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Machiko Ode, Hisao Esaka, Akira Ishida, Susumu Takamori, Hideyuki Mura ...
Article ID: F-M2024805
Published: 2024
Advance online publication: March 08, 2024
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The applicability of a cast-coating process for improving the oxidation resistance of cast Ni-based superalloys was evaluated. Specifically, metallic plates of Pr, Ir, and Re expected to improve oxidation resistance when they are enriched on the cast alloys were placed in a mold and cast coating using Ni-10at%Al alloy was performed in order to investigate the formation of the Pt, Ir, or Re-enriched layer on the casting surface. Then the microstructure of the Ni-based alloy/specimen interface was observed. To analyze the concentration profile in the interdiffusion region, solidification and diffusion simulations were performed. It was found that Pt easily dissolves into the molten Ni-based alloy, and Re cannot expected to modify cast metal surfaces due to its low solubility into the Ni-10at%Al alloy. On the other hand, Ir forms smooth interdiffusion layer, and numerical calculations predicted that Ir can maintain the modification ability even in a process time of 1 hour, which is equivalent to the casting time of Ni-based turbine blades.
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Salmawati, Yuichi Sugai, Kyuro Sasaki
Article ID: M-M2024801
Published: 2024
Advance online publication: February 02, 2024
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Increasing global temperatures due to high atmospheric carbon dioxide (CO2) concentrations may cause an imbalance in the carbon circulation on earth. It has been reported that CO2 emissions from natural soils in all terrestrial areas on Earth account for about 25% of atmospheric CO2 emissions in the global carbon cycle. A tendency is well known that the higher the soil temperature with the higher the metabolic activity of microorganisms in the soil. Furthermore, since the global soil CO2 emissions are huge amount that approximately seven times the total atmospheric CO2 emissions from human origin, it is necessary to investigate the increasing rate of soil CO2 emission rate per unit area and unit time on a global scale (global soil CO2 efflux) that is affected by soil temperature rise due to global warming expected in the coming decades.
In this paper, we modeled soil CO2 efflux vs. diurnal and seasonal variation in soil temperature at a measurement point using a formula that is an exponential function of soil temperature and then evaluated the effect of increasing average soil temperature due to surface air temperature rise by global warming. We have proposed a method to analogically evaluate the potential of increasing the rate of soil CO2 efflux against a change of 1°C in soil temperature based on the model equation. The power index b (°C−1) just indicates the potential of increasing the rate of soil CO2 efflux to soil temperature rise in any land area with different soil temperatures on earth. Finally, the values of b were obtained from the published literature with field measurement data at 71 locations in 10 countries including our data measured at the Ito campus, Kyushu University. The average rate of potential increase in soil CO2 efflux is 0.10°C−1 regardless of vegetation, annual rainfall (precipitation), soil type, and soil components (carbon and nitrogen content). In conclusion, assuming the average soil temperature rises by 1°C and ignoring any effects reducing soil CO2 reduction due to global warming, the potential increase in annual global soil CO2 efflux is roughly estimated at 22 billion tons-CO2/year.
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Masashi Mikami, Kosuke Ogasawara, Hidetoshi Miyazaki, Yoichi Nishino
Article ID: MT-E2023003
Published: 2024
Advance online publication: March 08, 2024
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The Heusler-type Fe2VAl alloy is a promising candidate for use in fabricating a thermoelectric power generation device because of its large Seebeck coefficient and high electrical conductivity. However, the high thermal conductivity of this alloy, as a thermoelectric material, degrades its power generation capacity. In this study, to reduce its thermal conductivity, the microstructure of a sintered Fe2V1.08Al0.92 alloy prepared via a powder metallurgical process was modified by adding oxide nanoparticles. Via the dispersion of Al2O3 nanoparticles, a sintered Fe2V1.08Al0.92 alloy with fine grains of approximately 200 nm in size was obtained due to the pinning effect on grain growth during sintering. The thermal conductivity was reduced from 16 to 11 W/mK. Upon La2O3 addition, the grain size of the Fe2V1.08Al0.92 alloy was reduced to approximately 100 nm and the thermal conductivity was further reduced to 10 W/mK. The difference in grain refinement could be caused by the lower stability of La2O3, which facilitated dispersion during ball milling, compared to that of Al2O3. As these microstructure refinements negatively affected the electronic properties, the thermoelectric performance of the Fe2V1.08Al0.92 alloy could not be enhanced. However, partial microstructure refinement with sparsely distributed La2O3 could slightly enhance the thermoelectric performance due to an appreciable reduction in the thermal conductivity without a considerable degradation in the electronic properties. By using these thermoelectric properties, a simple estimation of thermoelectric power generation, assuming a thermal resistance between the heat sources and thermoelectric module, was conducted. Remarkably, the results suggested that the reduction in thermal conductivity could enhance the output power density and conversion efficiency and reduce the optimal leg length. Thus, practically, controlling the balance between the electronic and thermal properties via microstructural modification is favorable in improving the practicability of the Fe2VAl alloy by enhancing the power generation capacity and reducing the sizes and masses of thermoelectric devices.
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Baolei Cui, Weijun Liu, Hongyou Bian
Article ID: MT-M2023191
Published: 2024
Advance online publication: March 08, 2024
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Due to its exceptional high temperature mechanical properties and low density, TiAl alloy has emerged as a promising structural material for high temperature applications. However, the inherent brittleness and susceptibility to cracking pose challenges during processing. In the additive manufacturing process of TiAl alloy, substrate preheating plays a crucial role in mitigating crack formation. This study focuses on the fabrication of crack-free Ti-48Al-2Cr-2Nb alloy via laser directed energy deposition(LDED), investigating the influence of preheating on sample cracks and microstructure. The results demonstrate that substrate preheating significantly affects the quality of formed samples. Without preheating, numerous cracks are observed in the samples; however, their severity gradually decreases with increasing preheating temperature. Notably, when the substrate was heated to 400°C, no cracks were detected in the samples. Moreover, higher preheating temperature lead to reduced grain length-diameter ratio and partial equiaxed crystal formation along with increased average grain size and α2 phase proportion while decreasing average orientation difference slightly. The microhardness exhibited a subtle declining tendency. With an increase in the proportion of α2 phase, the stress generated between different phases is reduced. Additionally, increasing the preheating temperature reduces dislocation density and releases stress, thereby inhibiting crack generation.
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Yuki Takahashi, Takashi Murata, Katsunori Yamaguchi
Article ID: MT-M2023192
Published: 2024
Advance online publication: March 08, 2024
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In the hydrometallurgical process used for the recycling of platinum group metals (PGMs), a residue containing Cr2O3 and PGMs is generated. In this study, a pyrometallurgical process was applied, in which PGMs from the residue generated in the hydrometallurgical processes were concentrated in a molten Cu phase as a collector metal, and Cr2O3 was separated into a slag phase with SiO2 and CaO as the flux. To reduce the loss of PGMs into the slag, the dissolution of PGMs into the slag must be reduced. Therefore, the distribution ratio of Rh, as a representative PGM, between the liquid SiO2–CaO–Al2O3–CrOx or the liquid SiO2–CaO–CrOx slag and molten Cu were measured at 1773 K under an oxygen partial pressure of pO2 = 10−10. The experimental results revealed that the distribution of Rh in the slag increased with increasing CrOx concentration. At a constant Cr2O3 concentration in the slag, the solubility of Rh increased with increasing slag basicity, which is defined as B = (mass%CaO)/(mass%SiO2). Furthermore, compared with the distributions of Rh and Pt between the slag system and molten Cu, Rh was more easily lost to the slag, and the dependence of Rh on basicity was greater than that of Pt.
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Hideaki Ikehata, Takashi Maeshima, Keiichiro Oh-ishi, Shinji Mitao
Article ID: MT-M2023199
Published: 2024
Advance online publication: February 16, 2024
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Segregation behaviors on the prior austenite grain boundaries for the B-doped high C case hardening steel (Fe-0.82C-0.22Si-0.86Mn-0.02P-1.1Cr-0.21Mo-0.005B (mass%)) were evaluated using a three-dimensional atom probe (3DAP). Results revealed the intense segregation of C, Mo, Cr, and B on the grain boundaries. Findings also confirmed suppression of the segregation of P, known as a strong segregation element for steel. Thermodynamic analysis based on the parallel tangent law by McLean–Hillert was conducted to validate the segregation of each element. To evaluate the chemical potentials while taking interaction with multiple elements into account, the Calculation of Phase Diagram (CALPHAD) method was used, where liquid phase was adopted to estimate the Gibbs free energy of grain boundaries. The calculation results represent the segregation tendencies obtained from 3DAP. Detailed investigations of the interaction effects of C, B, and Mo on the other elements were also conducted. Results showed the suppression of P segregation by increasing the B content, therefore demonstrating the efficiency of the segregation prediction method which implemented CALPHAD for the B-added high C steels.
This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 87 (2023) 193–199. Figure 6 was slightly modified.
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Takayuki Kojima, Taihei Wakayama, Yusuke Oi
Article ID: MT-M2024014
Published: 2024
Advance online publication: March 08, 2024
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Intermetallic compounds can be novel catalysts due to their unique structures consisting of multiple elements that occupy specific atomic sites. Heusler alloys (X2YZ) are a ternary intermetallic group consisting of various sets of X, Y, and Z. This group is useful in investigating the catalytic roles of individual elements under the same crystal structure. In this study, we investigated the catalytic characteristics of 3d transition metals and the group 13,14 elements in Heusler alloys for hydrogenation of propyne (C3H4). A larger number of valence electrons for 3d transition metals seemed to result in high activity for the hydrogenation reaction, as well as pure metal catalysts, the activity hierarchy of which was Ni > Co > Fe. For the group 13,14 elements, the alloys with Al and Si were slightly active, whereas the ones with Ga and Ge were active, in which the Ge alloys were highly selective for producing propylene (C3H6). All the Sn-containing alloys significantly caused side reactions producing C4 and C6 species. This indicates that Sn possesses the ability to crack and couple carbon chains.
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Mohammed Shahien, Kentaro Shinoda, Masato Suzuki, Hideyuki Takagi, Nor ...
Article ID: MT-T2023003
Published: 2024
Advance online publication: January 26, 2024
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In pursuit of achieving zero-emission power generation, the utilization of carbon-free fuels like H2 holds promise for enhancing the reliability of the next-generation turbines. To realize the necessary of new operational environment, the implementation of dense environmental barrier coatings (EBCs) becomes essential. This study delves into the investigation of the durability of dense Al2O3 coatings deposited using the Hybrid Aerosol Deposition (HAD) method under the harsh condition of a high-speed steam-jet test, operating at approximately 125 m/s and elevated temperatures. The durability assessment encompasses uncoated SUS304 substrates and SUS304 substrates with dense HAD Al2O3 coatings deposited on one side. These samples underwent a rigorous 20-hour steam-jet test within a temperature range of 600–800°C.
Results indicate that the erosion rate of uncoated SUS304 substrates steadily increased with temperature, reaching a recession rate of 4.4 µm/h at the point of impingement. Conversely, the erosion rate was nearly halved following the deposition of HAD Al2O3 coating on one side of the substrates. The dense 8–9 µm Al2O3 coatings applied via HAD exhibited exceptional environmental protection during continuous exposure to the high-speed steam-jet at temperatures up to 800°C for 20 hours. Furthermore, the HAD layer effectively prevented oxygen penetration into the substrate. Post-test analysis revealed no significant features at the coating-substrate interface. Importantly, there were no alterations in the lattice parameter of Al2O3 crystal post-test. The coatings remained exclusively composed of the α-Al2O3 phase, with gradual crystallinity recovery driven by thermal effects during the steam-jet test and increasing temperature. These findings underscore the robust durability of HAD Al2O3 coatings in demanding high-speed steam-jet environments, making them a promising solution for enhancing power generation reliability.
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Md. Saiful Islam, Masatoshi Sakairi, Akira Kaneko, Md. Shakhawat Hossa ...
Article ID: MT-C2023009
Published: 2024
Advance online publication: February 02, 2024
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The results of the corrosion nature of aluminum 7075 alloy in a cation-containing aqueous medium are reported by using gravimetric tests and surface analysis. The investigation showed a substantial increase in the mass of the specimens after the immersion experiments, while a minor mass change was seen in the Zn2+ containing solution. Energy dispersive spectroscopic mapping and cross-sectional pictures showed that the specimen submerged in the Zn2+ containing solution developed a zinc-linked layer. The results of X-ray photoelectron spectroscopy showed that aluminum hydroxide was deposited on the surface, and a tiny amount was deposited on the specimen that was sunk in the solution containing Zn2+. The present study suggests that the zinc-related layer prevents the alloy from corroding.
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Tomomi Iihara, Yuki Ito, Kosei Fukuoka, Kenichiro Suehiro, Kazunari Ma ...
Article ID: MT-D2023013
Published: 2024
Advance online publication: January 26, 2024
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Oxygen-free copper is an integral part of electric vehicles and renewable energy initiatives as the key conductor material owing to its high conductive properties. However, the poor heat resistance and poor stress relaxation resistance characteristics pose challenges for applications involving heat. This study aims to explore the potential for developing a new pure copper material with enhanced heat resistance and stress relaxation resistance characteristics while maintaining conductivity. Trace amounts of solute elements Mg, Sn, P, Ti, and Ag were added to oxygen-free copper, and the following results were obtained from the cold-rolled material:
(1) Mg, Sn, P, Ti, or Ag addition below 500 at ppm has little effect on yield strength.
(2) Mg or Ag addition below 200 at ppm has little effect on electrical conductivity.
(3) Mg or Sn addition above 100 at ppm increases the half-softening temperature to over 573 K.
(4) Mg, Sn, or Ag addition above 100 at ppm increases the residual stress ratio to over 60%.
(5) Mg or Ag addition yields a superior balance of electrical conductivity, half-softening temperature, and residual stress ratio; particularly, Mg addition between 100 and 200 at ppm results in an excellent balance.
This Paper was Originally Published in Japanese in J. Japan Inst. Copper 62 (2023) 251–256 with slight modifications, such as adjustment to the calculated half-softening temperatures for more accurate representation.
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Fakfa Payayam, Sutawee Jomrieng, Charoenkwan Kraiya, Somchai Kiatgamol ...
Article ID: MT-M2023179
Published: 2024
Advance online publication: January 26, 2024
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Graphene nanoplatelets (GNPs) were synthesized by an electrochemical exfoliation method. Four various conditions of the electrochemical exfoliation process: (I) 1 M NaOH with 4 V, (II) 0.5 M H2SO4 with 5 V, (III) a mixture of 1 M NaOH and 0.5 M H2SO4 with 5 V, and (IV) a two-step process of 1 M NaOH with 4 V and 0.5 M H2SO4 with 5 V, were compared. The as-synthesized GNPs obtained from all conditions were characterized by Raman spectroscopy and X-ray diffraction. The two-step process provided the GNPs with the low defect concentration and the lowest number of layers. Moreover, confirmed by field emission scanning and transmission electron microscopes (FE-SEM and TEM), the GNPs obtained from the two-step process were multilayer graphene. The GNPs obtained from each condition were added into an ultraviolet-cured acrylate adhesive to fabricate electrically conductive acrylate adhesive (ECAA). The GNPs acted as fillers to play an important role in conducting the electrical network of the ECAA without any other additive. The van der Pauw method was conducted to measure the electrical resistivity of the ECAA. The ECAA, containing 5 wt% of the obtained GNPs from the two-step process, had the lowest resistivity when compared to the ECAA which contained the obtained GNPs from other conditions. We found that the percolation threshold of the ECAA, containing the obtained GNPs from the two-step process, was at 3.26 wt%. Last, 6.92 wt% of the GNPs reached the lowest resistivity at 1.09 Ω·cm.
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T. Kawamata, R. Hayashi, K. Sugimoto, K. Sugiyama
Article ID: MT-M2023189
Published: 2024
Advance online publication: February 02, 2024
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The topological and chemical short-range ordering (TSRO and CSRO) of Pd82Ge18 amorphous alloys prepared by the single-roll liquid quench method were analyzed using a combination of anomalous X-ray scattering and reverse Monte Carlo (RMC) simulation. The degree of development of TSRO and CSRO in the amorphous structure model made with the RMC simulation (RMC model) was evaluated by comparison with the dense random packing model (DRP model) calculated using metallic and covalent atomic radii. In the RMC model, a shortening of the Pd–Ge nearest neighbor correlation and a decrease in the coordination number around Ge were observed. Voronoi polyhedral analysis was performed to evaluate the local geometrical structure around the Pd and Ge atoms. Although the DRP structure can reasonably approximate the local structure around the Pd atoms, the TTP structure corresponding to the local structure in crystalline Pd2Ge develops around the Ge atoms as a characteristic TSRO. However, the preferential coordination of Pd atoms around Ge, which is a CSRO associated with the TTP structure in the crystalline phase, was not observed. These results indicate that strong CSRO does not necessarily accompany the TTP structures in metal-semimetal amorphous alloys.
Fig. 3 Partial pair distribution functions,
g(
r)
PdPd,
g(
r)
PdGe, and
g(
r)
GeGe calculated from the DRP and RMC models.
Fullsize Image
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Toshikazu Yoshii, Muneyoshi Iyota, Kyozo Arimoto
Article ID: MT-H2023002
Published: 2024
Advance online publication: February 26, 2024
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The mechanism of curving that occurs during the quenching process of Japanese swords has not been clearly explained. Experiments on this phenomenon were conducted using Japanese sword type specimens made of the same steel and processes as Japanese swords, and model Japanese sword type specimens made of carbon steel (S55C) and austenitic stainless steel (SUS304) by machining. Applying the simulated strains-based approach to heat treatment simulation results for these experiments found that positive plastic strain and transformation strain on the cutting-edge side are main contributors to curving generation in Japanese sword.
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Kaveh Edalati
Article ID: MT-L2023022
Published: 2024
Advance online publication: February 26, 2024
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Light metals and alloys based on magnesium, aluminum, and titanium are of significance in daily life and industrial applications due to their low density and superior mechanical and functional properties. The formation of nanostructures and ultrafine grains can further improve the properties of these materials. High-pressure torsion (HPT), as a severe plastic deformation (SPD) method, is one of the most effective processes for nanostructuring these materials. Various modifications of HPT such as conventional HPT with discs, HPT with rings, and continuous HPT with strips and wires are currently applied to light metals and their alloys, composites, intermetallics, and metallic glasses. The HPT processing of these materials is effective for grain refinement, hardening through the Hall–Petch mechanism, lattice defect generation, phase transformations, and solid-state reactions through fast diffusion with reasonable time/thermal stability. This article after discussing these fundamental issues, reviews some mechanical and functional properties of nanostructured lightweight materials such as tensile, compression, and bending properties, superplasticity including room-temperature superplasticity, wear resistance, electrical conductivity, superconductivity, biocompatibility, hydrogen production, and hydrogen storage.
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Kaige Wu, Kaita Ito, Manabu Enoki
Article ID: MT-M2023190
Published: 2024
Advance online publication: February 26, 2024
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In this work, corrosion behavior and the concurrent acoustic emission (AE) signals of AZ31 alloy under NaCl and Na2SO4 solution droplets were comparatively investigated in combination with in-situ optical microscopy observations. It was observed that after a short initial corrosion accompanied by the growth and rupture of H2 bubbles, the later corrosion behavior of AZ31 alloy mainly developed into filiform corrosion under NaCl solution droplet and pitting corrosion under Na2SO4 solution droplet. AE signals were detected in both cases. In particular, AE parameters of amplitude and duration were found to well identify filiform and pitting corrosion. AE signals were mainly correlated with the observed evolution of H2 bubbles of different shapes and positions, i.e., regularly round bubbles grew and ruptured at the filament head near the metal surface during filiform corrosion; whereas irregularly-shaped bubbles grew and ruptured at the pit mouth during pitting corrosion.
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Saeka Sano, Haruhisa Shiomi
Article ID: MT-M2023221
Published: 2024
Advance online publication: February 26, 2024
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A two-step aging process was investigated in which the first step aging was carried out in zinc acetate aqueous solution and the second step in deionized water, using layered zinc hydroxide, ZHC, as a precursor with chloride ions in the interlayer. When the first step of aging was performed using a zinc acetate solution, hexagonal plate-shaped ZnO seed crystals with and without chipped corners were obtained, and at the same time, chloride ions incorporated in the interlayer of ZHC were exchanged with acetate ions to form ZHA. When the obtained mixture of ZnO seed crystals and ZHA was aged again in ion-exchanged water, coin-shaped or hexagonal plate-shaped ZnO particles with a particle diameter of about 1 um were obtained in a single phase. When the amount of zinc acetate solution used in the first step aging was small, the ion exchange of chloride ions to acetate ions between the layers of ZHC was insufficient and so ZHC remained, thus resulting in columnar ZnO with small particle size along with plate-like ZnO during the second step aging.
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Asuka Suzuki, Terumasa Fujishiro, Naoki Takata, Makoto Kobashi
Article ID: MT-M2023213
Published: 2024
Advance online publication: January 26, 2024
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The combustion foaming process enables the fabrication of closed-cell porous intermetallics by utilizing the combustion reactions generating a large amount of heat. A closed-cell porous Al3Ti (D022 crystal structure) fabricated by the combustion foaming process has a lightweight, high stiffness, high melting temperature, and good oxidation resistance but exhibits brittleness due to the poor deformability of Al3Ti. It is known that the addition of third elements (X = Cr, Mn, Fe, etc.) changes the crystal structures from D022 to L12, resulting in an improvement in the deformability in the case of dense materials. In the present study, an attempt was made to fabricate the closed-cell porous (Al, Fe)3Ti with an L12-ordered crystal structure through the combustion foaming. The effect of the amount of the exothermic agent, which was added to control the reaction heat of combustion foaming, on the porosity, pore morphology, microstructure, and constituent phases was investigated. The closed-cell porous L12-(Al, Fe)3Ti without any intermediate phases was successfully fabricated when the exothermic agent was added over 5 vol%. The porosity reached the maximum at approximately 80% when the exothermic agent of 10 vol% was added. The TiB2 particles, which were formed by the reactions of the exothermic agent, were aggregated in the porous sample with the exothermic agent of 5 vol% but uniformly dispersed in the porous samples foamed with the exothermic agent over 10 vol%. Based on the results above and the temperature measurements during the combustion foaming, it is important for fabricating highly porous L12-(Al, Fe)3Ti with the uniform microstructure to control the maximum temperature just above the liquidus temperature of (Al, Fe)3Ti. This study provides new insights into the hierarchical control of porous materials with the desired pore structures and cell wall materials.
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Takahiro Mineta
Article ID: MT-L2023021
Published: 2024
Advance online publication: February 16, 2024
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Mg-Li based alloys, distinguished by their low density among structural metallic materials, emerge as pivotal candidates in ushering in the era of next-generation lightweight metals. Their notable drawbacks encompass poor room-temperature strength and creep resistance, prompting diverse efforts to enhance these aspects through microstructure control techniques, including heat treatment. The amelioration of mechanical properties in Mg-Li based alloys holds significant promise for advancing various industries, spanning aerospace, automotive, and biomaterials sectors. This review article provides an overview of endeavors aimed at improving the mechanical properties of Mg-Li based alloys, with a specific focus on alloying, heat treatment, and severe plastic deformation as strategies for microstructure control.
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Hanae Kijima-Aoki, Katsuhiro Uchikoshi, Takamichi Miyazaki, Masato Ohn ...
Article ID: MT-M2023176
Published: 2024
Advance online publication: February 16, 2024
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Controlling the conductance of miniaturized electrical components via spin-dependent tunneling is a challenging step for nano-scale implementation. In this study, we demonstrate the fabrication of lateral nanogranular films with oblate magnetic metal nanoparticles and achieve variable out-of-plane intergranular gap. Changes in insulating layer thickness from 0.4 to 2.1 nm resulted in a marked increase of 10,000-fold for both in-plane and out-of-plane electrical resistivities. A 4% enhancement in permittivity, namely the magnetodielectric effect, was obtained under an in-plane magnetic field of 10 kOe. The frequency at which the maximum magnetodielectric effect is found shifts from 15 kHz to 880 kHz depending on the out-of-plane resistivity. We demonstrated frequency control of the magnetodielectric effect via electrical resistivity by structural modulation of the lateral nanogranular system.
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Kazushige Tokuno, Takayuki Yonezawa, Genichi Shigesato, Hideo Tsutamor ...
Article ID: MT-M2023185
Published: 2024
Advance online publication: February 16, 2024
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Surface relief formation processes of the high cyclic-loaded coarse-grained aluminum polycrystals with point defect clusters were investigated. Until the loading of 1 × 105 cycles with the stress ratio of −1 and the maximum stress of 8.0 MPa, the coarse ribbon-like primary persistent slip markings (PSMs) consisting of extrusions and intrusions had been formed, and the average extrusion height of the PSMs had reached 2.0 µm. This value was much higher than that of the ordinary aluminum single crystal. The high mobile dislocation density accompanied by the dislocation channeling effect inside the persistent slip bands (PSBs) were considered to produce the high extrusions. Until the loadings to 2.4 × 105 cycles with the stress ratio of −1 and the maximum stress of 8.0 MPa, activities of the primary PSBs had been weakened or terminated, and instead, the secondary slips had been activated and deformed the shapes of the preexisting primary PSMs. And the deep brittle-like cracks along the grain boundaries (GBs) were observed. The accumulation of the dislocations and the vacancies into the GBs were considered to be the trigger for the energy reduction of the GBs as the interfaces and the brittle-like cracks formation.
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Takayuki Kojima, Shunsuke Nakajima, Souta Tate
Article ID: MT-M2023212
Published: 2024
Advance online publication: February 16, 2024
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Intermetallic catalysts were investigated for ammonia decomposition, a key technology to extract hydrogen from an ammonia source as a hydrogen carrier. Since Mn, Cr, and V were active in pure 3d-transition metal catalysts, their IMCs with p-block metals were selected. The pure Mn, Cr, and V were nitrided during the reaction, while their IMCs resisted the nitridation. In the Cr- and V-based IMC catalysts, a larger composition of Cr and V resulted in a larger conversion. The Cr3X and V3X catalysts exhibited a high activity with any X elements. These results indicate that in IMC catalysts for ammonia decomposition, the activity is dominated by transition metals, and the resistivity against nitridation is improved by p-block metals.
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Hui Lin, Lidong Shao, Lin Lv, Jiusheng Bao
Article ID: MT-M2023216
Published: 2024
Advance online publication: February 16, 2024
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The nanoindentation test is a widely adopted technique for characterizing the mechanical properties of materials. In this study, a dislocation density-based and a phenomenological crystal plasticity hardening model are employed to investigate the evolution of plastic anisotropy and pile-up of a single-crystal aluminum specimen with varying crystallographic orientations during nano-indentation. Utilizing crystal plasticity finite element (CPFE) simulations, we delve into the influence of crystal orientations on key factors such as depth-load curves, stress distributions, shear strains across different slip systems, and dislocation density evolution. Our analysis highlights the plasticity anisotropy inherent in the material, elucidated through the evolving shear strain exhibited by activated slip systems. Furthermore, we gain insights into the pile-up phenomenon by examining the evolution of shear strains within slip systems and the associated dislocation density, employing various modeling approaches. The height of pile-up evolution is determined by the localized cumulative shear strains and evolution of dislocation density.
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Silvia Pomes, Nozomu Adachi, Masato Wakeda, Takahito Ohmura
Article ID: MT-MBW2023002
Published: 2024
Advance online publication: February 16, 2024
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Nanoindentation-induced deformation in Zr-based bulk metallic glasses in distinct structural states was studied over a broad temperature range, both below and above the glass transition temperature. These findings emphasize the occurrence of a predominant deformation mechanism, identified as a percolation or diffusion process, triggered by exceeding a chemical and topological short-range order-insensitive energy barrier.
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Nobuo Nagashima, Masao Hayakawa, Hiroyuki Masuda, Kotobu Nagai
Article ID: MT-Z2023006
Published: 2024
Advance online publication: February 09, 2024
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Fatigue limit is well predicted by tensile strength or hardness, and the relationship is often analyzed by linear regression using the minimum squared approximation. However, the prediction of the number of cycles to failure at a given stress amplitude, meaning the estimate of the S–N curve, has not been realized. Therefore, we aim to investigate the estimability of the S–N curve using the random forest method based on the data described in the NIMS fatigue data sheet. The random forest method is a machine learning algorithm and an ensemble learning algorithm that integrates weak learners of multiple decision tree models to improve generalization ability. It was clarified that the machine learning of the multiple decision tree model is excellent in fatigue limit prediction. The S–N curve can be accurately estimated by combining the prediction of fatigue limit and the number of cycles to failure at a given stress amplitude.
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Yuri Honda, Haruhisa Shiomi
Article ID: MT-M2023208
Published: 2024
Advance online publication: January 26, 2024
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ZnO is synthesized by aging layered zinc hydroxide acetate, ZHA, as a precursor. The effects of type and concentration of alkaline earth metal ions on the crystal growth of ZnO were studied by synthesizing ZnO by aging ZHA in calcium acetate (CaAc), strontium acetate (SrAc), and barium acetate (BaAc) aqueous solutions at various concentrations. In all cases, ZnO particles elongated in the c-axis direction were obtained, and the aspect ratio increased with increasing ion concentration. Especially, in BaAc solution, the longest particles in the c-axis direction were observed. This is due to the small hydration ionic radius of barium, which is easily adsorbed on the side of ZnO. When aging ZHA in 2.0 mol/L of BaAc solution, agglomerated particles were formed in the early stage of aging, and the growth of individual particles in the agglomerate and entire agglomerated particles proceeded in parallel, resulting in particles with characteristic bouquet-shapes. In conclusion, the c-axis growth of ZnO is controlled by the type and concentration of alkaline earth metal ions.
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Masaaki Nakai, Mitsuo Niinomi, Takahiro Oneda
Article ID: L-M2010824
Published: February 01, 2011
Advance online publication: January 13, 2011
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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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