Metal matrix composites (MMCs) were produced using iron (Fe) and niobium carbide (NbC) powders and synthesized with different NbC contents (0, 5, 10, and 20 wt.%) by high energy ball milling. As a result, a Fe_0.99Nb_0.01 solid solution was formed, which influenced the lattice distortion and peak shift. The Fe-NbC composites were subsequently consolidated by rapid sintering at 850°C and sintering pressure of 60 MPa. The hardness of Fe-NbC composites were ranged from 128.9±10.4 to 374.5±14.6 kg/mm², which was related to the hall petch relationship. This enhancement is attributed to the dispersion strengthening effect of the agglomerated powders through high energy ball milling, and the control of grain growth by the spark plasma sintering. Particularly, the oxidation resistance of Fe-NbC composites increased gradually as the NbC contents increased, indicating that the oxidation layer such as Nb₂O₅, Fe₂O₃, and Fe₃O₄ locally formed on the Fe-NbC composites surface. The oxidation layer decreased from 204.34 to 12.99 μm with the rise in NbC content.

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The monitoring of invasion/permeation hydrogen on entry/exit surfaces of cathodically charged SUS316 columnar crystals was conducted with a scanning Kelvin probe force microscope (SKPFM) under atmospheric pressure. Columnar crystal specimens covered with oxide films on their surfaces under room conditions were prepared for cathodic charging tests and subsequent SKPFM measurements. The invaded hydrogen on the entry surface was detected at the δ-ferrite phases for 7 d after charging, and the segregation of invaded hydrogen at the boundaries between the δ-ferrite and austenite matrix was prolonged for >10 d after charging. The permeated hydrogen on the exit surface was detected at the δ-ferrite phases for 3 d after charging, but was not substantial at some of the δ-ferrite phases regardless of the charging. Segregation of permeated hydrogen at the boundaries between the δ-ferrite and some of the intermetallic precipitates was prolonged for 7 d after charging. The behaviors of invaded/permeated hydrogen based on heterogeneous microstructures are discussed to improve understanding of the hydrogen embrittlement mechanism in weld metals.

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In this study, the electrical properties and stability of silver nanowire transparent conductive electrodes (TCEs) were improved through the platinum electroplating process (AgNWs@Pt TCEs). After electroplating, environmental and thermal stabilities increased considerably, whereas sheet resistance was greatly reduced. Sheet resistance sharply decreased from 181.3 Ω/□ to 16.59 Ω/□. Meanwhile, the thermal stability of the AgNWs@Pt TCEs was enhanced by 20 °C compared with that of TCEs based on silver nanowires. The sheet resistance of the AgNWs@Pt TCEs remained nearly constant after exposure to ambient air for five months. The optimal electroplating condition was achieved at an electroplating current of 10 µA for 30 s. Under this condition, the sheet resistance, transmittance, and figure-of-merit (FOM) values of the AgNWs@Pt TCEs were approximately 16.59 Ω/□, 83.89%, and 123 Ω⁻¹, respectively.

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The aluminum alloy shell fabricated by 'bending + high-frequency welding' is the core component of the Chinese new energy vehicle battery pack. Still, this process cannot produce the next generation of shell products with unequal wall-thickness. In this study, we take the unequal-wall-thickness square 3003 aluminum alloy battery shell with a wall thickness of less than 0.5mm and a tolerance range of ±30μm as the research object. According to the cold work, hardening characteristics of 3xxx series aluminum alloys, hot extruded hollow blanks were prepared, and a new cold drawing process was attempted to be developed on this basis. Based on the analysis of the stress-strain field during cold drawing of defective workpieces, the size of the die inlet's R angle and the blank's size were optimized to solve the problems of local fracture and tearing of the blank. The results show that the maximum stress during cold drawing occurs at the fillet where the sizing zone intersects with the wall-thinning zone. This location is subjected to tensile stress, normal pressure from the inner and outer dies, and tangential friction force, causing a material accumulation phenomenon; the material flow velocity along the cold drawing direction is inconsistent, which will cause U-shaped patterns on the surface of finished products; the strain value along the cold drawing direction first increases and then decreases with the rise of R angle, reaching the maximum when the R angle size is 1.5mm. After optimization, the maximum equivalent stress decreased from 205MPa to 190MPa, and the average strain along the cold drawing direction increased from 0.15-0.22 to over 0.3. This study successfully prepared precisely ultra-thin lithium iron phosphate battery shells by optimizing cold drawing process parameters and die structure.

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The use of biosynthesis is considered an environmentally friendly and more sustainable method for the production of metal nanoparticles. In this study, copper nanoparticles (Cu-NPs) were synthesized using tea stem extract as a reducing agent. Spectroscopic identification revealed that the CuO is the major crystalline structure with a particle size of 14.9 nm. The B_g mode of the Raman active mode is associated with the symmetric oxygen stretching of Cu-O and is consistent with the monoclinic crystal CuO in X-ray powder diffraction (XRD) measurement. X-ray photoelectron spectrometer (XPS) deconvolution revealed the split peaks for Cu 2p_3/2 and confirmed the coexistence of Cu⁺ and Cu²⁺ in the Cu-NPs. The Cu-NPs possessed effective catalytic ability for the degradation of methylene blue (MB) from the aqueous phase in a Fenton-like system. These results provide important evidence for the potential application of tea stem in synthesis of nanoparticle.

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Pure magnesium and Mg-(0.2-0.9 at.%) Y rolled sheets were subjected to three-point bending tests to individually investigate the effects of texture and yttrium addition on bending deformation behavior. Yttrium addition increased bending yield stress in both Specimen TR with the neutral plane parallel to the rolled plane and Specimen TN with the neutral plane perpendicular to the rolled plane, resulting from the increase in critical resolved shear stresses (CRSSs) for basal slip and {1012} twinning with yttrium addition. Bending ductility increased with increasing yttrium addition until 0.5 at.% yttrium addition, and then decreased at 0.9 at.% yttrium addition in Specimen TN. On the other hand, bending ductility increased until 0.9 at.% yttrium addition in Specimen TR since non-basal slip activities increased with increasing yttrium addition. Since neutral planes in Specimen TN with 0.9 at.% yttrium addition moved more to the center than those in Specimen TN with 0.5 at.% yttrium addition, resulting in the higher tensile strain at the tension side. Therefore, the bending ductility in 0.9 at.% yttrium addition was lower than that in 0.5 at.% yttrium addition.

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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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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–CrO_x or the liquid SiO₂–CaO–CrO_x slag and molten Cu were measured at 1773 K under an oxygen partial pressure of . The experimental results revealed that the distribution of Rh in the slag increased with increasing CrO_x 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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Empirical formulas were derived for the interface shape, mechanical properties, and electrical characteristics of accumulative roll bonded (ARB) Cu/Nb laminated materials, based on relevant literature data. These formulas were incorporated into a forward analysis model using finite element analysis, enabling the calculation of yield stress and conductivity from the spatial distribution of Cu/Nb two phases. By randomly varying the layer thickness and interface shape in the two-phase spatial distribution and conducting repeated forward analyses, a database linking microstructural descriptors with yield stress and conductivity was created. These microstructural descriptors include volume fraction, geometric features, topological features, spatial correlation functions, and persistent homology. The significance of each microstructural descriptor on yield stress and conductivity was quantified using machine learning techniques. The results revealed that the Cu volume fraction, layer thickness, and 0th Betti number are crucial for yield stress, while for conductivity, the Cu volume fraction has the strongest influence, followed by layer thickness and layer continuity. Based on these outcomes, the Pareto front for ARB Cu/Nb laminates in the strength-conductivity space was presented.

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Die casting has many advantages, such as high precision, mass production, and excellent recyclability. However, gas defects in the product have become a problem. One countermeasure to this problem is to design the injection input of the plunger appropriately. Recently, CFD has been used to design plunger injection inputs, and by combining with optimization techniques, auto-design of plunger injection inputs has been possible. However, CFD is difficult to apply because of the high cost of CFD resources, the need to resource IT engineers, and the time required for its auto-design. Therefore, we propose a new injection input design method based on an algebraic approach, enabling anyone to design a plunger injection input that prevents gas defects with ease and at a low cost. Simulation and experimental results verified the effectiveness of the proposed method.

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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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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 higher 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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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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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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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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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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A residue containing TiO₂ and PGMs is generated in the hydrometallurgical process used for recycling platinum-group metals (PGMs). In this study, a pyrometallurgical process was considered in which PGMs from the residue generated in the hydrometallurgical process were concentrated in a molten copper phase as a collector metal and TiO₂ was separated into the SiO₂–CaO–TiO₂ slag phase with SiO₂ and CaO flux. The dissolution of PGMs must be reduced to minimize the loss of PGMs to the slag. Therefore, the distribution ratios of Pt as representative PGMs between the liquid SiO₂–CaO–Al₂O₃–TiO₂ or liquid SiO₂–CaO–TiO₂ slag and molten copper were measured at 1773 K under an oxygen partial pressure of p_O2 = 10^-10. The experimental results showed that the distribution ratio of Pt increased with TiO₂ concentration in the slag, and the distribution ratio of Pt reached a maximum value at a TiO₂ concentration of approximately 10 mass%, and decreased with a further increase in TiO₂ concentration with the SiO₂–CaO–Al₂O₃–TiO₂ slag. However, as TiO₂ concentration in the slag increased, the distribution ratio of Pt decreased with the SiO₂–CaO–TiO₂ slag. Additionally, the experimental results showed that the distribution ratio of Pt between the SiO₂–CaO–Al₂O₃–TiO₂ slag and liquid copper increased with the slag basicity B, defined as B = (mass%CaO)/(mass%SiO₂) when the TiO₂ concentration in the slag was greater than 10 mass%.

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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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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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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 Fe₂V_1.08Al_0.92 alloy prepared via a powder metallurgical process was modified by adding oxide nanoparticles. Via the dispersion of Al₂O₃ nanoparticles, a sintered Fe₂V_1.08Al_0.92 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 Fe₂V_1.08Al_0.92 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 Fe₂V_1.08Al_0.92 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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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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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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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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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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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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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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