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

MATERIALS TRANSACTIONS Vol. 51 (2010), No. 6

  • Void Formation and Structure Change Induced by Heavy Ion Irradiation in GaSb and InSb

    pp. 1059-1063

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    DOI:10.2320/matertrans.M2010037

    Void formation and structure change by heavy ion irradiation were investigated in GaSb and InSb thin films. The voids were formed after irradiation in both materials. The average diameter of the voids was about 15 nm in GaSb and 20 nm in InSb irradiated with 60 keV Sn+ ions to a fluence of 0.25×1018 ions/m2 at room temperature. The void size in InSb is larger than that in GaSb. The large void size is quantitatively explained by the amount of induced vacancies obtained by the SRIM code simulation. The Debye-Scherrer rings were observed in the SAED patterns on both materials. The structure changes into a polycrystal by ion irradiation. Additionally, the 200 superlattice reflections in the [001] net pattern were almost absent, and the streak pattern along the ⟨110⟩ direction was observed in InSb. It is considered that the anti phase domains of different lengths are formed by ion irradiation. Ion irradiation transforms the structure of InSb from chemical ordering to chemical disordering via the formation of anti phase boundaries.
  • Influence of TiO2 Buffer on Structure and Optical Properties of ZnO Film on Si(100) Substrate

    pp. 1064-1066

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    DOI:10.2320/matertrans.M2009433

    ZnO films were prepared on p-Si (100) substrates by direct current (DC) sputtering with and without TiO2 buffer. The crystal structures, surface morphologies and optical properties were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence (PL). XRD results indicated that the growth mode of ZnO film was changed from strong (002) preferential orientation to several crystal orientations by introducing TiO2 buffer, and the residual strain was reduced. SEM manifested that ZnO film with TiO2 buffer had the uniform grain size and flat surface. In addition, stronger ultraviolet emission was observed from ZnO film with TiO2 than that without at room temperature. The low temperature photoluminescence was investigated to understand the different PL mechanism of ZnO films.
  • Evaluation of Dislocation Density in a Mg-Al-Mn-Ca Alloy Determined by X-ray Diffractometry and Transmission Electron Microscopy

    pp. 1067-1071

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    DOI:10.2320/matertrans.M2010021

    Metallic materials suffering deformation store elastic strain. Evaluation of this strain energy is important for understanding the mechanical and physical properties of the materials. Although direct evaluation of the stored energy is difficult, it can be evaluated by determining the defect energy of dislocations induced by the deformation. Thus, a practicable method of evaluating the strain energy is to measure the dislocation density in metallic materials. The average and representative dislocation density can be estimated by X-ray diffraction (XRD) analysis. We have estimated the dislocation density of a magnesium alloy with hexagonal crystals by a modified Warren–Averbach analysis based on a modified Williamson–Hall plot using XRD profiles. The dislocation density value obtained by this method agrees with those reported previously. We found that the modified Warren–Averbach method is still a powerful method for evaluating the dislocation density in hexagonal crystals.
  • Microstructures and Mechanical Properties of Pure V and Mo Processed by High-Pressure Torsion

    pp. 1072-1079

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    DOI:10.2320/matertrans.M2009375

    Two body centered cubic (bcc) metals, V and Mo, were processed by high pressure torsion (HPT) at ambient temperature. Hardness variation as well as microstructural evolution was examined with strain under a pressure of 2 to 6 GPa. It was shown that the hardness increases with straining and saturates to a constant level with the grain size of 330–400 nm in V irrespective of the applied pressures. Although the hardness variation with strain is the same for Mo with the grain size of ∼350 nm at the saturation level when the applied pressure is 6 GPa, the hardness level lowers below the saturation level and the grain size becomes coarser as the pressure is lowered. Tensile tests show that the strength significantly increases with some ductility for V after processing under any pressure and for Mo under lower pressures, but brittle fracture occurs in the Mo specimen processed at 6 GPa. The slower evolution of microstructure as well as the lower hardness levels observed in Mo is due to the applied pressure which is lower than the yield stress and thus due to the insufficient generation of dislocations for grain refinement.
  • Charging Effects on SEM/SIM Contrast of Metal/Insulator System in Various Metallic Coating Conditions

    pp. 1080-1083

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    DOI:10.2320/matertrans.M2010034

    Scanning electron microscope (SEM) and scanning ion microscope (SIM) observations were performed to investigate the charging effect and the related contrast variation for images of conductive and non-conductive specimens under electron and Ga+ ion beam irradiations. The contrast variation in the specimens was investigated by changing the coating conditions. It was found that the contrast in conductive specimens was basically caused by differences in atomic number and that the charging effect in conductive specimens is generally smaller than that in non-conductive specimens. On the other hand, the SEM contrast of non-conductive specimens varied widely, depending on the coating conditions. These contrast variations were found to be caused by negative charges accumulated on the surface of the specimens. The SIM contrast of non-conductive specimens changed to dark when the coating condition was insufficient. The contrast variations were found to be caused by the accumulation of positive charges on the surface of specimens.
  • Relationship between Microstructures and Tensile Properties of an Fe-30Mn-8.5Al-2.0C Alloy

    pp. 1084-1088

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    DOI:10.2320/matertrans.M2010013

    Owing to the presence of a large amount of fine (Fe,Mn)3AlC carbides within austenite (γ) matrix, the tensile property of the Fe-30%Mn-8.5Al%-2.0%C (in mass%) alloy in the as-quenched condition was clearly superior to that of the as-quenched FeMnAlC (C≤1.3%) alloys investigated by previous workers. After being aged at 823 K for 3 h, the present alloy could possess high yield strength up to 1262 MPa with an excellent 32.5% elongation. With almost equivalent ductility, the yield strength obtained was about 16% higher than that of the FeMnAlC (C≤1.3%) alloys after solution heat-treatment or controlled-rolling followed by an optimal aging at 823 K. Additionally, due to the pre-existing fine (Fe,Mn)3AlC carbides within the γ matrix in the as-quenched alloy, the aging time required for attaining the optimal combination of strength and ductility was much less than that of the FeMnAlC (C≤1.3%) alloys aged at 823 K. When the present alloy was aged at 823 K for a time period longer than 4 h, both the strength and ductility were drastically dropped due to the occurrence of γo⁄κ (γo: carbon-deficient austenite) lamellar structure on the γ⁄γ grain boundaries.
  • Analysis of 3D Random Al18B4O33 Whisker Reinforced Mg Composite Using FEM and Random Sequential Adsorption

    pp. 1089-1093

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    DOI:10.2320/matertrans.M2009208

    In order to understand the deformation behavior of randomly orientated ceramic whisker reinforced composite materials, three dimensional (3D) finite element models were developed. The actual distributions of the whiskers in the composite materials were reconstructed for the representative volume element of the composite, using a random sequential adsorption algorithm. The samples were random Al18B4O33 whisker reinforced magnesium matrix composites with a volume fraction of 15%. After modeling, the role of the random ceramic whisker in the deformation behavior of the magnesium matrix composite was investigated by the finite element method (FEM). The elastic modulus and stress-strain behaviors of the composite predicted by the microstructure-based model correlated well with the experimental results.
  • Dissolution Behavior of Solid 5CaO·SiO2·P2O5 in CaO-SiO2-FeOx Slag

    pp. 1094-1101

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    DOI:10.2320/matertrans.M-M2010810

    In order to clarify the dissolution behavior of solid P2O5 rich phase in slag, the solid phosphate compound silicocarnotite 5CaO·SiO2·P2O5 being the representative of P2O5 rich phase was dipped into the molten CaO-SiO2-FeOx slag at 1573 and 1673 K. Since the initial slag was free of P2O5, the increase of P2O5 content in the slag is the indication of the dissolution behavior of solid 5CaO·SiO2·P2O5. Therefore, the concentration profile of P2O5 across the interface between solid 5CaO·SiO2·P2O5 and slag was analyzed to evaluate the dissolution behavior.
    The results show that the dissolution of solid 5CaO·SiO2·P2O5 into slag can be divided into the following stages: interaction of solid phase with slag, disintegration of solid phase, reaction between disintegrated solid phase and surrounding slag, and diffusion of CaO and P2O5 from solid sample to slag. The diffusivity of P2O5 in the liquid slag was calculated. It was found that higher temperature is favored for the diffusion in some cases, whereas larger CaO/SiO2 ratio of the slag restrains the diffusion.
  • Production of Metallic Vanadium by Preform Reduction Process

    pp. 1102-1108

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    DOI:10.2320/matertrans.M2010027

    A fundamental study was conducted on a new process for producing vanadium (V) metal by the preform reduction process (PRP) based on metallothermic reduction of vanadium pentoxide (V2O5). Feed preforms with good mechanical strength even at elevated temperatures were prepared by adding either CaO or MgO to V2O5 feed powder because V2O5 has a low melting point of 963 K; thus complex oxides (CaxVyOz, MgxVyOz) with high melting point at more than 1273 K were obtained. Reduction experiments were conducted by using either Ca or Mg vapor at 1273 K for 6 h. V metal with a purity of more than 99% was successfully obtained when using Mg as a reductant. The feasibility of producing V metal by the PRP will be discussed on the basis of fundamental experiments.
  • Effect of Anodizing Potential on the Surface Morphology and Corrosion Property of AZ31 Magnesium Alloy

    pp. 1109-1113

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    DOI:10.2320/matertrans.M2009380

    Anodizing is a functional method for coating magnesium alloys and improves its corrosion resistance. The anodizing process was performed on AZ31 magnesium alloy in 1 M NaOH alkaline solution at various applied potentials. The surface morphology and phase structure of the anodic film were analyzed using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion property of the anodic film was characterized using potentiodynamic polarization measurement, electrochemical impedance spectroscopy (EIS) and salt spray test. The anodic film is composed of two phases, magnesium hydroxides and magnesium oxides. At low anodizing potential, the main constituent of the anodic film is magnesium hydroxide. By increasing the anodizing potential, magnesium oxide grows to be the main constituent of the film. The results show that the anticorrosion property was enhanced by anodizing and the film formed at 100 V has the best corrosion resistance.
  • Electromagnetic Nondestructive Evaluation of Graphite Structures in Flake Graphite Cast Iron

    pp. 1114-1119

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    DOI:10.2320/matertrans.F-M2010809

    This paper discusses the feasibility of characterizing the shape and size of graphite in flake graphite cast iron based on electromagnetic nondestructive methods. Several flake graphite cast iron specimens containing graphite of various shapes and sizes were prepared and their electromagnetic properties such as conductivity and relative permeability were evaluated systematically. Both the conductivity and the relative permeability were found to mainly depend on the shape and size of graphite. The conductivity was specifically found to have a good correlation with the shape and size of graphite and this was independent of the pearlite area fraction of matrix. The conductivity also correlates well to the ultrasonic velocity which indicates the amount and size of the graphite. The DC potential drop method was used to evaluate the structure of graphite and its capability was evaluated.
  • Synthesis of Graphite Reinforced Aluminum Nanocomposite by Mechanical Alloying

    pp. 1120-1126

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    DOI:10.2320/matertrans.M2009398

    Aluminum nanocomposite was obtained through mechanical alloying process using elemental powders of aluminum, copper and magnesium of high purity with the aim to obtain the 2024 aluminum alloy composition. Elemental powders and reinforcement particles were milled in a simoloyer mill for different times from 1 to 5 h. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) results indicated that even for milling time of 5 h some elemental copper remained in the microstructure and has not been incorporated completely in solid solution into the aluminum lattice. Furthermore, it was not observed formation of any second phase, however when the specimens were subjected to Differential Thermal Analysis (DTA), it was observed in the microstructure the presence of Al2Cu, Al4C3 and some oxide of the type CuO and CuO2. It was also demonstrated that average crystallite size of milled powders was refined to nanometric level while microhardness values were arising continuously with the milling time and were a maximum in the 2 mass% graphite specimen.
  • Thermoelectric Properties of Si2Ti-Type Al-Mn-Si Alloys

    pp. 1127-1135

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    DOI:10.2320/matertrans.M2010022

    By using the first principle band calculations, we identified that Si2Ti-type Al-Mn-Si C54-phase possesses an electronic structure suitable for the thermoelectric materials. The formation range of the Al-Mn-Si C54-phase was determined by preparing samples at a number of different compositions, and the samples solely consisting of the C54-phase were successfully obtained around Al:Mn:Si=1:1:1. The carrier concentration of the Al-Mn-Si C54-phase was controlled by the partial substitution of the constituent elements, and behaviors in electrical properties characteristic to n-type and p-type thermoelectric materials were alternatively observed for the samples of a larger electron concentration and a smaller electron concentration, respectively. The absolute value of the Seebeck coefficient |S| was found to exceed 300 μV/K for both n-type and p-type samples.
  • Pyrometallurgical Recovery of Indium from Dental Metal Recycling Sludge by Chlorination Treatment with Ammonium Chloride

    pp. 1136-1140

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    DOI:10.2320/matertrans.M2010020

    In the present paper we address the novel chlorination process for recovery of indium selectively from dental metal recycling sludge which contains considerably high amount of indium. The process is based on the utilization of ammonium chloride, NH4Cl, as chlorination reagent. It was found that indium could be successfully recovered from the sludge in the form of volatile indium chloride by heating the mixture of sludge and NH4Cl at the temperature of 400°C under inert atmosphere. The influence of process parameters, such as composition of NH4Cl, was investigated in order to achieve high process efficiency.
  • Controlling the Percolation Threshold of Conductor-Insulator Composites by Changing the Granular Size of Insulators

    pp. 1141-1144

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    DOI:10.2320/matertrans.M2010019

    When one attempts to modulate and control the characteristics of composite materials, limit of the modulation may be dictated by the mathematical threshold of the percolation transition. We report our computer simulation, in which percolation behavior can strongly be controlled by introducing size differences in the insulator particles rather than the conductor particles. This modulation effectively lowers the transition point to 0.52, from about 0.59 achieved with the conventional 2D site percolation model. Although a similar effect has already been reported for off-lattice systems and experiments, this is the first observation and analysis made in a basic 2D lattice model. Also, we show that this effect of threshold reduction is also related to the shape difference of the insulator particles. Such an observation in a basic model is believed to be fundamental to exploiting this phenomenon in real applications.
  • Electromagnetic Shielding by Composite Films Prepared with Carbon Fiber, Ni Nanoparticles, and Multi-Walled Carbon Nanotubes in Polyurethane

    pp. 1145-1149

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    DOI:10.2320/matertrans.M2009408

    Employing polymer blending method, conductive materials are mixed with waterborne polyurethane (WPU) to prepare conductive composite film, and applies it to electromagnetic shielding. Conductive materials, such as carbon fiber, nickel (Ni) nanoparticles and multiwalled carbon nanotubes are added to WPU substrate by a polymer blending method. After that, conductive composite film is prepared by means of coating. Since a conductive network is formed by the conductive material in this film, it has electromagnetic shielding effectiveness. The study applies ASTM 4935-99 standards to measure the far-field plane electromagnetic shielding effectiveness of the prepared conductive composite film within the inspection frequency range 50 MHz∼1.5 GHz. According to the experimental results, when the inspection frequency of the conductive composite film prepared by carbon fiber/Ni nanoparticles is 1000 MHz, its shielding effectiveness can reach 28 dB. Furthermore, when the composite film prepared by carbon fiber/carbon nanotube is 0.15 mm thick, its electromagnetic shielding effectiveness reaches 33.7 dB, and its shielding effect is 99.9%.
  • Spectral and Angular Responses of Surface Plasmon Resonance Based on the Kretschmann Prism Configuration

    pp. 1150-1155

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    DOI:10.2320/matertrans.M2010003

    The present study investigates the optical characteristics and the spectral and angular responses of a Kretschmann surface plasmon resonance (SPR) sensor configuration that is widely used in biological and chemical sensing applications. In order to examine the influence of wave interference and optical properties of thin films on angular variation of reflectance at different incident angles, the Kretschmann SPR configurations made of gold films with 30, 52, and 70 nm thicknesses were fabricated and the reflectance was detected using a 633 nm He-Ne laser, θ-2θ rotation stages, and a silicon pin photo-detector. In particular, this study involved the numerical analysis of angular and spectral variation of reflectance estimated using the characteristic transmission matrix (CTM) method. It was found that the SPR sensitivity became highly dependent on the gold film thickness, indicating that in the thinner gold film case, the reflectance was recovered slowly after the SPR angle, whereas as the gold film thickness increased, the magnitude difference between the maximum and the minimum reflectance measured near the SPR angle was smaller than in other cases. From the numerical analysis, it was shown that the phase shift is the most sensitive physical parameter for SPR sensor by comparing estimated FWHM values of reflectance, phase shift, and enhancement of magnetic field intensity. Therefore, it was concluded that an appropriate metal thickness of around 50 nm was found for higher sensitivity.
  • Femtosecond Laser Pulse Train Effect on Optical Characteristics and Nonequilibrium Heat Transfer in Thin Metal Films

    pp. 1156-1162

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    DOI:10.2320/matertrans.M2010009

    The objective of this study is to numerically investigate the electron-phonon interactions and the nonequilibrium energy transfer in metal thin films irradiated by ultrashort pulse train lasers. In particular, the temporal and spatial variations in the optical properties during laser irradiation are discussed; the influence of the number of pulses per train and the pulse separation time are also examined. The present study uses the well-established two-temperature model to describe laser-solid interactions and the quantum approach to determine various properties such as electron heat capacity, electron thermal conductivity, collision frequencies, reflectivity, and absorption rates. It is found that as the number of pulses per pulse train increases, the nonequilibrium state between electrons and phonons gradually disappears because of the energy relaxation and the low electron thermal conductivity. The results show that the electron-electron and electron-phonon collision frequencies vary significantly with the number of pulses per train and the separation time per pulse, and that they considerably affect the reflectivity and absorption rate, in turn leading to a change in the ablation mechanism of thin metal films for pulse train laser heating.
  • Electrical Properties of Semiconductive α-Fe2O3 and Its Use as the Catalyst for Decomposition of Volatile Organic Compounds

    pp. 1163-1167

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    DOI:10.2320/matertrans.M2010064

    We are so far involved in the development of complete decomposition of organic wastes as well as volatile organic compounds (VOCs) by the use of thermally activated holes in titanium oxide (TiO2) at high temperatures of about 350–500°C. In this study, we intend to replace TiO2 with α-Fe2O3 (red hematite) in order to lower the operation temperature and also to electrically characterize α-Fe2O3 on the basis of the temperature dependence of electrical conductivity and Seebeck potential. Powdered α-Fe2O3 is found to exhibit a higher electrical conductivity at 500°C by three orders of magnitude as compared with that of room temperature. In addition, the Seebeck potential is negative in the temperature range between room temperature and 380°C, indicating that the dominant charge carriers are mostly holes. Our α-Fe2O3-coated catalyst-system exhibits equivalent or even better characteristics than that of TiO2, although the specific surface of α-Fe2O3 (4.10 m2/g) is two orders of magnitude smaller than that of TiO2 (298 m2/g).
  • Formation of Hägg Carbide in an Fe-30Mn-10Al-4Cr-0.45C Alloy

    pp. 1168-1172

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    DOI:10.2320/matertrans.M2010055

    When the present alloy was aged at 550°C, Hägg carbides (M5C2-type carbides) formed at a/2⟨100⟩ anti-phase boundaries of the D03 domains. The Hägg carbide has never been observed by previous workers in FeMnAlC and FeMnAlCrC alloy systems. The orientation relationship between Hägg carbide and D03 matrix was determined to be (\\bar510)M5C2||(1\\bar10)D03 and (13\\bar4)M5C2||(10\\bar2)D03. The orientation relationship between Hägg carbide and bcc-type phase has also never been reported before.

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