To introduce kink deformation into a titanium alloy, a α/β two-phase Ti–12Mo alloy with a layered structure was developed through a series of thermal-mechanical treatments. The deformation kink bands were generated during uniaxial compression tests. Strain field maps of the kink-favored grain were plotted based on high-resolution digital image correlation (HR-DIC) analysis. The observed kink deformation occurred near the triple point and was significantly influenced by intergranular deformation of the adjacent grain. In grains without kink deformation, the deformation primarily exhibited in the form of slip lines with the same direction as the α phase interface. A crystal plasticity finite element model was developed using electron backscatter diffraction (EBSD) measurements to evaluate the equivalent strain field maps and von Mises stress maps. The grain with kink deformation exhibited low plastic activity and high von Mises stress.

In order to investigate the effect of boron on the precipitation behavior of β phase in Al–Mn–Mg–B alloy used as a material for cask baskets, 1.00 × 10⁴ hours aging treatment was carried out focusing on the temperature history in the cask as in the previous report, and the Time-temperature-precipitation diagram and Supersaturation-diffusion length-precipitation diagram were evaluated using the change tendency of the specific resistance obtained. In the Al–Mn–Mg–B alloy, although grain refinement by AlB₂ was confirmed, the effect of boron addition on the precipitation rate of β phase was hardly recognized. That is to say, it was confirmed that the grain boundary and the interface between B compounds and matrix phase hardly contributed as nucleation sites of β phase. In conclusion, it is considered that the reduction of the solid solution Mg content in the Al–Mn–Mg–B alloy does not occur even after 60 years if the Mg content is 1.0 mass% as in the Al–Mn–Mg alloy.

This Paper was Originally Published in Japanese in J. Japan Inst. Light Metals 72 (2022) 691–701.

In the contemporary world, carbon nanocoils (CNCs) act as mainspring in both fundamental and applied levels in nanotechnology advancements. They are attributed to their remarkable electrical, thermal, chemical, and mechanical properties inherited from the synthesis method; they are predestined for many potential applications. Catalytic chemical vapor deposition (CCVD) is the prevailing synthesis method for producing CNCs with controlled morphology and structural properties. In this study, Al₃YRh_x (x = 0, 0.2, 0.5, and 1.0) intermetallic catalyst series have been employed as a template for the catalytic conversion of an acetylene precursor into a solid material over the catalyst bed. The influence of reaction temperature, reaction duration, and Rh content in the catalyst in the structure and morphology of the CNCs prepared were analyzed through X-ray diffraction analysis, Raman spectroscopical investigation, and transmission electron microscopy. A detailed study on CNCS formed through spatial confinements by incorporating non-hexagonal rings in the graphitic skeleton leads to the coiling effect. Overall, nanotube synthesis has made significant progress by testifying the imperative reaction parameters in CCVD.

Microstructural evolution and changes in hardness and electrical conductivities of a cast hypoeutectic Cu–2.7 at%Zr alloy processed by high-pressure torsion (HPT) were investigated. The cast alloy had a net-like microstructure composed of a primary Cu phase and a eutectic consisting of layered Cu and Cu₅Zr phases. The Cu and Cu₅Zr phases in the eutectic had a cube-on-cube orientation relationship. The cast alloy with the hardness of 137 HV exhibited a value of electrical conductivity of 32%IACS. With increasing the number of HPT-revolutions, the eutectic was severely sheared and elongated along the rotational direction. In addition, mechanical dissolution of the Cu₅Zr phase into the Cu phase by the HPT was confirmed after 5 HPT-revolutions through XRD measurements and TEM observations. After 20 HPT-revolutions, the Cu phase was significantly refined and formed the lamellar structure having an average grain size of 15 nm. The electrical conductivity decreased and saturated at a value of 8%IACS after 50 HPT-revolutions. The significant decrease in the electrical conductivity was primarily attributable to the mechanical dissolution of the Cu₅Zr phase into the Cu phase by the HPT, followed by the formation of a nanocrystalline Cu–Zr supersaturated solid-solution alloy with the hardness of 430 HV.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 60 (2021) 98–103.

This study involved the fabrication of Ti–10Nb–3Mn–_XTaC composites through the vacuum sintering process of powder metallurgy, where different proportions of TaC powders (_X = 1, 2, and 3 mass%) were added. The composites were sintered under vacuum conditions at temperatures of 1225, 1250, 1275, and 1300°C for 1 hour each. The experimental findings indicate that the addition of 2 mass% TaC powders to the Ti–10Nb–3Mn alloys resulted in the optimal mechanical properties when sintered at 1275°C for 1 hour. The specimen exhibited a relative density of 96.24%, a hardness of 67.38 HRA, and achieved values of 1276.63 MPa for TRS (tensile rupture strength) and 40.37 GPa for the flexural modulus. The electron backscatter diffraction (EBSD) results revealed that the TaC facilitated the in-situ formation of TiC during the sintering process, which was uniformly dispersed in the Ti matrix. Additionally, the Ta atoms acted as β-stabilizing elements, forming a solid solution in the Ti matrix and improving both the microstructure and mechanical properties of the Ti alloys.

For a comprehensive understanding of the Nankai Trough seismogenic zone, the Integrated Ocean Drilling Program/International Ocean Discovery Program (IODP) conducted a deep ocean drilling project referred to as the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) from 2007 to 2019 off the Kii Peninsula, Japan. To investigate the subduction zone’s physical properties and reveal the sediments’ compressive strength, we carried out consolidated–undrained triaxial compression tests with pore water pressure measurements on NanTroSEIZE core samples. The core samples used were retrieved from depths of approximately 400 m below the seafloor at sites C0006 and C0007 with ∼4000 m water depths. The rocks are Pliocene siltstones with a porosity of ∼50%, classified as sedimentary soft rocks. As a result of the triaxial compression tests, the cohesion c_cu and internal frictional angle φ_cu derived from the total stress analyses ranged in 1.8–1.9 MPa and 15–17°, respectively. In addition, the cohesion c′ and internal frictional angle φ′ determined by the effective stress analyses were within 1.6–2.2 MPa and 18–28°, respectively. All the specimens tested caused brittle failure and formed clear shear fractures. In the case of these brittle failures, we found that post-failure specimen area correction when calculating differential stress in post-failure might cause a nonnegligible underestimation of the differential stresses. Therefore, we suggest that the area correction for undrained triaxial compressive tests of soft rocks should be conducted until reaching their peak strength if brittle failure occurs.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 71 (2022) 251–258. The abstract and caption of Fig. 6 are slightly modified.

Surrogate-based microstructural optimization was applied to model the relationship between local crystallographic microstructure and intergranular hydrogen embrittlement in an Al–Zn–Mg alloy, and a support vector machine with an infill sampling criterion was used to realise high-accuracy optimisation with a limited data set. This methodology integrates thoroughgoing microstructural quantification, two coarsening processes, and surrogate modelling. An objective function was defined together with 66 design parameters that quantitatively express size, shape, orientation and damage during specimen machining for surface grain boundaries and grains. The number of design parameters was then reduced from 66 to 3 during the two-step coarsening process. It has been clarified that intergranular crack initiation can be described using the simple size of grains and grain boundaries together with grain boundary orientation with respect to the loading direction. It can be inferred that these design parameters are of crucial importance in crack initiation through elevation in stress normal to grain boundaries. Correlation between the selected design parameters and crack initiation was somewhat weak compared to past applications of a similar technique to particle damage. The reason for this is discussed. The present approach offers a cost-efficient solution for the prevention of hydrogen embrittlement through 3D design of crystallographic microstructure that cannot be obtained using conventional strategies for developing materials.

Liquid-phase synthesis is suitable for controlling the morphological and structural properties of functional inorganic materials and such control is important because they strongly affect the functionality of the product. Cobalt-based materials is one group of materials that requires control of powder morphology and structure. Cobalt is an important metal element used in various industrial fields such as secondary batteries, superalloys, permanent magnets, hard metals, and catalysts. The ever-growing demand of cobalt highlights that there is an urgent necessity to develop high quality material synthesis methods and to secure cobalt resources for countries that rely on import like Japan. Especially, technologies to recycle cobalt in a form reusable for secondary batteries and catalysts are desired because further increase in demand is anticipated. Meanwhile, spherical porous tricobalt tetroxide secondary particles obtained by calcination of spherical cobalt carbonate precursors have been reported to be promising materials for battery applications. Moreover, porous metal cobalt obtained by hydrogen reduction of tricobalt tetroxide is known to be effective for catalyst applications. However, conventional methods to synthesize spherical cobalt carbonate requires addition of additives in the reaction mixtures or otherwise requires hydrothermal treatment in pressure vessels. These are unfavorable to develop a practical and sustainable process for cobalt-based material production and recycling. In this study, a facile room temperature synthesis method to prepare spherical cobalt carbonate precursors from solutions of cobalt chloride and ammonium hydrogen carbonate that does not require any additives or hydrothermal treatment is developed by optimizing the carbonate solution concentration, carbonate/cobalt salt molar ratio, and stirring time during reaction. Furthermore, we succeeded in obtaining porous tricobalt tetroxide and porous metal cobalt that carry on the exterior spherical morphology of the original cobalt carbonate precursor by calcination and hydrogen reduction. The developed process shall contribute to realize high quality cobalt-based material production and recycling.

Information on the microstructure of copper minerals is important for more detailed understanding and control of the Cu extraction processes such as flotation and direct leaching. For the first time, scanning tunneling microscopy (STM) observation with atomic resolution on CuFeS₂ surfaces has been achieved using cleaved natural chalcopyrite crystals at low temperatures. The surfaces with (011) and (012) orientations have been identified by STM observation, electron backscattering, and X-ray diffraction. (011) surfaces of two different types were observed. The one is a reconstructed surface, and the other surface has a structure that is close to that of a bulk terminated surface.

The contradiction between the supply and demand of nickel resources is intensifying, and it is urgent to develop new processing and smelting processes for laterite nickel ore. Gas based smelting with H₂ and CH₄ as reductants is of great significance to solve the “double carbon” problem faced by the traditional metallurgical industry. Taking low-grade laterite nickel ore as the research object, CH₄ as the reductant and elemental sulfur as the additive, under the conditions of different reduction temperature, reduction time, gas concentration and additive dosage, this paper discusses the reduction behavior of CH₄ and iron nickel oxide in laterite nickel ore. Combined with XRD, SEM-EDS, gas analysis and other characterization methods, the phase and morphology of laterite nickel ore and its reduction products were deeply analyzed. Results surface: under the conditions of reduction temperature 800°C, reduction time 60 min, CH₄ concentration 20%, elemental sulfur dosage 4%, the metallization rate of nickel and iron in the reduction product can reach 98.01% and 8.44%, respectively. Nickel oxide is almost completely reduced to nickel, and most of iron is reduced to low-price iron oxide. In the reduction process, the amorphous silicate recrystallizes into magnesium olivine phase in the reduction process. It hinders further reduction of nickel. According to SEM-EDS analysis, some metal iron and elemental sulfur generate FeS around the iron oxide region, which hinders the contact between reducing gas and FeO. Therefore, the reduction of iron is inhibited and the iron oxide content increases. It promoted the selective reduction of nickel.

A thermodynamic model (U-Cal model) is proposed to predict the fugacity and water content in the CO₂-rich phase (gas or supercritical fluid), and the CO₂ solubility and pH in aqueous solutions in a CO₂ capture and storage environment, i.e., a CO₂ environment in a supercritical state. The values predicted by the U-Cal model agree well with measured values. The water content in the CO₂-rich phase increases to 1–10 g/L as a result of the mutual dissolution of CO₂ and H₂O. The increase in the solubility of CO₂ in aqueous solution and the decrease in the pH with increasing pressure are small. The CO₂ corrosion behavior of carbon steel is discussed to use the U-Cal model. In iron dissolution-dominant CO₂ corrosion in an aqueous solution with carbon steel, the corrosion rate can be understood as a function of the pH. In FeCO₃ formation-dominant CO₂ corrosion, it is considered that the corrosion progresses as FeCO₃ dissolves to supersaturation and then FeCO₃ precipitates on the surface of the material. The FeCO₃ precipitation behavior is predicted from the crystal growth rate equation. Corrosion of carbon steel in the CO₂-rich phase involves similar mechanisms to corrosion in an aqueous solution; however, the corrosion rate is lower.

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 72 (2023) 131–141.

Alumina composites dispersed with 10 vol% AlN particles are prepared by commercial α-Al₂O₃ and AlN powder. The pulsed electric current sintering is used to densify the bulk samples. The high-temperature oxidation experiments are conducted at temperatures ranging from 1200 to 1350°C for 6, 12 and 24 h in the air environment. The internally oxidized zone (IOZ) is developed from the sample surface to consist of the Al₂O₃ matrix with small closed pores. The growth of IOZ obeys the parabolic law, which means the rate-controlling process is mass transport in IOZ. The high-temperature oxidation behavior of 10 vol% AlN/Al₂O₃ is compared with the 10 vol% Ni/Al₂O₃ composites. The differences in the microstructure at IOZ and the diffusion of oxygen through the Al₂O₃ matrix grain boundaries dependence on the oxygen partial pressure are discussed for understanding the high-temperature oxidation behavior of both composites.

Two types of TiO₂/g-C₃N₄ heterojunctions, physically and chemically contacted samples, were synthesized to investigate the effect of their contact modes on the photocatalytic activity for dye degradation. The physically contacted TiO₂/g-C₃N₄ heterojunction (TCN_PHY) was prepared by an electrostatic assembly process. In addition, the chemically connected heterojunction (TCN_CHE) was synthesized by a hydrothermal method accompanied by the formation of Ti–O–C covalent bonds. Fourier-transform infrared and X-ray photoelectron spectroscopies confirmed the formation of Ti–O–C covalent bonds in TCN_CHE. Subsequently, their photocatalytic activity for dye degradation was evaluated as a model reaction. The results showed that TCN_CHE exhibited higher degradation efficiency than TCN_PHY because of its higher UV light absorbance and lower recombination rate than those of the physically contacted sample. These results indicate that the hydrothermal method gives unique advantages in chemically contacted heterojunction construction, which can lead to the improvement of photocatalytic activity.

Recently, manufacturing of metallic titanium ingots based on a thermal decomposition process using titanium disulfide TiS₂ as the intermediate product with a significantly lower decomposition temperature of approximately 4000 K was reported. However, this process involves a carbothermic reaction for preparing the intermediate product. Carbonic acid gas, a cause of global warming, was generated, and the process is inadequate from the viewpoint of environmental protection. In the present study, a reaction process without the generation of carbonic acid gas was used. Dilute hydrogen-mixed argon gas was used for the synthesis of the intermediate product. The phases of the synthesized intermediate products were investigated using X-ray diffraction and were matched to several titanium sulfide phases, such as TiS, and Ti₂S₃, which have a higher titanium ratio than the product, TiS₂, synthesized by carbothermic reaction. The thermodynamic conditions of the synthesis process, such as the partial pressures of oxygen and sulfur, were also predicted from the product phases.

Ti implants used for the treatment of bones and teeth damaged by diseases and accidents must exhibit excellent bone-bonding ability. To develop novel Ti alloys with bone-bonding ability superior to that of conventional Ti alloys, we prepared alloy films of Ti and Ca, especially Ca is an essential element in the human body and the inorganic components of bones, via radio-frequency magnetron sputtering. Ti–Ca alloy films with various Ca concentrations were fabricated using different arrangements of Ti and Ca sources. The crystal and surface structures as well as in vitro bone-bonding ability of Ti–Ca alloy films with Ca concentrations of 6, 27, and 38 mass% were investigated. X-ray diffraction patterns revealed that the abovementioned Ti–Ca alloy films exhibit an amorphous structure. Results of X-ray photoelectron spectroscopy revealed that oxides and hydroxides of Ti and Ca were present on the surfaces of the Ti–Ca alloy films. In a simulated body fluid (SBF) immersion test, hydroxyapatite precipitated first on the surface of the Ti–27 mass%Ca alloy film, whereas the Ti–38 mass%Ca alloy film peeled off during immersion in the SBF solution.

In No. 3 hot strip mill at JFE Steel East Japan Works (Chiba), mild steels are produced by the endless rolling process, in which rough rolled bars are joined and rolled continuously in the finishing mill. However, this process is not applied to high tensile strength steels because the alloy elements contained in those steels, such as silicon and manganese, form an oxide layer at the joining interface, disrupting the joining process. In laboratory joining tests, heating the joining surface until it melted resulted in discharge of the oxide layer from the interface, and steels that form oxide with a low melting temperature were successfully joined. A FEM flow analysis revealed that the viscosity of the oxide is the most important parameter for discharge. The low melting temperature of the oxide leads to low viscosity, resulting in the discharge of the oxide layer.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Technol. Plast. 64 (2023) 1–6.

Verification of the manufacturing conditions for translucency ceramics are showed using powder forming and sintering method in order to establish the manufacturing technology for optical devices with arbitrary complex shape and shape retention, and optical excitation materials. However, this method is extremely difficult to obtain translucency ceramics because the combination of complex factors such as “the shape and particle size of the raw materials, forming conditions and sintering” adversely affect the translucency of the sintered material, which is caused by the transmitted light scattering of the sintered material. Therefore, we have succeeded in realizing transparent ceramics by examining these complicated factors (materials, molding, sintering conditions, crystallization) and specifying the amorphous sintering conditions and the densification-molding conditions necessary to eliminate the light scattering factors inherent in sintered materials. It is necessary to show the correlation of the volume change with respect to T_g-temperature and T_m-temperature, which are important regarding amorphization, considering the sintering treatment conditions that depend on the particle size of the raw material fine powder, and to specify the molding body-pressurization (pressure and time) conditions. These optimizations will make it possible to develop the expected high-functional-photoelectric optical devices with microstructures and, high-power laser light sources independent of materials.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 68 (2021) 409–414.

The equilibrium crystal structure of LnMnO₃ (Ln: lanthanide) is known to be orthorhombic when larger ions from La³⁺ to Dy³⁺ are used as Ln³⁺, and hexagonal when smaller ions from Ho³⁺ to Lu³⁺ are used. Research indicates that the hexagonal phase forms when the tolerance factor, expressed as functions of radii of the constituent ions, is less than 0.840. In this study, we attempted to induce oxygen deficiency in DyMnO₃ through solidification at low oxygen partial pressure using an aerodynamic levitator. The objective was to decrease the tolerance factor by reducing the valence of manganese ions and thereby increasing their ionic radius. The results showed an increase in oxygen deficiency as the oxygen partial pressure decreased. Based on the assumption that the manganese ions’ valence decreased due to an increase in oxygen deficiency, the corresponding tolerance factor evaluated from the average ionic radii of manganese and oxygen also decreased. This decrease promoted the formation of the hexagonal phase, similar to the effect observed when the ionic radius of Ln³⁺ is reduced.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 87 (2023) 226–230. The abstract and figure captions are modified.

We aimed to fabricate CrFeCoNiSi HEA deposits dispersed with Si compounds by low-pressure plasma spraying, and we evaluated the structure and properties of the alloy deposits. A heat treatment was applied to the fabricated alloy deposits, and the formation process of precipitates in HEAs was investigated. We fabricated HEA deposits without segregation on substrates with and without water-cooling. The fcc solid solution existed in the as-sprayed deposits and heat-treated deposits. Si compounds were dispersed in the deposits. The precipitates became coarser as the heat-treatment temperature increased. The 873 K heat-treated deposits had the highest hardness both with and without water-cooling. Nanoscale precipitates were formed inside the crystal grains in the as-sprayed deposits with water-cooling. The 1273 K heat-treated deposits satisfied the definition of HEAs.

Most Mg-based composites are reinforced with ceramic particles such as aluminum oxide and silicon carbide, which leads to relatively high strength and elastic modulus but moderate plasticity, especially when ceramic reinforcements are present at elevated concentrations. We offer a novel type of Mg-based composite reinforced micro-sized spherical Fe-based metallic glass powders (FMG_P) that positively mix heat with the matrix element to avoid the development of brittle intermetallic compounds. The composites are sintered at the temperature between the glass transition temperature and the first commencing crystallization temperature of metallic glass, i.e., the supercooled liquid region, to obtain improved densification due to lower sintering resistance. The results reveal that when the FMG_P concentration increases, so do the composites’ strength, plasticity, and densification. For example, adding 30 wt.% spherical FMG_P to pure magnesium increases yield strength, ultimate compressive strength, and fracture strain by 105%, 228%, and 450%, respectively. This intriguing discovery might provide valuable guidance for developing a novel kind of composite with great durability and flexibility for real engineering applications.

The six best papers were awarded by The Japan Institute of Light Metals (JILM) and The Japan Society for Technology of Plasticity (JSTP) in Materials Transactions. Here, the awarded papers are briefly summarized as current trends in research of Materials Transactions. Among the six best papers, three were from JILM and the two of the three were selected for young scientists whose ages are 30 or below. All the six best papers were originally published in Japanese in Journal of the Japan Institute of Light Metals and Journal of the Japan Society for Technology of Plasticity as cutting-edge research in JILM and JSTP which are major companions of Materials Transactions.

An as-cast Mg–6Zn–0.9Zr–0.9Nd (mass%) alloy was isothermally heat treated to form semi-solid microstructure, and its corrosion behaviors before and after heat treatment were revealed. During the isothermal heat treatment, the microstructure transformed into homogenous spheroidized structure, and the liquid phase presented network-shaped morphology. The electrochemical results showed that there is no passivation behavior and obvious local corrosion in the semi-solid formed alloy, and homogeneous general corrosion is the primary corrosion form. The network-shaped liquid phase prevented the flow of corrosion media between solid phases, and therefore inhibited the formation of pitting corrosion.