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MATERIALS TRANSACTIONS Vol. 55 (2014), No. 4

ISIJ International
belloff
ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678
Publisher: The Japan Institute of Metals and Materials

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MATERIALS TRANSACTIONS Vol. 55 (2014), No. 4

Magneto-Dielectric Properties of Epitaxial Ba(Fe0.5Sn0.5)O3−δ Thin Films on (001) SrTiO3 Substrates by Pulsed Laser Deposition

Ryoichi Shinoda, Akihiro Iwase, Toshiyuki Matsui

pp. 637-639

DOI:

10.2320/matertrans.M2013429

Abstract

Epitaxial thin films of a novel magneto-dielectric perovskite compound, Ba(Fe0.5Sn0.5)O3−δ(BFSO), have been synthesized on (001) SrTiO3 single crystalline substrates. The BFSO thin films have ferromagnetic nature, with saturation magnetization of 34 emu/cc at 300 K. The origin of the ferromagnetic nature of BFSO is the superexchange coupling of Fe4+(d4)–O2−–Fe4+(d4). Electrical conduction in BFSO can be determined to be space charge limited type conduction, but the leakage current increased under high electric fields.

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Magneto-Dielectric Properties of Epitaxial Ba(Fe0.5Sn0.5)O3−δ Thin Films on (001) SrTiO3 Substrates by Pulsed Laser Deposition

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Aging Behavior of Ultrafine-Grained Al–Mg–Si–X (X = Cu, Ag, Pt, Pd) Alloys Produced by High-Pressure Torsion

Daichi Akama, Seungwon Lee, Zenji Horita, Kenji Matsuda, Shoichi Hirosawa

pp. 640-645

DOI:

10.2320/matertrans.L-M2014802

Abstract

Age-hardenable Al–Mg–Si alloys containing additional elements of Ag, Cu, Pt or Pd were processed by high-pressure torsion (HPT) and they were subsequently aged at a temperature of 373 K for up to a total period of 5,400 ks. It was found that, in all alloys, the grain sizes after HPT were refined to 300–430 nm and there were significant increases in the hardness through the HPT processing. The hardness was further increased by the subsequent aging treatment, confirming the simultaneous strengthening by grain refinement and fine precipitation. However, the aging behavior was different depending on the alloying elements. In the Cu-added excess Mg alloy, the hardness increase was large and the higher hardness retained for longer aging time when compared with those of non-added alloys. It was suggested that the precipitation of a few particles within a single grain with the size of a few hundred nanometer contributes to appreciable age hardening.

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Aging Behavior of Ultrafine-Grained Al–Mg–Si–X (X = Cu, Ag, Pt, Pd) Alloys Produced by High-Pressure Torsion

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Influences of Fine-Particle Bombarding and Conventional Shot Peening on Surface Properties of Steel

Tatsuro Morita, Sho Noda, Chuji Kagaya

pp. 646-652

DOI:

10.2320/matertrans.M2013322

Abstract

This study was conducted to investigate the influences of fine-particle bombarding (FPB, maximum diameter of collision particles: 34 µm) and conventional shot peening (510 µm) on the surface properties of steel. The influence of injection pressure in FPB was also examined. The microstructures near surfaces were nano-crystallized by FPB and shot peening. Grain size of nano-crystals was more markedly decreased by FPB than shot peening, and further reduced by the use of high injection pressure in FPB. Surface hardness increased as the grain size of nano-crystals decreased. The hardened layers of the FPBed materials became thicker by the use of high injection pressure; however, they were still shallower than the hardened layers of the shot-peened materials. Compressive residual stress measured on surfaces was higher in FPBed materials than in shot-peened materials. The use of high injection pressure in FPB was not effective to further increase this stress.

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Influences of Fine-Particle Bombarding and Conventional Shot Peening on Surface Properties of Steel

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Transitory Embrittlement of Polycrystalline Silver by Liquid Gallium

Kohei Arakawa, Koudai Yamamoto, Kazumichi Sakai, Hirokazu Koizumi

pp. 653-657

DOI:

10.2320/matertrans.M2013394

Abstract

The phenomenon of embrittlement of polycrystalline silver (Ag) by liquid gallium (Ga) is known as liquid metal embrittlement (LME). An investigation was performed to determine the effects of holding the solid metal in contact with liquid Ga on the embrittlement. Solid Ag specimens in contact with liquid Ga were placed in a furnace at 308–573 K for different time periods before testing at 308 K. The specimens undergo severe embrittlement when the holding time is short, whereas ductility is recovered when the holding time is long. The duration of brittleness decreases with increase in furnace temperature, and it is proportional to the amount of Ga on the surface. The brittle to ductile transition is considered to occur during the formation process of an intermetallic Ga and Ag compound.

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Transitory Embrittlement of Polycrystalline Silver by Liquid Gallium

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3 KeV H2+ Irradiation to Li/Pd/Cu Trilaminar Neutron Production Target for BNCT

Shintaro Ishiyama, Ryo Fujii, Masaru Nakamura, Yoshio Imahori

pp. 658-663

DOI:

10.2320/matertrans.M2013403

Abstract

For the purpose of avoiding the radiation blistering of the lithium target for neutron production in BNCT (Boron Neutron Capture Therapy) device, trilaminar Li target, of which palladium thin layer was inserted between cupper substrate and Li layer, was newly designed. The Li/Pd/Cu trilaminar structures of the synthesized target were characterized under 3 keV H2+ irradiation by XPS and XAFS technique, which provides structural/electronic properties of solids, and information about the local structure, such as the nature and number of surrounding atoms and inter-atomic distances. The following conclusions were derived; Pd–Cu physical bonding was produced between the Pd and Cu interface by electro-less plating Pd deposition on a high purity Cu plate. From the XAFS observation of white line of Pd, the Pd L3 edge jump was found after H2+ irradiation, this fact indicates increase of hole density in Pd 4d-band. 0.9 eV chemical shift was also observed in Pd L3 white line for monolayer and 1 µm Pd/Cu samples, which will affect the quality of the Li/Pd/Cu target due to the formation of PdHx in palladium insert layer.

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3 KeV H2+ Irradiation to Li/Pd/Cu Trilaminar Neutron Production Target for BNCT

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Zone Refining of Aluminum and Its Simulation

Masayoshi Nakamura, Mahiko Watanabe, Kisaburou Tanaka, Atsushi Kirihata, Tsunetaka Sumomogi, Hiroaki Hoshikawa, Ichiro Tanaka

pp. 664-670

DOI:

10.2320/matertrans.M2013419

Abstract

Ultrahigh-purity aluminum with a residual resistivity ratio (RRR) of 60000–65000 was obtained by the ultrahigh-vacuum melting method. However, it was necessary to reduce the concentration of the elements with distribution coefficient k > 1 to further improve the purity of aluminum. Therefore, we prepared a sample with reduced concentrations of k > 1 elements from an ultrahigh-purity (99.9999%) aluminum material by the zone-refining method, and evaluated its purity by electrical resistance measurement and glow discharge mass spectrometry (GDMS). In addition, the zone-refining process was simulated, and the distribution of the solute atoms after approximately 10 passes of zone-refining was predicted. Moreover, the refining conditions were investigated with the aim of achieving higher purity. In experiments, when the zone width was increased from 60 to 80 mm at a zone speed of 60 mm/h, the concentrations of the elements with k > 1 in the second half of the material decreased and RRR improved. When the zone speed was decreased to 30 mm/h, a marked effect was observed and RRR increased to about 85000. The distribution of the solute atoms determined from the simulation was in good agreement with the results of GDMS analysis, thus confirming the usefulness of the simulation.

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Zone Refining of Aluminum and Its Simulation

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Effects of Homogeneous Low Energy Electron Beam Irradiation (HLEBI) on Water Absorption and Hydrolysis Suppression of High Strength Polycarbonate

Shohei Ogawa, Junhua Quan, Yoshiki Yamazaki, Masae Kanda, Takehisa Shibuya, Yoshitake Nishi

pp. 671-676

DOI:

10.2320/matertrans.MBW201314

Abstract

In order to evaluate effects of homogeneous low energy electron beam irradiation (HLEBI) on water absorption and hydrolysis suppression, the mass gain and loss of high strength polycarbonate (PC) dipped in boiling water after drying was obtained. Dipping for less than 5 × 103 s increased the mass gain ratio (Cw) for all PC samples, although remarkable mass gain could not be detected from 5 × 103 to 2 × 105 s. HLEBI with small dose from 0.04 to 0.13 MGy mostly suppressed the Cw value for initial dipping time for less than 5 × 103 s. 0.04 MGy-HLEBI slightly enhanced the experimental saturated Cw values at 104 s-dipping (eCw). Based on the Johnson-Mehl equation, the initial absorption index (n) for PC with and without HLEBE was approximately equal to 0.5, which was approximately equal to that of nylon6. Since esteratic sites attracted the water molecules in PC polymers, the water absorption can be explained. On the other hand, the small mass loss could be detected of PC dipped in boiling water for 105 s prior to drying, although that for 104 s could not be detected. HLEBI suppressed the mass loss, 40 +/− 20% smaller than that untreated, for PC dipped in boiling water for 2 × 105 s prior to drying. Since HLEBI probably cut off the >C=O bonds in aldehyde base in PC polymers. Based on the FT-IR (>C=O bonds) signals, the intensity of untreated PC polymer is more than 15.7% higher than that after 0.13 MGy irradiation. Thus, HLEBI suppressed the hydrolysis of PC.

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Effects of Homogeneous Low Energy Electron Beam Irradiation (HLEBI) on Water Absorption and Hydrolysis Suppression of High Strength Polycarbonate

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Interfacial Reaction Mechanisms of Dilute Gas on Pt Electrode by Using a Gas Controllable H2 | H+Electrolyte | Pt Cell

Kazuya Kazama, Shuji Harada

pp. 677-683

DOI:

10.2320/matertrans.M2014020

Abstract

The amount of dilute dissolved hydrogen and/or oxygen gas in a gas controllable electrochemical cell has been evaluated by using cyclic voltammetry method. The electromotive force of H2 | H+electrolyte | Pt cell has been measured as a function of hydrogen and/or oxygen gas in the cell. The interfacial reaction mechanism on the Pt electrode has been discussed on a random adsorption model.

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Interfacial Reaction Mechanisms of Dilute Gas on Pt Electrode by Using a Gas Controllable H2 | H+Electrolyte | Pt Cell

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Influence of Mo and W on High Temperature Hardness of M7C3 Carbide in High Chromium White Cast Iron

Kaoru Yamamoto, Sudsakorn Inthidech, Nobuya Sasaguri, Yasuhiro Matsubara

pp. 684-689

DOI:

10.2320/matertrans.F-M2014801

Abstract

The influence of Mo and W addition on the high temperature hardness of M7C3 carbide was investigated using unidirectionally solidified hypereutectic cast iron with 25 mass%Cr. Concentrations of alloying elements in primary M7C3 carbide were measured by EDS. As Mo or W content of the cast iron increases, the concentration of Mo and W in the carbide increased and that of Fe decreased. However, the Cr content was almost the same as about 60 mass% in spite of increasing the Mo and W contents. It was found from the XRD results that the lattice constant of M7C3 carbide changed and its attendant volume of a unit cell increased as the Mo or W content was increased. From this point of view, it can be considered that Fe atoms in the M7C3 carbide were substituted by Mo or W which has larger atomic radius than Fe. In all the specimens, the hardness of M7C3 carbides are about 1600HV0.3 at the room temperature, and it decreases gradually with a rise of the test temperature. The decreasing ratio of carbide hardness becomes smaller at high temperature as the Mo or W concentration in M7C3 carbide increases. Thus, the dissolution of Mo or W atom into M7C3 carbide is very effective to maintaining the high temperature hardness of carbide. However, the increment of the hardness became smaller at higher Mo and W contents, so that an excess addition of both elements gave less effect than expected. The fracture toughness of M7C3 carbide at the room temperature was measured using an indentation fracture method, and the values were very similar among the carbides regardless of Mo and W concentration in the M7C3 carbide.

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Influence of Mo and W on High Temperature Hardness of M7C3 Carbide in High Chromium White Cast Iron

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Synthesis of ZnO Crystals with Octahedral Morphology through Thermal Evaporation Technique in Air

Min-Sung Kim, Geun-Hyoung Lee

pp. 690-692

DOI:

10.2320/matertrans.M2013402

Abstract

ZnO crystals with octahedral morphology were synthesized in large quantity using a simple thermal evaporation of ZnF2 powder in air. No catalysts and impurities were not used in the synthetic process. Scanning electron microscopy image showed that the synthesized ZnO crystals were of well-defined octahedral shape with smooth surfaces. X-ray diffraction data revealed that the octahedral-shaped ZnO crystals had a hexagonal wurtzite structure. As the synthetic temperature increased, the crystal size increased without altering the octahedral morphology. Energy dispersive X-ray spectroscopy spectrum confirmed the high purity of the ZnO crystals. Two emission peaks at around 430 and 460 nm was observed in the cathodoluminescence spectrum of the octahedral-shaped ZnO crystals.

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Synthesis of ZnO Crystals with Octahedral Morphology through Thermal Evaporation Technique in Air

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Effects of Electro-Magnetic Stirring on Microstructural Evolution and Mechanical Properties in Semi-Solid Forming of a Hypo-Eutectic Al–Si–Cu–Ni–Mg Alloy

Young-Soo Jang, Byoung-Hee Choi, Chun-Pyo Hong

pp. 693-699

DOI:

10.2320/matertrans.M2013404

Abstract

A new piston alloy based on a hypo-eutectic Al–Si–Cu–Ni–Mg system was developed for semi-solid forming. The Si content was optimized to obtain proper semi-solid slurry based on thermodynamic calculations and experiments. The contents of Cu, Ni and Mg were kept similar to those of a commercial piston alloy to retain good heat resistance and high-strength properties. The high-quality semi-solid slurry with fine and uniform globular characteristics for semi-solid forming can be obtained at a low pouring temperature of 615°C. The conditions of a T6 heat treatment for the developed alloy are optimized as follows: solid solution treatment at 520°C for 6 h and an aging treatment at 160°C for 5 h. The mechanical properties, in this case hardness, high-temperature tensile strength, relative wear resistance, and high-temperature creep, were evaluated by the specimens which were taken from the rheo-diecast products and the results were compared with those of a conventional metal mold cast piston.

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Effects of Electro-Magnetic Stirring on Microstructural Evolution and Mechanical Properties in Semi-Solid Forming of a Hypo-Eutectic Al–Si–Cu–Ni–Mg Alloy

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Effect of Orifice Introduction on the Pneumatic Separation of Spherical Particles

Naohito Hayashi, Tatsuya Oki

pp. 700-707

DOI:

10.2320/matertrans.M2013292

Abstract

In order to recycle important rare metals (such as tantalum) in the print circuit boards of waste electronic equipment, the devices must first be delaminated from the board. The devices are then separated into each device type such as capacitors, resistors, thermistors and so on. In this study, the effect of orifices on spherical particles was clarified through numerical simulations of airflow and air–solid multiphase flow in a vertical single-column pneumatic separator. Airflow velocity profiles and particle trajectories were investigated for different numbers of orifices using spherical particles of identical size and different densities. By introducing multiple orifices, the eccentricity of the velocity profile in the vertical direction could be corrected. This eccentricity is caused by the presence of a mesh, which recovers heavy particles after they pass through the second orifice. When the distance between orifices ranged from 400 to 625 mm, it was expected that high-speed and high-efficiency separation between orifices would be possible. It implies that step-by-step separation could be conducted in a single separation column. However, under the calculation conditions of our study, the orifices did not affect the separation efficiency because this factor depends on the velocity profile around the feeding position. The separation rate was maximized when the orifices were separated by 625 mm.

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Effect of Orifice Introduction on the Pneumatic Separation of Spherical Particles

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Degradation of Chlorinated Organic Compounds by Mixed Particles of Iron/Iron Sulfide or Iron/Iron Disulfide

Masahiro Shiba, Md. Azhar Uddin, Yoshiei Kato, Tomoshige Ono

pp. 708-712

DOI:

10.2320/matertrans.M2013412

Abstract

Kinetic study was carried out in order to clear a mixing effect of Fe–FeS or Fe–FeS2 particles on increase in degradation rate of chlorinated organic compounds. Trichloroethylene (TCE) contained solution was used for dechlorination in 30 mL of vial bottle and mixed by rotary device. Estimating that TCE concentration in solution was proportional to TCE gas concentration in head space of vial bottle, gas was obtained from the head space with syringe and measured by GC-FID. TCE degradation occurred on Fe, FeS, Fe–FeS and Fe–FeS2 particles except FeS2. TCE degradation of mixed particles of Fe–FeS or Fe–FeS2 was explained by anode (Fe)–cathode (FeS or FeS2) reaction. TCE degradation rates of Fe–FeS and Fe–FeS2 caused by anode/cathode reaction were 2.81 × 10−6 and 1.37 × 10−5 (m/h), respectively, which were larger than those of pure Fe and FeS. There was no difference in TCE degradation rate of mixed particles of Fe–FeS or Fe–FeS2 between aerobic and anaerobic solutions. TCE degradation rate of mixed particles of Fe–FeS or Fe–FeS2 increased in decrease in size of FeS or FeS2. TCE degradation rate of mixed particles of Fe–FeS or Fe–FeS2 increased with increase in decomposition temperature.

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Degradation of Chlorinated Organic Compounds by Mixed Particles of Iron/Iron Sulfide or Iron/Iron Disulfide

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Near-Net-Shape Tungsten–Rhenium Alloy Parts Produced by Plasma Spray Forming and Hot Isostatic Pressing

Yueming Wang, Xiang Xiong, Weizhong Zhao, Lu Xie, Jianhui Yan, Xiaobing Min, Feng Zheng

pp. 713-721

DOI:

10.2320/matertrans.M2013314

Abstract

Tungsten–5.0 mass% rhenium (W–5.0 mass%Re) composite feedstock was fabricated by a new cover method. Complex and thin-walled W–5.0 mass%Re products (including one shaped charge liner and one throat) were produced by plasma spray forming (PSF) followed by hot isostatic pressing (HIPing). Scanning electron microscope (SEM), Archimedes method, Vickers hardness, tensile and compressive tests were employed to study microstructure, density, micro-hardness and mechanical properties of the parts.
A lamellar structure consisting of vertical columnar grains, micron-sized pores and rough interlamellar contacts with gaps of sub-micron sizes between lamellae were found in PSF deposits. The relative density, micro-hardness, ultimate tensile strength (UTS) and compressive strength of PSF deposits were about 87 ± 1%, 321 ± 4 HV0.025, 57 ± 2 and 390 ± 2 MPa, respectively. As dwell time of HIPing prolonging (from 2, to 4 and 6 h), internal defects of PSF deposits including inter-lamellar gaps and micro-pores could be gradually mitigated or eliminated with initial lamellar structure transforming into granular one. Relative density and mechanical properties of W–Re alloys were gradually increased under the combined action of high temperature and pressure. Especially for W–Re deposits after 6 h HIPing, the relative density, micro-hardness, UTS, compressive strength and yield stress were increased high up to 98 ± 1%, 490 ± 4 HV0.025, 384 ± 2 MPa, 1490 ± 2 and 879 ± 2 MPa, respectively. The mechanical properties and the ductility at room temperature of W–Re alloys were both higher than those of W deposits. ‘Re effect’ was revalidated and double checked in W–Re alloys fabricated by PSF and HIPing here.

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Near-Net-Shape Tungsten–Rhenium Alloy Parts Produced by Plasma Spray Forming and Hot Isostatic Pressing

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Preparation of Nano-Structured La0.6Sr0.4Co0.2Fe0.8O3−δ Cathode for Protonic Ceramic Fuel Cell by Bead-Milling Method

Hiroyuki Oda, Yuji Okuyama, Takaaki Sakai, Hiroshige Matsumoto

pp. 722-727

DOI:

10.2320/matertrans.M2013426

Abstract

Nano-structured La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF6428) cathode for protonic ceramic fuel cell (PCFC) prepared from planetary bead-milled nanoparticles was investigated. The cathode made by the bead-milled particles showed a porous structure consisting of homogeneous size particles and pores in the range 100 nm. The PCFC comprised of this cathode, Ni anode and BaCe0.6Zr0.2Y0.2O3−δ (BCZY622) electrolyte increased the cell performances about 6 times that of the cell using the cathode without milling. The cathode preparation using bead-milling is effective in improving the cell performance with an expanded contact area of the cathode/electrolyte interface due to decreasing particle size and good adhesion of the particles to the electrolyte.

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Preparation of Nano-Structured La0.6Sr0.4Co0.2Fe0.8O3−δ Cathode for Protonic Ceramic Fuel Cell by Bead-Milling Method

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Effects of Deposition Temperature on the Electrochemical Deposition of Zinc Oxide Thin Films from a Chloride Solution

Shigeo Hori, Toshimasa Suzuki, Tsukasa Suzuki, Shuhei Miura, Shuichi Nonomura

pp. 728-734

DOI:

10.2320/matertrans.M2013386

Abstract

The structural, electrical, and optical properties of ZnO thin films electrochemically deposited from a chloride solution are investigated. We focus on deposition temperatures. The band gap energy decreased from 3.50 to 3.44 eV as deposition temperatures increased from 60 to 80°C. This variation of band gap is discussed with respect to both conduction and valence band shifts, and the Burstein-Moss effect caused by numerous carriers. Increase in the carrier density of ZnO thin films was observed with increasing deposition temperature; a markedly-high carrier density of 1 × 1021 cm−3 was exhibited. The origin of the carrier density was also investigated. Although the Cl− content in ZnO thin films decreased with increasing deposition temperature, the increase of Cl− acting as a donor was indicated.

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Effects of Deposition Temperature on the Electrochemical Deposition of Zinc Oxide Thin Films from a Chloride Solution

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Microelectrochemical Study on the Surface Oxidation of Pt: The Effects of Crystal Orientation and Grain Boundary

Mayu Sasaki, Yu Sugawara, Izumi Muto, Nobuyoshi Hara

pp. 735-738

DOI:

10.2320/matertrans.M2013416

Abstract

Microelectrochemical polarization measurements of polycrystalline Pt were performed to clarify the effect of the crystal orientation and grain boundary on the surface oxidation of Pt. Cyclic voltammograms (CV) for Pt(100)-like and Pt(110)-like grains on polycrystalline Pt after mechanical polishing showed no anodic peak below 1.35 V, which is similar to that for well-annealed Pt(111) single crystal. The anodic current of Pt(110)-like grain was significantly larger than Pt(100)-like. A small but concrete current increase appeared around 1.05–1.3 V in the CV of the surface including grain boundaries. This suggests the grain boundary may be the preferential site for the dissolution.

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Microelectrochemical Study on the Surface Oxidation of Pt: The Effects of Crystal Orientation and Grain Boundary

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Microstructure and Mechanical Properties of Alternately-Compressed AZ31 Mg Alloy in Two Orthogonal Directions

Hyukjoon Kwon, Mamoru Mabuchi, Yasumasa Chino

pp. 739-741

DOI:

10.2320/matertrans.MBW201305

Abstract

AZ31 Mg alloy was compressed alternately in two orthogonal directions at room temperature. Many {10\bar{1}1} twins connected by {10\bar{1}2} twins were found in the alternately-compressed specimens. The compressed specimens exhibited much lower ductility than the non-compressed specimen, and their ductility decreased with an increase in the number of compression. It is therefore suggested that many triple junctions of {10\bar{1}1} and {10\bar{1}2} twin boundaries induced initiation of fracture, resulting in low ductility of the alternately-compressed specimens.

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Microstructure and Mechanical Properties of Alternately-Compressed AZ31 Mg Alloy in Two Orthogonal Directions

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Effect of Static Recrystallization on Texture Development and Formability in Mg–Al–Zn and Mg–Li–Zn Alloys

Jong-Youn Lee, Young-Su Yun, Seok-Hwan Jung, Won-Tae Kim, Do-Hyang Kim

pp. 742-744

DOI:

10.2320/matertrans.M2013456

Abstract

Effects of static recrystallization on texture evolution and formability in Mg–Al–Zn (AZ) and Mg–Li–Zn (LZ) alloys have been investigated. The effect of static recrystallization appears in an opposite way in AZ and LZ alloys, i.e., the basal texture becomes stronger in AZ alloys, while it becomes weaker in LZ alloys. Since LZ alloys have lower c/a ratio than AZ alloys, compression or double twin forms more abundantly in LZ alloys. The accelerated static recrystallization in the compression or double twinned region leads to a weaker basal texture evolution in LZ alloys. Double basal peak intensity maxima in as-rolled state changed into weaker single intensity maximum due to the effect of static recrystallization during post-annealing. As a result, LZ alloys exhibit much enhanced formability than AZ alloys.

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Effect of Static Recrystallization on Texture Development and Formability in Mg–Al–Zn and Mg–Li–Zn Alloys

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