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

MATERIALS TRANSACTIONS Vol. 54 (2013), No. 9

  • PREFACE

    pp. 1539-1539

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    DOI:10.2320/matertrans.MPR2013906

  • Application of High-Pressure Torsion to WC–Co Ceramic-Based Composites for Improvement of Consolidation, Microstructure and Hardness

    pp. 1540-1548

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    DOI:10.2320/matertrans.MH201318

    This study shows that ultrafine-grained composites of WC–11 mass% Co are successfully consolidated by high-pressure torsion (HPT) followed by sintering at lower sintering temperatures or shorter sintering time than hot isostatic pressing (HIP) and compression and sintering. For the samples processed by HPT and successive sintering, the grain size (∼700 nm) is smaller and the hardness (∼1700 Hv) is higher when compared to those consolidated by compression and sintering and HIP. A heterogeneous microstructure consisting of nanograins of Co and WC and coarse grains of WC ceramics with high dislocation density, 2 × 1016 m−2, is formed during HPT, but the average grain size is slightly increased by subsequent sintering. A W3Co3C carbide forms by sintering, while its fraction increases with increasing the shear strain or with increasing the sintering temperature.
  • Obtaining Copper with Harmonic Structure for the Optimal Balance of Structure-Performance Relationship

    pp. 1549-1553

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    DOI:10.2320/matertrans.MH201320

    Materials having bimodal grain structures are known for the good balance of strength and ductility. However, methods for their fabrication often lack the control of such structure characteristics. In this work, the principles of “harmonic” structure fabrication allowing to control both topology and scale of the bimodal structure heterogeneity have been concisely formulated. The feasibility to form the “harmonic structure” in pure copper has been demonstrated, and the advantages of tensile performance of the material with such a structure is analyzed.
  • Grain Refinement of As-Cast Pure Al by Cold-Rolled Al–Ti Alloy Refiner

    pp. 1554-1561

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    DOI:10.2320/matertrans.MH201322

    Addition of Al–Ti alloy refiners into an Al melt induces grain refinement of α-Al grains in as-cast pure Al. In this study, the effects of cold rolling for the Al–Ti alloy refiners on the grain refinement of as-cast pure Al were investigated. The Al3Ti particles in the refiners, which act as nuclei for the α-Al grains, were fragmented by cold rolling. Grain size of the α-Al grains is decreased as increasing the reduction ratio of the refiners. This decrease in grain size is due to the increase in the number of Al3Ti particles in the refiners. The mechanical properties of the as-cast pure Al are also improved as a result of its grain refinement. In particular, the wear properties of the as-cast pure Al were drastically improved. It is concluded that the cold rolling for the refiners is an effective process to enhance its grain refinement ability.
  • Bulky Averaged Microscopic Information for ECAP-Processed Cu Using Accelerator-Based Gamma-Ray-Induced Positron Annihilation Spectroscopy and Neutron Diffraction

    pp. 1562-1569

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    DOI:10.2320/matertrans.MH201310

    Bulky averaged microstructural parameters such as vacancy density, texture and intergranular stress for 99.99% Cu subjected to equal-channel angular pressing (ECAP) were investigated using accelerator-based gamma-ray-induced positron annihilation spectroscopy (AIPAS) and neutron diffraction. The Doppler-broadening parameter S for the AIPAS positron annihilation peaks increased after the first ECAP cycle and then decreased slightly with additional ECAP cycles. When the samples were annealed, the S value for the sample subjected to eight ECAP cycles was found to decrease at a lower temperature than that for the sample subjected to one ECAP cycle. The texture and intergranular stresses generated by ECAP were determined by neutron diffraction analyses. Changes in full width at half maximum and intensity of the (111) and (200) neutron diffraction peaks monitored in situ during annealing indicated the early onset of recrystallization in the sample subjected to eight ECAP cycles. These bulky averaged data show good agreement with both local scanning electron microscopy/electron backscatter diffraction observations and the results of mechanical tests.
  • Microstructures of Pearlite and Martensite Transformed from Ultrafine-Grained Austenite Fabricated through Cyclic Heat Treatment in Medium Carbon Steels

    pp. 1570-1574

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    DOI:10.2320/matertrans.MH201312

    This study investigated the microstructures of pearlite and martensite transformed from ultrafine-grained austenite in 0.45C steel and V-added 0.45C steel. The mean prior austenite grain sizes were refined to be 4.5 µm in the 0.45C specimen and 2.4 µm in the V-added 0.45C specimen through cyclic heat treatment of austenitizing and water quenching, i.e., repetition of martensite ↔ austenite transformations. The austenite with various grain sizes was either air-cooled or water-quenched to cause pearlitic or martensitic transformation, respectively. The fragmented lamellar structure and isolated cementite particles having particulate morphology were observed in the pearlite transformed from the ultrafine-grained austenite. Results indicated that the ferrite and cementite formed during eutectoid transformation from the ultrafine-grained austenite were not necessary to grow cooperatively maintaining lamellar shape. The packet size in lath martensite was refined significantly accompanied by decreasing of the austenite grain size, since several different variants of martensite were formed from different segments of austenite grain boundaries even when the austenite grain size was fine. In contrast, the block size did not depend on the austenite grain size.
  • Molecular Dynamics Study on Amorphization of TiNi by Severe Plastic Deformation

    pp. 1575-1579

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    DOI:10.2320/matertrans.MH201311

    Amorphous/nanocrystalline formation process of TiNi alloys induced by severe plastic deformation was studied by using molecular dynamics simulations. During the simulations of the extrusion process of TiNi specimens, we have observed nanocrystalline formation as well as amorphous formation. The relation between the area reduction by extrusion and the volume fraction of the amorphous phases has been calculated and agrees with the experimental observations. We have also observed the formation of arrays of edge dislocations or partial wedge disclinations prior to nanocrystalline formation.
  • Influence of Competition between Intragranular Dislocation Nucleation and Intergranular Slip Transfer on Mechanical Properties of Ultrafine-Grained Metals

    pp. 1580-1586

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    DOI:10.2320/matertrans.MH201313

    Huge-scale atomistic simulations of shear deformation tests to the aluminum polycrystalline thin film containing the Frank–Read source are performed to elucidate the relationship between the inter- and intragranular plastic deformation processes and the mechanical properties of ultrafine-grained metals. Two-types of polycrystalline models, which consist of several grain boundaries reproducing easy and hard slip transfer, respectively, are prepared to investigate the effect of grain boundary on flow stress. While the first plastic deformation occurs by the dislocation bow-out motion within the grain region for both models, the subsequent plastic deformation is strongly influenced by the resistance of the slip transfer by dislocation transmission through grain boundaries. The influence of the competition between the intragranular dislocation nucleation and intergranular slip transfer on the material strength is considered. The nanostructured material’s strength depending on local defect structures associated with grain size and dislocation source length is assessed quantitatively.
  • Comparative Analysis of Two Twist-Based SPD Processes: Elliptical Cross-Section Spiral Equal-Channel Extrusion vs. Twist Extrusion

    pp. 1587-1591

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    DOI:10.2320/matertrans.MH201315

    The present paper deals with numerical comparison of two twist-based severe plastic deformation processes: (i) the elliptical cross-section spiral equal-channel extrusion (ECSEE) proposed recently as a novel process and (ii) the classical twist extrusion (TE). ECSEE was developed in attempt to process cylindrical work pieces and to generate more uniform strain distribution compared to classical TE. However, the present finite element simulations showed that twist zones used in both methods impose identical stress and strain states. Furthermore, the ability of ECSEE to treat cylindrical billets is achieved at the expense of the possibility to perform multi-pass extrusion through the twist zone and it requires higher loads for the overall process of extrusion.
  • Atomistic Design of High Strength Crystalline-Amorphous Nanocomposites

    pp. 1592-1596

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    DOI:10.2320/matertrans.MH201316

    There is a long-standing demand for materials which could simultaneously demonstrate multiple promising properties like high strength, good ductility and toughness. In this study, a three-dimensional bulk nanocomposite material which is composed of nanoscale crystalline metal and metallic glass is revealed to present high strength and potentially good ductility by molecular dynamics. A critical high strength is achieved by varying the ratio between crystalline and amorphous phase. The critical strength is revealed to be higher than that expected from the rule of mixture. The mechanism underlying the occurrence of critical strength in the nanocomposite is elucidated by the interaction between dislocation and matrix of amorphous phase. Our concept could guide the engineers to design more advanced bulk nanostructured materials.
  • First-Principles Calculation of Grain Boundary Excess Volume and Free Volume in Nanocrystalline and Ultrafine-Grained Aluminum

    pp. 1597-1604

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    DOI:10.2320/matertrans.L-M2013816

    We applied first-principles calculations to study the relationship between the grain boundary energy (GBE) and grain boundary excess free volume (BFV) at the tilt grain boundaries in aluminum. GBE increased linearly as the grain BFV increased and the value of the proportionality constant between them, α, was 13.8 GPa for aluminum. The grain boundary elastic energies calculated on the basis of first principles using a dummy boundary as well as the classical elasticity theory were close to the grain boundary energies. We examined the free volume in nanocrystalline and ultrafine-grained materials and proposed a method for estimating GBE using the density of nanocrystalline and ultrafine-grained materials with the proportionality constant α. The GBE of nanocrystalline aluminum fabricated by ball milling and subsequent consolidation was estimated to be comparable to or lesser than that in coarse-grained aluminum.
  • Grain Size Variation during Low Temperature Creep and Tensile Deformation of Ultrafine-Grained Copper

    pp. 1605-1611

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    DOI:10.2320/matertrans.MH201304

    Creep and tensile tests at temperatures between 298 and 393 K were conducted on ultrafine-grained (UFG) copper processed by equal channel angular pressing. Steady-state deformation appeared in all the test conditions. Grain size distribution and average grain size were measured by an electron backscatter diffraction technique before and after the mechanical tests. The steady-state deformation behavior and grain size variation were investigated. From these experimental results together with the measurement of the activation energy of deformation, deformation mechanisms of UFG copper are discussed.
  • Cyclic Response of SUS316L Stainless Steel Processed by ECAP

    pp. 1612-1618

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    DOI:10.2320/matertrans.MH201308

    The cyclic response of the SUS316L stainless steel with the nanostructure induced by profuse twinning during equal channel angular pressing (ECAP) at 423 K was investigated with the focus on the shape of the hysteresis loops and their evolution with cycling. The SUS316L steel with the nanostructured twins showed a very high stress amplitude if compared to their conventional counterparts. However, unlike the as-quenched specimens, the ECAPed SUS316L steel revealed considerable cyclic softening at plastic strain amplitudes above 2 × 10−4. Besides, the ECAPed specimens showed characteristic stress asymmetry behavior during fatigue. At the initial stages of the fatigue tests, a tensile peak stress of the hysteresis loop was higher than a compressive one. Then, the tensile peak stresses gradually decreased with increasing cycles and finally became lower than the compressive peak stress under plastic strain amplitudes higher than 2 × 10−4. Since no stress asymmetry was detected for the as-quenched sample, the observed stress asymmetry behavior was attributed to the specific asymmetric response of the directionally sheared microstructure created during ECAP.
  • Mechanical Properties of Harmonic Structured Composite with Pure Titanium and Ti–48 at%Al Alloy by MM/SPS Process

    pp. 1619-1623

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    DOI:10.2320/matertrans.MH201317

    Ti–Al alloy demonstrates high strength in high-temperature environments. Thus, the Ti–Al alloys are expected in an application as high temperature materials. However, the Ti–Al alloys demonstrate low strength and limited ductility at room temperature. Harmonic-structured materials with a network fine grain structure and a dispersed coarse grain structure show high strength and sufficient ductility at room temperature. In addition, a composite of different materials is also effective in improving both strength and ductility. Therefore, the harmonic-structured composite with pure titanium (Ti) and Ti–48 at%Al alloy (Ti–48Al) were fabricated by the combination of the mechanical milling (MM) and the spark plasma sintering (SPS) process. The harmonic-structured composite has a fine grained network Ti–Al alloy and a dispersed coarse grain Ti region. The XRD result reveals that the harmonic-structured composite composes of Ti, TiAl and Ti3Al phases. The harmonic-structured composite demonstrates high strength and sufficient ductility compared with the conventional compact consisting of only Ti–48Al. Advanced ductility of the harmonic-structured composite is attributed to an obstruction of the crack propagation by the dispersed coarse grain region. After heat treatment of the Ti/Ti–48Al harmonic-structured composite, its hardness decreased to much lesser than that of the pure Ti compact.
  • Enhancement of Low Temperature Toughness in Bulk Nanostructured Metals

    pp. 1624-1628

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    DOI:10.2320/matertrans.MH201319

    Brittle-to-ductile transitions (BDT) in fine-grained Ti added ultra-low carbon steels were investigated. Temperature dependences of impact absorbed energy were measured using specimens with grain sizes of 0.4, 2, 9 and 70 µm of which the grain sizes were controlled by heat treatments after five cycles of accumulative roll-bonding process. Although the BDT temperatures were decreased with the decrease in the grain size, the shape of BDT curves in fine-grained steels are different from those of coarse grains. Specimens with coarse grains show abrupt increase in the absorbed energy at the BDT temperature while fine-grained steels exhibit slight jump of absorbed energy at the BDT temperature and then the energy gradually increases with temperature, showing the enhancement of toughness at low temperatures in fine-grained steels. In the present paper, the characteristic BDT in fine-grained steels was discussed in terms of the thermally activated process of dislocation glide.
  • Harmonic Structure Design of a SUS329J1 Two Phase Stainless Steel and Its Mechanical Properties

    pp. 1629-1633

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    DOI:10.2320/matertrans.MH201321

    In the pursuit of creating new structures with improved overall mechanical properties, we produced a duplex stainless steel with both high strength and good plasticity, which combines in a harmonized way a refined microduplex structure with a coarse structure. This is accomplished by applying a mixed process of mechanical milling followed by spark-plasma sintering for a duplex steel powder, leading to a microstructure with a gradual and continuous transition between coarse and ultra-fine-grained regions at the microscale. This type of structure is referred to as Harmonic. The grain refinement at the surface of the milled powder particles occurs through the recrystallization of the severely-deformed surface layers during sintering, and results in a microduplex structure which gradually transitions to a coarse duplex structure away from the particles surface. Both the recrystallization mechanism and the effect of this refined structure on the sinterability and final mechanical properties of the compacts are investigated.
  • Cross-Sectional Distributions of Mechanical Properties of Fine Cu–Sn Alloy Wire Manufactured by Continuous Rotary Draw Bending

    pp. 1634-1641

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    DOI:10.2320/matertrans.MH201323

    The changes in the mechanical properties on the inside and outside of the bend of Cu–0.3 mass% Sn wire specimens deformed by rotary draw bending were clarified, and the correlation between the changes in the misorientation of substructures and in the mechanical properties was systematically investigated. The specimens were each divided into two parts, i.e., the inside and outside of the bend, and their mechanical properties and microstructure evolution were measured by performing tensile tests. From the results, it was found that the ultimate tensile strength and 0.1% proof stress on the inside of the bend decreased markedly and that the total elongation was improved upon rotary draw bending. Although the tensile strength on the inside of the bend decreased, the change in grain size was very small. If rotary draw bending is performed on a wire specimen, it is considered that the dislocations generated by the tensile stress field are relaxed by the reversed stress induced during such bending.
  • Effects of High-Pressure Torsion on the Pitting Corrosion Resistance of Aluminum–Iron Alloys

    pp. 1642-1649

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    DOI:10.2320/matertrans.MH201301

    The effects of reducing the grain size by high-pressure torsion (HPT) on the pitting corrosion resistance of Al–Fe alloys with Fe contents of 0.5, 2 and 5 mass% were investigated by means of polarization curves in solutions containing 0.1 mol·dm−3 Na2SO4 and 8.46 mmol·dm−3 NaCl (300 ppm Cl) at 298 K and by surface analysis. The potentials for pitting corrosion of the Al–Fe alloys were clearly shifted to the noble direction by HPT, leading to an improvement in pitting corrosion resistance. This improvement was larger in the Al–0.5%Fe and Al–2%Fe alloys and smaller in the Al–5%Fe alloy. The Al–Fe alloys contained precipitates of Al–Fe intermetallic compounds, around which pitting corrosion occurred. The Al–5%Fe alloy, in particular, contained large precipitates tens of micrometers in size, and pitting corrosion was significant around these large precipitates. It is evident from the time-dependence of the corrosion potential and the polarization resistance of the corrosion reaction that the formation rate of Al oxide films increases as a result of HPT. It was therefore concluded that the improvement in pitting corrosion resistance of the Al–Fe alloys with HPT is caused by increasing the oxidation rate of Al.
  • Anisotropy of Electrical Resistivity in Cold Rolled Ti Sheet

    pp. 1650-1654

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    DOI:10.2320/matertrans.MH201306

    Observation and evaluation of lattice defects such as vacancy, dislocation and grain boundary are very important for understanding microstructure development during thermo-mechanical treatments. Electrical resistivity measurements are superior to electron microscopies in terms of obtaining average information on micro- and nano-structures including lattice defects. The purpose of this study is to quantify lattice defects and crystallographic features in cold rolled and annealed pure Ti by precise measurements of electrical resistivity. Electrical resistivities at 77 K (liquid nitrogen) and 300 K were measured in a cold rolled Ti sheet at angles of 0, 45, 90° from the rolling direction (RD) by a direct current (DC) four-point method. The resistivity at 90° from RD was slightly higher than that at 0°. A characteristic texture was developed in the sheet; accumulation of (0001) pole was confirmed to appear at an elevation angle of about 40° on the transverse plane. In Matthiessen’s empirical relationship for the cold rolled specimens, strong anisotropy in resistivity could also be confirmed. The gradient α and the intercept β values of the relationship might be employed as parameters to quantify the anisotropy of crystal structures and dislocation structures.
  • Temperature Dependency of Schottky Barrier Parameters of Ti Schottky Contacts to Si-on-Insulator

    pp. 1655-1660

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    DOI:10.2320/matertrans.M2013015

    We have investigated the temperature-dependent current–voltage (IV) characteristics of Ti Schottky structure on the Si-on-insulator (SOI) in the temperature range of 175–375 K by steps of 25 K. As decreasing temperature, the barrier height and ideality factor of Ti/SOI Schottky contact were found to be decreased and increased, respectively, indicating a considerable deviation from the ideal thermionic emission model in its current conduction mechanism. From the linear relationship between the barrier heights and ideality factors, the homogeneous barrier height was calculated to be 0.76 eV. The mean barrier height of 0.87 eV and the modified Richardson constant value of 30.63 A·cm−2·K−2 were obtained using modified Richardson plot. On the basis of a thermionic emission mechanism with a Gaussian distribution of the barrier heights, the temperature-dependent IV behavior of Ti/SOI Schottky contact was explained in terms of barrier height inhomogeneities at the interface between Ti and SOI.
  • The Barkhausen Effects and Nano-System Magnetizations in Fe

    pp. 1661-1666

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    DOI:10.2320/matertrans.MAW201305

    This article was retracted. See the Notification.
  • Full-Potential KKR Calculations for Point Defect Energies in Fe-Based Dilute Alloys, Based on the Generalized-Gradient Approximation

    pp. 1667-1672

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    DOI:10.2320/matertrans.M2013176

    We present systematically ab-initio calculations for defect energies of 3d and 4sp impurities (Sc–Ge) in Fe. The calculations are based on the Generalized-Gradient-Approximation in the density-functional formalism and the full-potential Korringa-Kohn-Rostoker (FPKKR) Green’s function method. First we examine the distance dependence, from the 1st- to the 10th-neighbors, of the impurity-impurity (I–I; I = Sc–Ge) interaction energies (Eint) and show that for most cases, the 1st-neighboring I–I interaction energies (Eint1) are dominant. We found that fundamental features of phase diagrams of Fe-based binary alloys, such as segregation, solid solution and order, known experimentally, may be classified by use of the sign and magnitude of Eint1. Second we discuss the calculated results for the 1st- and 2nd-neighboring interaction energies of 3d and 4sp impurities with perturbed-angular-correlation (PAC)-probe Sn in Fe. The comparison of the calculated results with available experimental results shows that the observed attraction for Sn–Co, Sn–Ni and Sn–Cu may be understood by the 1st-neighboring interaction energies of these impurity pairs, while the obsreved repulsion for Sn–Ga, and Sn–Ge by the 2nd-neighboring interaction energies of these impurity pairs. We also discuss the magnetism of single impurities X (= Sc–Cu) in Fe. The anti-parallel coupling to the bulk magnetization of the neighboring Fe atoms is stable for Sc–Mn, while the parallel coupling for Fe–Cu.
  • Magnetic Properties of MnBi Fine Particles Fabricated Using Hydrogen Plasma Metal Reaction

    pp. 1673-1677

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    DOI:10.2320/matertrans.MAW201306

    Fine particles of MnBi were prepared by the hydrogen plasma metal reaction method and their magnetic properties were investigated. The particle size of the as-prepared MnBi particles was 70–950 nm with a median diameter of 269 nm. Heat treatment and ball milling with a dispersant improved the magnetic properties of the particles. The sample annealed at 330°C for 5 h in Ar then ball-milled for 10 min with a dispersant showed the largest energy product of 105 kJ·m−3 and a saturation magnetization of 71.0 Am2·kg−1. High coercivity of 1380 kA·m−1 was also obtained for the sample that was ball-milled for 2 h.
  • Evaluation of Porosity and Its Variation in Porous Materials Using Microfocus X-ray Computed Tomography Considering the Partial Volume Effect

    pp. 1678-1685

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    DOI:10.2320/matertrans.M-M2013813

    The physical properties of two-phase materials depend on their internal structure. Therefore, segmentation of the structure of such materials is important in material sciences. In this study, we used a maximum likelihood thresholding method that considered the partial volume effect —i.e., the effect of mixels (mixed pixels)— to calculate the porosities of packed glass beads and the Berea sandstone using microfocus X-ray computed tomography (CT) images. We also examined the effects of scanning conditions on the segmentation results and assessed the porosity of possible packing structures of the glass beads to be segmented to be 33–37% based on histogram data. Moreover, we evaluated the porosity of the Berea sandstone to be 18%.
    Then, we examined variation in the porosity of biogrouted packing of glass beads using a microfocus X-ray CT scanner and histogram-based image analysis with the same thresholding method. Our results indicated that the ratio of grouted to ungrouted geomaterial porosities was 0.98, whereas the value estimated by measuring changes in the concentration of calcium ions was 0.98–0.99. Thus, we have confirmed that the proposed method can evaluate small changes in porosity with high accuracy.
  • Synthesis of Novel Pd/γ-AlOOH Composites and Its Electrooxidation toward Methanol in Alkaline Solution

    pp. 1686-1690

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    DOI:10.2320/matertrans.M2013118

    Well-dispersed palladium nanoparticles on the surface of three-quarter-sphere-like γ-AlOOH were prepared by an efficient, low-cost and facile reductive process that utilizes 0.01 mol/L NaBH4 solution. The morphology, structure and elemental composition of this Pd/γ-AlOOH composite were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The results showed that the Pd nanoparticles were homogeneously dispersed and their size distributed from 6 to 8.5 nm. Electrochemical performance of Pd/γ-AlOOH toward methanol in alkaline solution was examined using cyclic voltammetry (CV) and chronoamperometric techniques. The results indicated that this novel Pd/γ-AlOOH composite had excellent electro-catalytic activity and long-term stability.
  • Effects of P Addition on Corrosion Properties of Soft Magnetic FeSiB Alloys

    pp. 1691-1696

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    DOI:10.2320/matertrans.MAW201307

    Electrochemical behavior of Fe76Si9B15−xPx alloy (x = 0, 2, 5, 7, 10) ribbons in borate buffer solution of pH 8.45 had been investigated. The as-spun ribbons had an amorphous structure. The lower current densities of P-added FeSiBP ribbons with native oxide films were observed at low applied potentials. The minimum P concentration for enhancing the corrosion properties was estimated to be 5 to 7 at%. The current densities of the FeSiBP ribbons after removal of the oxide films were suppressed to lower levels in comparison with that of Fe76Si9B15 ribbons. The formation of a phosphate-containing layer helps passivating the ribbons due to the low solubility of iron phosphate compounds.
  • Application of Finite Element Method to Analysis of Ductile Fracture Criteria for Punched Cutting Surfaces

    pp. 1697-1702

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    DOI:10.2320/matertrans.P-M2013811

    Many types of punching processes are utilized in the production of automobile parts and other components. In normal punching with a punch and a die, a sheared surface and a fractured one are usually formed on the cut surface. Here, to produce highly accurate parts, it is important to estimate the ratio of the sheared surface to the cut surface and to economically produce smooth cut surfaces, optimal tools and punching conditions must be selected within the limits of cost constraints. The finite element method (FEM) has been applied to the analysis of the ratio of the sheared surface to the fractured surface on the cut surfaces. For this, the ductile fracture criteria for the fracture initiation of the cut surface have been proposed by several researchers. It is difficult to determine the fracture criteria on the cut surface by tensile tests or bending tests because the punching process consists of many complicated steps. In this study, we apply the FEM to four punching arrangements to evaluate the ductile fracture criteria proposed by Oyane and by Cockcroft and Latham. We find that the morphology of the cut surface is affected by clearance between the punch and the die, by blank holding conditions and by ductile fracture criteria.
  • Effects of Forming Conditions of Roll Offset Method on Sectional Shape at the Corner of Square Steel Pipe

    pp. 1703-1708

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    DOI:10.2320/matertrans.P-M2013815

    Square steel pipes are reshaped from welded round pipes by roll-forming. Effects of the roll diameter on the cross-sectional size of the square steel pipe were investigated by experimentation and three-dimensional finite element simulation. When the top roll diameter is greater than that of the side roll, then the width of a corner part of the formed pipe is greater than the height. The square steel pipe was formed by offsetting the small roll to the upstream side to make the width and height of a corner part equal. The offsetting result is affected by the longitudinal contact distance between a roll and a pipe. The geometric contact length and relative offset, the offsetting distance/geometric contact length, were defined. The optimum value of the relative offset was clarified, which increased with the expansion of the contact length of a top roll, the roll gap and the round pipe wall thickness.
  • Characterizations of Temperature-Dependent Tensile Deformation and Fracture Features of Commercially Pure Titanium

    pp. 1709-1714

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    DOI:10.2320/matertrans.M2013147

    Tensile deformation and fracture behavior of a commercially pure (CP) titanium were investigated at different temperatures through mechanical tests, microstructural observations and fractal analyses. It was found that, with increasing temperature, the number and size of microvoids formed along shear bands (SBs) or at the intersections of SBs on the deformed specimen surface increase, and the fractal dimensions of the scanning profile at the surface near fracture increase correspondingly, and the ones measured perpendicular to the tensile direction is obviously larger than those parallel to the tensile direction, indicating an increased concentration of plastic deformation of CP Ti along the tensile axis. The diameter and depth of dimples on the fracture surfaces of CP Ti increase significantly with increasing temperature, giving rise to a higher fracture surface roughness reflected by a higher fractal dimension. TEM observations demonstrated that the plastic deformation of CP Ti is gradually occupied by dislocation slipping rather than twinning with increasing temperature. This is in good agreement with the fractal analyses of the deformation and fracture features.
  • Electron Microscopy Study of Preferential Variant Selection in CoPt Alloy Ordered under a Magnetic Field

    pp. 1715-1718

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    DOI:10.2320/matertrans.MAW201313

    Transmission electron microscope (TEM) and scanning transmission electron microscope (STEM) observations were carried out to investigate microstructure formation and variant selection process in L10-type ordered CoPt alloy upon a two-step ordering heat-treatment. The first step corresponds to nucleation process carried out under a magnetic field of 10 T and the second step represents growth process without magnetic field. After the first step of ordering, ordered domains of about 5 nm in size were observed and fraction of the preferred variant with the c-axis parallel to applied magnetic field was slightly higher than that of the other two variants. Formation of tweed microstructure along {011}L10 was confirmed at the initial stage of ordering. This structure is considered to be derived from the periodic alignment of interface between two ordered variants with twin relation. At the early stage of the second step of ordering, numerous micro-twins were formed through tweed microstructure and the volume fraction of the preferred variant was increased accompanying with modulation of twins, while that of other two variants was decreased. After the second step of ordering, the twins were vanished and single variant was obtained.
  • Improvement of Fatigue Strength of Ti–6Al–4V Alloy by Hybrid Surface Treatment Composed of Plasma Nitriding and Fine-Particle Bombarding

    pp. 1719-1724

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    DOI:10.2320/matertrans.M2013228

    This study was conducted to improve the fatigue strength of Ti–6Al–4V alloy by hybrid surface treatment composed of plasma nitriding and fine-particle bombarding (FPB). Plasma nitriding to form a hardened layer was performed at relatively low temperature to suppress the growth of the microstructure of the substrate as far as possible. Subsequent FPB eliminated the outermost brittle compound layer leading to a reduction in fatigue strength, and also introduced compressive residual stress at the same time. Hybrid surface treatment formed a hardened layer that can improve wear resistance without marked deterioration of the mechanical properties. Since the formed layer possessed high compressive residual stress and relatively high hardness, initiation of fatigue cracks from the surface was strongly suppressed and the crack initiation site was located in the substrate under the formed layer. As a result, the fatigue strength improved by 47% and the fatigue ratio (fatigue strength/tensile strength) reached a very high level of 91%.
  • Experimental Observations and Numerical Modeling of a Single Coarse Lignite Particle Dried in Superheated Steam

    pp. 1725-1734

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    DOI:10.2320/matertrans.M-M2013817

    The drying characteristics of a single coarse lignite particle in superheated steam are investigated. Spherical particles of Loy Yang lignite 30 mm in diameter were used. The particles were dried with superheated steam at temperatures ranging from 110 to 170°C under atmospheric pressure, and their weights and temperatures were measured with electronic balance, thermocouples and infrared thermograph. Condensation of water droplets on the surface was observed initially, then constant drying rate period (CDRP) and decreasing drying rate period (DDRP) were observed successively. A numerical model of the drying process was developed based on the results, taking into account transfer of free water inside the particle, equilibrium moisture content and shrinkage of the lignite particle itself.
  • Platinum-Enriched Ni/Pt(111) Surfaces Prepared by Molecular Beam Epitaxy: Oxygen Reduction Reaction Activity and Stability

    pp. 1735-1740

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    DOI:10.2320/matertrans.M2013061

    Oxygen reduction reaction (ORR) activities and electrochemical stabilities were evaluated for Ni/Pt(111) model electrode-catalysts fabricated by molecular beam epitaxy (MBE). Exposure of clean Pt(111) to 1.0-Langmuir (i.e., fractional coverage, θ = 1.0 in the Langmuir isotherm) CO at 300 K produced linear-bonded and bridge-bonded CO–Pt IR bands at 2093 and 1858 cm−1. In contrast, 3.0-nm-thick Ni deposition onto Pt(111) at 823 K (823 K-Ni3.0nm/Pt(111)) showed broad IR bands for adsorbed CO at around 2064 cm−1; the separation of reflection high-energy electron diffraction (RHEED) streaks of the 823 K-Ni3.0nm/Pt(111) is greater than for clean Pt(111). In contrast, 923 K-Ni3.0nm/Pt(111) yielded a single sharp IR band because of linear-bonded CO at 2080 cm−1, and the separation of the RHEED streaks is almost the same as that for the Pt(111). The results suggest that a Pt-enriched topmost surface is generated above 923 K through surface segregation of the substrate Pt atoms during the Ni deposition. After transferring the sample from ultra-high vacuum to an electrochemical system, without being exposed to air, changes in ORR activities of the MBE-prepared 923 K-Ni3.0nm/Pt(111) were evaluated in a 0.1-mol L−1 HClO4 aqueous solution under applied potential cycles of between 0.6 and 1.0 V vs. RHE. The ORR activity enhancement factor vs. clean Pt(111) for the as-prepared 923 K-Ni3.0nm/Pt(111) was estimated to be twelve, and this factor was reduced to four after the application of 1000 potential cycles. However, a 943 K-Ni3.0nm/Pt(111) sample, which showed a relatively low ORR activity (an enhancement factor of eight), had the activity enhancement factor of six even after the application of 1000 potential cycles. These results reveal that the sub-surface structures and composition of Pt-based alloys determine not only initial ORR activity but also electrochemical durability of the ORR catalysts.
  • Fabricating Porous Glass with Needle-Shaped Hydrate Crystals by Hydrothermal Treatment of Blast-Furnace Slag and Borosilicate Glass Mixture

    pp. 1741-1749

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    DOI:10.2320/matertrans.M2013119

    Hydrothermal treatment is useful in the recycling of slag and glass discharged from metallurgical or ash melting processes, because it enables valuable porous ceramic materials to be fabricated. Under hydrothermal conditions, raw materials dissolve in a high pressurized water vapor or aqueous solution to form an intermediate hydrate phase containing water. Our previous studies revealed that the hydrothermal reaction of sodium borosilicate glass forms a hydrate glass phase with abundant water, and the glass containing water expands to form a porous glass when annealed, because of water vaporization in the hydrate glass phase. The blast-furnace (BF) slag forms needle-shaped hydrate crystals such as tobermorite (5CaO·6SiO2·5H2O) between the initial slag particles. In this study, we have fabricated functional porous glass with hydrate crystals by the hydrothermal treatment of a mixture of BF slag and sodium borosilicate glass particles. The glass/slag mixture can contain water in the hydrate glass phase after hydrothermal treatment, and porous glass was obtained by annealing the glass/slag containing water. Needle-shaped hydrate crystals were formed by the hydrothermal reaction of borosilicate glass and BF slag components with highly pressurized water, and have been observed in the porous glass microstructure. Furthermore, we have investigated the effect of slag/glass mass ratio and raw material size on water content and the formation of hydrate crystals in the resulting material after hydrothermal treatment.
  • Separation of Mo from Chloride Leach Liquors of Petroleum Refining Catalysts by Ion Exchange

    pp. 1750-1754

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    DOI:10.2320/matertrans.M2013141

    Separation of molybdenum from the synthetic chloride leach liquors of spent hydrodesulphurization catalysts was studied by employing cationic (Diphonix) and anionic resins (AG1-x8). The composition of the solution was Mo 394 ppm, Co 119 ppm and Al 1782 ppm. In the HCl concentration range from 1 to 6 kmol/m3, the loading of Co and Al was negligible. As the concentration of HCl increased, the loading percentage of Mo by AG1-x8 increased, while that by Diphonix decreased. The Mo in the loaded AG1-x8 was successfully eluted by using NaOH solution. In terms of the possibility of producing Mo compound from the eluant, AG1-x8 was found to be better than Diphonix. The loading capacity of AG1-x8 for molybdenum was determined. Column experiments verified that it was possible to separate Mo from Co and Al by ion exchange with AG1-x8.
  • Microstructure of Fe–TiC Composite Surface Layer on Carbon Steel Formed by Laser Alloying Process

    pp. 1755-1759

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    DOI:10.2320/matertrans.MAW201304

    Laser alloying using a carbon steel substrate pre-coated powder mixture of pure titanium and graphite was carried out to form an Fe–TiC composite surface layer for improving wear resistance. The microstructure of the composite layer was studied in detail using OM, SEM, XRD and STEM to reveal the effect of the laser alloying conditions on the distribution of carbides. Coarse particles (1–5 µm) and submicron particles of TiC were observed. TiC particles were distributed in a lath martensite matrix, and the area fraction of TiC was about 8 to 25%. The area fraction and size of TiC depended on the laser scanning speed. Under the condition of a high scanning speed, a composite layer with a high area fraction and a coarser size of TiC was obtained. These composite layers exhibit high hardness and superior wear resistance compared with a laser transformation hardened area of the same substrate.
  • Thermal Stability of BNCT Neutron Production Target Synthesized by In-Situ Lithium Deposition and Ion Implantation

    pp. 1760-1764

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    DOI:10.2320/matertrans.M2013062

    To testify thermal stability of the BNCT neutron target synthesized by in-situ lithium deposition and ion implantation, laser heating test of the Li3N/Li/Cu tri-layered target was conducted in high vacuum chamber of 10−6 Pa and thermal stability of the tri-layered target was characterized by X-ray photoelectron spectroscopy. The following conclusions were derived; (1) The Li3N/Li/Cu tri-layered target with very low oxide and carbon contamination was synthesized by in-situ lithium deposition and ion implantation techniques without H2O and O2 additions. (2) The starting temperature of evaporation of the Li3N/Li/Cu tri-layered target increased by 120 K compared to that of the Li/Cu target and (3) frequent repair synthesis of the damaged Li3N/Li/Cu tri-layered target caused by evaporation is possible.
  • Direct Synthesis of Li3N Thin Layer on Lithium Target Surface for BNCT in N2 Gaseous Conditions

    pp. 1765-1769

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    DOI:10.2320/matertrans.M2013212

    To prevent vaporization damage of BNCT (Boron Neutron Capture Therapy) lithium target during operation, direct synthesis of Li3N thin layer on lithium target surface was demonstrated in 0.1 MPa N2 gas at temperature below 548 K and the following conclusions were derived; (1) Synthesis of Li3N thin layer on lithium surface was confirmed after nitridation at 276–548 K with surface contamination by oxygen and carbon. (2) Rapid nitridation over 1–5 mass%/min was observed above Li melting temperature, whereas slow reaction under 0.02–0.5 mass%/min below melting temperature. (3) During nitridation, removal of oxygen contamination on Li3N thin layer is taken place by nitrogen below Li melting temperature.
  • Alloying Effect of Chromium on the Corrosion Behavior of Low-Alloy Steels

    pp. 1770-1778

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    DOI:10.2320/matertrans.M2013087

    Alloying effect of Cr in the interaction with other elements in low alloy steel for corrosion resistance was designed and prepared. The corrosion behavior of the alloy immersed in mild acid–chloride solution (200 atomic ppm Cl and pH 4) at room temperature in an ambient condition has been studied by electrochemical laboratory tests (potentiodynamic polarization test, potentiostatic test, electrochemical impedance spectroscopy) and surface analyses (SEM, XPS). The results reveal that Cr addition improved the localized corrosion resistance by promoting the formation of beneficial Fe and Cu compounds on the protective films of 0.1 and 0.3 mass% Cr steels. However, the over-alloying circumstance in 0.5 mass% Cr steel caused the negative effect of Cr addition due to metal chloride-induced hydrolysis which accelerated the propagation of the localized corrosion. To summarize, 0.3 mass% Cr addition was determined to be the optimum value for alloying to blank steel.
  • Effect of Pickling Treatment on the Pitting Corrosion of Hyper Duplex Stainless Steel in a Highly Concentrated Chloride Solution

    pp. 1779-1787

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    DOI:10.2320/matertrans.M2013093

    The effect of pickling treatment on the pitting corrosion of hyper duplex stainless steel was investigated in a highly concentrated chloride environment. Increasing the pickling time in 10 vol% HNO3 + 5 vol% HF solutions at 328 K improved the resistance to pitting corrosion by increasing the pitting potential and passive region. There are two primary reasons for the considerable enhancement of the corrosion resistance of the hyper duplex stainless steel pickled for 20 h. First, the oxide scale and Cr-depleted areas which decrease the resistance to pitting corrosion were removed. Second, chromium oxide (Cr2O3), chromium trioxide (CrO3), molybdenum dioxide (MoO2), molybdenum trioxide (MoO3), tungsten dioxide (WO2) and tungsten trioxide (WO3) in an oxide state, chromium hydroxide (Cr(OH)3) and molybdenum oxy-hydroxide (MoO(OH)2) in a hydro–oxide state, chromate (CrO42−) as corrosion inhibitor in an ion state, ammonium (NH4+) elevating the pH in an ion state, and chromium nitride (CrN) acting as a precursor for the formation of Cr2O3 in the nitride state were increased and assisted in improving the corrosion resistance.
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  • Effects of Injection Conditions in the Semi-Solid Injection Process on the Fluidity of JIS AC4CH Aluminum Alloy

    pp. 1788-1794

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    DOI:10.2320/matertrans.F-M2013812

    The semi-solid process is viewed as a promising manufacturing method for producing nearly net-shaped metal products with low porosity and shrinkage. However, the semi-solid slurry is inferior to liquid state in terms of fluidity; thus, the semi-solid process exhibits low formability. Therefore, improving the fluidity of the semi-solid slurry is an important issue. To address the issue, we attempted to improve the fluidity by applying shear stress on the slurry at the gate of the mold. In this study, the effect of shear rate on the fluidity of the semi-solid slurry of the AC4CH aluminum alloy was investigated. The shear rate at the gate was controlled by changing the thickness of the gate to 1.0, 2.2, 3.1 and 4.0 mm. The fluidity was evaluated by injecting through a narrow gate into a spiral cavity in terms of the length that has flowed into the cavity. The microstructures were observed by optical microscopy. The roundness and diameter of the solid particles in the specimens were measured by image analysis. According to the results, the fluidity increased with increasing gate velocity or increasing shear rate at identical injection velocities. However, both the mean roundness and diameter of the solid particles in the specimen decreased with increase in the shear rate obtained by decreasing the gate thickness. Therefore, the slurry composed of fine spherical solid particles could be obtained with a high shear rate. Additionally, both the mean particle roundness and diameter correlated with fluidity. These results suggested that the fluidity of the slurry improved with increase in the gate velocity and the shear rate because the viscosity of slurry decreased. As mentioned previously, the fluidity of semi-solid slurry could be improved by controlling the gate velocity and shear rate. It is expected that this method can enable the production of semi-solid forming products with complex configurations.
  • Creation of Adhesive Force between Laminated Sheets of Aluminum and Polyurethane by Homogeneous Low Energy Electron Beam Irradiation Prior to Hot-Press

    pp. 1795-1799

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    DOI:10.2320/matertrans.MAW201314

    2-layer aluminum/polyurethane (Al/PU) laminated sheets were prepared by a new adhesion method, a double-step treatment consisting of: (1) applying low dose ≦ 0.43 MGy homogeneous low energy electron beam irradiation (HLEBI) to the 2-layer assembly where the HLEBI penetrates through the Al and PU layers, respectively, prior to: (2) hot-press under 5 MPa and 403 K. Although the adhesion of the Al/PU sheets cannot be observed without the new double-step treatment, bonding forces were created as evidenced by the mean adhesive forces of peeling resistance (oFp). Based on the 3-parameter Weibull equation, the lowest oFp value at peeling probability (Pp) of zero (Fs) could be estimated. An increasing trend in Fs occurs by the double-step treatment applying HLEBI up to 0.22 MGy reaching a maximum at 34.0 Nm−1, improving the safety level without radiation damage. When HLEBI cuts the chemical bonds and generates dangling bonds with nonbonding electrons in Al and PU, the created adhesion between the laminated sheets can be explained.
  • Effect of Applied Voltage on the Microstructure and Bioactivity of MAO Film on Ti Substrate

    pp. 1800-1804

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    DOI:10.2320/matertrans.M2013004

    Various MAO films were prepared on Ti–6Al–4V substrate at voltages from 300 to 550 V in an electrolyte containing 0.18 M calcium acetate and 0.1 M sodium dihydrogen phosphate using an AC mode. Microstructures and phases of the MAO films were investigated by SEM with EDS and XRD. Bioactivity was examined using an apatite formation test in a simulated body fluid. The results show that the applied voltage has a significant influence on the microstructure and composition. With the increase in the applied voltage the sizes of micropores increase, and Ca P contents and Ca/P ratio in the MAO film increase too. And the Ca P contents in this work are increased obviously compared to DC MAO mode. The MAO films contain rutile, anatase and amorphous calcium phosphate, and higher voltage is favorable to form rutile phase. The results of the apatite formation test show that the AC MAO films exhibit higher ability to form apatite than DC mode. It is suggested that the AC MAO mode is more effective to incorporate calcium and phosphorous in the oxide layer than DC mode because higher applied voltages can be applied in it, and the AC MAO film present a better performance in the formation of calcium phosphate which may be result from a more effective release of CaP from MAO film into SBF.
  • Low Temperature Thermal Evaporation Process for the Synthesis of ZnO Nanowires

    pp. 1805-1808

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    DOI:10.2320/matertrans.M2013156

    ZnO nanowires were synthesized by thermal evaporation of ZnBr2 powder at relatively low temperatures of 600–700°C under air atmosphere. Any catalysts and substrates were not used in the synthesis of ZnO nanowires. The ZnO nanowires had a typical diameter of 100 nm and lengths up to several tens micrometers. The X-ray diffraction (XRD) pattern indicated that the ZnO had hexagonal wurtzite structure. The scanning electron microscope (SEM) image showed clearly that catalyst particles existed at the tips of nanowires. The energy dispersive X-ray (EDX) analysis revealed that the catalyst particles were composed of Zn and O. Based on the SEM and EDX results, it was suggested that the nanowires were grown via self-catalytic growth mechanism. A strong green emission was observed in the room temperature cathodoluminescence spectrum.
  • Characteristic Sorption of H3BO3/B(OH)4 on Magnesium Oxide

    pp. 1809-1817

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    DOI:10.2320/matertrans.M-M2013814

    The reaction mechanism of H3BO3/B(OH)4 with MgO in aqueous phase was investigated using sorption isotherm, XRD, 11B-NMR and FTIR. Release of Mg2+ was observed soon after contact of MgO with H3BO3 and maximum released Mg2+ was proportional to the initial boron concentration, suggesting ligand-promoted dissolution of MgO by H3BO3. The molecular form of H3BO3 was more reactive with MgO in releasing Mg2+ ions than B(OH)4. 11B-NMR results indicated that trigonal B ([3]B) was predominant over tetrahedral B ([4]B) in solid residues after sorption of H3BO3. The molar ratio of [4]B/[3]B increased with H3BO3 sorption density. XRD patterns for the solid residues were assigned to Mg(OH)2 and peaks broadened with increasing H3BO3 sorption density, except for (hk0) planes due to c-axis lattice strain induced by incorporation of H3BO3 between layers. These results indicated that H3BO3 interfered in the c-axis stacking of in Mg(OH)2. Molecular H3BO3 acted as a trigger when reacting with the MgO surface, releasing Mg2+ to produce an unstable complex leading to the precipitation formation of Mg(OH)2, which is a sink for the immobilization of H3BO3/B(OH)4.
  • Thermoelectric Properties of Perovskite-Type Oxide Ca–Mn–O System in Relation to A-Site Vacancies

    pp. 1818-1822

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    DOI:10.2320/matertrans.M2013121

    The orthorhombic perovskite-type oxide systems, Ca1−xNdxMnO3 and Ca1−xNd2x/3x/3MnO3 (□ indicates A-site vacancy) were synthesized by a standard ceramic technique. Thermoelectric properties such as Seebeck coefficient (S), electrical conductivity (σ) and thermal conductivity (κ) were evaluated as functions of temperature (T) and composition (x). The electrical conductivity increased and the absolute Seebeck coefficient decreased with increased composition, in both the systems. Jonker plots revealed that the insertion of A-site vacancies improved the carrier mobility of Perovskite-type oxides without resulting in a change in their carrier concentration. This insertion induced low thermal conductivity owing to the atomic unbalance of the crystal structure. A-site vacancies are key factors in obtaining higher electrical conductivity and lower thermal conductivity.
  • Differential Scanning Calorimetry of the α/γ Transformation in Fe–Co Alloys under a Magnetic Field

    pp. 1823-1828

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    DOI:10.2320/matertrans.M2013174

    This study investigates how a magnetic field affects the α/γ transformation in Fe–Co alloys, particularly its entropy of transformation. Pure Fe, Fe–9.5 at% Co alloy and Fe–19.2 at% Co alloy were analyzed by differential scanning calorimetry in a magnetic field. Both the latent heat and the α/γ transformation entropy for pure Fe and Fe–Co alloys decreased in a magnetic field. These reductions were more pronounced as the Co concentration increased and as the magnetic field strength increased.
  • Phase Stability of Iron Oxides on Palladium–Iron Alloy at Elevated Temperatures and Its Application to High Temperature Oxidation

    pp. 1829-1837

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    DOI:10.2320/matertrans.M2013122

    Phase stability of iron-oxides as a function of alloy composition in Pd–Fe–O system has been examined by emf measurement with solid electrolyte of CaO-stabilized zirconia at the temperature ranging from 973 to 1123 K. Phase boundary between the alloy and iron-oxide was determined with six alloys in which Fe-composition is ranging from 1 to 64 at%. The boundary composition of wüstite lies in between 34 at% Fe and 54 at% Fe and hematite was expected to be formed at the alloy composition less than 1 at% Fe. Thickness of iron oxide was estimated from the amount of consumed Fe in the alloy, which is given by the difference of initial and final composition at the temperature and oxygen partial pressure. Estimated thickness of iron oxide was in good agreement of that obtained from high temperature oxidation of Pd–Fe alloy. Emf measurement gives useful information to obtain single-phase iron-oxide with the expected thickness on Pd–Fe alloy by high temperature oxidation.
  • Formation of Fine Multicomponent Precipitates and Enhanced Precipitation-Hardening in an Al–Cr–Pr–Zr Alloy

    pp. 1838-1843

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    DOI:10.2320/matertrans.M2013149

    The microstructure of the Al–1.0Cr–1.4Pr–1.6Zr (mass%) alloy after homogenized at 500°C for 400 h has been investigated. Addition of Cr, Pr and Zr in combination into pure aluminum results in the formation of submicron Zr-containing PrCr2Al20 and nanoscale Cr, Pr-containing Al3Zr dispersed phases. Compared with the Al–1.0Cr–1.4Pr and Al–1.6Zr alloys, a denser distribution of new fine multicomponent dispersed phases and their superimposition effect are associated with enhanced precipitation-hardening behavior of Al–1.0Cr–1.4Pr–1.6Zr alloy.
  • Effect of Minor Alloying Substitution on Glass-Forming Ability and Crystallization Behavior of a Ni57Zr22X8Nb8Al5 (X = Ti, Cu) Alloy Synthesized by Mechanical Alloying

    pp. 1844-1850

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    DOI:10.2320/matertrans.M2013184

    Ni57Zr22X8Nb8Al5 (X = Ti, Cu) metallic glass (MG) and nanocomposite powders were synthesized by mechanical alloying. Outstanding differences in glass-forming ability (GFA), thermal property, particle size and crystallization behavior were found for the two synthesized alloy powders with different alloying substitutions. The Ti-containing MG powder exhibits better GFA, higher thermal stability, lower enthalpy of crystallization and smaller particle size compared with the Cu-containing nanocomposite powder, respectively. Meanwhile, the crystallization of the Ti-containing MG powder is governed by typical volume diffusion-controlled three-dimensional growth. The better GFA for the Ti-containing alloy system could be explained by appropriate atomic-size mismatch and large negative heat of mixing among main constituent elements. The higher enthalpy of crystallization for the Cu-containing nanocomposite powder leads to the lower thermal stability and larger particle size of the powder than Ti-containing MG powder.
  • The Effect of Arc Current on the Microstructure and Wear Characteristics of Stellite12 Coatings Deposited by PTA on Duplex Stainless Steel

    pp. 1851-1856

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    DOI:10.2320/matertrans.M2013103

    Plasma transferred arc welding (PTAW) is widely employed to improve the quality of components whose surface is subjected to severe wear conditions. However, the wear properties of these coatings is significantly affected by the welding process adopted during the deposition of the coatings. This paper details an investigation of the microstructure, composition, hardness and wear characteristics of Stellite12 Co-based coatings with different welding currents. Optical microscopy (OP), scanning electron microscopy/energy dispersive spectrum analysis (SEM/EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the microstructure. An increase in the arc current increased the dilution of the DSS and changed the composition as well as the dendritic arms coarsening of the Co-based coatings. Increasing the arc current gives rise to a reduction in the hardness of the coatings, whereas reduction in the hardness of the coatings is accompanied by a reduction in their wear resistance with the exception of the lowest current sample. Additionally, the microstructure of the welding heat affected zone (HAZ) during PTAW was also studied. The heat affected zone was decorated with some needle-type austenites nucleated from grain boundary austenite, but without σ-phase. Moreover, some chromium-rich precipitates were also detected in the welding heat affected zone of the specimens during PTAW.
  • Effects of Vacuum Sintering, HIP and HP Treatments on the Microstructure, Mechanical and Electrical Properties of Cr70Cu30 Alloys

    pp. 1857-1862

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    DOI:10.2320/matertrans.M2013173

    The aim of this paper is to study and produce Cr70Cu30 alloys via vacuum sintering, hot isostatic pressing (HIP) and hot pressing (HP) of powder metallurgy technology. The experimental results show that a lower density of Cr70Cu30 alloys is produced after vacuum sintering, owing to the many pores existing in the sintered Cr70Cu30 alloys, which are not completely removed by HIP treatment. Conversely, the HP treatment of Cr70Cu30 alloys at 1000°C 60 MPa for 1 h achieves the optimal density (97.82%), lower apparent porosity (0.65%) and higher international annealed copper standard (IACS) value (22.78%). Moreover, it also obtains the highest hardness (HRB 68.7) and transverse rupture strength (TRS) value (843 MPa). The results indicate that the closed pores can be effectively eliminated and that the mechanical properties of Cr70Cu30 alloys are obviously improved by HP treatment. Meanwhile, the Cr70Cu30 alloys also have an improved microstructure and electrical conductivity.
  • Exfoliation Corrosion Behavior of Cold-Rolled Mg-14 mass% Li-1 mass% Al Alloy in NaCl Solution

    pp. 1863-1866

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    DOI:10.2320/matertrans.MAW201301

    Cold-rolled Mg–Li system alloys represent the exfoliation corrosion on the surface of the longitudinal and the transverse sections. In this study, the origination of the exfoliation corrosion of the cold-rolled Mg–Li alloy was clarified. In the initial stage of the corrosion, the oxide film formed immediately on the surface of each section, and then the film destruction with a remarkable bubble generation was observed in a certain spot. There were microcracks on the trace of the film destruction along the grain boundary. The corrosion resistance in the annealed specimen was more than that in the as-rolled specimen because the microstructure of the as-rolled specimen has elongated and thinned grains by severe cold rolling. The exfoliation corrosion was not observed in the annealed specimen, because the annealed specimen has homogeneous equiaxial grains. The successive film destruction in annealed specimen progressed along the grain boundary to random direction. Moreover, the initiation time of the bubble generation was delayed in the annealed specimen.

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