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MATERIALS TRANSACTIONS Vol. 54 (2013), No. 12

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. 54 (2013), No. 12

First Principles Investigations on Structural, Elastic, Electronic, and Optical Properties of Li2CdGeS4

Weimin Peng, Xiaofeng Li, Junyi Du

pp. 2167-2172

DOI:

10.2320/matertrans.M2013186

Abstract

First principles calculations have been carried out to investigate the crystal structure, elastic constants, chemical bonding, electronic and optical properties of Li2CdGeS4. The calculated equilibrium lattice constants, bulk modulus and its pressure derivative are in reasonable agreement with the available experimental results. We have predicted the elastic constants as well as bulk and shear moduli. By the elastic stability criteria, it is found that Li2CdGeS4 is mechanically stable and is a ductile system. Electronic and chemical bonding properties have been studied through the calculation of band structure, density of states and Mulliken population. We found that the energy band gap is 2.817 eV in LDA (2.421 eV in GGA) for Li2CdGeS4. Moreover the complex dielectric function, refractive index, extinction coefficient, absorption coefficient, reflectivity and loss function are also calculated, which show significant optical anisotropies in the components of polarization directions (1 0 0), (0 1 0) and (0 0 1).

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First Principles Investigations on Structural, Elastic, Electronic, and Optical Properties of Li2CdGeS4

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Electrical Properties and Interface States of Rare-Earth Metal Ytterbium Schottky Contacts to p-Type InP

V. Rajagopal Reddy, L. Dasaradha Rao, V. Janardhanam, Min-Sung Kang, Chel-Jong Choi

pp. 2173-2179

DOI:

10.2320/matertrans.M2013281

Abstract

The electronic parameters and interface state properties of Yb/p-InP Schottky diode have been investigated by current–voltage (I–V), capacitance–voltage–frequency (C–V–f) and conductance–voltage–frequency (G–V–f) measurements at room temperature. The barrier height and ideality factor of the Yb/p-InP Schottky diode are found to be 0.68 eV (I–V)/0.79 eV (C–V) and 1.24, respectively. As well, the values of barrier heights, ideality factors and series resistance are estimated by Cheung and Norde methods are compared. Under forward bias conditions, ohmic and space charge limited conduction (SCLC) mechanisms are identified at low and higher voltages, respectively. The C–V characteristics of the Yb/p-InP Schottky diode are also measured at different frequencies at room temperature. Further, the C–f and G–f measurements of the Yb/p-InP Schottky diode are performed at various biases. The interface state density Nss and relaxation time τ of the diode are estimated from the C–f and G–f measurements. The Nss and the τ show a decrease with bias from the top of the valence band toward the midgap. The profile of series resistance dependent on frequency and voltage confirms the presence of interface states in Yb/p-InP Schottky structure.

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Electrical Properties and Interface States of Rare-Earth Metal Ytterbium Schottky Contacts to p-Type InP

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Microstructural Evolution and Mechanical Response of the Surface of 18CrNiMo7-6 Steel after Multistep Shot Peening during Annealing

Peng Fu, Chuanhai Jiang, Vincent Ji

pp. 2180-2184

DOI:

10.2320/matertrans.M2013287

Abstract

The variations of micro-structure, residual stress and micro-hardness for 18CrNiMo7-6 steel after triple shot peening (SP) against annealing temperature were studied. X-ray diffraction line profile analysis (XRDLPA) was used to identify the change of micro-structure and residual stress relaxation behaviors of the top surface for 18CrNiMo7-6 steel after SP. The results show that the micro-strain, dislocation density, stored energy, compressive residual stress (CRS) and micro-hardness of the top surface of 18CrNiMo7-6 steel after SP decrease with the increase of annealing temperature while the domain size increases with increasing annealing temperature. Meanwhile, the change rates of micro-structure the residual stress and micro-hardness are bigger at higher annealing temperatures.

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Microstructural Evolution and Mechanical Response of the Surface of 18CrNiMo7-6 Steel after Multistep Shot Peening during Annealing

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Effect of Thermal Cycling on Multistage Martensitic Transformation in Aged Ti–50.8 at% Ni Alloy

Banafsheh Karbakhsh Ravari, Masatoshi Mitsuhara, Sahar Farjami, Minoru Nishida

pp. 2185-2188

DOI:

10.2320/matertrans.M2013309

Abstract

The effect of thermal cycling on multistage martensitic transformation (MMT) in aged Ti–50.8 at% Ni alloy was investigated. The specimens were solution-treated at 1273 K for 3.6 ks and then aged at 773 K for 3.6 ks in vacuum without atmosphere regulation. Upon cooling, the aged specimens clearly showed quadruple-stage transformation denoted as B2 → R → M1 → M2 → M3. The peak temperatures of exothermic reactions R*, M1*, and M2* (corresponding to the R-phase, M1 and M2 transformations, respectively) in the differential scanning calorimetry (DSC) cooling curve were rather stable up to 100 thermal cycles, since there were fine Ti3Ni4 precipitates with high distribution density in the intermediate and grain boundary regions. These precipitates prevented the formation of dislocations during thermal cycling. On the other hand, the peak temperature of exothermic reaction M3* (corresponding to the M3 transformation) drastically decreased with increasing the number of thermal cycles since there were large Ti3Ni4 precipitates with low distribution density. Many dislocations were observed in the central regions of grains after 100 thermal cycles.

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Effect of Thermal Cycling on Multistage Martensitic Transformation in Aged Ti–50.8 at% Ni Alloy

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Effects of Ellipse Preforming on Cross-Sectional Shapes of Square Steel Pipe Formed by Roll Forming

Takuo Nagamachi, Takeo Kitawaki, Kazuhiro Matsumura

pp. 2189-2194

DOI:

10.2320/matertrans.P-M2013834

Abstract

A square steel pipe is reshaped from a welded round pipe by roll forming. The effect of ellipse preforming on the cross-sectional size of the square steel pipe was investigated by experiment and three-dimensional finite element simulation. When designing a roll-forming machine for a square steel pipe, the diameter of the paired top and bottom rolls is usually set larger than that of the side roll pair, thereby avoiding interference between the roll axes driven by electric motors. When the diameter of the top roll is larger than that of the side roll, the width of a corner part of the formed pipe is larger than the height. A square pipe was formed from a preformed elliptical pipe to make the width and height of the corner part equal. As a result of ellipse preforming, the peripheral length of a square product increases and the size of the corner part of that product decreases. Therefore, elliptical preforming is effective in forming square pipe with a sharp corner. However, excessive preforming causes a hollow at the flat surface of a square product.

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Effects of Ellipse Preforming on Cross-Sectional Shapes of Square Steel Pipe Formed by Roll Forming

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Effects of Hydrogen Micro Pores on Mechanical Properties in A2024 Aluminum Alloys

Hiroyuki Toda, Takaaki Inamori, Keitaro Horikawa, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki, Masakazu Kobayashi

pp. 2195-2201

DOI:

10.2320/matertrans.L-M2013832

Abstract

It has been reported that most aluminum alloys contain high-density micro pores, which make an appreciable contribution to damage evolution during ductile fracture. It is reasonable to assume that the mechanical properties of aluminum alloys are more or less improved by controlling micro pores in aluminum alloys. In the present study, the volume fraction of micro pores is controlled by controlling hydrogen content over a wide range. Tensile tests are performed using smooth and notched specimens at room and elevated temperatures, together with a fracture toughness test. It has been shown that both strength and ductility increase with decreasing micro pore volume fraction. The elimination of micro pores has pronounced effects especially on high-temperature ductility, notched tensile strength and fracture toughness. It has been observed in the in-situ observation of a room temperature tensile test that pre-existing hydrogen micro pores exhibit premature growth immediately after the onset of plastic deformation, whereas the well-known particle fracture mechanism operates only after the maximum load in the alloys with the least micro pores fraction. It can be inferred that in the notched and pre-cracked specimens, the premature growth of micro pores are driven by triaxial stress state, thereby inducing more degradation in mechanical properties.

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Effects of Hydrogen Micro Pores on Mechanical Properties in A2024 Aluminum Alloys

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Creep Mechanism in Several Grades of Aluminum at Low Temperatures

Tetsuya Matsunaga, Eiichi Sato

pp. 2202-2208

DOI:

10.2320/matertrans.L-M2013833

Abstract

Creep tests were performed at less than 0.4 Tm (Tm is the melting temperature) for 99.999, 99.57 and 99.52% aluminum with several grain sizes in the range of 50–330 µm. These Al materials show remarkable creep behavior with an apparent activation energy (Q) of 30 kJ/mol, a stress exponent of 4, and a grain-size exponent of zero, and with a larger creep rate with increasing purity. These parameters resemble those of conventional dislocation creep, which is rate-controlled by the usual diffusion processes, except for the extra-low Q value. This means that a non-diffusional process affects the steady state deformation in this temperature region. Transmission electron microscopy revealed the development of a cell structure in the steady state and dislocations without any tangles in the cell interiors. Therefore, because the rate-controlling process could not occur inside of the cells, dislocation annihilation occurred through cross slip around the cell walls. According to these creep parameters and microstructural observations, the observed creep region is suggested to be a new creep region occurring through a non-diffusional process within the existing deformation mechanism map of Al at less than 0.4 Tm.

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Creep Mechanism in Several Grades of Aluminum at Low Temperatures

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Effect of Alloying Elements with Positive Heat of Mixing on the Free Volume and Compressive Plasticity in ZrCoCuAl Bulk Metallic Glasses

Z. Liu, K. C. Chan, L. Liu

pp. 2209-2214

DOI:

10.2320/matertrans.M2013241

Abstract

In this work, the effect of alloying an element with positive heat of mixing with Co on the free volume and compressive plasticity of a ZrCoAl bulk metallic glass was investigated. By substituting Co with Cu, fully amorphous rods of 2 mm diameter can be obtained over a wide composition range. With the addition of Cu, the free volume changes from 0.09 to 0.18%, and the fracture plastic strain changes from 1 to 12.4%. However, there is no strong correlation between the free volume and the compressive plasticity. In addition to the free volume content, other factors such as the size, shape and distribution of the free volume sites may also affect the plasticity of BMGs.

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Effect of Alloying Elements with Positive Heat of Mixing on the Free Volume and Compressive Plasticity in ZrCoCuAl Bulk Metallic Glasses

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Crack Growth Characteristic and Damage Evaluation under Creep-Fatigue Interactive Condition for W-Added High-Cr Steel

Takashi Matsuzaki, Ryuji Sugiura, Yoshiko Nagumo, A. Toshimitsu Yokobori, Jr.

pp. 2215-2224

DOI:

10.2320/matertrans.M2013340

Abstract

Crack growth characteristic under the conditions of high temperature creep and fatigue interaction is dominated by both of cyclic dependent mechanism due to fatigue and time dependent mechanism due to the time of load application (creep). For many cases with decrease in load frequency, this characteristic changes from the cyclic dependent mechanism to the time dependent mechanism through an unstable transition region induced by creep and fatigue competitive mechanisms. To understand the physical mechanism of the interactive effects of creep and fatigue, it is important to clarify the damage mechanisms around the crack. In the present study, the experiments of creep-fatigue crack growth tests and the quantitative analysis of damage by measuring Vickers hardness were conducted to understand the interactive effects of creep and fatigue on the crack growth characteristic. Additionally, by observing the material microstructure using EBSD, damage mechanisms were clarified. As a result, it was found that the creep effect contributes the expansion of damage region and the fatigue effect increases the density of damage within a given region. Interaction of these effects resulted in the occurrence of unstable transition region on the characteristic of creep-fatigue life.

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Crack Growth Characteristic and Damage Evaluation under Creep-Fatigue Interactive Condition for W-Added High-Cr Steel

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Electrochemical Crevice Corrosion Behaviors of Low-Pressure Steam Turbine Materials in the Simulated Boiler Water Added Chloride and Sulfate Ions

Li-Bin Niu, Hodaka Kato, Kunio Shiokawa, Kenji Nakamura, Mitsuo Yamashita, Yoshihiro Sakai

pp. 2225-2232

DOI:

10.2320/matertrans.M2013202

Abstract

Using a rotor material, 3.5NiCrMoV steel, and a blade material, 13Cr steel, for low-pressure (LP) steam turbines of thermal power plants, electrochemical crevice corrosion tests were conducted in the simulated AVT (All Volatile Treatment) boiler water added chloride and sulfate ions. The crevice corrosion behaviors as well as the films formed on the specimen surfaces inside crevices were investigated. The 3.5NiCrMoV steel and the 13Cr steel in the test water showed crevice corrosions in a general type and a pitting type, respectively. For both the two steels, however, passive films formed on the specimen surfaces inside crevices. It was found that the passive film formed on 3.5NiCrMoV steel was composed mainly of Fe3O4, while that on 13Cr steel was composed mainly of Cr-oxides and partly of inward Fe-oxides. Especially, it was confirmed that CrOOH and CrO3 were concentrated in the outermost surface of the passive film formed on 13Cr steel.

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Electrochemical Crevice Corrosion Behaviors of Low-Pressure Steam Turbine Materials in the Simulated Boiler Water Added Chloride and Sulfate Ions

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Low Temperature and Pressure Synthesis of Lithium–Nitride Compound with H2O Addition on Lithium Target for BNCT

Shintaro Ishiyama, Yuji Baba, Ryo Fujii, Masaru Nakamura, Yoshio Imahori

pp. 2233-2237

DOI:

10.2320/matertrans.M2013242

Abstract

Low temperature synthesis of lithium–nitride compound was conducted on the lithium target for BNCT by N2/H2O mixing gas squirt in the ultra high vacuum chamber, and the following results were derived. (1) Lithium–nitride compound was synthesized on the lithium target under 101.3 Pa N2 gas squirt at room temperature and in the ultra high vacuum chamber under the pressure of 1 × 10−8 Pa. (2) Remarkable contamination by O and C was observed on the lithium–nitride compound synthesized under the squirt pressure of 13.3–80 Pa/1.33–4.7 Pa N2/H2O mixing gas. (3) No contamination and synthesis of Li–N compound was observed under the squirt pressure of 0.013–0.027 Pa/0–0.005 Pa N2/H2O mixing gas. (4) Contamination by O and C was enhanced with excessive addition of H2O at the pressure of over 1.33 Pa.

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Low Temperature and Pressure Synthesis of Lithium–Nitride Compound with H2O Addition on Lithium Target for BNCT

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Effect of Surface Treatment on Glossiness of Al–Mg–Zn Alloy Casting

Makoto Hino, Koji Murakami, Norihito Nagata, Chie Ibata, Hideki Kanetsuki, Sadao Kawai

pp. 2238-2244

DOI:

10.2320/matertrans.F-M2013830

Abstract

In this study, the effects of various surface treatments on the glossiness of AC4CH-T6 casting and newly developed bright aluminum alloy casting were examined.
With the AC4CH-T6 casting, it was difficult to obtain a bright surface by buffing, because of the surface irregularity between the hard eutectic silicon and the aluminum matrix. On the other hand, with the developed silicon-free alloy casting, it was possible to produce a bright surface by buffing, and this glossiness was superior to that of the AC4CH-T6 casting covered with the decorative chrome electroplating. The glossiness of the developed casting decreased sharply after chemical polishing, depending on the generation of local dissolution close to the intermetallic compound and pin-hole. However, electropolishing under an optimum conditions helped realize a smooth and bright surface.
As with the anodization from sulphuric acid solution, glossiness of the developed alloy casting decreased because of the prior dissolution of the intermetallic compound. However, anodization from the developed solution suppressed this dissolution, forming a uniform oxide film. As a result, bright surface could be produced for the developed alloy casting by anodization.

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Effect of Surface Treatment on Glossiness of Al–Mg–Zn Alloy Casting

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Temperature Dependence of Tensile Properties and Fracture Behavior of Welded Joints of Titanium Matrix Composites in Gas Tungsten Arc Welding

Jianwei Mao, Liqiang Wang, Weijie Lu, Di Zhang, Jining Qin

pp. 2245-2251

DOI:

10.2320/matertrans.M2013250

Abstract

The characteristics of gas tungsten arc weldments of in-situ reinforced titanium matrix composites were investigated, and the joint quality was evaluated by means of weld morphology, microstructure and tensile tests. With an increase of welding process parameters, sound welded joints were fabricated. The weld zone had a refinement microstructure and TiBw exhibited smaller sizes and dispersed distribution, forming a novel network structure in the weld. Tensile tests indicated that the weld presented excellent high temperature strengths, even superior to the base metal under the welding conditions. The welded joints displayed a slower downtrend in strength than that of base metal with an increase of temperature, and the elongation values of joints were higher than the base metal because of the refined grain microstructure and dispersed distribution of TiBw in the weld. The strengthening mechanism of high temperature properties of welded joints is ascribed to smaller sizes and network structure of TiBw in the weld. The fracture surfaces of butt joints for TMCs include the hybrid ductile of matrix and brittle fracture/decohesion of TiBw at different temperatures.

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Temperature Dependence of Tensile Properties and Fracture Behavior of Welded Joints of Titanium Matrix Composites in Gas Tungsten Arc Welding

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Effect of Thermal History on Microstructural Changes in Aluminized Nickel-Based Single-Crystal Superalloy

Kazuki Kasai, Hideyuki Murakami, Kazuhiko Noda

pp. 2252-2257

DOI:

10.2320/matertrans.M2013205

Abstract

The effect of the thermal history on microstructural changes in aluminized and Pt-aluminized Ni-based single-crystal superalloys was investigated. The superalloy substrates were first electropolished to get rid of the residual surface strain. Then, Pt was electrodeposited and vacuum annealing was conducted for some of the substrates, and aluminized and Pt-aluminized specimens were prepared using the conventional aluminizing process. It was found that in the aluminized specimens, voids were formed in the vicinity of the substrate/coating interfaces during thermal cyclic heating, whereas secondary diffusion zones (SDZ) were formed by isothermal heating. These different microstructural changes of the aluminized specimens can be explained by the kinetics of diffusion between the coating layer and the substrate during the heating/cooling processes. In the Pt-aluminized specimen, on the other hand, secondary reaction zone (SRZ) formation was observed after both thermal cyclic and isothermal treatments. These results can be explained by the polycrystallization of the substrate surface during the annealing process, which promotes interdiffusion, resulting in the formation of an SRZ.

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Effect of Thermal History on Microstructural Changes in Aluminized Nickel-Based Single-Crystal Superalloy

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Effects of Metal (Ag, Sn and Zn) Nanoparticles Inserted into MgB2 Grain Boundaries on Transport and Superconducting Properties

Satoshi Akamaru, Fumitaka Ishikawa, Katsuhiko Nishimura, Takayuki Abe, Masao Matsuyama

pp. 2258-2264

DOI:

10.2320/matertrans.M2013254

Abstract

MgB2 grains were coated with metal nanoparticles (Ag, Zn and Sn) using the barrel sputtering technique, and transport and superconducting properties were evaluated. Almost all MgB2 grains were uniformly coated with metal nanoparticles with average diameters of less than 20 nm. The electrical resistivity of the coated MgB2 decreased as the amount of metal coating increased. The critical current densities of almost all coated MgB2 were enhanced compared to those of bare MgB2. These results explained the improvement of intergranular connectivity between MgB2 grains by the insertion of metal nanoparticle in grain boundaries. After annealing at 473 K, only MgB2 coated with Sn nanoparticles showed a decrease in electrical resistivity and the enhancement of the critical current density. These results can be understood by the effect of improvement of intergranular connectivity between MgB2 grains by annealing.

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Effects of Metal (Ag, Sn and Zn) Nanoparticles Inserted into MgB2 Grain Boundaries on Transport and Superconducting Properties

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Adsorption Property of Water Vapor on AlPO4-5 Synthesized from Aluminum Dross

Norihiro Murayama, Makoto Baba, Jun-ichi Hayashi, Junji Shibata, Marjorie Valix

pp. 2265-2270

DOI:

10.2320/matertrans.M-M2013831

Abstract

The aluminophosphate type zeolitic material, AlPO4-5 was synthesized by hydrothermal method using aluminum dross as a raw material, and its water vapor adsorption property was studied. Porous AlPO4-5 and nonporous AlPO4 were formed, and the selectivity of their formation was determined by varying the reactant ratios. Both AlPO4-5 and tridymite type AlPO4 (nonporous phosphate) were obtained from aluminum dross when the reaction products were synthesized with the following composition, Al2O3 : P2O5 : triethylamine (TEA) : H2O = 1 : 1 : 1 : 40. While AlPO4-5 was preferentially synthesized as a main product when the compositions were Al2O3 : P2O5 : TEA : H2O = 2 : 1 : 1 : 40 and 1 : 1 : 2 : 40. The variation in the reactant ratio dictated the specific surface area of the resulting reaction products. The formation of AlPO4-5 with a composition of 1 : 1 : 2 : 40 generated surface area of 353 m2/g. The reaction products synthesized at 2 : 1 : 1 : 40 and 1 : 1 : 1 : 40 generated surface areas of 187 and 75 m2/g, respectively. All the aluminophosphate products exhibited the type IV or V isotherm by IUPAC classification for water vapor adsorption due to the AlPO4-5 pore with strong affinity. This study demonstrated the efficacy of AlPO4-5 obtained from aluminum dross as desiccant, that is, the aluminum dross-derived AlPO4-5 demonstrated high adsorption capacity and adsorption properties suitable as an adsorbent or a desiccant.

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Adsorption Property of Water Vapor on AlPO4-5 Synthesized from Aluminum Dross

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Indium Recovery from Bearing Alloy via Pyrometallurgical Chlorination Process Utilizing Ammonium Chloride

Osamu Terakado, Hiroaki Ishikawa, Masahiro Hirasawa

pp. 2271-2275

DOI:

10.2320/matertrans.M2013206

Abstract

The chlorination process utilizing ammonium chloride as chlorination reagent has been employed for the recovery of elements with emphasis on indium from bearing alloy through vaporization of the chlorides. It was found that the chlorination took place by the heating of the model sample in the presence of ammonium chloride. The influence of the process parameters, such as reaction temperature and gas flow rate, has been investigated. The addition of activated carbon resulted in the adsorption of chloride on the carbon surface. The present result indicates the possibility of the recovery process through transport of the target element from the sample to pores of activated carbon.

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Indium Recovery from Bearing Alloy via Pyrometallurgical Chlorination Process Utilizing Ammonium Chloride

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Microstructure Development of Oxide Scale during Steam Oxidation of the Fe–20Cr–30Ni–2Nb (at%) Austenitic Steel at 1073 K

Lyta, Mitsutoshi Ueda, Kenichi Kawamura, Masao Takeyama, Toshio Maruyama

pp. 2276-2284

DOI:

10.2320/matertrans.M2013258

Abstract

Novel austenitic steel of which composition is Fe–20Cr–30Ni–2Nb (at%) is one of the promising material for further advanced steam power plants, which will be operated at 973 K or higher temperature such as 1073 K. This steel is strengthened by intermetallic compounds and has creep rupture strength 80 MPa at 973 K for 105 h. Further investigations are needed to improve both creep rupture strength and steam oxidation resistance of the steel for application at 1073 K. This paper focuses on steam oxidation resistance of the steel at 1073 K. Steam oxidation has been conducted to clarify microstructure development of the oxide scale and to evaluate long-term steam oxidation resistance based on the kinetic data. Microstructure observation reveals that Cr2O3 layer is easy to form at the scale/steel interface compared with the commercial austenitic steels, because the transition from internal to external oxidation has finished within about 20 ks. Surface oxygen potential measurement by using oxygen concentration cell is also useful technique to detect Cr2O3 formation in the scale. Based on the kinetics data, this steel has a good steam oxidation resistance compared with the commercial austenitic steel such as type 316 steel and is applicable to further advanced steam power plants.

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Microstructure Development of Oxide Scale during Steam Oxidation of the Fe–20Cr–30Ni–2Nb (at%) Austenitic Steel at 1073 K

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Suppression of Hydrogen-Assisted Fatigue Crack Growth in Carbon Steels

Etsuo Takeuchi, Masao Hayakawa, Saburo Matsuoka

pp. 2285-2290

DOI:

10.2320/matertrans.M2013237

Abstract

Carbon steels with high resistance to hydrogen-assisted fatigue crack growth were successfully produced by the addition of a carbide-forming element and the refinement of ferrite grain size. In carbon steels containing vanadium, titanium, or niobium, fine carbide (VC, TiC, or NbC, respectively) precipitation and the refinement of grain size below 1 µm were achieved by caliber rolling at 833 K. Hydrogen charging increased the fatigue crack growth rate in standard JIS-S45C carbon steel to about 25 times that in uncharged steels. In contrast, in carbon steels containing carbide-forming elements, hydrogen-assisted fatigue crack growth was either absent or at most two times faster than that in uncharged steels.

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Suppression of Hydrogen-Assisted Fatigue Crack Growth in Carbon Steels

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Arsenic Removal from Mine Tailings for Recycling via Flotation

Junhyun Choi, Kyuhyeong Park, Jeongsik Hong, Jayhyun Park, Hyunjung Kim

pp. 2291-2296

DOI:

10.2320/matertrans.M2013285

Abstract

In this study, we propose a flotation process to remove the arsenic from Samkwang mine tailings in South Korea, which contained a high arsenic content, in order to render them suitable for recycling. In order to maximize the arsenic removal from the mine tailings, three variables (type of collectors and activators, and solution pH) were systematically investigated. Characterization experiments (X-ray diffraction and electrokinetic property analyses) were carried out to complement the flotation results, and the results showed that the mine tailings were mainly composed of arsenopyrite (FeAsS), arsenic trioxide (As2O3, As4O6), arsenic pentoxide (As2O5) and quartz (SiO2). The flotation results obtained using different collectors (i.e., potassium amyl xanthate (PAX), sodium oleate, sodium dodecyl sulfate) revealed that arsenic removal efficiency was greatest in the presence of PAX, which was explained by the difference in the electrokinetic properties and the interaction type of collectors with arsenic-bearing minerals. Meanwhile, the addition of activators (Na2S, CuSO4, Na2S+CuSO4) and the pulp pH significantly affected the arsenic removal efficiency. The arsenic removal was maximized in the presence of mixed activators (Na2S+CuSO4) at low pH. The effect of activator type and pulp pH on the arsenic removal efficiency was attributed to the coupled role of the sulphidization of arsenic oxides (e.g., AS2O3, AS4O6 and AS2O5), the activation of sulphidized minerals, and the formation of dixanthogen. Lastly, based on the results obtained from the parameter optimization tests (i.e., type of collector and activator, and pulp pH), a series of flotation processes consisting of rougher flotation and two subsequent scavenging flotations was designed. The results demonstrated the capability of the process to successfully remove arsenic from Samkwang mine tailings for recycling.

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Arsenic Removal from Mine Tailings for Recycling via Flotation

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Biomimetic Fabrication of Indicalamus-Leaf-Like Structured Copper Surface with Superhydrophobic Properties

Lijing Chang, Tianchi Wang, Jian Kong, Chingping Wong

pp. 2297-2300

DOI:

10.2320/matertrans.M2013224

Abstract

Some plant leaves possess a superhydrophobicity because of the exclusive structures on their surfaces. Many methods were developed to imitate the leaf structures in order to obtain the superhydrophobic copper. However, it is difficult to simulate the natural complex structures perfectly through the traditional methods. Here, we report a method to use an indicalamus leaf as a template to fabricate superhydrophobic biomorphic copper on a carbon substrate (Cu/C). This Cu/C retained the microstructures of the leaf well. It exhibited excellent superhydrophobicity after it was modified with fluorine silane. The water contact angles of the resulting products were >160°, which exceed that of the indicalamus leaf (158°). Its sliding angle was <5°.

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Biomimetic Fabrication of Indicalamus-Leaf-Like Structured Copper Surface with Superhydrophobic Properties

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Rapid Consolidation and Mechanical Properties of Binderless Nanostructured (W,Ti)C by High-Frequency Induction Heating

Hyun-Su Kang, Hanjung Kwon, In-Jin Shon

pp. 2301-2304

DOI:

10.2320/matertrans.M2013273

Abstract

Commercial (W,Ti)C powder was high-energy ball milled for various durations and consolidated without a binder using the high-frequency induction heated sintering method (HFIHS). The effect of milling on the sintering behavior, crystallite size and mechanical properties of (W,Ti)C hard materials was evaluated. A dense nanostructured (W,Ti)C hard material with a relative density of up to 99% could be readily obtained within 3 min. The ball milling effectively refined the crystallite structure of (W,Ti)C powders and facilitated the subsequent densification. The sinter-onset temperature was reduced appreciably by the prior milling for 10 h from 1200 to 1000°C. Accordingly, the relative density of (W,Ti)C hard material increased as the milling time increases. It is clearly demonstrated that the quick densification of nanostructured (W,Ti)C bulk materials to near the theoretical density could be obtained by the combination of HFIHS and the preparatory high-energy ball milling process.

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Rapid Consolidation and Mechanical Properties of Binderless Nanostructured (W,Ti)C by High-Frequency Induction Heating

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Fabrication of Large-Scale Porous Aluminum by Enhanced Friction Powder Compaction Process through Traversing Tool Based on Sintering and Dissolution Process

Yoshihiko Hangai, Kousuke Zushida

pp. 2305-2308

DOI:

10.2320/matertrans.M2013318

Abstract

Open-cell porous aluminum with a controlled pore structure can be fabricated by sintering and dissolution process. To overcome the size limitation of porous aluminum fabricated by the sintering and dissolution process, an enhanced friction powder compaction (FPC) process for fabricating porous aluminum was proposed. In this process, the rotating tool plunged into the powder mixture and die during the FPC process is made to traverse perpendicular to the direction of plunging. It was found that long porous aluminum can be fabricated with a length equal to the tool traversing length. By scanning electron microscopy (SEM) observation of the pore structures, it was found that although the region in the vicinity of the traversing rotating tool had an elongated pore structure, almost the entire sample had a pore structure that was similar to the NaCl morphology, regardless of the traversing direction. From compression test, fabricated porous aluminum exhibited ductile fracture, which is considered to be attributed to the good bonding between aluminum particles.

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Fabrication of Large-Scale Porous Aluminum by Enhanced Friction Powder Compaction Process through Traversing Tool Based on Sintering and Dissolution Process

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Magnetic and Electronic Structures of Cobalt or Copper Substituted Mn2Sb

Junya Goto, Takatoshi Kakimoto, Shinpei Fujii, Keiichi Koyama

pp. 2309-2312

DOI:

10.2320/matertrans.M2013327

Abstract

First-principles total-energy calculations have been performed for the hypothetical case of x = 1 in Mn2−xXxSb (X = Co and Cu) for several magnetic states, using the full-potential linearized augmented plane wave method based on the generalized gradient approximation. The calculated total energy indicates that the Co (Cu) atom prefers the site Mn(I) to the site Mn(II) (Mn(II) to Mn(I)). This result of Co is consistent with the available neutron diffraction experiment. For CoMnSb where Co occupies the site Mn(I), the change of lattice constants (a and c) and c/a from AF2 to F is in good agreement with experimental trends. Our results indicate that the optimization of the ratio c/a (lattice distortion) is crucial to determine the most stable magnetic state and that the optimization of the atomic positions of the sites Mn(II) and Sb is also crucial.

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Magnetic and Electronic Structures of Cobalt or Copper Substituted Mn2Sb

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Preparation of Spherical Titanium Powders from Polygonal Titanium Hydride Powders by Radio Frequency Plasma Treatment

Sangsun Yang, Ji-Na Gwak, Tae-Soo Lim, Yong-Jin Kim, Jung-Yeul Yun

pp. 2313-2316

DOI:

10.2320/matertrans.M2013329

Abstract

This paper describes a novel dehydrogenation and spheroidization method using in-situ radio frequency (RF) thermal plasma treatment process to prepare spherical titanium (Ti) powders. Polygonal titanium hydride (TiH2) powders were successfully converted into spherical Ti powders and the size of the powders decreased from 30 to 21 µm by means of evaporation at the powder surface during the plasma treatment. Contaminants in the final products were drastically decreased due to the evaporation and emission of vapors during the plasma treatment.

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Preparation of Spherical Titanium Powders from Polygonal Titanium Hydride Powders by Radio Frequency Plasma Treatment

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