MATERIALS TRANSACTIONS
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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 59 (2018), No. 7

  • Roles of Carrier Doping, Band Gap, and Electron Relaxation Time in the Boltzmann Transport Calculations of a Semiconductor’s Thermoelectric Properties

    pp. 1013-1021

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    DOI:10.2320/matertrans.E-M2018813

    Although there is a growing demand for first-principles predictions of the thermoelectric properties of materials, the contribution of various errors in Boltzmann transport calculations is not negligible. We conducted a typical first-principles calculation and a Boltzmann transport analysis on a typical semiconductor (Si) at various temperatures T while varying the band gap εg, electron relaxation time τel, and phonon thermal conductivity κph to demonstrate how the calculated thermoelectric properties, which are functions of the carrier doping level, are affected by these parameters. Bipolar conduction drastically decreased zT via a degradation of the Seebeck coefficient S and an increase in the effective Lorenz factor Leff, indicating the importance of a wide enough εg (several multiples of kBT or higher) for high zT. Thus, the underestimation of εg, which frequently happens in first-principles calculations, could induce large errors in calculations for narrow-gap semiconductors. The calculation of the electron thermal conductivity without Peltier thermal conductivity was found to limit the zT of typical semiconductors to below 1. A small value of κphel, where κphel is the degree to which a material is a phonon-glass electron-crystal, was necessary to achieve a high zT. Fitting the calculations with experimental thermoelectric properties showed that τel can vary by an order of magnitude from 10−15 to 10−14 s, depending on both T and the samples. This indicates that the use of a fixed relaxation time is inappropriate for thermoelectric materials.
  • Synthesis of High-Density Bulk Tin Monoxide and Its Thermoelectric Properties

    pp. 1022-1029

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    DOI:10.2320/matertrans.E-M2018804

    SnSe exhibits exceptionally high thermoelectric (TE) figure of merit zT mainly due to its ultralow lattice thermal conductivity (κlat) [L.-D. Zhao et al.: Nature 508 (2014) 373.]. It is considered that strong lattice anharmonicity caused by the lone pair electrons of Sn2+ results in the ultralow κlat. Here, we focus on SnO because it has the lone pair electrons of Sn2+ like SnSe. Bulk samples of SnO were synthesized by low-temperature high-pressure spark plasma sintering and their TE properties were examined. The present study revealed that SnO exhibits very low κlat (1.44 Wm−1K−1 at 573 K) compared with SnO2 which has no lone pair electrons. The Grüneisen parameter (γ) of SnO was evaluated to be 1.70 and this high γ leads to large lattice anharmonicity and thereby low κlat. Even though SnO has low κlat, the zT values were significantly low compared with SnSe. The maximum zT value of SnO was 0.00141 at 573 K. Since the main reason of this low zT is its non-optimized carrier concentration, the zT of SnO can be enhanced through the carrier concentration optimization.
  • Thermoelectric Properties of p-Type Half-Heusler Compounds FeNb0.9M0.1Sb (M = Ti, Zr, Hf)

    pp. 1030-1034

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    DOI:10.2320/matertrans.E-M2018806

    Recently, it has been reported that Hf-substituted Fe(Nb1−xHfx)Sb-based p-type half-Heusler compound exhibits exceptionally high thermoelectric (TE) figure of merit zT = 1.5 at 1200 K [C. Fu et al.: Nat. Commun. 6 (2015) 8144.]. However, the effect of substitute elements on the TE properties of FeNbSb is still unclear. Here, we synthesized polycrystalline samples of Fe(Nb0.9M0.1)Sb (M = Ti, Zr, Hf) by arc-melting followed by spark plasma sintering, and examined their high-temperature TE properties. The Ti-substituted sample was nearly single phase while the Zr- and Hf-substituted samples contained small amounts of secondary phase. The Ti-substituted sample exhibited the best TE performance. In the present case, Ti is better substituted element than Zr and Hf for enhancement of TE properties of FeNbSb.
  • Observation of Interface between Thermoelectric Material Zn4Sb3 and Electrodes by Resistance Scanning and Seebeck Coefficient Mapping Techniques

    pp. 1035-1040

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    DOI:10.2320/matertrans.E-M2018814

    A ready-for-soldering thermoelectric element composed of Zn4Sb3 with Ni–Al diffusion barrier layer and Cu electrode was fabricated by means of a hot-press method. Batch-to-batch variation of the resistance of the element was within 7%, the average resistance was 3.23 mΩ and the standard deviation 0.25 mΩ. Annealing effects on the interface structure between the electrodes and Zn4Sb3 were investigated using microprobe techniques such as Seebeck coefficient mapping and resistance scanning. The element showed lower Seebeck coefficient and resistivity than those of the pristine Zn4Sb3 without the electrodes. After annealing for 3.6 ks, the Seebeck coefficient and resistivity returned to the intrinsic values of Zn4Sb3. Increased resistivity was clearly observed near electrode/Zn4Sb3 interfaces of all annealed samples. Seebeck coefficient maps also indicated variation near the interfaces, showing good consistency with the resistance variation.
  • Fabrication and Thermoelectric Properties of Al/Mg2Si Composite Materials

    pp. 1041-1045

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    DOI:10.2320/matertrans.E-M2018815

    Mg2Si has attracted interest as a potential thermoelectric material that can convert waste heat into electricity. To improve thermoelectric performance of Mg2Si, Al/Mg2Si composite materials with nominal composition of xAl/Mg2Si (x = 0.25, 0.5, 0.75, 1.0, or 1.5) were fabricated, i.e., an Al metal phase was introduced to an Mg2Si matrix. Reflecting an increase in the electrical conductivity and a decrease in the Seebeck coefficient with increasing x, the power factor was successfully enhanced by the incorporation of the Al phase. The increase in electrical conductivity was discussed in terms of electron carrier density and carrier mobility.
  • PREFACE

    pp. 1046-1046

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    DOI:10.2320/matertrans.MPR2018902

  • Crystalline Approximant of Amorphous Fe-Si-B Structures

    pp. 1047-1050

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    DOI:10.2320/matertrans.MD201711

    We have examined the local atomic configurations of amorphous Fe-Si-B alloys by means of electron diffraction pair-distribution-function analysis and compared them with those of a metastable sigma phase formed during the crystallization process. We found a great structural similarity, not only at short range but also at medium range up to 1.0 nm, between amorphous Fe-Si-B and sigma phase structures. The results imply that the sigma phase structure can be regarded as a good crystalline approximant for the glass structures in this alloy system. The connections of coordination polyhedra in the sigma phase structure were also discussed.
  • Crystallographic Relationship between the ν (Mn82Si18) and H (Mn7Si2V) Phases in the Mn-Si-V Alloy System

    pp. 1051-1056

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    DOI:10.2320/matertrans.MD201712

    There are the intermetallic-compound ν (Mn82Si18) and H (Mn7Si2V) phases in the Mn-Si-V alloy system. These two phases can be regarded as approximant phases of the dodecagonal quasicrystal, and their crystal structures involve similar structural hierarchies consisting of dodecagonal atomic columns and giant dodecagonal structural units. To understand the crystallographic relationship between these approximant phases, we examined their crystallographic features mainly by transmission electron microscopy. It was found that there is a simple orientation relationship of N(001)ν // N(0001)H and N(010)ν // N(0110)H between the ν and H structures. In addition, H-structure regions have an antiphase boundary with a π phase shift along a column axis as a structural defect. A notable feature of the antiphase boundary is that it consists of decagonal columns, not dodecagonal columns present in the H structure, where both 11 dodecagonal columns and eight decagonal columns form one dodecagonal unit in the ν structure. The ν structure can thus be produced in the following two steps. First, eight outer dodecagonal columns in each dodecagonal unit in the H structure are replaced by eight decagonal columns. The second step is the periodic introduction of antiphase boundaries, consisting of decagonal columns present in the replacement.
  • Ab-Initio Multiplet Calculations Using Iterative Algorithms for X-ray Absorption Spectra at Transition Metal L2,3-Edges

    pp. 1057-1061

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    DOI:10.2320/matertrans.MD201706

    X-ray absorption spectra at the L2,3-edges of transition metals show widely spreading multiplet structure due to the strong electronic correlations between the 2p and 3d electrons. The ab-initio multiplet method based on the relativistic configuration interaction (CI) theory is one of the most reliable theoretical methods to reproduce and predict such spectra. In this method, a many-electron Hamiltonian matrix is fully diagonalized in order to obtain the many-electron wavefunctions for the initial and final states of transitions simultaneously. Since the dimension of the Hamiltonian matrix grows exponentially with an increase in the number of active orbitals, the method has been only computationally feasible only for small systems. In the present study, iterative algorithms, including the Davidson-like algorithm for obtaining the wavefunctions for the initial states, and Lanczos algorithm for evaluating the spectral functions solely from the initial states, were implemented. The theoretical spectra obtained by the new algorithms are identical to those obtained by the full-diagonalization method. As the iterative algorithms adopted in this study require much less memory space, the ab-initio multiplet method with iterative algorithms can be applied to larger systems that are unmanageable by a conventional full-diagonalization method.
  • First-Principles Calculations of Ionic Conduction in Olivine-Type LixFePO4

    pp. 1062-1067

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    DOI:10.2320/matertrans.MD201707

    Super ionic conductors are required for all solid Li ion batteries. Conduction mechanism of LixFePO4 has been revealed by first-principles calculations using plane-wave basis. Crystal structures were constructed using a unit cell and a 1 × 2 × 1 super cell. Transition of Li site occupation with the smallest energy fluctuation was searched through graph theory. Trajectories of Li ions and migration energies were obtained by Nudged Elastic Band Method. Results show the migrating atoms pass through faces of O polyhedra. At dilute limit of Li, a single ion migrated and had very low migration energy of 0.14 eV. Increasing the carrier concentration resulted in pairing of Li atoms and raised the migration energy. At higher concentration region, cooperative ionic conduction mechanisms of two Li ions occurred. Low migration energies were obtained to be 0.20 and 0.22 eV for x = 0.25 and 0.5 of LixFePO4, respectively. Considering the migration energy and carrier concentration, LixFePO4 with the concentration region 0.25 ≤ x ≤ 0.5 should have high ionic conductivity. These mechanisms would be applied to develop new superionic conductors.
  • Crystal Structure and Magnetic Properties of La0.8R0.2(Fe0.88Si0.12)13 (R = Sm and Tb) Compounds

    pp. 1068-1070

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    DOI:10.2320/matertrans.MD201716

    This study discusses the crystal structure and magnetic properties of the rare-earth doped La0.8R0.2(Fe0.88Si0.12)13 (with R = Sm, Tb) compounds. All the samples were prepared by using arc-melting technique in argon atmosphere and the obtained result shows that after heat treatment, the samples exhibited the NaZn13-type cubic phase with a small amount of a secondary α-Fe phase. The magnetic properties and magnetic entropy change were determined by mean of the temperature and field dependence magnetizations. Besides the decrease in the lattice constants, there was also observed a significant increase of Curie temperature and magnetic entropy change −ΔSM which reached a maximum of 4.5 J/kg K for La0.8Sm0.2(Fe0.88Si0.12)13, corresponding to a relative cooling powers (RCP) of 102 J/kg for the sample.
  • Enhancements of Critical Current Density in the Bi–Pb–Sr–Ca–Cu–O Superconductor by Na Substitution

    pp. 1071-1074

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    DOI:10.2320/matertrans.MD201715

    In this paper, we investigated the influences of Na substitution on the enhancements of critical current density (Jc) in the Bi–Pb–Sr–Ca–Cu–O (BPSCCO) superconductors. The Bi1.6Pb0.4Sr2Ca2−xNaxCu3O10+δ (where x was ranged from 0 to 0.1) polycrystalline samples were fabricated using solid state reaction technique. The zero electrical critical temperature (Tc) of Na-substituted BPSCCO samples was found to be slightly higher than that of Na-free BPSCCO one. Magnetization Jc data measured at 65 K with field applied parallel to the c-axis of the samples showed that Jc of Na-substituted BPSCCO samples were enhanced. Possible reasons for the Jc enhancements were attributed to the effective flux pinning by crystal defects at Ca layers generated by Na substitution. Improvements of volume pinning force (Fp) in terms of magnitude and position of Fpmax were also obtained.
  • Dynamical Susceptibility and Elementary Excitations in Monolayer Ferroic Films Described by XZ Heisenberg Model

    pp. 1075-1080

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    DOI:10.2320/matertrans.MD201714

    The dynamical susceptibility and finite temperature collective excitations in monolayer spin film are calculated using the anisotropic exchange XZ-Heisenberg model for different spin magnitude and the functional integral method. Combining mean field and Gaussian approximation, it is shown that the internal transverse field induced by internal transverse exchange interaction, leads to a decrease (increase) of the spin wave energy in the temperature region below (above) the spin reorientation temperature. This temperature is of the same nature as the critical temperature of the transverse Ising model studied previously. Reduction of the external spin reorientation transverse field (the critical tuning parameter) by intrinsic transverse exchange is demonstrated.
  • Role of Gap Size and Gap Density of the Plasmonic Random Gold Nanoisland Ensemble for Surface-Enhanced Raman Spectroscopy

    pp. 1081-1086

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    DOI:10.2320/matertrans.MD201701

    Surface-enhanced Raman spectroscopy (SERS) using plasmonic effect relies on the amplification of the Raman signals of targeted molecules due to a strong near-field enhancement of plasmonic nanostructures. The SERS intensity, therefore, depends strongly on the geometry of plasmonic structures wherein nanogaps between plasmonic objects play a significant role in the near-field enhancement. Here, using the random gold nanoisland assemble as a plasmonic medium and the Rh6G as the targeted molecule, we show that not only the size of the nanogaps but also their density influence strongly on the SERS intensity. The SERS intensity is found to be significantly improved if the gap size decreases and gap density increases. Our work provides additional information that might be useful for optimizing the SERS signal strength of the random plasmonic media.
  • Interaction of Arachidic Acid Langmuir Monolayers with Trivalent Ions La3+ and Fe3+ Studied by Vibrational Sum-Frequency Spectroscopy

    pp. 1087-1090

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    DOI:10.2320/matertrans.MD201708

    Interaction of carboxylic acid headgroups of arachidic acid (AA) monolayers with trivalent ions Fe3+ and La3+ is studied by using vibrational sum-frequency generation (VSFG) spectroscopy. Comparing SFG spectra of AA Langmuir monolayers on 10−3 M LaCl3 solutions and 10−3 M FeCl3 solutions with various pH values, we show that, the cation La3+ binds to carboxylic groups by Coulombic interaction as the AA monolayers deprotonate at high pH (pH ≥ 7). On the other hand, insoluble Fe(OH)3 complexes in the FeCl3 solution bind to the carboxylic headgroups of AA molecules enhances the ordering structure of AA monolayers as well as that of the OH network at the interfacial layers.
  • Fabrication of Microsized Magnetic Materials by Ink-Jet Printing

    pp. 1091-1094

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    DOI:10.2320/matertrans.MD201702

    Micro-magnetic structures including Nd-Fe-B microsized particles were produced by the ink-jet printing technique. The Nd-Fe-B particles were commercial MQP-B particles with a Nd2Fe14B phase and an average diameter of 6 µm. The particles were milled to a mean particle size of about 300 nm before being added to the standard ink, MFL-003. The resultant magnetic suspension contained nanosized Nd-Fe-B particles with a suitable weight percentage (43%) and displayed a negligible difference in parameters, such as viscosity, pH, etc., compared to those of the standard ink. The produced magnetic structure, that can be used to trap magnetic particles and can be developed into a microsized magnetic source, consists of squares with thickness of 40 µm and surface area of 500 × 500 µm2. Also, the properties of the magnetic structure were discussed. The obtained results show that the ink-jet printing technique is a simple and fast method for fabricating microsized magnetic structures.
  • Synthesis and Properties of Fe3O4/Polyaniline Nanomaterial and Its Ability of Removing Arsenic in Wastewater

    pp. 1095-1100

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    DOI:10.2320/matertrans.MD201703

    The synthesis of Fe3O4/polyaniline (Fe3O4/PANI) nanomaterials by a chemical method is presented in this paper. The X-ray diffraction (XRD) shows that the lattice constant a = 8.376 A0 and the particle size of is about 14.5 nm for all samples, since polymer cannot influence the crystal structure of Fe3O4. The transmission electron microscopy (TEM) images show that the Fe3O4 grain sizes vary from 13 nm to 20 nm. The results of Raman spectral analysis and thermal gravimetric analysis reveal that the PANI partly forms in the Fe3O4/PANI nanomaterials samples. Thus, the grain size of Fe3O4/PANI nanomaterials is about of 25–30 nm, which has been confirmed by a scanning electron microscope (SEM). The saturated magnetic moment of Fe3O4/PANI samples is decreased from 66 emu/g to 39.7 emu/g with PANI content varying from 5% to 15%. However, Fe3O4/PANI nanomaterials are stable on chemical-physical properties and lead to improve an arsenic adsorption ability. In addition, Fe3O4/PANI sample with PANI 5% content has the highest arsenic adsorption ability in pH 7. In strong acidic or basic media, the arsenic adsorption of magnetic nanoparticles is insignificant. The results suggest the desorb can be conducted at pH 14 then the materials could reabsorb in further trials.
  • Application of Nano-Ag Fabricated by the Electrical Spark Discharge Method for Restraining Aspergillus Niger

    pp. 1101-1105

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    DOI:10.2320/matertrans.MD201705

    The traditional nano preparation method is costly and time-consuming, and contains hazardous chemical constituents, thus affecting the characteristics and applications of nanocolloid. The Electrical Spark Discharge Method (ESDM) used in this paper prepares Nano-Ag colloid in deionized water, which is characterized by low cost, continuous and rapid production, and is free of chemical substances. According to the UV-Vis analysis of Nano-Ag, it has a peak at about 392 nm. Based on Zetasizer analysis, the minimum size is distributed below 50 nm, and the zeta potential is about −35 mV which the value of pH is almost equal to 7, proving its good suspension stability. According to the results of SEM, Nano-Ag colloid prepared by ESDM has nanoscale particles, and the constituent is Ag only. As this method is free of any surfactants and chemical agent, the Nano-Ag is added in the human body by imitating agar, and coated with Niger, the Nano-Ag restrains the growth of Niger. The higher the concentration of Nano-Ag, the stronger the inhibitory effect on the growth of Niger.
  • An Investigation of Silver Nanoparticles Formation under Presence of Graphene Quantum Dots as Reducing Reagent and Stabilizer

    pp. 1106-1111

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    DOI:10.2320/matertrans.MD201713

    In this work, we have studied effect of various reaction conditions for silver nanoparticles (AgNPs) production by a green and simple method. In our proposed method, silver nanoparticles have been formed and growth under presence of graphene quantum dots (GQDs) as reducing reagent and stabilizer. First, the small sized graphene quantum dots (GQDs) (5 nm ± 2 nm) with abundant oxygen containing functional groups have been synthesis by hydrothermal method, then GQDs have been used to adsorb Ag+ ions from solution onto GQDs’s surface and after that, Ag+ ions have been reduced into silver nanoparticles (AgNPs) by GQDs without adding any reducing reagents. GQDs were coated on the surfaces of the resultant AgNPs, leading to the formation of AgNPs/GQDs nano-hybrids. The optimized reaction conditions (such as pH, reaction time, temperature…) for synthesis of AgNPs using GQDs as a reducing reagent and stabilizer have been investigated. The synthesized AgNPs/GQDs have been characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Ultraviolet–visible spectroscopy (UV-Vis), and Dynamic Light Scattering (DLS). Results indicated that mono-dispersed AgNPs were obtained with particles size around 20 nm–40 nm.
  • Synthesis of ZnTiO3 and Ag/ZnTiO3 and Their Antibacterial Performances

    pp. 1112-1116

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    DOI:10.2320/matertrans.MD201717

    Antibacterial materials, namely ZnTiO3 and Ag/ZnTiO3, were prepared by a sol–gel method from tetra-n-butyl orthotitanate, zinc nitrate, and ethylenediaminetetraacetic acid (EDTA) as a complexing agent. The effects of the synthetic conditions on the properties of the obtained ZnTiO3 samples, i.e., the Zn2:Ti4:EDTA ratios and the calcination temperature, and the effects of different Ag:Ti4+ ratios on the properties of ZnTiO3 doped with Ag were investigated. These materials were characterized by powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, and their antibacterial activities against Staphylococcus aureus were also evaluated. The results showed that the optimum conditions for ZnTiO3 synthesis were Zn2+:Ti4+:EDTA ratios of 1:1:1 and calcination at 650°C for 2 h. Spherical Ag/ZnTiO3 nanoparticles of average diameter 30–50 nm showed effective antibacterial properties with and without exposure to sunlight. Ag/ZnTiO3 (Ag:Ti4+ = 1:20) at a concentration of 10 mg/mL killed over 99.86% of S. aureus bacteria within 4 h.
  • Photoactivity of Reducing Graphene Oxide and Titanium Dioxide Composite for Cinnamic Acid Degradation

    pp. 1117-1123

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    DOI:10.2320/matertrans.MD201721

    Reducing graphene dioxide (rGO) and titanium dioxide (TiO2) composites with various rGO/TiO2 ratios were prepared by hydrothermal method, in which rGO was synthesized from graphene powder according to modified Hummers method using microwave. Physico-chemical characteristics of the samples were investigated by the methods of N2 adsorption-desorption measurements, X-ray diffraction, Raman, Fourier transform infrared spectroscopy (FT-IR), UV-Vis spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). rGO-TiO2 (1:25) catalyst had smaller particle size and higher surface area than whose of pure TiO2. Moreover, this modification also extended the region of photon absorption of TiO2 towards the visible range of 397–437 nm. The catalytic activity was investigated by photodegradation of cinnamic acid (CA) solution, which have been shown higher activity than that of the pure TiO2 catalyst. The optimum conditions in this study for the degradation of CA were determined as follows: the ratio rGO/TiO2 of 1:25, catalyst concentration of 0.75 g·L−1, oxygen supply of 0.5 L·min−1, initial pH solution of 3.8 and reaction temperature of 25°C. In this condition, cinnamic acid conversion in the solution reached approximately 90% after 60 minute reaction.
  • Effects of Tempered Microstructure and Hydrogen Concentration on Hydrogen-Induced Embrittlement Susceptibility of 10B21 Screws at Low Temperature

    pp. 1124-1129

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    DOI:10.2320/matertrans.M2017342

    Secondary ion mass spectroscopy (SIMS) was used to examine the hydrogen atoms in low-carbon boron (10B21) steel screws. The effects of baking and tempering treatments on the hydrogen-induced embrittlement (HIE) susceptibility of the screws were investigated. SIMS results confirmed that hydrogen concentration decreased with increasing baking duration, and thus increased the engineering reliability of the screws. For low-temperature applications, 10B21 screws must be baked for a longer duration to prevent HIE. The observed tempered martensite was composed of ferrite and cementite, which could limit the movement of hydrogen atoms. At higher tempering temperature, the structure of the screw matrix became finer, reducing the HIE susceptibility. 10B21 screws tempered at a high temperature thus had good ability to resist low-temperature HIE.
  • Mechanical Properties and Fatigue Behavior of Cast/Forged Al–1.2%Mg–1.0%Si–1.0%Cu Aluminum Alloys

    pp. 1130-1134

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    DOI:10.2320/matertrans.M2018054

    Alloy samples were prepared from Y-block castings. After homogenization treatment, the block samples were held at 195 K, forged using a set of open dies, and then subjected to T6 heat treatment. The tensile specimens were tested to obtain UTS of 420 MPa and an elongation of 12%. After high-cycle fatigue testing, the bare sample exhibited fatigue strength of 117 MPa at 1 × 107 life cycles; and the anodized samples yielded fatigue strength of 110 MPa. The fracture morphologies were observed using SEM and they were used to compute the stress intensity factor for crack initiation (ΔKinit). It was 1.97 MPa√m (at 7.2 × 106 life cycles) for a bare sample fractured at 120 MPa stress amplitude.
  • Determination Approach of Dislocation Density and Crystallite Size Using a Convolutional Multiple Whole Profile Software

    pp. 1135-1141

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    DOI:10.2320/matertrans.M2017380

    Neutron diffraction profile analysis using the whole profile fitting method is useful for obtaining microscopic information on metallic materials. To determine an appropriate fitting approach for obtaining reasonable and non-arbitrary results, we applied diffraction line profile analyses using the Convolutional Multiple Whole Profile (CMWP) method to diffraction patterns obtained using the Engineering Materials Diffractometer (TAKUMI, BL19) at the Materials and Life Science Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). The tensile specimens of 780 MPa grade bainitic steel were uniaxially stretched until the plastic strain reached a value of 0.05. We performed CMWP analyses on the obtained diffraction patterns during tensile test with various initial parameters of dislocation density and crystallite size. These parameters were optimized in the fitting procedures to minimize the weighted sums of squared residuals (WSSRs). Following this approach, we found that unsuitable initial parameter values resulted in unreasonable convergence. Therefore, initial fitting parameters should be chosen to ensure that the initial profiles are as broad as possible. Reasonable results were obtained following this suggestive approach even when the strain anisotropy parameter is set to arbitrary values.
  • Effect of Rotary Forging on Microstructure and Mechanical Properties of Mg–3Al–1Zn Magnesium Alloy

    pp. 1142-1146

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    DOI:10.2320/matertrans.M2018077

    Mg–3Al–1Zn alloy extruding rods were subjected to rotary forging at temperatures ranging from room temperature to 723 K. The effect of rotary forging on formability, microstructures, and hardness of the samples was investigated. Compared to common forging, rotary forging appeared to significantly promote formability at elevated temperatures, especially at 673 K and 723 K. Dynamic crystallization occurred in both samples prepared at these two temperatures, whereas newly generated grains in the 673 K were much finer. A special tilted basal texture was discovered in both samples, exhibiting strong anistropy, and the hardness in the cross section increased from the center to the edge of the samples.
  • Texture and Mechanical Properties of Al–Mg Alloy with Unimodal and Bimodal Grain-Structures Formed by Accumulative Roll Bonding and Annealing

    pp. 1147-1155

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    DOI:10.2320/matertrans.L-M2018820

    The structural and mechanical properties of a commercial A5052 aluminum–magnesium alloy processed by accumulative roll bonding (ARB) and subsequent annealing were investigated. Unimodal and bimodal grain-structures were formed in the ARB-processed specimens by annealing at 250°C and 300°C, respectively. In the specimen ARB-processed and annealed at 300°C, {001} 〈100〉 cube orientation became the main texture component which corresponded to coarse recrystallized grains in the bimodal grain-structures. The preferential formation of the cube texture could be explained by existing theories regarding stored energy and grain boundary mobility. High strength and high ductility was both managed in the specimens with bimodal grain-structures as well as those with unimodal grain-structures. In order to achieve both high strength and high ductility in bimodal grain-structures, the area fraction of coarse grains to fine grains played a critical role. It was also suggested in this study that bimodal structures were not only the structure to provide the coexistence of high strength and high ductility.
  • Characterization of All Solid State Batteries with LiPON Thin Films Obtained with Different Substrates and RF Sputtering Times

    pp. 1156-1160

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    DOI:10.2320/matertrans.M2017419

    All-solid-state lithium batteries consisting of LiPON thin films were prepared by radio-frequency (RF) magnetron sputtering, and the influences of substrates and RF sputtering times have been investigated. For the preparation with different substrates, the Cu, Mo, Al and FTO (SnO2: F) were chosen to grow LiPON films, respectively. The results indicate that the small particles of FTO-sub film can aggregate together and form the particles clusters, which contribute to a fairly rough surface and high discharge capacity of the lithium cell during the cycle test. For the preparation with different sputtering times, the 0.5, 1.0, 1.5 and 2.0 hours are taken to evaluate the characteristics and electrochemical properties of the films, respectively. The results show that long sputtering time (1.5 and 2.0 h) could prevent the formation of polycrystalline phases, which may increase the capacity of all-solid-state Li+ battery.
  • Analysis of Microstructure and Its Effect on Yield Strength of Pure Alpha-Titanium Consolidated by Equal Channel Angular Pressing

    pp. 1161-1165

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    DOI:10.2320/matertrans.M2018033

    The recycling value of chips of pure alpha-Ti was demonstrated with eco-friendly equal channel angular pressing (ECAP) to replace energy intensive melting and casting. Electron backscatter diffraction (EBSD) was used to reveal the microstructure formed after single- or multi-pass ECAP, characterized by a heterogeneous structure containing high- and low-angle grain boundaries (HAGBs, with misorientation ≥15°, and LAGBs, <15°). Grain formation was analyzed by considering the shear strain due to tooling features of ECAP die, and thermal effect because of elevated temperature. The strength was properly predicted by the Bailey-Hirsch relation, consistent with the analysis of the contributions from alpha-matrix, HAGBs, and LAGBs, respectively. The paper makes clearly the underlying physical metallurgy principles to achieve high yield strength in pure alpha-Ti.
  • Formation of Corrosion-Resistant Films on Al–Zn–Mg Alloy by Steam Coating Using Acidic Zn(NO3)2 Aqueous Solutions

    pp. 1166-1172

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    DOI:10.2320/matertrans.L-M2018819

    Corrosion-resistant films were fabricated on Al–Zn–Mg alloy by steam coating using an acidic aqueous solution of Zn(NO3)2 at different concentrations. X-ray diffraction patterns and Fourier transform-infrared spectrometer spectra demonstrated that nitrate-type Zn–Al layered double hydroxide (LDH) and ZnO films were formed on the Al–Zn–Mg surface by steam coating at temperatures of 373, 433, and 473 K, using Zn(NO3)2 aqueous solution at 1000 mM. At 513 K, γ-AlO(OH) films were formed on the Al–Zn–Mg surface by steam coating using 1 to 100 mM Zn(NO3)2 aqueous solution. The corrosion resistance of the films was investigated by potentiodynamic polarization curve measurements, which revealed that the γ-AlO(OH) films prepared by steam coating at 513 K using 1 mM of Zn(NO3)2 aqueous solution was the most effective treatment for suppression of pitting corrosion and anodic current density. This Paper was Originally Published in Japanese in J. JILM 68 (2018) 194–200.
  • Effects of Solution Treatment on Corrosion Properties of Mg–6 mass%Al–1 mass%Zn–2 mass%Ca (AZX612) and Mg–6 mass%Al–1 mass%Zn (AZ61) Alloys

    pp. 1173-1179

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    DOI:10.2320/matertrans.M2018085

    The effects of solution treatment on the corrosion properties of Mg–6 mass%Al–1 mass%Zn–2 mass%Ca (AZX612) alloy were investigated, and the results were compared with those for Mg–6 mass%Al–1 mass%Zn (AZ61) alloy. Solution treatment at 693 K for 48 h significantly reduced the corrosion rates of both AZX612 and AZ61 alloys in 5 mass% NaCl solution. After solution treatment, not only intermetallic phases but also the Al-rich α phase around intermetallic phases reduced or dissolved in both alloys. The microstructural evolution induced by solution treatment may inhibit galvanic corrosion and pit-like corrosion, leading to improvement in the corrosion resistance of AZX612 and AZ61 alloys.
  • Reduction of Nickel and Iron from Low-Grade Nickel Laterite Ore via a Solid-State Deoxidization Method Using Methane

    pp. 1180-1185

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    DOI:10.2320/matertrans.M2017351

    This work focuses on the solid-state deoxidization of low-grade nickel laterite ore under various conditions using methane. The effects of the reduction temperature, reduction time, and methane concentration on the metallization rates of nickel and iron were investigated. The nickel metallization rate increased as the temperature increased to 600°C; it then decreased as the temperature was further increased. The iron metallization rate increased gradually as the temperature increased. The nickel metallization rate sharply increased to over 90% when the CH4 concentration was increased to 20 vol%. The reduction time, which ranged from 30–90 min, had a negligible effect on the reduction of nickel and iron. In the case of the reduced product, the nickel and iron metallization rates were 91.17% and 23.67%, respectively. The optimal conditions were determined to be a reduction temperature of 700°C, a reaction time of 60 min, and a CH4 concentration of 20 vol%. The nickel oxide was almost completely reduced to metallic nickel, and the majority of the iron was reduced to low-valence iron oxide. During the reduction process, a magnesium olivine phase (Mg2SiO4) was produced by the recrystallization of amorphous silicate in the reduction process, and hindered the reduction of nickel and iron.
  • Influence Factors for the Determination of Vermicular Graphite Ratio in Cast Iron Measured by Ultrasonic Method

    pp. 1186-1191

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    DOI:10.2320/matertrans.M2018083

    The ultrasonic method was used to detect vermicular graphite ratio according to the relationship between them. However, there is little report how the factors affect the vermicular graphite ratio detection and ultrasonic velocity measurement. In this paper, using ECHOMETER1076 ultrasonic tester, stylus surface roughness tester and quantitative metallography, the influences of sample two-plane parallelism, probe incident angle, coupling agent type, surface roughness and matrix on the ultrasonic velocity were further studied by experiments and simulation. The parallelism and probe incident angle were found to have important influence on the ultrasonic velocity, increasing more than 4.58 m/s every 0.1°. Contrarily, the influence of coupling agent, surface roughness less than 5 and pearlite percentage were little, and even neglected. So, the parallelism and probe incident angle must be kept as small as possible and the surface roughness is not more than 5. This provide a basis for accurately measuring the ultrasonic velocity and predicting the vermiculate graphite ratio.
  • Joining of Metals by Super-Spread Wetting on Surface Fine Crevice Structure Created by Reduction-Sintering Copper Oxide Powder

    pp. 1192-1197

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    DOI:10.2320/matertrans.M2018073

    A surface fine crevice structure, created by laser irradiation, results in a region-selective super-spread wetting and the joining of metals is possible by taking advantage of this wetting. Through reduction-sintering of copper oxide (CuO) powder, we are able to obtain a sintered-Cu layer that possesses a complex sponge-like structure in which a porous network is formed. The wettability of molten tin (Sn) on the obtained sintered-Cu layer is investigated to confirm whether the super-spread wetting occurs on the surface fine crevice structure created by the method of reduction-sintering CuO powder. In addition, a joining experiment is accomplished using two Cu substrates. Therefore, a successful super-spread wetting of Sn on the surface fine crevice structure and the joining of Cu substrates are demonstrated.
  • Formation of Multiscale Protrusions on Commercially Pure Titanium and Stainless Steel by Two-Stage Sputter Etching Using Different Cathode Disks

    pp. 1198-1205

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    DOI:10.2320/matertrans.M2018025

    Argon ion sputter etching was applied to two types of commercially pure titanium (JIS: TP340 and 550) and a martensitic stainless steel (JIS: SUS420J2) specimens placed on a SUS304 stainless steel cathode disk, and a second sputter etching stage was carried out by placing these specimens on a tungsten or tantalum cathode disk. The first sputter etching formed cone-shaped protrusions with base diameters of about 3 µm on the titanium specimens and 20–30 µm on the SUS420J2 specimen, and the second sputter etching yielded fine ridge-shaped protrusions less than 1 µm thick on the cone-shaped protrusions. In addition, nanometer-scale fine stick-shaped protrusions were formed along the tops of the ridge-shaped protrusions. Thus, surfaces with multiscale protrusions were obtained by two-stage sputter etching using different cathode disks. The specimens with ridge-shaped protrusions ensured high absorptance of more than 96% of visible light.
  • Effects of Milling Time and Process Control Agent on the Austenite Stability of Nanocrystalline Fe–10%Mn Alloy Obtained via Spark Plasma Sintering

    pp. 1206-1209

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    DOI:10.2320/matertrans.M2018099

    The effects of milling time and addition of a process control agent (PCA) on the austenite stability of a nanocrystalline Fe–10%Mn alloy were investigated via X-ray analysis and micrograph observation. Fe–10%Mn alloy samples with nanosized crystallites were successfully fabricated by spark plasma sintering. The crystallite size was decreased by approximately 67% with an increase in milling time and the addition of the PCA. As a result, a fully austenite phase was successfully obtained owing to nanosized crystallites in the sintered samples, which enabled an increased stability of the austenite phase.
  • Sterilization by a Pulsed Electric Field with Dendritic Gold Electrodes

    pp. 1210-1213

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    DOI:10.2320/matertrans.M2018102

    The dendritic gold electrodes effectively inactivated Escherichia coli (E. coli) by pulsed electric field (PEF) sterilization. Two phenomena are involved: (1) The dendritic structures induce a dielectrophoretic (DEP) force which drives E. coli toward the vicinity of the dendrites. (2) High-intensity electric fields around the dendrite tips distort the cell walls of E. coli as a result of potential disturbance, which subsequently kill the E. coli. The inactivation rate of E. coli on the dendritic electrodes depended on the pulse frequency more strongly than on an as-sputtered smooth electrode, suggesting that the DEP force is operative during PEF sterilization.
  • Erratum

    pp. 1214-1214

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    DOI:10.2320/matertrans.ERM201802

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