The microstructure and fatigue crack initiation process of Ti-6Al-4V alloys were measured using a multimodal technique combining synchrotron X-ray microtomography and electron backscatter diffraction (EBSD) serial sectioning techniques. Various microstructural design variables were generated to describe the shape, size and crystallographic information of the polycrystalline microstructure that is the fatigue crack initiation point. The microstructural information was coarsened based on the similarity between the design variables and their correlation with fatigue crack initiation. An objective function describing the resistance to fatigue crack initiation was also established. By combining these variables, the relationship between the microstructural information and fatigue crack initiation resistance was described by a metamodel in the form of a multidimensional response surface using a support vector machine. A limited number of design variables with a high correlation with transgranular and intergranular fatigue cracking were identified, and the optimum or weakest microstructural patterns for fatigue crack initiation were quantitatively represented. This approach is expected to allow much more efficient microstructure control to enhance the fatigue crack initiation resistance than has previously been possible with the conventional surface-based approach.

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The stress-strain curves, glass-forming ability, and fracture properties of bulk metallic glasses with the composition Cu_47.5Zr_(45.5−x)Al₇Y_x, where yttrium content (x) is 1, 3, and 5 atomic percent (at%) are examined subjected to compressive strain rates between 10⁻³ and 4×10³ s⁻¹. The findings indicate that adding yttrium increases the reduced glass transition temperature T_rg. Moreover, the γ parameter, which indicates the ability to form glass, rises as the yttrium concentration goes from 0 to 3 at%, but experiences a slight decrease when the yttrium content is increased to 5 at%. In all the alloys that were tested, the fracture stress rises with increasing strain rates, whereas the fracture strain diminishes. The addition of 3 at% yttrium results in the highest fracture strain under tested conditions. The fracture surface observations reveal molten droplet structures, vein patterns, and dimples. The results demonstrate that strain rate and yttrium content are the primary factors influencing the fracture behavior of Cu_47.5Zr_(45.5-x)Al₇Y_x bulk metallic glasses.

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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.

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We investigate the synthesis of nickel and cobalt nanoparticles at low temperatures (40 °C) via a sonochemical process with nickelocene and cobaltocene as starting materials. The reduction and decomposition behaviors of nickelocene and cobaltocene are studied using ultrasound irradiation for different concentrations of hydrazine. At 5 and 10 vol% of hydrazine, nickel nanoparticles are synthesized from nickelocene by direct hydrazine reduction without intermediate formation. However, at a hydrazine concentration of 50 vol%, nickel nanoparticles are formed from Ni-hydrazine complexes. In contrast, from cobaltocene, microsized cobalt particles are formed by multistep reduction at 50 vol% hydrazine. Because nickelocene is more unstable than cobaltocene, it is assumed that nickel is formed by direct reduction under ultrasound irradiation at low concentrations of hydrazine. This sonochemical process using metallocene is expected to be an eco-friendly synthetic process as it does not require pH control, as in the conventional processes, and can be conducted at 40 °C using a simple apparatus.

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High-strength joints used in timber structures are increasing to utilize the shear properties of wood. Thus, it is important to understand the long-term shear performance. Therefore, we proposed the tensile shear testing method to investigate the long-term shear performance of wood. This testing method is to apply stabilized axial load for a long-term and to be able to measure the shear deformation. In order to evaluate the method, the results were compared with results of JIS block shear test. As a result, the mean value of shear strength in the proposed method was 30% lower than the block shear test. The reason for the small results of the proposed method is that the specimen has two shear face and breaks at the weak side, and the shear face is affected by rotation due to the tensile deformation of the perpendicular to grain direction. Therefore, the coefficient of variation of 6.8% in the proposed method shows smaller than 11.1% in the block shear test. And the shear strength value of the proposed method was little bit higher than one of the four-point-bending type shear test methods, and all specimens were shown the shear failure. Based on these results, the proposed method was judged to be useful as a shear test method.

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In order to fabricate multi-materials such as joining between aluminum alloy and engineering plastics for the purpose of lightening the weight of automobiles, this study investigated surface treatments to improve the adhesion and corrosion resistance of A5052 aluminum alloy. The two-step anodizing process of phosphoric acid anodizing + sulfuric acid formed a two-layer film with a phosphoric acid treated film on the upper layer and a sulfuric acid treated film on the lower layer. In this two-layer coating, the sulfuric acid-treated film on the lower layer improves the corrosion resistance, and the phosphoric acid-treated film on the upper layer improves adhesion, showing excellent adhesion and corrosion resistance.

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Surface hardening treatment is used to have strength to mechanical parts, and carburizing and quenching are the most widely used. There are reports on various carburizing efforts to deal with recent environmental issues. The authors have proposed an ultra rapid carburizing above the eutectic temperature, due to realize in–line carburizing. Since this is an unprecedented carburizing treatment method, setting the carburizing conditions that are suitable for efficiency has been the future challenge.

In this paper, we investigated a method for predicting the carbon concentration profile in the steel based on the known carburizing reaction mechanism of ultra rapid carburization. In order to predict the carbon concentration profile in the steel, it was calculated by the finite difference method using the carbon penetration rate F, the use of F=4.04×10⁻¹¹e^{(1.20×10-2・T)}, which penetrates from the surface, and the carbon diffusion in the steel based on Fick’s law. In addition, among various carbon diffusion coefficients D_c, the use of D_c(T, C)=4.53×10⁻⁷{1+y_c(1-y_c)8339.9/T}・e^{{-(1/T-2.221・10-4)(17767-y_c・26436)}}, which takes into consideration the dependence of carbon concentration, gave a good agreement with the actual measurement results by EPMA. Furthermore, as a result of investigating efficient carburizing conditions using a prediction method, we could minimize the time required to obtain an effective case depth of 0.8 mm. In addition, the amount of carburizing gas used was also reduced. In other words, it suggests that the accumulation of a huge amount of condition data and the condition setting skills are no longer necessary.

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In order to develop a new oxide-dispersion strengthened Cu alloy for heat sinks of fusion helical reactors, Cu alloy powders containing Ti, Fe and Y were prepared by atmosphere controlled gas atomization, and the effect of oxygen was investigated. The microstructure of the Cu alloy powder had a typical solidification structure regardless of the alloying element and gas species. The Fe atom was uniformly solid-soluted in the matrix, while the Ti and Y atoms were swept out from the matrix to the grain boundaries and particle surfaces during solidification. The average particle size and aspect ratio of the obtained powders decreased with the use of the N₂+O₂ gas mixture. This is due to the lower surface tension of Cu in the oxygen atmosphere, suggesting that the frequency of the strip breakage stage in the gas atomization process was suppressed due to the formation of oxide film on the particle surface.

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Regarding the permanent mold casting (PM) method for spheroidal graphite irons castings, the attractive method has been developed to obtain a full graphite structure without forming Fe₃C in the as-cast condition by controlling the free-nitrogen. When using this method, additional processes, such as heat treatment, are not necessary. However, heat treatment must be applied when using conventional methods owing to the formation of ledeburite (chills). In this study, sample castings were cast using conventional and developed PM casting methods, and the relationship between graphite distribution and impact properties investigated. Consequently, the graphite distribution of conventional samples was determined that order tendency was higher than developed samples. Furthermore, the impact absorbed energy of the samples with high ordinal tendency was lower than that of the samples with high random tendency graphite distribution. The total absorbed energy, crack initiation or propagation energy were strongly correlated with randomization or not in characteristic graphite distribution by both developed and conventional manufacturing methods. Therefore, the developed methods confer the benefits of not only less processing for casting but also better impact properties that enhance design safety.

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The classification of complex microstructures in low-carbon steels is sensitive to imaging conditions, often causing domain shifts that degrade the accuracy of deep learning classifiers and confuse visual identification by experts. In this study, we constructed two SEM image datasets of low-carbon steels with eight heat treatments using field emission (FE) and tungsten (W) SEM sources. The accuracy of classifiers trained on images from one source and tested on images from another source showed a significant drop, from over 90% to around 40%. This finding underscores the significant impact of domain shift on both automated and visual classification. To address this problem, we used cycle-consistent generative adversarial networks (cycleGAN) to translate images between domains. This approach restored classifier accuracy to above 90% and successfully reproduced the distinct visual characteristics of each SEM source, confirming the effectiveness of cycleGAN in standardizing imaging conditions for reliable microstructural analysis.

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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.

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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.

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In this study, a Ni-selective reduction process utilizing Ni laterites was developed to enhance the production efficiency of Fe-Ni metal. The reduction behavior of two distinct types of Ni laterites (limonite and saprolite) was investigated using high-temperature reduction experiments at 1380 °C for no more than 30 min, using coal as the reductant. The results revealed that Ni was preferentially reduced relative to Fe, achieving a maximal reduction fraction of 91% and a Ni-grade of 11–13% in the metal. A comprehensive mineralogical analysis indicated that goethite, serpentine, and silicate (Ni-, Fe-, and Mg-free) were the predominant minerals in the Ni laterites, collectively constituting over 85 mass%. The contents of these three minerals significantly influence the reduction reaction from both thermodynamic and dynamic perspectives, i.e., reduction activity of Ni and Fe in silicates and the meltability of the sample, respectively. These findings strongly suggest mixing of limonite and saprolite for Ni-selective reduction.

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The effect of carbon elements on the microstructures and mechanical properties of pure Ti alloys fabricated through extruded powder metallurgy route was investigated. Furthermore, the strengthening mechanism of the extruded materials was investigated quantitatively. In Ti-C materials, the lattice parameter in c-axis of α-Ti increased due to solid solution of carbon atoms in the most stable octahedral interstitial sites. As the carbon contents increased, tensile strength was increased while maintaining a high elongation at break. The 0.2% yield stress of Ti-2.0 mass% TiC increased by 242 MPa compared with that of pure Ti. The elongation at break exceeded 35.0% for all specimens. According to this analysis, it was clarified that F_m value of Ti-C materials was 2.90×10^-10 by using Labusch model. The estimated strengthening improvement using these values was significantly agreed with the experimental results of PM Ti alloys with carbon solution atoms. Furthermore, the strengthening mechanism of the alloys was quantitatively clarified that carbon solution strengthening was the dominant factor in this study.

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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.

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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.

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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.

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Composites of DNA and gold nanoparticles are expected to be stimuli-responsive and photo-functional materials that can synergistically utilize both the stimuli-responsiveness derived from DNA and the optical properties derived from gold nanoparticles. However, conventional methods require the bottom-up synthesis of artificial DNA modified with functional groups such as thiols that can form chemical bonds with gold nanoparticles, which limits the flexible design of the resulting composite. Therefore, we conceived the idea of introducing a “linker” that can interact with both gold nanoparticles and the bases naturally exist in DNA. The introduction of such a linker allows naturally occurring DNA, which is abundant in nature and has long strand lengths, to utilize as the multi-functional material platform. In this work, we designed and synthesized a linker complex with disulfide group and platinum(II) ion to interact with gold nanoparticles and the bases of DNA, respectively. Furthermore, the interaction between gold nanoparticles and naturally occurring DNA via the platinum linker complex was confirmed using UV–visible absorption spectroscopy.

 

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 123–127.

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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.

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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.

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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.

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The authors proposed direct reduction from metallic oxides to their metals in 2000–2003. This concept was firstly applied for direct reduction of TiO₂, and called the OS process in comparison with FFC Cambridge process. Both processes commonly used the CaO-CaCl₂ melt, the electrolysis with the carbon anode, and TiO₂ as the starting oxide. OS process is designed as a 1-pot operation, the combination of thermal reduction by Ca in CaCl₂-CaO melt and the simultaneous electrolysis of the byproduct CaO to form metallic Ca. O^2- is extracted as CO/CO₂ gas from the carbon anode, and Ca²⁺ forms Ca (dissolved as the metallic state in the molten salt). This reducing environment near the cathode is suitable for metal formation from various oxides. This overview (part I) summarizes the basic concept of OS process, and the subsequent overview (part II, III) will report its experimental confirmation and its applications, respectively.

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Announcement Concerning Article Retraction
The following paper has been withdrawn from the database of Mater. Trans., because a description based on a misinterpretation of the experimental results was found by the authors in advance of publication after acceptance.
Mater.Trans. 52(2011) Advance view.
Improvement in Fatigue Strength of Biomedical β-Type Ti-Nb-Ta-Zr Alloy while Maintaining Low Young’s Modulus through Optimizing ω-Phase Precipitation

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