Series of Ni-base single-crystal superalloys with superior thermal durability have been developed to improve thermal efficiency of gas turbine systems. Microstructural transition during creep so called “raft structure” formation enhances creep properties at lower stress and higher temperature condition. Furthermore, larger perfection degree of the raft structure contributes to better creep properties under the same creep condition. To control the perfection degree of the raft structure, magnitude of a lattice misfit and an elastic misfit between γ and γ′ phases should be controlled. In the current situation, the lattice misfit can be controlled by using alloy design program NIMS has developed. In this review, we focused on the role of the raft structure in alloy design. Observation results and predicted mechanisms about strengthening by the microstructural transition, in addition to the mechanism about microstructural transition itself during creep, were summarized and explained. Finally, under these recognitions mentioned above, our effort to establish a new alloy design approach to control the perfection degree of the raft structure by modifying the elastic misfit were introduced.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 86 (2022) 157–171.

We prepared a catalyst-coated wire-mesh filter by thermal plasma spray method in order to develop a new type of carbon soot particulate matter (PM) removal component. The halftone plate of a 316 stainless steel (SUS316) mesh was newly used as a substrate for a PM oxidation catalyst. A thermal plasma-spray method was applied to form a Ni-Pd alloy catalytic layer on the filter. As for the performance of Ni-Pd supported filter, the PM oxidation started from approximately 420°C, and the combustion at the catalytic surface took place at around 500–540°C, and finally a noncatalytic oxidation proceeded at around 650°C. The catalyst lowered a peak temperature around 110–220°C than that of only PM. Furthermore, the catalytic performance was maintained after a 5 times-repeated PM oxidation test. By the characterization of the catalyst layer, it was found that Pd particles were dispersed in a matrix of Ni and segregated on the surface and upper part of the plasma-sprayed film on the wire. The surface morphology did not change after the repeated cycle test. In this study, we found the availability of the plasma-spray catalyzed mesh filter was fabricated and as an environmental material with PM removal catalytic function.

This Paper was Originally Published in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 217–222.

Corson (Cu-Ni-Si) alloys were unidirectionally solidified via the Mizuta method under air or water cooling. To replicate the microstructure of a Corson alloy during solidification, phase-field (PF) simulations were performed, and the numerical results were compared with the experimental findings. The comparison between the air- and water-cooling conditions revealed that the primary dendrite trunks were thinner, and the secondary dendrites were longer and more developed under air-cooling conditions. These results were consistent with the experimental observations. Furthermore, the secondary dendrite arm spacings were evaluated via PF simulations, and the calculated results were consistent with the experimental observations. The interface energy and its anisotropy adopted in the present PF simulations were reasonable for the Corson alloy when compared with the values reported in other studies.

A secondary liquid phase with a droplet shape is separated from the primary liquid phase in Cu-Ni-Fe-Mo-Si alloy during laser cladding processing. During the subsequent quenching process, the secondary liquid phase solidifies into hard particles that are dispersed in the primary matrix phase. An increase in Ni content suppresses coarsening of the hard particles, while the mechanism of the suppression has not been clarified. In this study, we investigated the effect of Ni content on hard particle size, mainly emphasizing the Marangoni effect controlled by the temperature dependence of interfacial energy. The effects on the hard particle size were analyzed based on changes in the starting temperature of the separation of two liquid phases (L1 and L2) and the temperature dependence of interfacial energy, calculated for various Ni contents using CALPHAD software. Our findings revealed that the Ni content had little effect on the temperature dependence of interfacial energy. However, an increase in the Ni content decreases the temperature of L2 droplet formation and shortens the time to solidification, thereby reducing a moving distance of droplet. Therefore, the collision frequency of L2 droplets caused by the Marangoni effect was reduced, and coarsening of the droplet was suppressed.

This Paper was Originally Published in Japanese in J. Japan Inst. Metals 86 (2022) 191–200. Abstract, Table 3, Fig. 3, Fig. 4, Fig. 14, were slightly modified.

Morphology of eutectic in a hypoeutectic Cu-Zr alloy can be changed to various structures dependent on plastic deformation methods. This study reports morphological evolution of eutectic caused by unidirectional- and cross-rolling in a hypoeutectic Cu-2.7 at%Zr alloy. A graph-based method was applied to analyze the SEM images to characterize the morphological evolution of eutectics in terms of orientation, length, thickness, and connected structure of eutectics. Before rolling processes, an as-cast Cu-2.7 at%Zr alloy possessed a net-like morphology of eutectic with random orientations. The morphology of eutectic changed to the elongated and oriented one along the rolling direction by the unidirectional-rolling, and one along the two rolling directions by the cross-rolling. Variations of electrical conductivity by the unidirectional- and cross-rolling were also discussed based on the morphological evolution of eutectic.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 61 (2022) 68–75.

In this paper, a systematic approach utilizing clusters and mixing entropy is proposed to design efficient glass-formers and evaluate glass forming ability (GFA) without relying on thermal properties’ parameters. Firstly, under the guidance of this method, glass-formers in Zr-Al-Co-Cu system were designed as mixtures of topologically packed Zr-Al, Zr-Co and Zr-Cu clusters. Among these, two novel clusters, namely a trigonal prism Co-Zr₉ and an Archimedean octahedral anti-prism Co-Co₂Zr₈ were obtained and used. The best composition is Zr_55.79Al_12.66Co_7.74Cu_23.81, expressed as Cu (Cu₇+Zr₅)+0.867Co (Co₂+Zr₈)+0.851Al (Al₄+Zr₈), which exhibits a critical diameter of up to 10 mm. Additionally, based on this method, a novel parameter (ξ), independent of thermal properties’ parameters, was proposed to predict the GFA of metallic glasses. The results indicate that the lower ξ value correlates with better GFA. Simultaneously, the average local five-fold symmetry (ALFFS) from molecular dynamics (MD) simulations was employed to provide supplementary explanations for a few outlier points, further validating the proposed method’s effectiveness. The findings not only confirm the effectiveness of the clusters and mixing entropy approach in designing high-GFA metallic glasses, but also demonstrate the new parameter’s potential in predicting GFA. This study provides important theoretical and practical guidance for optimizing the design of metallic glasses.

This study investigates the microstructure and mechanical properties of four different Cr-Fe-Mn-Ni medium entropy alloys (MEAs) for potential nuclear applications. In this work, Cr-Fe-Mn-Ni medium entropy alloys were fabricated and analyzed. Nano hardness measurements showed higher hardness in Cr_0.8FeMn_1.3Ni, attributed to the increased atomic size difference caused by higher Mn content. The strength of Cr-Fe-Mn-Ni MEAs is mainly affected by solid solution strengthening and grain boundary strengthening. The tensile test revealed that Cr_0.8FeMn_1.3Ni exhibited the highest strength, which is correlated with its large hardness and small grain size. The increase of Mn content leads to greater atomic size difference, enhancing the hardness and reducing the grain size. Cr_0.8FeMn_1.3Ni shows superior strength and higher hardness compared to other Cr-Fe-Mn-Ni MEAs, suggesting its potential for nuclear applications.

Silver, Ag, in secondary raw materials such as printed circuit boards is recovered by nonferrous metal thermochemical processes. Because printed circuit boards contain bromine, Br, which is highly reactive with Ag, as a flame retardant, there is concern that Br may affect the recovery of Ag. In this study, the FeO_x–CaO–SiO₂ slags were equilibrated with liquid AgBr and Ag in a MgO crucible at 1473 K, and the effects of concentration of Br in the slags, oxygen partial pressure, p_O2, and slag composition on the dissolution of Ag were experimentally investigated. The results showed that the concentration of Ag in the slag coexisting with Ag and AgBr was higher than that coexisting with only Ag. Moreover, the concentration of Ag in the slag increased with increasing concentration of Br in the slag coexisting with Ag and AgBr. At p_O2 = 10⁻⁹, the concentrations of Ag and Br in the slag in equilibrium with AgBr were minimum at neutral slag basicity Q = 0.45, defined as Q = (mass%CaO + mass%MgO)/(mass%CaO + mass%MgO + mass%SiO₂). The slag loss of Ag can be reduced using neutral basicity slag and by reducing the bromine partial pressure in the system to reduce the concentration of Br dissolved in the slag.

The weldability of an Al-11%Zn-3%Mg-1.4%Cu alloy by friction welding was investigated, and the effects of T6 treatment during and after welding on the microstructure and joint properties were clarified. Fine grains were formed at the interface of the as-welded joint and were coarsened by the T6 treatment. η′ phase was coarsened at the interface due to friction welding, on the other hand, fine η′ was precipitated again by T6 treatment after welding. The joint efficiency in tensile tests was 72% for the as-welded joint but recovered to 89% by T6 treatment after friction welding, and all fracture locations were near the interface layer. Tensile strength differed depending on whether the grain elongation direction was parallel or perpendicular to the tensile direction, suggesting that the grain shape near the interface was the cause of joint failure.

This Paper was Originally Published in Japanese in J. Japan Inst. Light Metals 73 (2023) 611–615.

The GA steel sheets with various strengths (590, 780, and 980 MPa classes) from which the Zn-Fe film was removed and 6061-T6 sheets were lap joined magnetic pulse welding under the conditions of gap length d of 1.17 mm and discharge energy W of 3.0 kJ. Before welding the GA steel sheets, a Zn-Fe film with a width of 5 mm was removed by grinding or acid treatment. In the case of acid treatment with dilute sulfuric acid, the film was removed within 3 minutes. On the other hand, when the film was removed by grinding, burrs were formed on the GA steel plate side. With either film removal method, the film was removed and a lap joint between GA steel sheet and 6061-T6 sheet was able to be achieved. This means that the joining position can be selected by magnetic pulse welding. The corrosion resistance of the lap joint sheets was investigated through salt spray test for 120-hours. The results showed that even under conditions where GA steel plates corrode, the weld interface did not corrode and bonding strength remained as well as before the corrosion test.

This Paper was Originally Published in Japanese in J. JILM 74 (2024).

Carburizing and quenching is known as a surface modification treatment applied to impart mechanical properties to materials. The authors have developed an ultra-rapid carburizing using induction heating above the eutectic temperature, which enables in-line carburizing as a next-generation heat treatment method, in order to coexist in the future carbon-neutral society. Previous studies have reported on carbon penetrating behavior at a constant 1523 K, for carburizing on an alloyed steel SCM420. However, in order to apply it to various steels, it is necessary to elucidate the carburizing mechanism of this treatment, which is different from gas carburizing and vacuum carburizing. In this study, the temperature range was expanded to 1473 K and 1573 K to investigate the carbon penetration characteristics as a detailed mechanism elucidation. As a result, it was shown that the tendency of carbon penetration characteristics was similar to that of 1523 K. Moreover, the rate of carbon penetration varied exponentially with the carburizing temperature. The activation energy of the ultra-rapid carburizing reaction obtained by the Arrhenius plot was equivalent to that of the methane decomposition reaction, which was the raw material gas. Thereby, it was verified that carburizing reaction was rate-controlled by the decomposition reaction of methane.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Heat Treatment 62 (2022) 95–101. Reference [12] was added as the English translation edition of Ref. [11].

Amorphous silicon carbon nitride (a-SiCN) films are known for their exceptional mechanical properties. This study explores the impact of tetramethylsilane (TMS) concentration on the deposition of a-SiCN films utilizing a microwave sheath-voltage combination plasma (MVP) source. A mixture of TMS and N₂ gases served as the reaction medium. The substrate temperatures were maintained between 905°C and 981°C. We observed that the deposition rate escalated with an increase in TMS concentration, reaching a peak rate of approximately 270 µm/h at a 20% TMS concentration. Concurrently, as TMS concentration increased, the carbon content rose from 11 at% to 51 at%, while nitrogen and silicon contents decreased to 15 and 18 at%, respectively. Hence, at lower TMS concentrations, the a-SiCN film predominantly comprised Si-N bonds, but at higher TMS concentrations, it transformed into a composite of Si-N, Si-C, C=N, and C=C bonds. The film hardness also augmented with rising TMS concentrations, achieving a maximum of 28 GPa in 20% TMS films. The friction coefficient for the film with 20% TMS concentration was approximately 0.29. In summary, the study successfully deposited a high-hardness a-SiCN film at an accelerated deposition rate using MVP from a high TMS concentration.

Semi-solid high pressure die casting is known as a process capable of forming high quality products. JIS ADC12 aluminum alloy is widely used for high pressure die casting, but this alloy has a narrow semi-solid temperature range, making it difficult to apply the semi-solid process. In this study, the preparation of ADC12 aluminum alloy slurry by applying mechanical vibration was attempted. Mechanical vibration was applied during the solidification of ADC12 alloy from the liquid to semi-solid state, and the effects of parameters of mechanical vibration and pouring temperature on the morphology of slurry have been investigated.

The application of mechanical vibration transformed the solid phase in the slurry from dendritic shape to fine spherical shape with increasing acceleration amplitude and velocity amplitude. As a result, slurry with solid particles dispersed in the liquid phase could be obtained. Moreover, it was found that high frequencies and displacement amplitudes above a certain value are required to obtain slurry with fine spherical solid particles. Fraction solid of slurry was affected by both the pouring temperature and vibration applied time, increasing with decreasing pouring temperature and increasing vibration time. Consequently, slurry with sufficiently fine spherical particles could be obtained by applying mechanical vibration with the frequency of 50 Hz and acceleration amplitude and velocity amplitude higher than 49.0 m/s² and 0.19 m/s, respectively. In this way, the fraction solid of ADC12 alloy slurry could be controlled by controlling the pouring temperature and vibrations time.

This Paper was Originally Published in Japanese in J. JFS 95 (2023) 16–22. Figures 8 and 9 were slightly changed.

The magnetite-silica (Fe₃O₄-SiO₂) composites with high magnetite contents for microwave heating elements were fabricated by the non-firing solidification method. Although the obtained solidified composite had a relative density of 47–57% and was not a dense body, it had sufficient mechanical strength due to the solidification of the silica phase. The magnetite in the composite functions as the microwave heating phase, and the SiO₂ phase and pore phase function as the microwave permeable phase, resulting in a structure that allows uniform heating to reach the inside of the composite structure. It was clarified that the solidified composite could generate heat up to about 500°C without oxidizing during the microwave heating process.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 296–300.

Characteristics of VO₂ films prepared on alkali-free glass substrates by chemical solution deposition (CSD) using vanadyl oxalate n-hydrate as the raw material are investigated. Diffraction peaks corresponding to VO₂ are observed in the samples obtained at firing temperatures of 350 to 550°C. However, diffraction peaks of the samples obtained at 500 and 550°C show a mixture of VO₂ and V₆O₁₃ phases. Regarding the surface and cross-section morphology of the films, the crystal grain size and porosity of the films steadily increase with firing temperature. The samples show an abrupt change in resistivity around 70°C. The change in resistivity caused by the metal-insulator transition are about three orders of magnitude. The sample transmittance in the near-infrared region decreases sharply with the phase transition. The maximum reduction in transmittance at 2000 nm is 55.4%.

Iron phosphate conversion coatings that precipitate on steel prevent corrosion and improve paint adhesion. Although this coating is composed of FePO₄ and iron oxides, separating the chemical species of the constituent elements using conventional analytical methods is challenging; hence, the detailed structure and deposition mechanism of the coating are not understood. This study used X-ray absorption and emission spectroscopy to analyze the coatings. The results showed that the main component of the coatings was FePO₄, mixed with FeO for short treatment times and γ-Fe₂O₃ for long treatment times. These results suggested a new reaction pathway between FeO and FePO₄, generated by eluted Fe²⁺ ions within solutions.

The leakage of fluorocarbon refrigerants due to corrosion of phosphorus copper tubes, which are widely used in air conditioners, is a growing environmental threat. In this study, to prevent this leakage, which is caused by stress corrosion cracking, we attempted to detect corrosion using a sensor that comprises a galvanic couple consisting of the copper tube and a carbon electrode. On testing in the presence of ammonia, the sensor detected a rise in background current, revealing the formation of a water film in which ammonia gas dissolves, with current noise identifying localized corrosion and oscillation of the background current indicating gas leakage. These phenomena can be detected by simply monitoring the current.

Aluminum alloys with open-channel structure are fabricated by casting the melt of aluminum alloys using wire-extraction method. Template stainless steel wires are coated with release agents such as boron nitride and alumina, which are embedded in the melt of aluminum alloys. After solidified, the wires are extracted by tensile test machine to fabricate channel holes so that open-channel aluminum alloys are produced. The microvoids are formed in alloys AC4CH and Al-7%Si, when the wires are coated with boron nitride. However, no microviods are observed in the alloys A1050 and A6063. It is found that the formation of microvoids is attributed to the addition of silicon, which may evolve nitrogen gas pores. Cross-flow type microchannel heat exchangers are fabricated, and heat exchange performance is investigated. The experimental results of heat exchange rate and pressure loss are in good agreement with the predicted results based on heat transfer calculation, which suggests that open-channel aluminum alloys are superior for heat exchangers.

The Fe-15Mn-10Cr-8Ni-4Si alloy, which has excellent low-cycle fatigue durability, was developed as a core material for steel-based vibration dampers that are effective against large-amplitude, long-period earthquake motions, and was put into practical use in 2014. However, manufacturing using small-scale equipment was expensive, so the authors tried manufacturing using stainless steel continuous casting facility and rolling facility, and succeeded in mass production. The authors also developed welding materials and welding techniques to assemble a buckling restraint brace damper with flat plasticizing section and one with cruciform plasticizing section, and successfully put these two types of brace dampers into practical use. The alloy plate has been recognized as an industrial product that can be manufactured with stable quality, and has been approved by the Minister of Land, Infrastructure, Transport and Tourism as a steel material for construction.

This Paper was Originally Published in Japanese in Bulletin of the Japan Institute of Metals Materia Japan 63 (2024) 60–62.

The Japan Institute of Metals and Materials (JIMM) awarded the nine best papers in 2023 presenting cutting edge research. Here, we introduce brief summaries of the awarded papers as current trends in research of Materials Transactions. Among the nine best papers, four were specially selected for young scientists whose ages are 35 or below. The awarded papers cover a wide range of metals and materials such as magnesium-based, aluminum-based and titanium-based alloys including high-entropy alloys, SUS304 stainless steel, Si/solder/Si joints and fine copper powder. In association with all the awarded papers, special issues edited in Materials Transactions are also briefly introduced to show the recent activities of Materials Transactions.

The special issue on recent research and development in the processing, microstructure, and properties of titanium and its alloy contains four review articles on metal additive manufacturing (AM) focusing on the processing, microstructural and/or crystallographic control, and biomedical applications of titanium and its alloys, and seventeen regular articles on metal AM, refining, microstructural evolution, and mechanical and fatigue properties related to the microstructure, and biomedical applications of titanium and its alloys, which have been published in Materials Transactions in 2023. This study briefly addresses this issue.

This paper investigated the effect of cooling rate after solution heat treatment and pre-aging at 303 K after cooling on aging behavior of Al–6 mass%Zn–0.75 mass%Mg alloy to elucidate the aging behaviors and strengthening mechanism throughout aging heat treatment in the case of low cooling rate, such as furnace cooling, followed by solution heat treatment. Regardless the absence of pre-aging, the maximum hardness obtained in the materials with furnace cooling after solution treatment was almost the same as that of water-cooled and pre-aged materials during the same aging time. The result of microstructure observations using transmission electron microscope show that fine precipitates consisting of η phase have been formed in all peak-aged materials.

Sn58Bi–Cu composite solder, in which copper (Cu) particles were applied as a reinforcement material, was synthesized to address the material limitations and improve the bonding properties of Sn–58Bi eutectic solder. To evaluate the impact of Cu particle concentration on the solderability and mechanical properties of Sn58Bi–Cu composite solder, five variants with different Cu particle concentrations (0, 3, 5, 10, and 15 vol%) were synthesized. Wetting, ball shear, and microhardness tests were then performed. The wetting test revealed that the Sn58Bi–Cu composite solder containing Cu particles up to 10 vol% exhibited satisfactory wetting morphology and a wetting angle of approximately 30°, indicating appropriate wetting behavior. In contrast, the Sn58Bi–Cu composite solder containing excessive amounts of Cu particles (15 vol%) demonstrated weak wetting angle and solderability due to increased viscosity from the intensified chemical reaction between the molten solder and Cu particles. The solder ball shear and microhardness test results for the Sn58Bi–Cu composite solder containing Cu particles up to 10 vol% showed that the mechanical properties of the solder joint improved with increasing Cu particle concentrations. This improvement in mechanical properties was attributed to the grain refinement of the joint and the reinforcement effect of Cu particles.