Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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Award type：Award from international society, conference, symposium, etc.  Country：Japan

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

ABSTRACT

In this study, it is attempted to improve the fracture toughness of 3/2‐mullite (3Al₂O₃ 2SiO₂ or Al₆Si₂O₁₃) by precipitating α‐cristobalite. All specimens were prepared from raw‐alumina (Al₂O₃) and raw‐silica (SiO₂) powders using spark plasma sintering. Excess raw‐silica over the ideal composition of 3/2‐mullite was added to the powders to produce α‐cristobalite precipitated in the 3/2‐mullite matrix. The fracture toughness increased to a maximum of 2.60 MPa m^0.5 with 31 vol% α‐cristobalite. The precipitation reinforcement can be explained by an analogy to the residual stress effect based on the conventional crack‐tip shielding model in particle‐dispersed composite. This finding reinforces the fracture toughness based on the precipitated phase in the composite rather than using conventional additives.

DOI： 10.1111/ijac.15144

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1142/S3082805825500050

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Language：English   Publishing type：Research paper (scientific journal)  

This study explored the application of a high-density pulsed electric current (HDPEC) to mitigate strain hardening in a cold-rolled A6061 aluminum alloy while examining the simultaneous application of HDPEC with furnace heating to reveal the contributions of thermal and athermal effects. The results showed that significant strain-hardening relief was achieved through the HDPEC treatment, particularly at 300 A/mm² for 260 ms, resulting in a 23% reduction in strength and an 86% increase in ductility. Microstructural analysis revealed a shift to fine and equiaxed grains with reduced dislocation density, which was primarily attributed to thermal effects. HDPEC annealing exhibits superior efficiency compared to the conventional annealing treatment, offering cost and time advantages. In addition, this study validated the synergistic impact of HDPEC and furnace heating, with furnace heating supplementing energy requirements, facilitating practical HDPEC implementation. These findings suggest that the HDPEC method and the combined method with conventional heating are promising alternatives for strain-hardening alleviation in A6061 aluminum alloy manufacturing, supporting the development of an eco-friendly and efficient process. Graphical Abstract: (Figure presented.)

DOI： 10.1007/s12540-024-01778-7

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s11661-024-07522-5

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Other Link： https://link.springer.com/article/10.1007/s11661-024-07522-5/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Scientific Publishers  

Fe₂O₃ holds promising n-type semiconductor material in the field of solar water splitting due to its excellent photocatalytic properties. However, the photoelectrochemical performance of Fe₂O₃ is limited by its inherent properties such as poor conductivity, and charge separation efficiency owing to its recombination rate. Therefore, researchers are more focused on nanostructuring, doping, and surface coating to overcome these issues of Fe₂O₃. In this study, we have investigated a low-cost way to fabricate a Ti coating layer on a high-density Fe₂O₃ single-crystal nanowire array for solar water splitting. Firstly, we have prepared a high-density single-crystal Fe₂O₃ nanowire array at lower temperatures by a new approach stress-induced atomic diffusion method. Thereafter, the prepared nanowire array was coated by Ti film using RF sputtering. The optimal film thickness of 13 nm titanium coatings layer into Fe₂O₃ single crystal nanowire array exhibited a high photocurrent density of 1.36 mA/cm² at 1.23 V versus RHE and solar to hydrogen conversion efficiency (STH) of 1.67%, which could be resulting from adjusted optoelectronic properties of the nanowires.

DOI： 10.1166/mex.2024.2704

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/mej.23-00551

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/mej.24-00015

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.ijpvp.2024.105178

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.jallcom.2023.172892

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.msea.2023.145845

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

Metallic materials are widely employed due to their exceptional mechanical attributes. Plastic deformation is a common issue that influences both the mechanical and electrical properties, with profound implications for the longevity of engineered structures and components. Dislocation density is the core factor in the plastic deformation process. Traditional methods for the evaluation of dislocation density include electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and x-ray diffraction (XRD), requiring meticulous specimen preparation and sophisticated equipment posing challenges for industry-wide fitness-for-service (FFS) monitoring. To address these challenges, a non-contact method to quantitatively evaluate the dislocation density in stainless steel 316L (SUS316L) by employing a microwave reflection method is reported in this study. A dedicated microwave measurement system, coupled with a coaxial line sensor, was used to measure the amplitude of the reflection coefficient of the microwave signal at a constant standoff distance and frequency, closely associated with the electrical resistivity of the SUS316L specimens, a parameter that exhibits variation in response to changes in dislocation density. The results indicate a proportional increase in the amplitude of the microwave signal with higher dislocation density. By establishing a linear correlation, we demonstrate the feasibility of evaluating dislocation density with a minimum detectable difference of 1.824 × 10¹³ m^-2 using the dedicated microwave system under the designed conditions in this study. This approach holds promise for better understanding and monitoring of plastic deformation in metallic materials across various applications.

DOI： 10.1299/mej.24-00155

CiNii Research

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

This study investigates the inhibitory effects of high-density pulsed electric current (HDPEC) treatment on fatigue crack initiation in directionally solidified nickel-based superalloy. Experiments were conducted under fully reversed conditions (<i>R</i> = -1) using low-cycle fatigue tests to assess the impact of HDPEC on crack initiation. The distribution of misorientation at different stages before and after crack initiation of untreated and HDPEC-treated samples was analyzed through kernel average misorientation maps by electron backscatter diffraction method. The results demonstrate that the HDPEC treatment significantly delays the initiation life of cracks, extending from approximately 2000 cycles to 5000 cycles. Additionally, the average fatigue life of the samples increased from 3851 cycles to 10881 cycles, more than doubling the fatigue life. Furthermore, the formation of persistent slip markings on the surface of the HDPEC-treated samples was completely suppressed, indicating changes in the persistent slip band’s structure. This phenomenon led to a distinct pattern of crack formation and propagation compared to untreated samples, suggesting that HDPEC treatment effectively alters the pattern of crack initiation and propagation by homogenizing dislocation distribution and alleviating residual stresses caused by cyclic loading. The result confirms the potential of HDPEC technology to enhance the fatigue life of nickel-based superalloys, and underscores the potential for further research in this domain.

DOI： 10.1299/mej.24-00178

CiNii Research

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Publishing type：Research paper (scientific journal)  

This study explores the efficacy of high-density pulsed electric current (HDPEC) in healing plastic deformation damage in single-crystal Ni-based superalloys. Single-crystal specimens are prepared from directionally solidified nickel-based superalloy to assess the potential of electric current treatment in restoring plastic deformation capability. Experiments involving various current densities and pulse durations reveal that a pulsed electric current of 17 ms at 400 A mm−2 yields optimal results, enhancing fracture elongation from 7.8% to 12.3% without compromising strength. The study conducts a comprehensive analysis of microstructural changes induced by pulsed electric current, employing quasi-in-situ electron backscatter diffraction and transmission electron microscopy techniques. The results demonstrate that HDPEC disrupts the planar dislocation network, homogenizes dislocation distribution, and promotes dislocation entanglement. Consequently, microdefects in the alloy are eliminated, restoring the material's ductility. The findings suggest that this technology holds significant promise for repairing fatigued components and underscore the potential for further research in this domain.

DOI： 10.1002/adem.202401409

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

This study comprehensively investigates the effects of high-frequency alternating current (AC) on the adhesion strength between metallic thin films and substrates as well as on the resistivity of metallic films. Under AC treatment at the optimal frequencies of 26, 37, and 38 MHz, the adhesion strengths of the Al, Cu, and Pt films to a substrate increase by 44.9%, 42.0%, and 101.8%, respectively, whereas their resistivities decrease by 22.6%, 38.4%, and 8.1%, respectively, at optimal frequencies of 30, 40, and 20 MHz. Microstructural characterization results show that the metallic films exhibit nanometer-scale crystal grains with numerous defects (i.e., disordered atoms). However, the application of high-frequency AC significantly reduces these defects and improves the crystallinity, thereby promoting adhesion enhancement and resistivity reduction. The different optimal frequencies of the Al, Cu, and Pt films are attributable to the different atomic weights and resistivities of the materials. The high-frequency AC method proposed herein is a highly efficient and energy-conserving technique with a maximum temperature increase of less than 7.1 °C. This study provides a promising alternative to conventional heat treatment methods for enhancing the reliability and durability of wiring in semiconductor components.&amp;#xD;

DOI： 10.1088/1361-6463/ad1469

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Other Link： https://iopscience.iop.org/article/10.1088/1361-6463/ad1469/pdf

Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.tsf.2023.140084

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME International  

Abstract

Molecular dynamics studies were performed to assess tensile and compressive behaviors at high temperatures up to 1200 °C for nanostructured polycrystalline AlCoCrFeNi high entropy alloy (HEA). As the temperature increased, the tensile yield stress, tensile/compressive ultimate strengths, and elastic modulus decreased, whereas the compressive yield stress remained constant. The temperature dependence of the phase structures (face-centered cubic (FCC) and hexagonal close-packed (HCP)) showed notable features between tension and compression. The HEA underwent FCC → HCP phase transformation when strained under both tension and compression. The evolution of the intrinsic stacking faults (ISFs) and extrinsic stacking faults (ESFs), which underwent FCC → HCP phase transformation, was observed. During compression, the ISFs → ESFs transition produced parallel twins. The evolution of mean dislocation length for the perfect, Shockley, and stair-rod partial dislocations was observed. Changes in the Shockley and stair-rod partial dislocations were observed after experiencing strain. The temperature dependence of the Shockley partial dislocation was high, whereas the stair-rod partial dislocation exhibited low-temperature dependence. From the simulation results, the structural usage of nanostructured polycrystalline AlCoCrFeNi HEA at elevated temperatures is recommended.

DOI： 10.1115/1.4063802

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.mtla.2023.101922

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

For the first time, the thermal stress-assisted formation of submicron pillars (SPs) from a high entropy alloy (HEA) thin film is made possible, and novel molecular dynamics (MD) simulations are proposed to assess the underlying mechanisms.

DOI： 10.1039/d3ra04759h

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s10853-023-08721-y

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Other Link： https://link.springer.com/article/10.1007/s10853-023-08721-y/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s11665-023-08522-z

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Other Link： https://link.springer.com/article/10.1007/s11665-023-08522-z/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.mtcomm.2023.107082

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Language：English   Publishing type：Research paper (scientific journal)  

In this study, an energy-saving and highly efficient high-density pulsed electric current (HDPEC) method was used to improve the formability of the aluminum alloy A6061 after T6 heat treatment (A6061-T6). An interrupted tensile test was performed, and the HDPEC treatment was applied after tensile deformation. The results showed that the ductility of A6061-T6 improved by approximately 33% after three HDPEC treatments. The Vickers hardness and residual stress were measured to investigate the effect of the pulsed electric current on formability, and they were recovered after HDPEC treatment. Furthermore, the microstructural morphology and dislocation density were investigated to understand the mechanism of formability enhancement. Detailed analysis shows that the formability enhancement of A6061-T6 after HDPEC treatment is mainly attributed to dislocation elimination, while grain size and crystalline orientation changes are side effects. In addition, the results of equivalent heat treatments demonstrate that the athermal effect of the HDPEC treatment plays a crucial role in the removal of dislocations. Thus, due to the contribution of the athermal effect, HDPEC treatment realizes the advantages of low consumption and high efficiency, and can be dedicated to green processing and manufacturing of metallic materials.

DOI： 10.1007/s00170-023-11841-z

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.msea.2023.145534

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.mtcomm.2023.106892

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.engfailanal.2023.107230

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s13105-023-00960-6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.engfracmech.2023.109235

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/adem.202300115

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

A non-contact quantitative method for measuring the electrical conductivity of a SnO₂ nanobelt field-effect transistor (FET) with nanometer-scale spatial resolution is reported. The topography and microwave images of the nanobelt FET were measured by microwave atomic force microscopy (M-AFM) under a constant source voltage and different back-gate voltages. The output characteristics of the nanobelt FET were measured using a two-probe measurement method. The local conductivity of the SnO₂ nanobelt FET measured by M-AFM concurred with that obtained by the two-probe measurement. Therefore, M-AFM is a promising method for measuring the local conductivity of nanomaterial FETs.

DOI： 10.35848/1882-0786/acaaf3

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Other Link： https://iopscience.iop.org/article/10.35848/1882-0786/acaaf3/pdf

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

INTRODUCTION: Metabolic strategies in different microenvironments can affect cancer metabolic adaptation, ultimately influencing the therapeutic response. Understanding the metabolic alterations of cancer cells in different microenvironments is critical for therapeutic success. METHODS: In this study, we cultured non-small cell lung cancer cells in three different microenvironments (two-dimensional (2D) plates, soft elastic three-dimensional (3D) porous 2 wt% scaffolds, and stiff elastic 3D porous 4 wt% scaffolds) to investigate the effects of different matrix elasticity as well as 2D and 3D culture settings on the metabolic adaptation of cancer cells. RESULTS: The results revealed that PGC-1α expression is sensitive to the elasticity of the 3D scaffold. PGC-1α expression was markedly increased in cancer cells cultured in stiff elastic 3D porous 4 wt% scaffolds compared with cells cultured in soft elastic 3D porous 2 wt% scaffolds or 2D plates, enhancing mitochondrial biogenesis and oxidative stress resistance of non-small cell lung cancer through increased reactive oxygen species (ROS) detoxification capacity. However, phosphofructokinase-1 (PFK-1) expression, a key rate-limiting enzyme in glycolysis, did not change significantly in the three microenvironments, indicating that microenvironments may not affect the early stage of glycolysis. Conversely, monocarboxylate transporter 1 (MCT1) expression in 3D culture was significantly reduced compared to 2D culture but without significant difference between soft and stiff scaffolds, indicating that MCT1 expression is more sensitive to the shape of the different cultures of 2D and 3D microenvironment surrounding cells but is unaffected by the scaffold elasticity. CONCLUSIONS: Together, these results demonstrate that differences in the microenvironment of cancer cells profoundly impact their metabolic response.

DOI： 10.1007/s12195-022-00751-x

PubMed

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Accidental chemotherapy extravasation exacerbates the side effects of anticancer drugs. Therefore, drug-delivery nanocarriers should be designed to avoid persistent drug release at off-target sites and promote burst drug release at on-target. Considering these requirements, poly(allylamine)-co-poly(allylurea) (PAU), a ureido-derivatized temperature responsive polymer with upper critical solution temperature (UCSTs), is an ideal material. This report describes the fabrication, characterization, and in vitro cellular toxicity of PAU polymer-grafted magnetic mesoporous silica nanoparticles as drug-delivery nanocarriers. A UCST of 43 °C and an ultranarrow transition temperature range of 39-43 °C was realized, ensuring that the nanocarriers suppressed undesirable leakage to below 10 % of the drug loading for 8 h in the absence of a thermal stimulus. A drug release burst of up to 75 % of the drug loading was achieved within 30 min after the stimulus, reducing the viability of the in vitro cancer cells to 12 %. Therefore, the ureido-derivatized polymer is one of the most suitable gatekeepers for drug-delivery nanocarriers.

DOI： 10.1016/j.bioadv.2022.213026

PubMed

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.matlet.2022.132737

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Acute myeloid leukemia (AML) is the most lethal leukemia with an extremely poor prognosis and high relapse rates. In leukemogenesis, adhesion abnormalities can readily guide an imbalance between hematopoietic progenitor cells and bone marrow stromal cells, altering the normal hematopoietic bone marrow microenvironment into leukemic transformation that enhances leukemic proliferation. Here, we have firstly studied the PLEKHA7 expression in leukemic cells to assess their growth capability affected by the restoration of PLEKHA7 in the cells. The efficacy of PLEKHA7-loaded cRGD-mediated PEGylated cationic lipid nanoparticles for efficient PLEKHA7 delivery in leukemic cells as well as the effect of PLEKHA7 on the regulated induction of AML behavior and growth alterations were investigated. PLEKHA7 re-expression diminished colony-forming ability and reinforced the incidence of growth retardation without apoptosis in AML cell lines. PLEKHA7 regulated the restoration of cell surface adhesion and integrity during normal homeostasis. Our findings revealed that PLEKHA7 functions as a behavior and growth modulator in AML. To our knowledge, the role of PLEKHA7 in AML had not been studied previously and our data could be exploited for further mechanistic studies and insights into altering human AML behavior and growth.

DOI： 10.1016/j.bbiosy.2022.100045

PubMed

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

The {101} texture of deformed face-centered cubic metals, such as 316 stainless steel and Ni-based alloy Inconel 718, was successfully alleviated by high-density pulsed electric current (HDPEC) treatment. Furthermore, the deformed grains recovered after the HDPEC treatment. The HDPEC induced the rapid dislocation motion and grain refinement that resulted in random grain orientation and equiaxed grain morphology, which led to anisotropy recovery in the deformed metals. This method provides a promising way to modify the microstructure of materials with short time and low cost, after forming or during service.

DOI： 10.1016/j.vacuum.2021.110855

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

This study evaluated the low-cycle fatigue (LCF) life of type 316 austenitic stainless steel to determine the effect of multiple high-density pulsed electric currents (HDPECs). Fatigue properties were analyzed with the fatigue crack growth (FCG) and LCF tests by considering different conditions of multiple HDPECs and its application. The HDPEC densities of 100, 150 and 200 A/mm2 with application numbers from 1 to 17 times were used. The LCF results were assessed by using fatigue models, and the effectiveness of the application methods was examined. Under the HDPEC density of 200 A/mm2, increasing the number of HDPECs during the period of crack propagation is the best way for delaying FCG. Multiple applications of HDPEC caused a decrease in the length and an increase in the depth of striations in the specimen's fatigue fracture surface, and the degree of ductility was increased thereby leading to the delay in FCG. The proposed conditions pave the way toward improving the LCF life of the material.

DOI： 10.1016/j.ijfatigue.2021.106639

Scopus

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/mej.21-00178

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract: The effect of high-density pulsed electric current (HDPEC) on the microstructure evolution and corresponding changes in the mechanical properties of the deformed Ni-based alloy Inconel 718 was investigated. After HDPEC treatment, the strain hardening was fully relieved and the ductility recovered correspondingly. The results show that the dislocation density plays a dominant role, and the grain size has a side effect on the strain-hardening relief. Furthermore, the correlation between the mechanical properties and microstructure evolution affected by HDPEC was clarified. HDPEC treatment provides a way to alter the microstructure and thus tailor the mechanical properties of the deformed components. Hence, it is applicable to the metal-forming field to achieve rapid relief of strain hardening and enhance formability. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s10853-021-06344-9

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

In this paper, we report a non-contact and quantitative method to evaluate the permittivity of semiconductor nanomaterials. A microwave atomic force microscopy (M-AFM) was used to obtain the topography and microwave images of nanomaterials in one scanning process. Morphology and microwave images of ZnO and CuO nanowires, and SnO2 nanobelts with high spatial resolution were obtained in the non-contact mode of M-AFM. The local relative permittivity of these one-dimensional metal oxide nanomaterials was quantitatively evaluated.

DOI： 10.1063/5.0049619

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Institute of Metals  

The application of high-density pulsed electric current (HDPEC) is one of the effective methods for the modification of material properties in metals. To evaluate fracture behavior modified by HDPEC, critical fracture parameters such as fracture strength, fracture toughness, and fracture profile of crack tip are important criteria. This work investigates the finite element analysis (FEA) based evaluation of improved fracture characteristics by the application of HDPEC in a SUS 316 austenite stainless steel. Tensile tests were first conducted to deduce the modified material properties with different conditions of HDPEC. A series of theoretical considerations was employed to estimate the modified fracture toughness. The relationship between critical fracture strength and critical crack length was numerically determined based on the estimated fracture toughness. The results in FEA showed that critical von Mises stress on the singularity at the crack tip increases as the effect of HDPEC increases. The evolution of increased fracture toughness with respect to conditions of HDPEC was specified. Crack opening profiles were simulated to assist the explanation. The evaluation of fracture parameters in this study proposes that the modified material properties by HDPEC play a positive role to resist crack propagation.

DOI： 10.2320/matertrans.mt-m2020333

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Though dislocation emission was known to be critical in the deformation and fracture process of metallic nanowires, the corresponding mechanism in cold-welded metallic nanowires has never been clarified. In order to understand the dislocation-mediated deformation mechanism in cold-welded nanowires, large-scale atomistic simulations are employed in this work. During dislocation emission, the formation and motion of only unclosed shear loops are observed inside nanowires. We prove from a theoretical viewpoint that unclosed shear dislocation loops can induce material transport and hence plastically deform cold-welded nanowires. For a better clarification, through running simulation replicates, we propose a novel approach to single out the displacement field solely due to shear loop emission. Regarding the pattern of material transport, our simulated atom arrangement near the dislocation core is found consistent with that captured by high-resolution transmission electron microscopy (HRTEM) of a stressed Au nanocrystal. Our analysis clarifies that the emission of unclosed shear loop plays a crucial role in not only the tensile deformation, but also the fracture process of cold-welded nanowires. It should be regarded as a general mechanism that shear loop emission can induce surface deformation and redistribute mass in the process of plasticity.

DOI： 10.1016/j.commatsci.2020.110214

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

A drastic size effect in cold-welded metallic nanowire for surface fasteners was observed in our previous experiment. In this work, a large-scale molecular dynamics (MD) simulation and a finite element (FE) simulation coupled with the nonsingular dislocation theory are combined to probe the true origin of this drastic size effect. Very large diameter (up to 200 nm) is involved in the direct MD simulation, leaving no gap between the simulation and the experiment. It was once believed that the drastic size effect comes from the Van der Waals (vdW) force transmitted through the bonding interface, which does give a mathematically agreeable scaling law. However, based on present simulations, new understanding is established-the drastic size effect is linked to dislocation emission, rather than vdW force. Compared with a single nanowire, the externally induced stress surges near the bonding corner of cold-welded nanocrystals due to the enormous stress concentration. The dislocation emission is hence triggered. It is also revealed that, overwhelmingly, dislocation emission should be energetically favorable in cold-welded nanocrystals. Additionally, MD simulations with polycrystalline nanocrystals reveal that both the random orientation effect and the grain boundary effect are secondary to the enormous stress concentration effect. Under such less ideal situation, dislocation emission still determines the maximum stress.

DOI： 10.1016/j.ijmecsci.2020.106102

Web of Science

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/5.0011417

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Void growth, as a critical stage in ductile fracture, could play some important role in the ductility of high entropy alloys (HEAs). Under a high-strain-rate tension (strain rate: 0.1 similar to 0.4/ns), our atomistic simulations reveal a severely suppressed growth of void (initial diameter: 4.0 similar to 9.1 nm) in HEAs at a low temperature, compared with that in Ni metal or Ni-based binary alloys. The emission of unclosed glide loops is found critical to void growth. Void growth is suppressed, once dislocation emission is suppressed due to the solute drag effect. Regarding the alloying elements, we find the void suppression relevance as Fe>Co and Cr>Fe>Mn. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2020.03.056

Web of Science

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1557/mrc.2019.135

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1557/mrc.2019.68

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Language：English   Publishing type：Research paper (scientific journal)  

This paper reports on the relationship between the mechanical properties and the grain size of Cu microwires modified by Joule heating. The increase in yield strength as the grain size of a metal or alloy decreases is known as the Hall-Petch relation. Because the crystal grain size in thin metallic wires is fine, these have higher strength compared to their bulk counterparts. To improve the formability of 25 ?m-thick Cu microwires, the wires were heat-treated at various temperatures by Joule heating, and the grain size of the wires was evaluated quantitatively by cross section method. Larger crystal grains grew at higher temperatures, and the wire heat-treated at the highest temperature of 600oC had a bamboo structure, in which the grain boundaries were only in the radial direction of the wire. Small-span, three-point bending tests were performed on the heat-treated Cu microwires to determine their mechanical properties. The Young's modulus of the wires was found to be independent of grain size, with an average value of 86.4 ± 2.4 GPa. On the other hand, the yield stress of the wires clearly depended on the grain size. The yield stress of a Cu microwire that had not been subjected to Joule heating was 311 MPa, and this decreased to 75 MPa after heat treatment at 600oC. Finally, we confirmed that the Hall-Petch relation was applicable to the Cu microwires, except for those that, due to insufficient heat treatment, had crystal grain structures in which the grains were highly elongated in the axial direction of the wire.

DOI： 10.2472/jsms.68.443

Scopus

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1115/1.4042980

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/mej.18-00269

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/mel.17-00604

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Verlag  

Electromigration (EM) evaluation near contact corners in interconnection structures composed of dissimilar materials in particular is becoming increasingly important. A theoretical analysis of the atomic density distribution around a right-angled corner in a passivated line composed of dissimilar metals is performed. The 2D structure considered, including the corner, is assumed to consist of dissimilar single-crystal metals with uniform passivation and line widths. While the atomic density distribution in the passivated 1D straight line has been reported previously, the atomic density distribution in a passivated 2D structure that contains a right-angled corner composed of two dissimilar metals has not been studied. This work clarifies the atomic density distribution in the 2D structure under equilibrium conditions for the two fluxes, which are the atomic flux due to the electron wind force and the flux due to the back flow caused by the atomic density gradient in EM, and presents the predicted locations of EM damage in the form of voids and hillocks. In addition, this paper proposes countermeasures to increase the threshold current density for EM, which contributes to enhancement of the reliability of the metal line against EM. The selection of suitable values for several material properties are discussed from the viewpoint of preventing initiation of EM damage by increasing the EM threshold current density. Suitable material combinations to increase the threshold current density are also discussed.

DOI： 10.1007/s00542-016-3178-7

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Electromigration (EM) is a serious problem for an Al line subjected to high-density electron flow. The present work reports a strategy for achieving a suitable passivation thickness on the line against EM damage. Experiments carried out in this work indicated that the threshold current density, a measure of EM resistance, increased with increasing passivation thickness and became saturated for thicknesses greater than 1700 nm. The saturation was shown to begin at the situation in which the level of the passivation top surface beside the Al line and that of the Al top surface are the same. A suitable passivation thickness for effectively increasing EM resistance was determined based on this finding. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matlet.2016.08.059

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/mel.15-00714

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Applied Physics  

Atomic flux divergence (AFD) near a right-angled corner composed of dissimilar metals is theoretically analyzed in the present paper. A basic model of layered interconnect lines involving a right-angled corner is constructed. A two-dimensional electromigration (EM) problem near the corner is analyzed by treating the angled line as a single-crystal line without a passivation layer and with a uniform width. The material combination was found to play a significant role in determining the amount of AFD that occurs near the corner. The analysis of AFD in the present paper provides a unique insight into EM from the viewpoint of AFD singularities governed by the material combination. In addition, in terms of EM reliability issues in interconnects, several countermeasures for reducing the EM-induced damage are proposed. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.53.075504

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications  

Electromigration (EM) is the phenomenon of atomic diffusion in a metallic film with a high-density electron flow. Our group used EM to fabricate Al micro-materials. The EM technique can be used to fabricate micro-materials with a high aspect ratio, pure metal components, an arbitrary form, and a single-crystal structure. Recently, two micro-materials have been simultaneously fabricated using an array pattern consisting of parallel or series connections. However, multiple micro-materials have not been fabricated simultaneously thus far. In this study, a new comb sample pattern was used with a conductive passivation film to produce multiple Al micro-materials. © (2014) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/AMR.909.36

Web of Science

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications  

The technique for fabricating Al micro-materials using a conductive passivation film by electromigration (EM), which is the physical phenomenon of atomic transport with high-density electron flow, has been reported. Conductive passivation film precludes the unplanned hillock formation and substantially simplifies the sample preparation time for fabricating Al micro-materials by EM. To date, TiN that is electrical conductive material has been used as a passivation film. However, the TiN passivation oxidizes during heat and current test for fabricating Al micro-materials by EM because of inherent poor oxidation resistance of TiN. Oxidation of passivation causes a problem that applying current occasionally becomes difficult. The present paper proposes a new conductive passivation made of CrN for fabricating Al micro-materials by EM. CrN is used as a countermeasure against the oxidation problem. Additionally, the growth of Al micro-materials by EM is investigated in the relation with the experimental conditions of current and substrate temperature. As a result, we report that the fabrication of Al micro-materials using the CrN passivation is successfully demonstrated in the relation with the experimental conditions. © (2014) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/AMR.909.67

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Techniques for the fabrication of Al micro-wires by utilizing and controlling electromigration (EM), the phenomenon of atomic diffusion in a metallic film with high-density electron flow, have been investigated. These fabrication methods are based on atomic diffusion, using which accumulation was purposely induced in a specific area of a sample and discharged at a certain position by utilizing EM. In the creation of Al micro-wires, a passivation film is necessary. The passivation film forms the topmost layer and prevents unintended hillock formation. Passivation film is composed of the nonconductive material SiO2. We propose an improved approach for the fabrication of micro-wires using an electrically conductive passivation film composed of TiN. Conductive passivation film simplifies the process of fabricating samples and decreases the risk of the interruption in the current supply caused by open circuits along the Al line. As a result, the time and cost associated with the proposed method are less than half of those of the previously used techniques. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matlet.2013.11.044

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