WO₃-based composite films synthesized using peroxo iso-polytungstic acid (W-IPA) and a transparent urethane resin exhibit reversible photochromic properties when irradiated with light. In this study, low-molecular-weight polyethylene glycols (PEGs, average molecular weights: 200–1000) were added to WO₃-based composite films and their photochromic properties were evaluated. The WO₃ particles in the composite films did not vary significantly in size, irrespective of the molecular weight of the added PEG. The addition of low-molecular-weight PEGs led to composite films with higher coloring and bleaching rates, with a remarkably high bleaching rate observed for the composite film containing PEG with a molecular weight of 400. The improved bleaching properties of the prepared films are mainly attributable to electron transfer associated with the presence of low-molecular-weight PEGs in the composite films.

The Heusler-type Fe₂VAl alloy is a promising candidate for use in fabricating a thermoelectric power generation device because of its large Seebeck coefficient and high electrical conductivity. However, the high thermal conductivity of this alloy, as a thermoelectric material, degrades its power generation capacity. In this study, to reduce its thermal conductivity, the microstructure of a sintered Fe₂V_1.08Al_0.92 alloy prepared via a powder metallurgical process was modified by adding oxide nanoparticles. Via the dispersion of Al₂O₃ nanoparticles, a sintered Fe₂V_1.08Al_0.92 alloy with fine grains of approximately 200 nm in size was obtained due to the pinning effect on grain growth during sintering. The thermal conductivity was reduced from 16 to 11 W/mK. Upon La₂O₃ addition, the grain size of the Fe₂V_1.08Al_0.92 alloy was reduced to approximately 100 nm and the thermal conductivity was further reduced to 10 W/mK. The difference in grain refinement could be caused by the lower stability of La₂O₃, which facilitated dispersion during ball milling, compared to that of Al₂O₃. As these microstructure refinements negatively affected the electronic properties, the thermoelectric performance of the Fe₂V_1.08Al_0.92 alloy could not be enhanced. However, partial microstructure refinement with sparsely distributed La₂O₃ could slightly enhance the thermoelectric performance due to an appreciable reduction in the thermal conductivity without a considerable degradation in the electronic properties. By using these thermoelectric properties, a simple estimation of thermoelectric power generation, assuming a thermal resistance between the heat sources and thermoelectric module, was conducted. Remarkably, the results suggested that the reduction in thermal conductivity could enhance the output power density and conversion efficiency and reduce the optimal leg length. Thus, practically, controlling the balance between the electronic and thermal properties via microstructural modification is favorable in improving the practicability of the Fe₂VAl alloy by enhancing the power generation capacity and reducing the sizes and masses of thermoelectric devices.

In this paper, we report a phenomenon that equiaxed-to-columnar transition occurs during directionally solidified Ti46Al8Nb0.5B (at%) alloy. By analyzing microstructure and composition, it is found that this transition is induced by macro-segregation during directional solidification. Macro-segregation changes the solidified primary phase from β phase to α phase, which governs the microstructural evolution. At the early stage of solidification, β phase is the primary solidification phase, resulting in the formation of fine-equiaxed grains. As solidification proceeds, Al element enrichment and Nb weakened in liquid phase causes the primary phase transforms from β phase to α phase. The continuous growth of primary α phase forms columnar grains in the later stage of solidification. Flexural strength test shows the average value of bending strength with 652 MPa at equiaxed-grain region is much higher that at columnar-grain region with 395 MPa. These results reveal that even a small change in the composition of TiAl intermetallics will have a great effect on the solidification structure and mechanical properties.

Pure magnesium and Mg-(0.2–0.9 at%) Y rolled sheets were subjected to three-point bending tests to individually investigate the effects of texture and yttrium addition on bending deformation behavior. Yttrium addition increased bending yield stress in both Specimen TR with the neutral plane parallel to the ND (normal direction of the rolled sheets) plane and Specimen TN with the neutral plane perpendicular to the ND plane, resulting from the increase in critical resolved shear stresses (CRSSs) for basal slip and {1012} twinning with yttrium addition. Bending ductility increased with increasing yttrium addition until 0.5 at% yttrium addition, and then decreased at 0.9 at% yttrium addition in Specimen TN. On the other hand, bending ductility increased until 0.9 at% yttrium addition in Specimen TR since non-basal slip activities increased with increasing yttrium addition. Since the neutral plane in Specimen TN with 0.9 at% yttrium addition moved more to the center than that in Specimen TN with 0.5 at% yttrium addition, resulting in the higher tensile strain at the tension side. Therefore, the bending ductility in 0.9 at% yttrium addition was lower than that in 0.5 at% yttrium addition.

This study investigates the effect of the line weld angle with respect to the load axis on the strength properties of cross-type LSW joints with four line welds. Static and fatigue tests, finite element method analysis, and three-dimensional crack observation were performed on joints with line welds at three different angles 30°, 45°, and 60°, respectively to investigate the effect of the line weld angle. As a result, the cross-type LSW joints showed superior strength properties compared with those of the Φ-type LSW joints regardless of the line welding angle. The fatigue strength was particularly superior in the region with a high test force amplitude. The amount of fatigue crack propagation in the thickness direction increases as the line welding angle increases. This trend is similar to that observed for the Φ-type joints reported by Sannomiya et al. It can be inferred that an increase in the amount of crack propagation in the thickness direction increases the crack propagation path length, and thus the crack propagation life. Furthermore, FEM analysis showed that the line weld angle does not significantly affect the fatigue crack initiation life. The results of three-dimensional observations showed that too large a line welding angle increased the number of crack initiation points and reduced the crack growth life relative to the total life, resulting in a significantly shorter crack growth life compared with the fracture life. These results indicate that the strength properties of LSW joints can be improved by increasing the number of line welds, and that further strength improvement can be expected by welding line welds at the appropriate angles with respect to the load axis. For the conditions considered in this study, the line welding angle that exhibits the highest fatigue strength is estimated to be between 45° and 60°.

Mean torsional stress is considered to have less effect on the torsional fatigue strength of steels, but several experimental results have been recently reported that mean torsional stress caused significant reduction in torsional fatigue strength in the very high cycle region for shot-peened spring steel. To investigate the effect of mean torsional stress on high strength steel, ultrasonic torsional fatigue tests with mean torsional stress were conducted for spring steel and bearing steel, which are used for mechanical components subjected to cyclic shear stress. Torsional fatigue strengths up to 10⁹ cycles were obtained for fully-reversed torsional loading (R = −1) to pulsating torsional loading (R = 0). The results revealed that mean torsional stress caused a reduction in fatigue strength in the very high cycle region for both spring steel and bearing steel, and applying higher mean shear stress would result in transition of the fracture origin from a surface to an internal inclusion. The reduction in torsional fatigue strength was discussed from the viewpoint of the transition of the fatigue origin, and applicability of a √area parameter model was discussed for predicting the reduction in torsional fatigue strength.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 71 (2022) 976–982. Abstract, Sec. 2.2, Sec. 4.1, and Ref. 5 are slightly modified.

Trace analysis for Au contents in three different gold ores was investigated from aspects of acid digestion conditions of ore samples, the analytical techniques of Au determination, and quantification methods. The results were evaluated in comparison with the reference values by the fire assay. In the standard calibration method, acid digestion of Au in highly reverse aqua regia followed by determination of Au using ICP-OES showed good agreement results with the reference values, when the standard solutions include the same Fe concentration as in unknown samples. Meanwhile, the standard addition method produced the best-fit values to the reference values when the ore samples were digested in highly reverse aqua regia and then Au concentration was determined by ICP-MS. Under the optimal condition with ICP-MS, the limit of detection and the limit of quantification were recorded 0.24 ppb and 0.80 ppb, respectively. The ICP-OES was not suitable in the standard addition method causing the overestimation of Au probably due to the multi-element interference in plasma emission. In case of the limited amounts of samples, the present finding will be practically useful.

A residue containing TiO₂ and PGMs is generated in the hydrometallurgical process used for recycling platinum-group metals (PGMs). In this study, a pyrometallurgical process was considered in which PGMs from the residue generated in the hydrometallurgical process were concentrated in a molten copper phase as a collector metal and TiO₂ was separated into the SiO₂–CaO–TiO₂ slag phase with SiO₂ and CaO flux. The dissolution of PGMs must be reduced to minimize the loss of PGMs to the slag. Therefore, the distribution ratios of Pt as representative PGMs between the liquid SiO₂–CaO–Al₂O₃–TiO₂ or liquid SiO₂–CaO–TiO₂ slag and molten copper were measured at 1773 K under an oxygen partial pressure of p_O2 = 10^-10. The experimental results showed that the distribution ratio of Pt increased with TiO₂ concentration in the slag, and the distribution ratio of Pt reached a maximum value at a TiO₂ concentration of approximately 10 mass%, and decreased with a further increase in TiO₂ concentration with the SiO₂–CaO–Al₂O₃–TiO₂ slag. However, as TiO₂ concentration in the slag increased, the distribution ratio of Pt decreased with the SiO₂–CaO–TiO₂ slag. Additionally, the experimental results showed that the distribution ratio of Pt between the SiO₂–CaO–Al₂O₃–TiO₂ slag and liquid copper increased with the slag basicity B, defined as B = (mass%CaO)/(mass%SiO₂) when the TiO₂ concentration in the slag was greater than 10 mass%.

Die casting has many advantages, such as high precision, mass production, and excellent recyclability. However, gas defects in the product have become a problem. One countermeasure to this problem is to design the injection input of the plunger appropriately. Recently, CFD has been used to design plunger injection inputs, and by combining with optimization techniques, auto-design of plunger injection inputs has been possible. However, CFD is difficult to apply because of the high cost of CFD resources, the need to resource IT engineers, and the time required for its auto-design. Therefore, we propose a new injection input design method based on an algebraic approach, enabling anyone to design a plunger injection input that prevents gas defects with ease and at a low cost. Simulation and experimental results verified the effectiveness of the proposed method.

Cast iron welding improves the performance of joints using welding rods for cast iron. However, such rods are more than twice as expensive as those for mild steel. The authors found that when spheroidal graphite cast iron is melted and rapidly solidified, spherical graphite nodules aggregate and moved to the surface. If the spherical graphite nodules in the fusion zone moved to the surface, the carbon concentration may reduce, thereby suppressing the generation of ledeburite. In this study, by irradiating with YAG laser, I-type butt-welded joints were fabricated using L materials (with an average spherical graphite nodule diameter of 52 µm) specimen without groove width. Ferrite and pearlite matrices joints were undermatch joints. Applying PWHT (Post Weld Heat Treatment) restored the joint strength to more than 90% that of the base metal. The impact value as-welded joint dropped to less than 15% of that for the base metal. However, it could be recovered up to about 40% of that for the base metal by PWHT. Ferrite matrix joints after PWHT exhibited similar level impact values as the as-welded pearlite matrix joints. Moreover, the surface of spheroidal graphite cast iron with different numbers and size of spherical graphite nodules was irradiated with YAG laser. As the result, at irradiation feed rates above 100 cm/min L materials specimen exhibited a much lower hardness in the fusion zone than S materials (with an average spherical graphite nodule diameter of 27 µm) specimen. The spherical graphite nodules in the fusion zone moved to the surface during rapid melting by laser irradiation. In the S materials specimen studied, more ledeburite, martensite and retained austenite formed near the fusion boundary than with the L materials specimen.

This Paper was Originally Published in Japanese in J. Japan Foundry Engineering Society 95 (2023) 615–621.

Additive manufacturing for open-cell aluminum foam is attracting attention because the cell morphology determined by the characteristics of the aluminum foam can be accurately controlled according to the application. However, there are few reports on the additive manufacturing of closed-cell aluminum foams. Wire arc additive manufacturing (WAAM) is a low-cost additive manufacturing method and has potential for manufacturing closed-cell aluminum foams from a wire precursor. In this study, WAAM was used to produce closed-cell aluminum foam. The precursor round bar was obtained by hot-pressing a mixture of pure aluminum powder, 3 mass% TiH₂ powder, and 1 mass% Al₂O₃ powder. After the precursor round bar with a diameter of 15 mm was inserted into an A5052 aluminum alloy tube with an outer diameter of 19 mm and inner diameter of 15.5 mm, the assemblage was swaged to a precursor wire measuring ϕ1.6 × 100 mm. The WAAM equipment was based on the torch of a TIG arc welding machine that moved under numerical control. Foam formation tests were carried out with the precursor wire at a torch travel speed range from 120 mm/min to 620 mm/min. An additive foaming test was also carried out using a precursor wire measuring ϕ1.6 × 100 mm to investigate welding of the second layer to the first layer while the second layer was foaming. The density of the aluminum foam was measured by Archimedes’ method to calculate the porosity. The aluminum foam samples were cut perpendicular to the long axis, and cross-sections were observed with an optical microscope. For the single-layer aluminum foam formed with a TIG arc, the maximum porosity of 60% was obtained at a travel speed of 320 mm/min. A two-layer aluminum foam with a porosity of 18% and mean pore diameter of approximately 86 µm was obtained in the additive experiment. The second and first layers were bonded without forming a boundary. These results indicate that closed-cell aluminum foam was successfully produced using WAAM. However, the viscosity of the base aluminum of the precursor wire must be high to obtain a high-porosity aluminum foam with WAAM.

Empirical formulas were derived for the interface shape, mechanical properties, and electrical characteristics of accumulative roll bonded (ARB) Cu/Nb laminated materials, based on relevant literature data. These formulas were incorporated into a forward analysis model using finite element analysis, enabling the calculation of yield stress and conductivity from the spatial distribution of Cu/Nb two phases. By randomly varying the layer thickness and interface shape in the two-phase spatial distribution and conducting repeated forward analyses, a database linking microstructural descriptors with yield stress and conductivity was created. These microstructural descriptors include volume fraction, geometric features, topological features, spatial correlation functions, and persistent homology. The significance of each microstructural descriptor on yield stress and conductivity was quantified using machine learning techniques. The results revealed that the Cu volume fraction, layer thickness, and 0th Betti number are crucial for yield stress, while for conductivity, the Cu volume fraction has the strongest influence, followed by layer thickness and layer continuity. Based on these outcomes, the Pareto front for ARB Cu/Nb laminates in the strength-conductivity space was presented.

Exhaust gas recirculation (EGR) coolers are a standard technology for reducing the emission and fuel consumption levels of internal combustion engines. These coolers are composed of stainless steel brazed with Ni-based brazing filler metals that can internally withstand high exhaust gas temperatures and corrosive environments. The use of continuous conveyor belt furnaces has increased in brazing because the investment and operating costs are lower than those of conventional vacuum furnaces. Therefore, the demand for brazing at low temperatures must be considered to improve the durability of the conveyor belt. A novel Ni-based amorphous brazing foil with a liquidus temperature of 1243 K and a high corrosion resistance has been commercialized to meet the abovementioned demand. In this report, by using a continuous conveyor belt furnace in a low-oxygen atmosphere, the brazeability of the brazing foil on ferritic stainless steel, the microstructure resulting from the interfacial reaction between the brazing foil and ferritic stainless steel, and the shear strength of a ferritic stainless steel single-lap joint brazed with the brazing foil were investigated. Therefore, the novel brazing foil showed good spreadability on ferritic stainless steel. Moreover, the ferritic stainless steel single-lap joint that was brazed with the brazing foil demonstrated approximately the same shear strength as that brazed with a conventional brazing filler metal.

We developed surface treatment method of titanium for proton exchange membrane fuel cell bipolar plate. The surface-treated titanium achieved good corrosion resistance in H₂SO₄ solution (pH = 3) containing 10 ppm F⁻ at 80°C in a simulated proton exchange membrane fuel cell environment. The average corrosion current density was under 0.1 µA cm⁻² during potentiostatic polarization testing for 24 h. Further, the contact resistance value was 8.9 mΩ cm² at a pressure of 1 MPa after corrosion testing, which was very low compared to typical etching samples.

The corrosion of diesel fuel storage tanks in the US was first reported in 2007, when the transition to more sustainable fuels, such as E10 and biodiesel, was underway, along with the adoption of ultra-low-sulfur diesel. Corrosion is caused by acetic acid produced by contaminating bacteria in fuel storage tanks. This study aimed to investigate the relationship between fuel improvements and microbiologically influenced corrosion in diesel fuel storage tanks by isolating acetic acid-producing bacteria and examining their effects on the deterioration of diesel-related fuels. The results revealed that the bacterium isolated from the two samples was Gluconacetobacter sp. (named as strain US-001). Among the carbon sources tested relevant to recent fuels, ethanol was dissimilated with acetic acid production and decreasing pH. Furthermore, the presence of 0.5% ethanol enabled the deterioration of n-dodecane, although it did not affect the pH. Dibenzothiophene, among the tested sulfur compounds present in previous low-sulfur diesel, inhibited the growth of the isolated strain US-001. In a sealed cup with a limited oxygen supply, the culture of strain US-001 experimentally induced severe steel corrosion when ethanol/n-dodecane was used as the carbon source. In conclusion, we speculate that ethanol contamination through E10 gasoline in diesel fuel tanks facilitates the growth of acetic acid bacteria, leading to the accumulation of acetic acid and a decrease in the pH of the sludge. Simultaneously, the introduction of ultra-low-sulfur diesel created more favorable growth conditions by removing their growth inhibitors, thereby resulting in microbiologically influenced corrosion of diesel fuel storage tanks.

The use of biosynthesis is considered an environmentally friendly and more sustainable method for the production of metal nanoparticles. In this study, copper nanoparticles (Cu-NPs) were synthesized using tea stem extract as a reducing agent. Spectroscopic identification revealed that the CuO is the major crystalline structure with a particle size of 14.9 nm. The B_g mode of the Raman active mode is associated with the symmetric oxygen stretching of Cu-O and is consistent with the monoclinic crystal CuO in X-ray powder diffraction (XRD) measurement. X-ray photoelectron spectrometer (XPS) deconvolution revealed the split peaks for Cu 2p_3/2 and confirmed the coexistence of Cu⁺ and Cu²⁺ in the Cu-NPs. The Cu-NPs possessed effective catalytic ability for the degradation of methylene blue (MB) from the aqueous phase in a Fenton-like system. These results provide important evidence for the potential application of tea stem in synthesis of nanoparticle.