Cryogenic applications require careful material selection due to severe property degradation at low temperatures. Face-centered cubic (FCC) alloys like high-manganese steel offer good low-temperature toughness but become brittle at cryogenic temperatures. This brittleness increases safety risks due to sudden, unpredictable fractures. Therefore, novel technologies are urgently needed to improve the mechanical properties of FCC alloys for cryogenic applications. This research presents a new surface-cracking process for high-manganese steels to address the degradation of mechanical properties at cryogenic temperatures. This technique involves the intentional introduction of surface micro-cracks, which significantly enhances the Charpy impact toughness of the steel at low temperatures. To observe the effect of surface cracks, specimens with varying crack densities were fabricated: 5 lines (5L) and 10 lines (10L). These were compared with a standard specimen without surface cracks (0L). Microstructural observations reveal that the dispersion of crack propagation energy by the surface micro-cracks improves Charpy impact toughness, promoting a ductile fracture mode even under cryogenic conditions.

In this study, CNN models were developed to predict the changes in creep properties of long-term aged CMSX-4 alloy based on heat treatment time by training deep neural networks with microstructure images of the material. To predict the creep rupture time and fracture strain of specimens heat-treated for 0 to 10,000 hours, the CNN models were trained using BSE images of the specimens and their two-point spatial correlation images. As the heat treatment time of CMSX-4 alloy increases, topological inversion occurs, where the arrangement of the γ phase and γ′ phase changes, leading to significant microstructural changes. When the CNN models, built to predict the creep properties based on microstructural evolution, were trained with 8-bit grayscale BSE raw images, γ-γ correlations, or γ-γ′ correlations, the model trained on γ-γ′ correlations exhibited the best performance in predicting creep rupture time and strain. With the development of CNN models and computational resources, it has become possible to directly learn from raw microstructure images. However, it remains essential to capture microstructures from areas large enough to adequately represent the characteristics of the specimen. In microstructures composed of γ and γ′ phases, two-point spatial correlation analysis serves as a microstructure descriptor, providing sufficient information for artificial neural networks to predict material properties. This study demonstrates such findings and is expected to contribute to various artificial neural network research utilizing microstructure images.

The application of reactor pressure vessels (RPVs) in small modular pressurized water reactors is gaining traction, driven by the need for advanced manufacturing techniques that support complex geometries and extended lifespans. This study evaluates the tensile and Charpy features of SA508 Gr.3—a commonly used material for nuclear RPVs—produced using powder bed fusion (PBF) additive manufacturing. By varying the hatch distance, the study investigates how thermal properties influence microstructural evolution and mechanical performance. Results showed significant variations in grain morphology, dislocation density, and martensite phase fraction across different hatch distances. Because of the finer grain structure and increased dislocation activity made possible by the formation of dislocation cells during the PBF process, the PBF-fabricated specimens showed a 130% increase in yield strength and an improved ductile-to-brittle transition temperature when compared to samples that were manufactured conventionally. These findings suggest that additive manufacturing holds great potential for advancing the mechanical properties and lifespan of RPV components, marking it as a promising strategy for next-generation nuclear reactor design.

The recycling process for rare earths (RE) is regarded as necessary process that can alter unstable and unsustainable RE production. One of the promising methods is the liquid metal extraction (LME) using magnesium (Mg). The mechanism of LME for RE has been elucidated with various assessments. However, there is lack of understanding on the practical reduction behavior of RE-oxides in the permanent magnets. In this study, we investigated the unrevealed mechanism of reaction between RE-oxide and Mg during LME process. The thermodynamic calculation and practical experiments are carried out simultaneously for observing theoretically reversed reduction of RE-oxide from Mg masses. After the reaction between RE-oxide and Mg, the microstructural studies, crystallography and quantitative analysis are examined. The reaction yields 100% and 41.94% of reduction efficiency for Nd-oxide and Dy oxide, respectively, which have good consistency with Gibbs free energy calculation results. Finally, RE-oxide reduction behavior during LME can be explained by observation on the radical mechanism and kinetics in this study. Furthermore, it is suggested that the Mg mass can control the reduction of RE-oxide for complete recovery of RE with metallic form based on collected understanding.

This study presents an innovative approach to the fabrication of Barium stannate (BaSnO₃) nanofibers for carbon dioxide (CO₂) gas sensing applications. The nanofibers were synthesized using the electrospinning method, enabling the formation of one-dimensional structures with high surface area and enhanced electron mobility. These structural properties significantly improve gas sensing performance, allowing for rapid resistance changes when exposed to CO₂ concentrations ranging from 2,000 ppm to 10,000 ppm. Additionally, the sensor exhibits excellent response and recovery times of 5–7 seconds, confirming its applicability for real-time environmental monitoring. BaSnO₃ nanofibers also offer substantial advantages over conventional detection methods, including superior cost-effectiveness, scalability, and high sensitivity. The study further suggests that dopant incorporation could enhance performance, demonstrating the feasibility of BaSnO₃ nanofibers as a scalable and efficient material for advanced environmental monitoring systems.

Recently, there has been a lot of research on the third generation of advanced high-strength steels as a solution to reduce CO₂ emissions. The effect of Co addition on the austenitic stability of nanocrystalline Fe-7%Mn alloy was investigated by X-ray diffraction (XRD) analysis and microscopic observation. Fe-7%Mn-Co alloy samples with nano-sized crystal size were successfully prepared by spark plasma sintering. The austenite fraction in the sintered alloys was determined by the Averbach-Cohen model. The austenite fraction decreased with Co addition. The Burke-Matsumura-Tsuchida (BMT) model was also used to evaluate the austenite stability of the alloy as a function of Co addition. The austenitic stability decreased with increasing Co addition. This is because Co reduces the stacking fault energy (SFE), which reduces the austenite stabilizing effect and promotes martensitic transformation.

The present work proposes a low-cost and scalable methodology to produce electrocatalytic layers based on nickel phosphide deposition for oxygen evolution reaction. Through controlled heat treatment, the composition of the Ni–P layer can be tailored to achieve a Ni–Fe–P composite layer, which is expected to enhance the electrochemical catalytic effect. The electrochemical performance of heat-treated electrodes is evaluated by examining the effects of heat treatment temperature and electroless deposition thickness. This study not only demonstrates an innovative approach for constructing heterogeneous interfaces for high-performance electrocatalysts but also hints at the potential extension of this strategy to modulate interfaces between other binary and ternary electrocatalysts, thus propelling the frontier of water splitting technologies.

Magnesium (Mg) metal is an attractive material for various industries due to its superior properties. Currently, the Pidgeon process is commercially used for primary Mg metal production. However, due to its high carbon dioxide (CO₂) gas emissions, electrolytic processes have attracted attention in recent years. Industrial electrolytic processes that use anhydrous magnesium chloride (MgCl₂) feedstock have a lower impact on global warming. Unfortunately, toxic chlorine (Cl₂) gas is generated during metal production, and anhydrous MgCl₂ production is energy intensive. In response, efforts have been made to improve industrial electrolytic processes and develop new electrolytic processes. Among these processes, the electrolysis of magnesium oxide (MgO) in molten fluoride salt is currently considered a promising alternative for the environmentally sustainable production of Mg metal with the generation of oxygen (O₂) gas. This paper comprehensively reviews industrial and innovative electrolytic processes, aiming to propose the next-generation Mg metal production method.

One-dimensional (1D) sodium hexa-titanate (Na₂Ti₆O₁₃) nanorod has garnered considerable attention as a sorbent because of its intrinsic crystal structure and a large specific surface area. This unique characteristic enables it to irreversibly immobilize and entrap a great number of hazardous radionuclides and heavy metal cations and thus ensure permanently safe disposal. Although molten salt synthesis (MSS) has attracted much attention, it faces challenges in controlling the nanoscale, one-dimensional structure of Na₂Ti₆O₁₃ owing to large reactor size and long processing times, frequently leading to excessive overgrowth and reduced sorption efficacy.

In this study, we propose a novel synthesis method—ultrasonic spray pyrolysis (USP) combined with molten salt synthesis (MSS)—designed for the cost-effective and scalable production of ultrafine Na₂Ti₆O₁₃ nanorods. This synthesis process yielded Na₂Ti₆O₁₃ nanorods with an average length of 246.15 nm and a diameter of 35.98 nm. The sorption and ion exchange capacities of Ba²⁺ were estimated to be 53.3 mg/g and 0.56 mmol/g, respectively, due to the ultrafine size of the particles and minimal aggregation. This study is expected to provide useful information for the cost-effective mass production of various alkaline titanate nanostructures with ultrafine size.

The aging properties of boron/potassium nitrate (B/KNO₃) igniter were investigated using an accelerated aging test. Stabilization of the crystal structure of the oxidizer (KNO₃) was attributed to degradation by aging. A well-known igniter material, B/KNO₃ is used in solid propellants for aerospace applications. Because the ignition efficiency of this ignition agent decreases with prolonged storage, a variety of aging studies have been carried out to ensure its igniting reliability. Although most studies have investigated changes in the properties associated with aging, few studies have examined changes in the component materials as causes. The accelerated aging conditions used herein induced changes in the microstructure, crystal structure, and thermal properties of B/KNO₃. In particular, the impact of KNO₃ crystal structure change on igniter behavior was investigated.

For the recycling of titanium turning scraps, residual cutting oil and tool abrasion particles must be removed from the surface. In this study, a novel surface treatment was developed to remove cutting oil and tool abrasion particles by cleaning and drying titanium scrap using the two-step process of alkali cleaning-acid cleaning. The surface residues before and after cleaning were compared through SEM, confirming that tool abrasion particles were removed thoroughly via acid cleaning. Elemental analysis and thermogravimetric analysis of titanium scrap confirmed that most of the cutting oil was removed by alkali cleaning, and XPS analysis confirmed that tool abrasion particles embedded on the scrap surface were removed by acid cleaning. After dissolving the scraps to make an ingot, the microstructure and tensile strength were measured. It was confirmed that acid cleaning after alkali cleaning provides the optimal condition.

This study compares the properties of aluminum targets manufactured through casting, rolling, and extrusion processes, examining thin films produced via DC magnetron sputtering using each target. Despite minimal differences in density, electrical conductivity, and resistivity among the targets, the extrusion target exhibited higher internal deformation energy than the casting and rolling targets. Thin films fabricated from each target showed similar grain sizes and deposition rates. However, thin films produced using the extrusion target demonstrated a higher frequency of hillock formations and displayed resistivity values approximately 1.5 µΩ-cm higher than those produced with other targets.

Pure copper and Cu-30 mass% Zn (Cu-Zn) alloy were subjected to tensile deformation at room temperature (approximately 298 K) and 573 K. Dislocation multiplication and motion during deformation were analyzed using neutron diffraction line-profile analysis. For the pure copper specimens, the dislocation density during deformation at 573 K was lower than that at room temperature. In contrast, the Cu-Zn alloys exhibited comparable levels of dislocation multiplication at both temperatures. Line-profile analysis revealed that the crystallites in the pure copper specimens became finer as the dislocation density increased, while the crystallite size of the Cu-Zn alloy specimens deformed at 573 K was considerably large and beyond the range that can be evaluated by the line-profile analysis. In the Cu-Zn alloys, although the dislocation density at 573 K was comparable to that at room temperature, the texture evolved by dislocation motion was weakened at 573 K, suggesting suppressed dislocation motion under these conditions. Transmission electron microscopy observations further demonstrated distinct dislocation substructures in the Cu-Zn alloys deformed at room temperature and 573 K. At room temperature, a Taylor lattice structure was observed, characterized by dislocations accumulating on planar slip planes. In contrast, at 573 K, dislocations were randomly distributed in a wavy form without forming tangles. This behavior suggests that the mobility of dislocations is reduced owing to interactions between solid solution elements and dislocations in the Cu-Zn alloys at 573 K.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 63 (2024) 1–7. Title and abstract were slightly modified.

The mechanical property, macro and micro-structure of AA6181 aluminum alloys sheets during twin roll casting (TRC) process with pulse electric current (PEC) of different intensity were tested and observed. With increased PEC intensity, the effect of controlling macro-segregation of sheet was more apparent the flow and temperature field during the TRC process was substantially unchanged with the different intensity of PEC. The primary dendrite arm of Al-Mg-Si alloy was increased, but the growth of secondary dendrite arm spacing was restrained. The elongation was increased from 8.1% to 24.2% when PEC strength reaches from 100 A to 500 A. But the yield strength and tensile strength with increasing strength of PEC show a change slightly.

The microstructural and mechanical properties investigation on powder metallurgy (PM) Ti-Zr composite alloys dispersed with TiC particles via sintering and hot rolling process was carried out in this study. PM Ti-Zr-TiC composites were fabricated from the pre-mixed pure Ti, metal Zr and TiC powders, and heat treatment was applied to the sintered materials to homogenize Zr solid-solution in α-Ti matrix. XRD analysis results of these rolled composite materials indicated complete solid-solution of Zr elements. Microstructures observation clarified the binary Ti-(10–20%)Zr alloys had a mean grain size of around 4 µm, which was much smaller compered to pure Ti material with 10 µm grain diameter. According to the tensile test results, Ti-Zr alloys showed a remarkable increment of tensile strength due to Zr solid-solution and α-Ti grain refinement, and also had a large elongation. On the other hand, since Young’s modulus gradually decreased with increased in Zr content, TiC particles were added into Ti-10%Zr alloy to improve the modulus. The uniform dispersion of (2.5–5 wt%)TiC particles in the matrix resulted in the increase of both Young’s modulus and tensile strength. The experimental values of Young’s modulus showed a good agreement with the calculated one by using the law of mixture.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 492–498.

Hydrogen embrittlement in Al-Zn-Mg-Cu alloys is suggested to originate from debonding of the η phase interface. Previous studies have shown that intragranular T phase precipitation, facilitated by increased Mg content, contributes to the mitigation of quasi-cleavage fracture. However, the role of T phase precipitation on the grain boundary in suppressing intergranular fracture remains unclear. In this study, in-situ observational techniques were used to examine the relationship between grain boundary precipitates and hydrogen-induce intergranular cracking. Obtained results showed that while the T phase precipitates in the matrix of Mg-enhanced alloy, the η phase predominates on grain boundaries, which lead intergranular fracture. The presence of numerous voids at intergranular crack tips suggests that void nucleation along grain boundaries and subsequent coalescence is the primary mechanism of crack propagation. The observed void formation at η phase interfaces is consistent with first-principles calculations and supports the concept that intergranular fracture originates from debonding at η phase interfaces.

This Paper was Originally Published in Japanese in J. JILM 75 (2025) 96–102.

Cellulose nanofiber (CNF) is regarded as a new-generation reinforcement fiber with its low density and high mechanical properties. However, it has been considered that CNF could lose its outstanding properties due to carbonization. Therefore, CNF has never been consolidated with metal powders. On the other hand, titanium carbide (TiC) fiber is probably obtained by the chemical reaction between the carbonized CNF and titanium (Ti). This study evaluated the morphology transformation of CNF in Ti during consolidation. Moreover, the tensile properties of CNF-added Ti were investigated. CNF was carbonized around 350°C and micrometer-sized and round-shaped TiC crystals were precipitated. In addition, the O atom was distributed into Ti during the CNF carbonization process. Ti–CNF 3.25 wt% compact showed an ultimate tensile strength (UTS) of above 700 MPa and a good fracture elongation. It was demonstrated that the UTS of Ti–CNF 3.25 wt% compact was a higher UTS than the theoretical value estimated from the increment of 0.2% yield stress of Ti by O atoms.

This study investigates the effect of loading direction on the compression behaviour of extruded pure magnesium with different grain-sizes and at different strain-rate. At the same grain-size level, samples compressed at 45 degrees to the extrusion direction have lower yield stress than samples compressed parallel to the extrusion direction. However, the loading direction has a negligible effect on the dominant deformation modes in the studied conditions.