. Finally, charge-discharge and cycle tests were conducted on battery cells made from two types of cathode slurry. Cathode Slurry I, prepared by mixing 10 mass% of coarse- and medium-sized fractions, exhibited almost the same battery performance as the original product. Cathode Slurry II, prepared by mixing 10 mass% of fine-sized fraction, along with a higher amount of organic matter, resulted in a higher internal resistance and a 5.3% decrease in initial battery capacity. This study demonstrated the potential for direct recycling of CAMs from manufacturing scrap using a simple grinding and classification process.

In this study, the delamination toughening mechanism of medium manganese steel (MMnS) study was investigated and enhanced this mechanism through tempering, resulting in a further improvement in impact toughness. Hot rolling at non-recrystallization region of austenite resulted in a lamellar configuration, which contributed to the initiation and propagation of the secondary cracks along the prior austenite grain boundaries (PAGB) to release the triaxial stress and achieve a delamination toughening. However, if secondary cracks connected to each other, delamination toughening failed. Austenite formed by inter-critical annealing (IA) was the key phase to hinder cracks connection. Moreover, through the precipitation and dissolution of carbides caused by tempering before IA, austenite with higher volume fraction and higher stability was formed at the PAGB than ones without tempering. Thus, tempering enhanced the delamination toughening in the whole temperature range.