In this study, an equiaxed fine-grained copper specimen was fabricated by powder injection molding, followed by hot isostatic pressing. The specimen showed a yield point phenomenon with a Lüders-type deformation during a uniaxial tensile test. This study aimed to identify the cause of the yield point phenomenon in the fine-grained copper specimen. First, the Lüders band was designed to partially propagate within the gauge section through an interrupted uniaxial tensile test equipped with a digital image correlation system. The microstructures of the Lüders and non-Lüders band regions were compared by electron backscatter diffraction. It was observed that self-annealing was accelerated by the applied stress in the Lüders band region. Consequently, the microstructure of the Lüders band region transformed into a bimodal structure composed of fine grains and abnormally coarse grains containing numerous large twins. Identification of active twin variants in the abnormally coarse grains suggested that a significant tensile strain can be accommodated by this twinning. Based on these results, it was confirmed that the strain burst generated by the sudden occurrence of numerous large twins induces the yield point phenomenon in the fine-grained copper.

Densification of amorphous powder is crucial for preventing magnetic dilution in energy-conversion parts owing to its low coercivity, high permeability, and low core loss. As it cannot be plastically deformed, its packing fraction is controlled by optimizing the particle size and morphology. This study proposes a method for enhancing the densification of an amorphous powder after compaction, achieved by mixing three types of powders of different sizes. Powder packing behavior for various powder mixing combinations is predicted by an analytical model (i.e., Desmond’s model) and a computational simulation based on the discrete element method (DEM). The DEM simulation predicts the powder packing behavior more accurately than the Desmond model because it incorporates the cohesive and van der Waals forces. Finally, a machine learning model is created based on the data collected from the DEM simulation, which achieves a packing fraction of 94.14% and an R-squared value for the fit of 0.96.

Ti–6Al–4V alloy is widely used as a system material in high temperature and high pressure environments in various industrial fields and is difficult to mechanically machine. Thus, high temperature processing methods such as hot forging, rolling, and hot forming are usually applied. Among various methods for deriving optimal molding conditions during high-temperature processing, the dynamic material model suggests energy dissipation efficiency according to the flow stress of the material. However, the energy dissipation efficiency merely numerically represents the change in flow stress, not the metallurgical behavior of the material. Therefore, it is necessary to understand the difference in energy dissipation efficiency in relation to the high-temperature deformation mechanism. In this study, high temperature compression tests were performed on the Ti–6Al–4V alloy. The temperature range was set at 800°C∼1200°C at intervals of 50°C, and the strain rate was set at 1 × 10⁰/sec∼1 × 10⁻³/sec at intervals of 10⁻¹/sec. Based on the results of the experiments, flow stress and processing maps were derived, and the high temperature plastic deformation behaviors of Ti–6Al–4V alloy were analyzed in correlation with the microstructural changes and mechanical properties according to temperature and strain rate. And the prior beta grain size according to the difference in energy dissipation efficiency was explained for each condition.

The structure-property relationship of lattice truss metals is investigated by correlating effective properties with quantitative structural parameters such as Maxwell stability parameter, truss thickness, and coordination number excluding porosity. Even at the same porosity, the effective properties can vary many folds due to the structural difference. The elastic modulus and the thermal conductivity of nine representative lattice trusses are calculated using finite element analysis and are correlated with the structural parameters. It is confirmed that the structural dependence of the elastic modulus is higher than that of the thermal conductivity, as stated by M. F. Ashby. The Maxwell stability parameter and the coordination number have more effects than the truss thickness. All structural parameters except the porosity show weak correlation with properties. In other words, each parameter makes a little contribution. Overall, it seems that their combination causes a significant difference in the physical properties.

We investigated the relationship between the microstructure and mechanical properties of Ti–6Al–4V alloy subjected to friction welding (FW). In this work, specimens with a diameter of 15 mm and length of 50 mm were prepared, and FW was performed at a constant rotation speed (1600 rpm) and different upset lengths (1 mm and 3 mm). The electron backscattered diffraction (EBSD) method was used to analyze the grain boundary characteristic distributions (GBCDs) such as the grain size, misorientation angle, and the phase distributions for the weld zone and base material. We found that the microstructures in the weld zone were developed by a combination of continuous dynamic recrystallization and phase transformation. In addition, a decrease in the upset length led to accelerated grain refinement, and the average grain sizes in weld zone were refined from that of the base material (5.75 µm) to 1.45 µm and 1.85 µm at upset lengths of 1 and 3 mm, respectively. Consequently, the maximum microhardness value increased by ∼20% at an upset length of 1 mm relative to the base material, and the yield and tensile strengths of the welded materials were maintained at the same levels as those of the base material. Therefore, based on the developed microstructure and mechanical properties, the application of FW to Ti–6Al–4V alloy could be obtained joints with superior performance.

We suggested the multi-phase phase-field model of Fe–Cr system with consideration of not only α-α′ but also σ phase. In the prior phase-field study, one assumes the specific mechanism of phase separation, i.e., spinodal decomposition or nucleation and growth. On the other hand, our phase-field model can concurrently consider spinodal decomposition or nucleation/growth without any assumptions. With developed phase-field model of Fe–Cr system, we modelled three types of two-phase structures: α-α′, α-σ, α′-σ and single-phase σ region at T = 700 K and 1000 K.

In this study, friction welding was applied to carbon steel tubes at a high speed condition to achieve an eco-friendly welding process and a superior mechanical performance. Friction welding is a very efficient process for joining materials without defects, especially with joint rods or tubes. For this study, cold drawn carbon steel tubes (AISI 1020) were introduced as the base material and successfully joined by friction welding. Friction welding was performed with parameters of a burn-off length (1, 2 and 5 mm). In order to analyze the welds, the electron backscattering diffraction method was introduced and observed the grain boundary characteristic distributions such as grain size, shape and orientation. To evaluate the relationship between the mechanical properties and microstructure, Vickers microhardness and tensile tests were introduced. As a result, the yield strength of the welds significantly increased relative to the base material at all conditions, and which derived from the microstructure development like a refined acicular ferrite grains through the dynamic recrystallization during the welding. Consequently, we suggest the optimum conditions of the friction welding with the interdependence of the microstructures and mechanical properties in this study. This demonstration substantially offers the possibility of an eco-friendly environment and superior tube welding quality without any defect and harmful gases at the high speed welding process as well as at the lowest cost. This technology can be extended to mass production processes with exceptional benefits for various industries.

An environmental crisis urges people to investigate alternative energy sources for the future. As research on energy conversion and storage increases, electrochemistry is recognized as a sustainable approach for developing renewable energy systems without any emissions. Electrochemical reactions such as hydrogen evolution reaction (HER), ammonia productions, battery systems, and supercapacitors strongly rely on catalysts for their efficiency. In this study, we aim to report the synthesis of nickel phosphide by applying different variables and establishing their correlations with electrochemical reaction outcomes. In contrast to the conventional techniques of analyzing results through material data, this study’s essential part is to obtain higher performance for the HER and supercapacitor with fewer synthesis times through correlation analysis of variables and their outcomes. Accordingly, robust synthesis process design and optimization are expected to reduce cost and time in future research.

Effect of crystallographic orientation of nucleus on discontinuous dynamic recrystallization (DDRX) behavior in 304LN stainless steel is investigated using a multiscale model, namely a coupled crystal plasticity finite element method and DDRX-based cellular automata model. The three orientation selection schemes of nucleus are specially exploited in the simulation; i.e., (1) random orientation, (2) inheritance of orientation of parent deformed grain, and (3) generalized strain energy release maximization theory. The DDRX behaviors such as flow stress, DDRX volume fraction, grain size, and texture predicted by the three schemes are compared and the differences are explained through the simulated microstructure evolutions. This study suggests that it is reasonable to assign a random orientation to the nucleus through comparisons with experimental evidence.

Magnesium, the lightest structural metal, needs to improve its strength and formability at room temperature for commercialization. Manganese is an alloying element that can improve the strength of magnesium through forming intermetallic compounds. However, its effect on the formability of magnesium has not yet been clarified. To identify the effect, an interatomic potential for the Mg–Mn binary system has been developed on the basis of the second nearest-neighbor modified embedded-atom method formalism. The Mg–Mn potential reproduces the structural, elastic, and thermodynamic properties of the compound and solution phases of its associated alloy system, consistent with experimental data and higher-level calculations. The applicability of the developed potential is demonstrated by calculating the generalized stacking fault energy for various slip systems of the Mg–Mn alloy.

This paper presents a machine learning model to predict the γ/(γ + θ) transformation temperature, which is also known as the A_cm temperature in the Fe–C phase diagram. From the literature, 25,920 usable data points are collected, and the dataset is analyzed using a boxplot. The hyperparameters of the machine learning models are adjusted using fivefold cross-validation and grid-search techniques. An artificial neural network (ANN) model is selected based on the determination coefficient. The ANN model is compared with an empirical equation to verify the improvement in the accuracy of the model. The significance of the variables was analyzed using the Shapley additive explanations method. Further, the variable prediction mechanisms are discussed.

In this paper, the effects of small amounts (0∼1.0 wt%) of carbon nanotubes (CNTs) on the microstructures and properties of Ni–Cr–P filler metal and brazed joints have been investigated. Various content of CNTs were successfully blended into Ni–Cr–P paste for preparation novel filler metals, the results indicate that small amount of CNTs can increase the melting temperature ∼3°C, enhance the wettability of filler metals on steel substrate, and improve the shear strength of brazed joints. Moreover, the microstructures can be refined obviously. However, excessive addition of CNTs will induce the nano-agglomeration, which degrade the wettability of filler metals and shear strength of brazed joints, coarsen the microstructures. Based on the optimization content of CNTs, 0.1% CNTs can maximize the properties of filler metals and brazed joints.

In this paper, we investigate the temperature dependence of Yb valence in an Au–Al–Yb intermediate-valence quasicrystal by Yb L₃-edge synchrotron X-ray absorption near-edge structure spectroscopy. The Yb valence of 2.61+ at room temperature decreases monotonically as the temperature decreases, indicating that the Yb ionic radius increases as the temperature decreases and is consistent with the anomalous suppression of the thermal shrinkage of this quasicrystal by cooling, as previously reported. The Yb valence changes by −0.053 on cooling from 298 to 2 K, and its change is more gradual on the high-temperature side than on the low-temperature side with the boundary around 200 K. Additionally, the effect of the changes in the Yb valence on the volume is quantitatively examined. The ratio of the volume changes due to the change in Yb valence per Yb atom, ΔV_Yb, to the amount of change in Yb valence, Δν, which is expressed as ΔV_Yb/Δν, was evaluated. The value of ΔV_Yb/Δν was estimated to be −2.8 ų/unit Yb valence/Yb atom, whose value was close to that evaluated for YbInCu₄.

The strength of Cu–Ni–Si alloy can be improved by finely dispersing a Ni–Si-based compound as a precipitate into the Cu parent phase by heat treatment. In order to investigate the strengthening effect of the precipitate, quantitative evaluation of the size distribution and dispersion state is necessary. In this work, we utilized transmission electron microscopy, small-angle X-ray scattering, small-angle neutron scattering, and atom probe tomography to analyze this Ni–Si precipitated phase. The small-angle X-ray and neutron scattering results showed that the precipitated phase gradually became coarser as the aging temperature increased. The atom probe tomography and small-angle scattering provided complementary measurements of the diffusion layer at the interface between the Cu parent phase and the precipitated phase.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 60 (2021) 309–314.

Li₄GeO₄-based solid electrolytes can be synthesized at low temperatures, and their formability is improved by adding Li₂SO₄. Glass–ceramic Li₄GeO₄ exhibits a relatively high ionic conductivity of approximately 10⁻⁶ S cm⁻¹ at room temperature, which is higher than that of glass Li₄GeO₄. Thus, Li₄GeO₄ has promising applications in all-solid-state lithium ion batteries. To understand the correlation between the ionic conductivity, formability, and microstructure of the synthesized materials, the microstructures and crystallization process of glass and glass–ceramic Li₄GeO₄ and 80Li₄GeO₄·20Li₂SO₄ (Li_3.6Ge_0.8S_0.2O₄) were observed by transmission electron microscopy (TEM). Since Li_3.6Ge_0.8S_0.2O₄ glass exhibits a halo diffraction pattern, the addition of Li₂SO₄ to Li₄GeO₄ stabilizes its amorphous phase. In addition, glass–ceramic samples were found to be characterized by an amorphous state containing nanocrystallites with a crystallinity degree of approximately 40%, which improves the ionic conductivity of the material.

This study is aimed to optimize the tensile properties and fracture toughness of rapidly solidified (RS) ribbon-consolidated Mg–0.85Zn–2.05Y–0.35Al (at%) alloys by changing the pre-consolidation heat-treatment temperature. The alloys prepared from RS ribbons heat-treated below 673 K consisting of bimodal α-Mg grains; coarse-worked grains (∼2.8 µm) with high Kernel average misorientation (KAM) values (∼1.8°), and ultrafine dynamically recrystallized (DRX) grains (∼0.68 µm) with intermediate KAM values (∼1.1°). The DRX grains involve cluster arranged layers (CALs) and thin plate-shaped long-period stacking ordered (LPSO) phase precipitation. The fine grain structure strengthens the alloy, significantly while they have little beneficial effects in retarding the crack propagation, thus resulting in low fracture toughness. The alloys that were heat-treated above 723 K prior to consolidation possessed a three kind of α-Mg grain structure; it consisted of fine DRX grains (∼2.3 µm) with low KAM values (∼0.5°) in addition to the coarse-worked grains and ultrafine DRX grains. The fine DRX grains improved strain hardening and ductility, resulting in fracture toughness increase. Furthermore, high-temperature pre-consolidation heat treatment produces block-shaped LPSO phase grains associated with α-Mg. This LPSO phase appears to work as an effective feature to toughen the materials, due to the frequent formation of microcracks in the phase and promotion of crack deflection.

Recent studies have revealed that hydrogen embrittlement in Al–Zn–Mg alloys appears to be dominated by hydrogen partitioning to MgZn₂ precipitates. A method has recently been proposed for reducing the hydrogen concentration at MgZn₂ precipitates by adding specific intermetallic compound particles that have high hydrogen trap energy. In the present study, the effectiveness of Al₇Cu₂Fe particles on suppression of hydrogen embrittlement in Al–Zn–Mg–Cu alloys was evaluated using X-ray microtomography. Quasi-cleavage cracks were found to be initiated in regions where local volume fractions of the Al₇Cu₂Fe particles were relatively low. Hydrogen partitioning to the MgZn₂ precipitate interface was suppressed, even in high hydrogen concentration material, by adding Al₇Cu₂Fe particles. However, the fractional area of the quasi-cleavage fracture in the material with high hydrogen concentration was higher due to insufficient hydrogen diffusion inside the Al₇Cu₂Fe particles and at the interface between the aluminum matrix and the particles. It appears that finely distributed small Al₇Cu₂Fe particles might effectively suppress hydrogen embrittlement.

In the present study, microstructure characteristic and texture evolution of TB18 titanium alloy were studied by isothermal hot compression under different strain with strain rate of 0.001 s⁻¹ and 0.1 s⁻¹ in the β phase zone. Electron Back-Scattered Diffraction (EBSD) and XRD were used to characterize the microstructure and macrotexture. Microstructure characteristic demonstrated that coarse β grains flatten and elongated to the compression direction as strain increased. The dynamic recrystallization mechanism is continuous dynamic recrystallization (CDRX) at lower strain rate, while discontinuous dynamic recrystallization (DDRX) at higher strain rate. The deformation is strongly dependent on the dislocation density, geometrically necessary dislocations density increased with strain at different strain rate. The limited faction of dynamic recrystallization has little effect on texture evolution, and the texture evolution is ascribed to the strain induced boundary migration and activity of slip system. At lower strain rate, the lower activity of {110}〈111〉 slip system and higher activity of {123}〈111〉 enhanced the 〈110〉 texture and weakened the 〈111〉 texture; at higher strain rate, the higher activity of {123}〈111〉 slip system modified the 〈111〉 β texture intensity and enhances the 〈110〉 texture.

The 5000 series non-heat-treatable Al–Mg alloys are widely used as structural members, because of excellent combination of weldability, corrosion resistance and mechanical properties. It is well known that these alloys can become susceptible to inter-granular stress corrosion cracking. In the previous paper, the authors revealed that hydrogen embrittlement (HE) takes place in weld corner (fusion zone adjacent to HAZ) in an MIG-welded joint of 5083 alloy.

In this study, the base material and MIG-welded joint of the 5083 alloy were sensitized, and their resistance to HE was investigated by two methods: humid gas stress corrosion cracking (HG-SCC) and slow strain rate tensile (SSRT) tests. The results obtained were discussed, in comparison with the previous results obtained in the non-sensitized joint. Discussion was also made in terms of the difference of the two testing methods.

Extension of HG-SCC cracks were observed for all sensitized 5083 alloy samples, base and welded samples tested in humid air, and hence HE was confirmed. Fractography and surface observation on the crack tip of HG-SCC revealed that the crack propagates in a transgranular manner. The extent of HG-SCC was greater in the present sensitized specimens in all the locations except the weld corner, but the position dependency has been the same: crack propagation amount was largest in the weld corner. On the other hand, SSRT test results did not indicate any reduction in ductility or strength when testing environment was changed from dry nitrogen gas to humid air. Therefore, it is concluded that HG-SCC test is more sensitive for detecting HE of 5083 alloy.

The effects of beryllium (Be) content and heat-treatment conditions on the development of the heterogeneous nanostructure and mechanical properties of Cu–Be alloys were systematically examined. With increasing Be concentration from 0.4 to 2.14 mass%, the volume fraction of eye-shaped twin domains developed in the 90% cold-rolled samples increased up to 4.9%. Additionally, the volume fraction further increased to 7.1% when Co was excluded, even for a Be concentration of 1.86 mass%. Therefore, Be addition promotes mechanical twinning, while the precipitates appear to impede it. Furthermore, it was revealed that excess Be was consumed for formation of γ- and β-phases in the Cu–Be alloy with 2.14 mass% Be. The age hardenability at 588 K was more significant with increasing Be content, although the increase in tensile strength was not highly significant. These tendencies were more significant when the alloy was solution treated at higher temperatures and for longer times. The highest tensile strength (1.7 GPa) was observed for the Cu–Be alloy with 2.14 mass% Be when tested along the transverse direction, which was slightly higher than the 1.5 GPa measured along the rolling direction. The above results indicated the important role of age hardenability and the volume fraction of eye-shaped twin domains in the heterogeneous nanostructure.

This Paper was Originally Published in J. Japan Inst. Copper 60 (2021) 74–80. Some sentences and captions were slightly modified according to suggestions given by English editing service.

Neodymium magnets are widely used as high-performance magnets, but there is a problem that thermal demagnetization is relatively significant because of low Curie temperature. Prevention of oxidation for the Nd-rich phases in the grain boundary phase to which improve coercivity is required. Since oxygen dissolution occurs mainly during melting in alloy preparation process, it is necessary to know the affinity between the molten magnet alloy and oxygen. For the proper understanding of this process in practical use, neodymium magnets are made by replacing some of the Nd with Pr in order to cut costs, so the investigation of the system including Pr is required. In this study, Nd–Pr–Fe–B molten alloys and Nd₂O₃ crucibles were equilibrated in a sealed system, and oxygen solubility was investigated as a function of alloy compositions. It is confirmed that the affinity between the alloy and oxygen increases as the rare earth concentration increases. On the other hand, little effect of Pr ratio was found on the affinity between the molten Nd–Pr–Fe–B magnet and oxygen. It indicates that Nd and Pr have the similar effects on the affinity of the Nd–Pr–Fe–B magnet to oxygen. In addition, as a way to utilize the thermodynamic data obtained in this report, we did calculations regarding deoxidation to prevent oxidation of the Nd-rich phase.

Silver-containing glass powder can be used as a sustainable source of silver ions in inhomogeneous synthetic systems of strictly size-controlled silver nanoparticles using an aqueous solution of reducing sugars. The caramelization products derived from sugars in this synthetic system contained promoters of silver ion release from silver-containing glass powder and suppressers of nanoparticle growth. In this study, the effects of caramelization products on the size control of nanoparticles were investigated using four types of reducing sugars: glucose, fructose, maltose, and lactose. It was found that acidic components of caramelization products were corresponding to promoters of silver ion release. The acidity of the product suspensions increased with increasing initial concentrations of each sugar. For monosaccharides, glucose and fructose, nanoparticle sizes significantly increased (3.5–50 nm) with the acidity of the product suspensions. In contrast, for disaccharides, maltose and lactose, the nanoparticle sizes slightly increased (4.1–7.1 nm) with acidity. This difference arose from a balance of the effects of both silver ion release promoters and nanoparticle growth suppressers: the monosaccharide systems were dominated by the effect of silver ion release promoters to promote particle growth, whereas the disaccharide systems were regulated by the relationship between the effects of both components.

The Al–9Si–0.3Fe–0.15Mn alloy was chosen as the base alloy, 0.2Mo and 0.2Zr were added in combination (0.2Mo+0.2Zr) to the base alloy to maintain the ductility and improve the strength in tensile properties. The 0.2Mo+0.2Zr addition alloy showed improvement in both ultimate tensile strength (σ_UTS) (160 MPa) and fracture strain (ε_f) (7.1%) at the as-cast conditions, compared with those (145 MPa, 6.1%) of the base alloy. The increment in the σ_UTS and ε_f by 8% and 14%, respectively, was obtained by 0.2Mo+0.2Zr addition. The eutectic α-Al with the smallest minimum nanoindentation hardness (H_{IT, min}), showing high Al or low ΔMk_eα due to heavy micro-segregation existed as a continuous phase in the 0.2Mo+0.2Zr addition alloy led to improvement in ductility. The size of the cell structure caused by the dense tangles of dislocations was about 250 nm, which corresponded to a similar size to the high Al or low ΔMk_eα regions in the 0.2Mo+0.2Zr addition alloy. It was found on the basis of improvement in tensile properties that both usage of the gravity casting method and the addition of Mo and Zr, suggested the possibility for the as-cast application because the eutectic Si particles were refined, and the eutectic α-Al phase was characterized by high Al content or low ΔMk_eα region caused by micro-segregation of the Mo and Zr atoms. The inhomogeneity eutectic grains including IMCs acted as the harmonic structure for the improvement in both strength and ductility.

In recent years, it has been a challenge for the transportation sector to reduce the weight of vehicles for higher fuel efficiency. This expands the use of light metals such as Al alloys. However, these materials have low hardness and surface strength. In this study, Al-alloy (AC8A; Al–Si–Cu–Ni–Mg) composites reinforced with Al₂O₃ fibers were used as base materials and were coated with multilayer diamond-like carbon (DLC) films to improve their properties. The multilayer DLC films were deposited on the Al alloy composites by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) using methane and acetylene gases as the raw materials. As the number of DLC film layers increased, the Young’s modulus of the samples decreased and the following ratios of hardness (H) to elastic modulus (E) also increased: H/E, H³/E², H²/E. In addition, the critical number of peeling slides increased as the composite volume fraction and the number of layers increased.

This Paper was Originally Published in Japanese in J. JILM 72 (2022) 265–270.

The effects of ultrasonic treatment (UST) using a titanium (Ti) sonotrode in a fully liquid stage on the grain refinement and mechanical properties of as-cast Al–Mg alloy billets were investigated. To clarify the grain refinement mechanism, the grain size (GS) and dendrite arm spacing (DAS) were examined as functions of the growth restriction factor (Q) dependent on the Ti dissolution from the sonotrode, and compared to those in the as-cast and re-melted states of the samples inoculated using an Al–10 mass%Ti master alloy. In addition, the formation and dissolution behavior of Al₃Ti intermetallic particles acting as a heterogeneous nuclei was indirectly observed by measuring the electrical resistivity during isochronal annealing. In comparison with the chemical refiner inoculation, the UST effectively refined not only the GS but also the DAS, both of which showed similar slightly concave upward curves with an increasing slope against 1/Q. Electrical resistivity measurement results provided indirect evidence that the dissolved Ti was present as a solute during the solidification stage. The GS, DAS, and electrical resistivity results all suggest that the dissolved Ti refined the GS primarily by solute-induced growth restriction effect rather than by providing heterogeneous nucleation sites. The UST effect on the microstructure refinement was efficient when the Ti-dissolution content was as low as less than 0.05 mass%. The refinement of grains, Al₃Fe particles, dendrites, and pores by the UST significantly improved mechanical properties, especially the elongation at break.

Flux-free brazing of aluminum alloys was carried out under high purity nitrogen gas with ultra-low oxygen partial pressure prepared by zirconia oxygen pump. The flux-free brazability of the aluminum alloys was improved by adding a small amount of magnesium into the sample, which was more effective in the core alloy than in the brazing filler alloys. Higher heating rate of the sample increased the fillet length. When the oxygen partial pressure of atmospheric gas was much reduced to the order of 10⁻²⁵ Pa using a zirconia oxygen pump, a long fillet, comparable to that formed by flux brazing, was obtained. The reason for the improved brazability was discussed from the viewpoint of the fine segmentation of the oxide caused by the combined effects of reduction of the oxide, thermal expansion at melting the filler alloy, and gas phase formation reaction from the molten filler alloys.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 85 (2021) 352–358. Figure 6 is modified, and eq. (9) is added.

This contribution demonstrates the effects of mole ratio, concentration of perovskite components and fullerene derivatives used as electron transport layer (ETL) on the stability and performances of inverted perovskite solar cells (PSCs). C60, C70, PC61BM and PC71BM are selected as ETL materials. Methylammonium iodide (MAI):Lead (II) iodide (PbI₂):Lead(II) chloride (PbCl₂) are used to form MAPb₂I₂Cl which is a mixed halogen perovskite structure. The fabricated perovskite device containing PCBM with optimized concentration and mole ratio gives high power conversion efficiency (PCE) of 9.07% with an open-circuit voltage (Voc) of 0.91 V, short circuit current density of 14.1 mA/cm², and fill factor of 0.71. The lifetime characteristics and the stability are found significantly dependent on the fullerene type. The devices containing PC61BM and PC71BM are able to maintain 50% and 30% of its initial performances, respectively, even after 1100 hours. Overall, the obtained results represent an important step understanding the impacts on the p-i-n type perovskite lifetimes.

We have systematically investigated the crystalline and electronic structures, magnetic and magnetocaloric properties of polycrystalline SrRu_1−xFe_xO₃ (x = 0 and 0.1) samples fabricated by the solid-state reaction method. The X-ray diffraction analyses of the samples indicated single phase orthorhombic perovskite structure. A thorough analysis of X-ray-absorption-based electronic structure revealed that both Fe²⁺ and Fe³⁺ ions are present in x = 0.1, in which concentration of Fe³⁺ ions is higher than that of Fe²⁺ ions. More careful analyses on the isothermal magnetization data derived from the Banerjee’s criterion demonstrated that the ferromagnetic-paramagnetic phase transition in all samples belongs to the second-order phase transition type. These results were also confirmed by a recently proposed quantitative criterion, which considered an exponent n from the magnetic field and temperature dependences of the magnetic entropy change (ΔS_m). Especially, around T_C, we have found that the ΔS_m reaches the maximum values of 1.65 and 1.32 J.kg⁻¹.K⁻¹ for x = 0 and 0.1, respectively, for a field change of ΔH = 50 kOe. Magnetic-field dependences of the maximum magnetic-entropy change (ΔS_max) obey a power law of ΔS_max(H) ∝ Hⁿ, where the values of n = 0.92–0.94 are far from the mean-field-theory value (2/3), indicating short-range magnetic order existing in the samples.

Cu–Bi–S powders were synthesized by a polyol method at 180°C and a speed of 600 rpm for 70 min. X-ray diffraction patterns of the Cu–Bi–S powders showed that single-phase Cu₃BiS₃ was obtained at a thiourea concentration of 197 mmol·L⁻¹. Microstructural analysis of the Cu–B–S powders revealed that the sizes of the Cu–Bi–S particles with single-phase Cu₃BiS₃ were 200–400 nm and their composition was Cu-poor, Bi-rich, and slightly S-poor. From the optical measurement by an ultraviolet-visible-near infrared spectroscopy, the optical bandgap of the Cu–B–S powder with single-phase Cu₃BiS₃ was estimated to be 1.24 eV. Based on the obtained results, the influences of thiourea concentration on synthesis of Cu₃BiS₃ were discussed.

Media stirred mills have been used in various fields to efficiently produce fine products. The scale-up of such mills is required to increase efficiencies and applications for industrial processes. Despite such circumstances, established scale-up laws remain unavailable, and scale-up has been conducted empirically. This study aims to propose essential requirements for the scale-up of a media stirred mill according to experiments and discrete element method (DEM) simulations. The experimental results were evaluated qualitatively by using particle size distributions of ground products and fitted using grinding kinetic theory as a quantitative evaluation. The grinding performance in the laboratory model was equivalent to the results using the scaled-up model (SU-model) with the modified Froude number, regardless of the rotation speed. DEM simulations identified the main factor that contributed to the agreement. The average collision energy of the media particles was almost identical. To set optimal conditions to fulfill this core requirement, the SU-model operation conditions need to follow the modified Froude number, and the intervals of each arm should be fixed to the same distance. These insights encourage the application of scaled-up media stirred mills.

In this paper, we investigated the vacuum arc-deposited tetrahedral amorphous carbon (ta-C) and nitrogen-doped ta-C (ta-C:N) thin films grown on silicon and stainless-steel foil substrates by the visible Raman Spectroscopy. We found that carbon films grown on silicon surfaces prefer more sp³ hybridized carbon compared to the stainless-steel foil, which prefer more sp² hybridized carbon even though the films are grown concurrently under the same conditions. The impact energy of plasma ions modifies the interfacial layer formation, giving a strong dependence of the sp²/sp³ ratio with the substrate bias, behaving differently for different substrates. However, nitrogen doping in amorphous carbon thin films helps to increase sp² contents uniformly on both the surfaces for a fixed substrate bias. Understanding such interfaces are of interest for many electronic, optoelectronic, and energy storage devices as these interfaces get buried and can influence the properties significantly.