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MATERIALS TRANSACTIONS Vol. 51 (2010), No. 12

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

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MATERIALS TRANSACTIONS Vol. 51 (2010), No. 12

Composition Control of Pd-Cu-Si Metallic Glassy Alloys for Thin Film Hydrogen Sensor

Susumu Kajita, Shin-ichi Yamaura, Hisamichi Kimura, Akihisa Inoue

pp. 2133-2138

Abstract

Pd-Cu-Si metallic glassy alloys were investigated as materials for a hydrogen sensor. We prepared thin films of Pd-Cu-Si metallic glassy alloys with varying compositions by RF magnetron sputtering method. And effects of their composition on thermal properties (Tg: glass transition temperature, Tx: crystallization temperature) and H2 response were examined. The H2 response was examined by measuring changes of electric resistance of the thin films exposed in N2 and H2. Thermal stability depending on thermal properties and large response to hydrogen are key requirements of the hydrogen sensor.
Tg and Tx and H2 response were significantly affected by Si content. Tg and Tx became higher and H2 response decreased when Si content was increased. As for metals, Pd and Cu, Tg increased and H2 response decreased with decreasing Pd/Cu atomic ratio among the samples having almost the same Si contents. These results can be explained by a trigonal prism cluster that is reported as a structural unit of Pd-based amorphous alloy. We discussed the effects of a trigonal prism cluster on thermal properties and H2 response, as well as the effects of Si content and Cu content on constructing trigonal prism clusters.

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Composition Control of Pd-Cu-Si Metallic Glassy Alloys for Thin Film Hydrogen Sensor

The Effects of Element Substitution on Electronic Structure, Electron Transport Properties, and Lattice Thermal Conductivity of Fe2VAl Thermoelectric Material

Hiroki Goto, Yu-ichi Terazawa, Masashi Mikami, Tsunehiro Takeuchi

pp. 2139-2144

Abstract

By using the first principles cluster calculation together with the band calculation, we identified that (a) Ru or Rh substitution for Fe and (b) Zr, Nb and Mo substitution for V are presumably useful for decreasing the lattice thermal conductivity without greatly affecting the electron transport properties. The Fe2V1−xZrxAl0.9−xSi0.1+x (x=0, 0.02, 0.04, 0.06, and 0.1) alloys indeed possessed the effective reduction in lattice thermal conductivity with increasing Zr concentration while the Seebeck coefficient showed very weak Zr concentration dependence. The Fe2−yIryV0.9−yTi0.1+yAl (y=0, 0.02, 0.04, 0.06, and 0.1) alloys, on the other hand, possessed drastic reduction of Seebeck coefficient most likely due to the newly introduced Ir 5d states. These experimental facts agree with the present theoretical-prediction, and it was clearly proved that the combinational use of cluster calculation and band calculation is very useful in developing new thermoelectric material.

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The Effects of Element Substitution on Electronic Structure, Electron Transport Properties, and Lattice Thermal Conductivity of Fe2VAl Thermoelectric Material

Preparation and Thermal Analysis of Sn-Ag Nano Solders

Tran Thai Bao, Yunkyum Kim, Joonho Lee, Jung-Goo Lee

pp. 2145-2149

Abstract

In this study, Sn-Ag nano solders of three different compositions (Sn-1.0 mass%Ag, Sn-3.5 mass%Ag and Sn-6.5 mass%Ag) were synthesized via arc-discharge process. The properties of Sn-Ag nano solders were analyzed using X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX), and Differential Scanning Calorimetry (DSC). Particle size relatively widely ranged from 10 nm to 340 nm. For Sn-1.0 mass%Ag and Sn-3.5 mass%Ag, average size was 200∼240 nm, and that for Sn-6.5 mass%Ag was 40∼50 nm with some extra-ordinary large particles of ∼100 nm. The melting points of the prepared SnAg nano solders were examined with DSC at different heating rates 1 K, 3 K and 5 K/min. The congruent melting point of Sn-Ag nano solders was found to be 487 K.

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Preparation and Thermal Analysis of Sn-Ag Nano Solders

All-Electron GW Calculations of Silicon, Diamond, and Silicon Carbide

Soh Ishii, Shohei Iwata, Kaoru Ohno

pp. 2150-2156

Abstract

All-electron GW calculations of Si, diamond, and SiC were carried out to obtain the quasiparticle energy spectra, for the first time, including both valence and core levels, corresponding to the ultraviolet and X-ray photoemission spectra (UPS and XPS). We used an all-electron mixed basis approach, in which wave functions are expanded with both plane waves and numerical atomic orbitals. In particular for the core states, our results obtained using the perturbative (non-self-consistent) GW approach are in good agreement with available experimental data. The quasiparticle energies of core levels so obtained are also in good agreement with experiments when we do not take into account the renormalization factor z. Moreover, we refer to the bandwidth of diamond and compare with experiments.

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All-Electron GW Calculations of Silicon, Diamond, and Silicon Carbide

Organic Suspension Behavior of Rutile TiO2 Nanoparticles with High Specific Surface Area

Min Ku Lee, Young Rang Uhm, Chang Kyu Rhee, Yong Bok Lee

pp. 2157-2161

Abstract

Sedimentation properties of the TiO2 nanoparticles with very high specific surface area (about 180 m2/g) based on the BET method have been investigated in various organic solvents. The TiO2 nanocolloid in the isopropyl alcohol displayed a considerably high electrostatic repulsive force, compared to that in other solvents, with negligible coalescence between the particles. Both the backscattered light flux measurements and scanning electron microscopy confirmed that in the cases of water, methyl alcohol and ethyl alcohol, a progressive sedimentation of the TiO2 particles was observed at the bottom due to a flocculation-induced particle growth, while a very stable TiO2 dispersion was observed in isopropyl alcohol.

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Organic Suspension Behavior of Rutile TiO2 Nanoparticles with High Specific Surface Area

{001} Texture Map of AA5182 Aluminum Alloy for High Temperature Uniaxial Compression

Hyeon-Mook Jeong, Kazuto Okayasu, Hiroshi Fukutomi

pp. 2162-2167

Abstract

The behavior of texture formation in AA5182 aluminum alloy was investigated by uniaxial compression tests under strain rates and temperatures ranging from 5.0×10−4 s−1 to 5.0×10−2 s−1 and from 673 K to 823 K, respectively. After the deformation, {011} (compression plane) or {001} fiber texture appears. It was found that {001} fiber texture was formed after the development of {011} fiber texture. The size of {001} grains is larger than the average grain size, suggesting that the {001} texture formation is attributed to grain boundary migration. In order to understand the relationship between texture sharpness of {001}, temperature and strain rate, the texture map is proposed. The {001} texture map elucidates that the balance between flow stress and deformation temperature is important for the development of {001} component when the viscous motion of dislocation is the dominant deformation mechanism.

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{001} Texture Map of AA5182 Aluminum Alloy for High Temperature Uniaxial Compression

Co-Axially Laminated Continuously Porous Composites in Al2O3-(m-ZrO2)/t-ZrO2 System for High Mechanical Strength

Swapan Kumar Sarkar, Byong Taek Lee

pp. 2168-2172

Abstract

A micro-channeled composite with a laminated microstructure was fabricated in Al2O3-ZrO2 composite system through a multipass extrusion process. Using this approach, Al2O3-(monoclinic-ZrO2)/tetragonal-ZrO2 continuously porous composites with concentric laminates were fabricated. The entire matrix phase had a laminated microstructure of alternate lamina of Al2O3-(m-ZrO2) and t-ZrO2 with a homogeneous thickness and central channel. Each of the continuous channels was coaxially encircled by a group of 5 alternate laminates. The laminate plane was oriented along the axis of the continuous channels. The design strategy was to incorporate concentric lamellar microstructural units in a macro scaled ceramic body comprising a central channel for each. The frame modification was intended to improve the material properties of the channeled body which in turn could act as a porous space for the inclusion of additional functional attributes. Filaments of polymer mixed ceramic powders and pore forming agent carbon were stacked in a pre-designed arrangement to obtain the desired microstructure and then extruded to obtain green composites. The channel diameter and channel frame thickness were approximately 198±10 μm and 158±10 μm, respectively. The channel frame region was furnished with 9 alternating shells of Al2O3-(m-ZrO2) and t-ZrO2 with a thickness of around 10∼20 μm. The material properties including the relative density and bending strength, which depend on temperature, were evaluated. The detailed microstructure of the channeled bodies was also characterized by Scanning Electron Microscope (SEM).

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Co-Axially Laminated Continuously Porous Composites in Al2O3-(m-ZrO2)/t-ZrO2 System for High Mechanical Strength

Synthesis of ε-FexN (2≤x≤3) Submicron Particles and the Diffusion Mechanism of Nitrogen Atoms

Makoto Minagawa, Hideto Yanagihara, Mikio Kishimoto, Eiji Kita

pp. 2173-2176

Abstract

We synthesized submicron-sized ε-FexN (2≤x≤3) particles by heating 180-nm Fe3O4 particles in an atmosphere of NH3, both with and without H2, and we studied their structural and magnetic properties. The nitride samples (first step nitridation) prepared by NH3 and annealed at 623 K (ε-Fe2N) had an expanded unit cell and were paramagnetic at room temperature. The purpose of H2 annealing, which was successively applied on the first step nitride sample, was to dissolve excess nitrogen atoms and reduce the lattice constant. The nitrogen concentrations were estimated from X-ray diffraction patterns. Saturation magnetization was found to increase with the H2 annealing time. The nitrogen diffusion constant in the submicron hcp particles was found to be 6.33×10−20 m2/s, which is about three orders of magnitude smaller than that of the bulk hcp iron nitrides. This may result from the coating materials, such as SiO2 and others, covering the inner core nitrides, where nitrogen atoms passed through during diffusion.

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Synthesis of ε-FexN (2≤x≤3) Submicron Particles and the Diffusion Mechanism of Nitrogen Atoms

FCC Surface Precipitation in Cu-Zn-Al after Low Angle GA+ Ion Irradiation

Eugenia Zelaya, Dominique Schryvers

pp. 2177-2180

Abstract

The precipitation of a disordered FCC surface structure after low angle Ga+ ion irradiation during focused ion beam thinning of a B2 Cu-Zn-Al alloy with ea=1.48 is reported. Conventional as well as high-resolution transmission electron microscopy techniques reveal FCC layers on both sides of the thinned sample. The occurrence of this structure is attributed to disordering and dezincification of the alloy resulting from the sputtering process during the irradiation. Changes in crystallographic sample orientation with respect to the incoming ion beam do not have a significant effect on the appearance of the FCC surface structure.

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FCC Surface Precipitation in Cu-Zn-Al after Low Angle GA+ Ion Irradiation

Response of Hydrogen-Induced Bending Deformation in ZrNi Amorphous Membranes

Keitaro Horikawa, Keita Yamaue, Hidetoshi Kobayashi

pp. 2181-2187

Abstract

When one side of the surface-modified ZrNi amorphous alloy membranes was hydrogen charged cathodically, the membrane with Pd plating bent rapidly with an increase in the hydrogen charging time. It was also found that the bending disappears completely when hydrogen gas was released from the specimen by heating. The repetitious bending movement was identified by a combination of hydrogen absorption and desorption without any surface damages in the membrane with Pd plating. On the basis of an X-ray diffraction analysis of the specimen surfaces before and after hydrogen charging, it was shown that the absorbed hydrogen was simply solved in the specimens and did not form hydrides during the bending. The hydrogen microprint technique revealed that the hydrogen-induced bending deformation was closely related to the gradient of the hydrogen concentration in the thickness direction of the membranes.

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Response of Hydrogen-Induced Bending Deformation in ZrNi Amorphous Membranes

Prediction of Nominal Stress-Strain Curves of a Multi-Layered Composite Material by FE Analysis

Long Li, Satoshi Iwasaki, Fuxing Yin, Kotobu Nagai

pp. 2188-2195

Abstract

In order to predict the nominal stress-strain (S-S) curve in tensile test for a multi-layered composite material consisting of a commercial purity titanium (hereafter, CP-Ti) with texture and an isotropic polycrystalline Ti-15V-3Cr-3Sn-3A1 (hereafter, Ti-15-3) alloy, three-dimensional finite element (FE) analysis with an equal strain hypothesis is employed. The validity of the present approach is verified by comparing the FE prediction with the tensile test. The results show that the yield stress and tensile stress of multi-layered composite material can be successfully predicted by FE analysis with the deviation smaller than 5%, and the uniform elongation of multi-layered composite material can be well predicted with the deviation smaller than 1%. The FE analysis also shows that the tension stress normal to interface between components is introduced at the onset of localized necking of multi-layered composites.

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Prediction of Nominal Stress-Strain Curves of a Multi-Layered Composite Material by FE Analysis

Temperature Dependence of Twinning Pseudoelasticity in Fe3Ga Single Crystals

Hiroyuki Y. Yasuda, Takuya Kishimoto, Yukichi Umakoshi

pp. 2196-2200

Abstract

Temperature dependence of twinning pseudoelasticity in D03-ordered Fe3Ga single crystals was examined. In the crystals annealed in the D03 single-phase region, 2.2T-type pseudo-twins were frequently introduced during loading at and below room temperature. Since the pseudo-twins had a high energy compared with a perfect twin, the untwinning took place during unloading to decrease their energy resulting in the twinning pseudoelasticity. Moreover, the twinning pseudoelasticity became more dominant with decreasing temperature, in contrast to that based on dislocation motion. In particular, high strain recovery during unloading was observed even at −180°C. Furthermore, the formation and annihilation stresses of the pseudo-twins were almost constant irrespective of deformation temperature at and below 100°C. This means that high driving force for the twinning pseudoelasticity was preserved even at low temperatures.

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Temperature Dependence of Twinning Pseudoelasticity in Fe3Ga Single Crystals

Crack Growth Behavior of IN100 Alloy Using In-Situ Observational Methods under High Temperature Creep and Fatigue Conditions

Daisuke Kobayashi, A. Toshimitu , Jr. Yokobori, Ryuji Sugiura, Akio Fuji

pp. 2201-2207

Abstract

The Ni-base IN100 super alloy, developed as a heat-resistant material for gas turbines, is subject to complex thermal and mechanical histories during a typical cycle of operation; i.e., the material is used under conditions of creep-fatigue interaction. To maintain operational safety and minimize maintenance costs, it is necessary to clarify the characteristics of fracture life, taking into account the effect of both creep and fatigue interaction on fracture lifespan. In this paper, an in situ observational testing method under the conditions of creep-fatigue interaction was conducted using IN100, and the effects of cycle- and time-dependent crack growth on the fracture life tf were investigated from the experimental relationship between the inverse value of fracture life 1⁄tf and the load frequency f. So far it has been difficult to comprehend the characteristics of the load frequency of the fracture life under creep and fatigue interaction, since the characteristics indicate nonlinear fluctuations depending on stress, stress holding time, material properties and temperature. In this research, creep ductility, stress holding time tH and temperature T were found to be unified as promoting factors of time dependent crack growth. Finally, the multiple effects of creep and fatigue on fracture life tf were clarified.

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Crack Growth Behavior of IN100 Alloy Using In-Situ Observational Methods under High Temperature Creep and Fatigue Conditions

Dye Degradation Activity and Stability of Perovskite-Type LaCoO3−x (x=0∼0.075)

Mengmeng Sun, Yinshan Jiang, Fangfei Li, Maosheng Xia, Bing Xue, Darui Liu

pp. 2208-2214

Abstract

Perovskite-type LaCoO3−x(x=0∼0.075) porous powder was synthesized via citrate sol-gel method. With calcination temperature increasing, its crystal structure changed from LaCoO3 to LaCoO2.925 with the increase in oxygen vacancy. The synthesized LaCoO3−x contains a large amount of adsorbed oxygen on its surface due to the existence of oxygen vacancy to some extent. Dye degradation activity of LaCoO3−x in methyl orange solution was investigated both under the visible light irradiation (>400 nm) and in the dark. LaCoO3−x exhibited dye degradation activity in the dark when being preserved in methyl orange solution for a long time caused by the reducibility of Co3+ in LaCoO3−x, and then dye molecule was oxidized gradually and slowly. The degradation rate was improved under the visible light due to the optical property of LaCoO3−x in visible light region. After degradation, methyl orange molecule may be decomposed to acetate group in a small amount. After use for a long time, some Co3+ was reduced to Co2+ accompanied by the formation of oxygen vacancy, and then LaCoO3 transformed to LaCoO2.925 gradually. For LaCoO3−x calcined at 800°C, LaCoO3−x perovskite skeleton structure was stable, and can be reused in recycle dye degradation.

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Dye Degradation Activity and Stability of Perovskite-Type LaCoO3−x (x=0∼0.075)

Degradation Process of Graphite Furnace Estimated from the Atomic Gas Temperature of Iron in Graphite Furnace Atomic Absorption Spectrometry

Tetsuya Ashino, Haruki Shimabukuro, Kazuaki Wagatsuma

pp. 2215-2219

Abstract

GF-AAS has been employed for determining several trace impurities in metallic materials. The analytical precision in the continuous analysis tends to worsen due to thermal degradation of the graphite furnace at the atomization stage. Changes of the atomization condition along with increasing the number of measurements were investigated by monitoring the temporal variation in the atomic gas temperature of iron. In a working solution containing low-concentration of acid, the inner wall of the graphite furnace was gradually damaged and then the efficiency for the atomizing process was reduced. In a working solution containing sub-mol/L order of sulfuric acid, thinning or cracking of the graphite furnace progressed more rapidly and the function of it was greatly deteriorated.

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Degradation Process of Graphite Furnace Estimated from the Atomic Gas Temperature of Iron in Graphite Furnace Atomic Absorption Spectrometry

Chemical State of Iron of LiFePO4 during Charge-Discharge Cycles Studied by In-Situ X-ray Absorption Spectroscopy

Katsuya Inoue, Shun Fujieda, Kozo Shinoda, Shigeru Suzuki, Yoshio Waseda

pp. 2220-2224

Abstract

In-situ X-ray absorption spectroscopy (XAS) at the Fe K-edge X-ray absorption near edge was used to investigate the chemical change of LiFePO4, which is a candidate cathode material for lithium ion batteries, during charge-discharge cycles. The relative amount of FePO4 formed in the LiFePO4 by the charge-discharge cycles was estimated from the XAS spectra. The results show that the amount of FePO4 in the LiFePO4 increased with charging and decreased with discharging. While a linear relationship between the relative amount of FePO4 and electrical capacity was observed during the initial charging, it deviated from linearity during the charge-discharge cycles. This may be attributed to the irreversible diffusion paths of lithium ions and/or the partial formation of inactive FePO4 in the LiFePO4 during the charge-discharge cycles. It is shown that in-situ XAS has sufficient potential to nondestructively characterize heterogeneous electrochemical reactions in electrode materials during charge-discharge cycles.

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Chemical State of Iron of LiFePO4 during Charge-Discharge Cycles Studied by In-Situ X-ray Absorption Spectroscopy

Fine Patterning of Titanium Oxide Film Loaded with Hydroxyapatite Using Photopatterning and Anodic Oxidation

Yasuhiro Tamagawa, Yuh Yatsuo, Hiroshi Horikawa, Mitsunobu Iwasaki

pp. 2225-2229

Abstract

The patterned titania gel film fabricated by UV-irradiation through a mask and leaching was anodized by direct current electrolysis or pulse electrolysis. The patterning prepared through the two electrolyses was quite contrasted in that masking part and unmasking part was anodized in direct electrolysis and in pulse electrolysis, respectively. In addition, the oxide film thickness obtained using pulse electrolysis was thinner than that using direct current electrolysis. Thus, a combination of the photopatterning and pulse electrolysis made it possible to fabricate hydroxyapatite (HAp)-fixed and thinner titanium oxide film with fine pattern on titanium plate.

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Fine Patterning of Titanium Oxide Film Loaded with Hydroxyapatite Using Photopatterning and Anodic Oxidation

Predicting the Adiabatic Temperature of Transparent Y3Al5O12 Prepared via Combustion Synthesis under Ultra-High Gravity

Yuepeng Song, Hyoung Soep Kim, Chong Soo Lee, Jiangtao Li, Jun Pei

pp. 2230-2235

Abstract

In this paper, the adiabatic temperature of a transparent yttrium aluminum garnet (YAG) preparation using a NiO/Al/Y2O3 aluminothermic system was calculated based on a thermodynamic theory. The results show that the adiabatic temperature without preheating reaches the 2891 K, which is higher than the melting points of YAG and Ni. The liquid phase mixture products can be separated and densified under ultra-high gravity (UHG). In the preheating temperature range of 620K∼2790K to the reactants of this system, the adiabatic temperature is the same as 3156 K, the boiling point of Ni products. The theoretical analyses and experimental results prove the effectiveness of the YAG fabricated via combustion synthesis under an ultra-high gravity field.

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Predicting the Adiabatic Temperature of Transparent Y3Al5O12 Prepared via Combustion Synthesis under Ultra-High Gravity

Effects of Steel Coatings on Electrode Life in Resistance Spot Welding of Galvannealed Steel Sheets

X. Hu, G. Zou, S. J. Dong, M. Y. Lee, J. P. Jung, Y. Zhou

pp. 2236-2242

Abstract

The effects of different galvannealed (GA) coatings, containing Fe varying from 7.0 to 11.4 mass%, on steel sheets on the electrode life in resistance spot welding (RSW) have been investigated with metallurgical analysis of the coating microstructures and properties, and the surfaces and cross-sections of failed electrodes. The results showed that the electrode life in RSW of GA steel with 11.4 mass% Fe in coating was 110% higher than that with coatings containing 7.0 or 9.6 mass% Fe. The improvement was believed to be caused by the build-up of a Fe-rich alloy layer on the electrode surface, which could serve as a barrier to prevent copper loss from the electrode surfaces to the steel sheets, thus reducing the growth rate of the electrode tip face diameters. In addition, higher Fe content in the coating resulted in increased contact resistance and hence a lower welding current needed in RSW.

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Effects of Steel Coatings on Electrode Life in Resistance Spot Welding of Galvannealed Steel Sheets

Enhanced Mechanical Properties of Injection Molded 17-4PH Stainless Steel through Reduction of Silica Particles by Graphite Additions

Che-Wei Chang, Po-Han Chen, Kuen-Shyang Hwang

pp. 2243-2250

Abstract

Silica particles are often found in sintered 17-4PH stainless steels when water atomized powder is used. To eliminate the SiO2 particles and to improve the mechanical properties and corrosion resistance, graphite powders were mixed in this study with 17-4PH powders and binders during the kneading step of the powder injection molding process. The measurements of carbon and oxygen contents in tensile specimens and microstructure observations confirm the reduction of silica particles by graphite powders during vacuum sintering. The optimum content of the graphite addition is 0.26 mass%, with which most SiO2 particles are reduced and the final carbon and oxygen contents are 0.03 and 0.01 mass%, respectively. These changes of compositions decrease the amount of δ-ferrite in the as-sintered compact to 4 vol%, lower than the 10 vol% of the compact without any graphite additions. After solutioning and aging treatment, the hardness, tensile strength, and ductility are HRC 41, 1310 MPa, and 9.0%, respectively. These properties are better than the typical values of 17-4PH reported in the literature and the corrosion resistance remains similar to that without any graphite additions. The relevant mechanisms on the changes of these properties are discussed with a focus on the effects of graphite addition on the residual carbon content, fractions of δ-ferrite and martensite, silica amount, and density.

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Enhanced Mechanical Properties of Injection Molded 17-4PH Stainless Steel through Reduction of Silica Particles by Graphite Additions

Swelling of Copper Powders during Sintering of Heat Pipes in Hydrogen-Containing Atmospheres

Yueh-Ju Lin, Kuen-Shyang Hwang

pp. 2251-2258

Abstract

Swelling of copper powders often occurs during sintering of heat pipes and causes problems in removing core rods from the fixture. To address this problem, this study examines the effects of sintering atmospheres (H2, N2-10%H2, N2, and vacuum) and oxygen content in copper powders on the density and dimensional changes of loose-powder-sintered copper compacts. The results show that serious powder cracking occurs when high oxygen content is present in the as-received powder and when the sintering atmosphere contains hydrogen due to the hydrogen-oxygen reaction forming water vapors. The dilatometer curve indicates that such reaction starts between 673 and 723 K. Comparison of the pycnometer density and Archimedes’ density of sintered compacts suggests that the swelling is mainly caused by cracking of the powder, and that the plastic deformation caused by the expansion of trapped gas in isolated pores plays a minor role. To prevent such cracking and swelling, copper powders with low oxygen content should be used, and the sintering should be carried out in an atmosphere with low hydrogen content or under vacuum or inert gas atmosphere.

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Swelling of Copper Powders during Sintering of Heat Pipes in Hydrogen-Containing Atmospheres

Effects of Electron Beam Irradiation on Impact Value of Novolak-Type Phenol CFRTP

Hiroaki Takei, Keisuke Iwata, Michelle Salvia, Alain Vautrin, Yoshitake Nishi

pp. 2259-2265

Abstract

Homogeneous low voltage electron beam irradiation (HLEBI) improved the Charpy impact value (auc) of carbon fiber reinforced thermoplastic novolak-type phenol polymers (CFRTP) composite sheets with 2 mm thickness, although the irradiated depth estimated was 182.5±33.5 μm on both side surfaces. The auc values at low fracture probability (Pf) of 0.06 for CFRTP irradiated at 0.30 MGy (kJg−1) was 60 kJm−2, which was 32% higher (46 kJm−2) than for CFRTP before irradiation. Although the lowest impact values (as) estimated by three-parameter Weibull equation was zero for CFRTP before irradiation, HLEBI enhanced the as value. The highest as value was more than 59 kJm−2 for CFRTP irradiated at 0.30 MGy. Thus, HLEBI remarkably enhanced the as value, as well as the auc value at low Pf value. Since HLEBI enhanced the Weibull coefficient (n), it also enhanced the reproducibility of CFRTP samples. The maximum n value was found at 0.22 MGy HLEBI dose. The interfacial friction force, as well as the strengthening of both carbon fiber and novolak-type phenol resin probably contributed to the HLEBI effects to enhance the as value of CFRTP, as well as enhancement of reproducibility.

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Effects of Electron Beam Irradiation on Impact Value of Novolak-Type Phenol CFRTP

Synthesis of Ultrafine ZrC Powders by Novel Reduction Process

Dong-Won Lee, Sun-Mi Jin, Ji-Hoon Yu, Hye-Moon Lee

pp. 2266-2268

Abstract

Zirconium carbide (ZrC) is becoming a promising hard material for high-temperature applications in the tool and nuclear energy industries. There are few methods for fabricating micrometric ZrC particles including the carbothermal reduction of zirconium dioxide and direct exothermic reaction of pure zirconium and graphite powder. A novel reduction method has been developed in this study to fabricate ultrafine ZrC powders using ZrCl4 and carbon black as source materials and sodium bicarbonate (NaHCO3) as a reductant. Simple rotation ball-milling was used to reduce the Cl-components in zirconium chloride by the sodium component in sodium bicarbonate, leading to the formation of non-toxic and stable sodium chloride. ZrC particles 150 nm in size were successfully obtained after heat treatment at 1673 K. The carbon content in the product could also be controlled by changing the initial carbon fraction.

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Synthesis of Ultrafine ZrC Powders by Novel Reduction Process

Effects of Actuating Pressure Waveforms on the Droplet Behavior in a Piezoelectric Inkjet

Hsuan-Chung Wu, Huey-Jiuan Lin

pp. 2269-2276

Abstract

This paper presents a numerical analysis of a piezoelectric actuated droplet generator. A three-dimensional finite difference numerical model based on a SOLA (solution algorithm) scheme for the solution of governing equations of the flow field and a volume-of-fluid method for tracing the fluid interfaces are presented. The surface tension is modeled using a continuum surface force concept and thus computed as a function of the interfacial curvature. The pressure pulse at the nozzle inlet, which is related to the applied voltage, was imposed according to the propagation theory of acoustic waves. The effects of the pressure waveforms, including positive and negative pressure amplitudes, operating period and acceleration of the positive pressure, on the droplet ejection process are simulated. The performance of piezoelectric inkjet: droplet break time, droplet tail length, droplet velocity and droplet volume are analyzed. The simulation results show that the tail length and volume of the droplet increase with the amplitude of the positive pressure and operating period. The breakup time of the droplet is shorter when the amplitude of the negative pressure increases. The factors that influence satellite droplets are also investigated in this study.

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Effects of Actuating Pressure Waveforms on the Droplet Behavior in a Piezoelectric Inkjet

Fabrication of Hydroxyapatite Film on Ti-29Nb-13Ta-4.6Zr Using a MOCVD Technique

Harumi Tsutsumi, Mitsuo Niinomi, Masaaki Nakai, Tatsuya Gozawa, Toshikazu Akahori, Kazumi Saito, Rong Tu, Takashi Goto

pp. 2277-2283

Abstract

A hydroxyapatite (HAp) film was fabricated on the surface of Ti-29Nb-13Ta-4.6Zr (TNTZ) using a metal-organic chemical vapor deposition (MOCVD) technique, and the mechanical biocompatibility and HAp formability of HAp-coated TNTZ were evaluated and discussed in this study. HAp film is fabricated on the surface of TNTZ by controlling the heating temperature of the source (bis-dipivaloylmethanatocalcium (Ca(dpm)2) and (C6H5O)3PO). An α-phase precipitates in the TNTZ matrix after heating the substrate, and the mechanical properties and Young’s modulus of HAp-coated TNTZ are improved. HAp-coated TNTZ maintains excellent mechanical biocompatibility. The formability of HAp on HAp-coated TNTZ in Hank’s balanced salt solution is better than that of HAp on non-coated TNTZ.

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Fabrication of Hydroxyapatite Film on Ti-29Nb-13Ta-4.6Zr Using a MOCVD Technique

Creep Behavior of Hypoeutectic Mg-Ca Binary Alloys

Atsushi Shibayama, Yoshihiro Terada, Yoshinori Murata, Masahiko Morinaga

pp. 2284-2288

Abstract

The creep behavior of hypoeutectic Mg-xCa (x=2.8, 8.7, and 14.8 mass%) cast alloys was investigated at 473 K under stresses between 30 and 60 MPa. The microstructure of the alloys is characterized by the discontinuously distributed primary α-Mg phase in a continuous eutectic fine lamellar structure consisting of α-Mg and C14-Mg2Ca phases. The creep curves of the alloys exhibit three stages: a normal transient creep stage, a minimum creep rate stage, and, finally, an accelerating stage. The decrease in the creep rate during the transient stage becomes pronounced and the onset of the accelerating stage is delayed with increasing calcium concentration. The stress exponent of the minimum creep rate is four for each alloy for stresses below the yield stress. The creep of the alloys is controlled by the high-temperature climb of dislocations. The effect of the eutectic fine lamellar structure on creep strength is prominent when the volume fraction is below 50%.

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Creep Behavior of Hypoeutectic Mg-Ca Binary Alloys

Synthesis of LnCuS2 (Ln=Ce, Pr, Nd, Sm, Gd, and Tb) Powder by Polymerized Complex Method and CS2 Gas Sulfurization

Omar Massoud Saad, Toshihiro Kuzuya, Shinji Hirai, Michihiro Ohta

pp. 2289-2293

Abstract

Rare earth copper sulfides, LnCuS2 (Ln=Ce, Pr, Nd, Sm, Gd and Tb), powders were synthesized by the following procedure: (1) Ln-Cu complex oxide was synthesized using the polymerized complex method, and (2) LnCuO2 was sulfurized by the CS2 gas. CS2 gas sulfurization combined with a polymerized complex method can reduce a reaction temperature and a duration time. TG-DTA and XRD results indicated that Ln′-Cu polymerized complex (Ln=Pr, Nd, Sm and Gd) was decomposed into Ln′2O3 (via Ln′2OCO3) and Cu/CuO. Ln′2O3 reacted with CuO to form Ln′2CuO4 complex oxide. In the case of Ce and Tb (Ln″), a Ln″-Cu polymerized complex was decomposed into Ln″O2 and Cu/CuO. Ln″2CuO4 phase was not observed in these cases. In sulfurization reaction, XRD indicates that Ln′CuS2 was formed via a formation of Ln′OCuS. On the other hand, Ln″CuS2 is considered to be formed via a solid state reaction between Ln″2S3 and Cu2S. The contents of oxygen and carbon impurities in the products depend on the sulfurization reaction conditions. For example, the PrCuS2 powder was obtained with low impurity contents of 0.07 mass% C and 0.073 mass% O by sulfurization at 1223 K.

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Synthesis of LnCuS2 (Ln=Ce, Pr, Nd, Sm, Gd, and Tb) Powder by Polymerized Complex Method and CS2 Gas Sulfurization

Transformation Characterization of Ni(OH)2/NiOOH in Ni-Pt Films Using an Electrochemical Quartz Crystal Microbalance for Ethanol Sensors

Jian-Jia Huang, Weng-Sing Hwang, Yu-Ching Weng, Tse-Chuan Chou

pp. 2294-2303

Abstract

The transformation characterization of Ni(OH)2/NiOOH in Ni-Pt films was investigated using an electrochemical quartz crystal microbalance (EQCM) in an alkaline electrolyte under various experiment conditions. The Ni-Pt films were prepared by electro-deposition on gold-coated quartz crystal chips. When cyclic voltammetry (CV) was performed continually, the OH ions diffused into the Ni-Pt film to form Ni(OH)2. The transformation from mixed type Ni(OH)2/NiOOH to β-Ni(OH)2/β-NiOOH occurred gradually. The phase transformation of Ni(OH)2/NiOOH was strongly affected by the composition, deposited weight, and aging conditions of the Ni-Pt films. The results show that high Pt content or high deposited weight of Ni-Pt films postponed the transformation to the β-Ni(OH)2/β-NiOOH phase. β-Ni(OH)2 was directly formed by dipping fresh Ni-Pt films in KOH solution while mixed type Ni(OH)2 was obtained after aging fresh Ni-Pt films in humid O2 atmosphere. These two pre-aging conditions accelerate the phase transformation of Ni(OH)2/NiOOH into β-Ni(OH)2/β-NiOOH. After 1050 and 2100 cycles of the electro-oxidation process of ethanol, the Ni(OH)2 phase in Ni-Pt films still remained in a β-Ni(OH)2-like phase with some α-Ni(OH)2. The well-defined β-Ni(OH)2 phase that formed in the Ni-Pt film after 1050 cycles of CV was more stable in a KOH solution than in a humid O2 atmosphere at room temperature. Ni-Pt films were also evaluated as a sensing element for an ethanol sensor.

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Transformation Characterization of Ni(OH)2/NiOOH in Ni-Pt Films Using an Electrochemical Quartz Crystal Microbalance for Ethanol Sensors

Tensile Strength Enhancement by Shortening Glass Fibers with Sub-Millimeter Length in Bulk Molding Polymer Compound

Michael C. Faudree, Yoshitake Nishi

pp. 2304-2310

Abstract

Effects of short fiber with sub-millimeter length on tensile strain, εf and tensile strength, σf were investigated for a bulk molding compound (BMC) glass fiber reinforced polymer (GFRP) composite with 20 mass% E-short glass fibers. The εf and σf values of BMC-GFRP samples with 0.44 mm short fibers were almost 40 and 60% higher than that of BMC-GFRP samples with long fibers (3.2 and 6.4 mm in length), as well as more than 65 and 110% higher than that of the filled fiber free resin, respectively. The reduced fracture strain (εf⁄εf,6.4) and reduced tensile strength (σf⁄σf,6.4) as a function of the fiber end density, ρE (cm−3) were expressed by the following equations with linear regression as (εf⁄εf,6.4=1.21×10−7ρE+0.965) and (σf⁄σf,6.4=1.51×10−7ρE+0.998). Acoustic emission (AE) analysis detected microcracking was increased threefold by shortening the mean fiber length from 6.4 to 0.44 mm. Scanning electron microscopy (SEM) results showed increased fiber/matrix debonding at fiber ends and along fiber lengths in the 0.44 mm samples compared with that reported for 6.4 mm samples. The fiber debonding is thought to impart an internal strain field in the matrix surrounding each fiber resulting in volume expansion sites, hence compressive stress sites which absorb energy from an approaching crack tip front in the nearby vicinity halting the crack’s advance. Therefore, more microcracks can be tolerated increasing fracture strain. Moreover, the critical crack length range for thermoset polymers was calculated to be approximately 0.50<2ac<5.0 mm from reported KIC results in the literature, and is greater than the 0.44 mm mean fiber length. The probability of a microcrack propagating above 0.44 mm before it encounters a matrix compressive site, therefore is reduced. Furthermore, increased microcracking in the vicinity of the main crack tip acts to reduce the main crack tip stress concentration. All of these serve to prevent crack propagation resulting in enhancement of fracture strain in the BMC-GFRP.

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Tensile Strength Enhancement by Shortening Glass Fibers with Sub-Millimeter Length in Bulk Molding Polymer Compound

The Influence of Technological Process on Dry Sliding Wear Behaviour of Titanium Carbide Reinforcement Copper Matrix Composites

Jian Zhuang, YongBin Liu, ZhanYi Cao, YueYing Li

pp. 2311-2317

Abstract

Two types of milled process are used in SPS to prepare TiC reinforcement Cu matrix composites: (a) Ti and C powders are milled together, and then mixed with Cu powders; (b) All the three kinds of powders are milled together. The microstructures of specimens were analyzed with XRD, SEM and TEM. The pin-disk wear test was carried. It was found that TiC reinforcement formed in sintering by direct reaction in the method (a). However, in method (b), diffused reaction mechanism has also been confirmed in TiC forming process. All the composites exhibit good wear resistance at 200N normal load with lowest wear lose 1.4×10−5 mm3/Nm (method (a)) and 1.12×10−5 mm3/Nm (method (b)) respectively. The composite sintered from the powders of the method (b) shows lower wear lose and a steadier friction coefficient at even normal load then the composites sintered from the other powders which show third body abrasion in wear test.

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The Influence of Technological Process on Dry Sliding Wear Behaviour of Titanium Carbide Reinforcement Copper Matrix Composites

A New Austenitic FeMnAlCrC Alloy with High-Strength, High-Ductility, and Moderate Corrosion Resistance

GowDong Tsay, ChihLung Lin, ChuenGuang Chao, TzengFeng Liu

pp. 2318-2321

Abstract

In this study, a new austenitic Fe-28%Mn-9%Al-6%Cr-1.8%C (in mass%) alloy is developed. Because the alloy contains a high density of fine (Fe,Mn)3AlC carbides within the austenite matrix, the alloy in the as-quenched condition exhibits an excellent combination of strength and ductility comparable to that of the aged FeMnAlC alloys. In addition, owing to the formation of a layer of Cr and Al oxides in the passive film formed on the alloys, the corrosion potential Ecorr (−538 mV) and the pitting potential Epp (−25 mV) of the present alloy in 3.5% NaCl solution are considerably higher than the Ecorr (−920∼−789 mV) and Epp (−500∼−240 mV) values of the as-quenched and aged FeMnAlC alloys. Whereas the tensile strength of the present alloy is almost the same as that of conventional AISI 410 martensitic stainless steel, the present alloy possesses superior ductility than AISI 410 martensitic stainless steel. Furthermore, in 3.5% NaCl solution, the Epp (−25 mV) of the present alloy is noticeably higher than that (−250∼−100 mV) of the conventional AISI 410 martensitic stainless steel. These results indicate that the present alloy in the as-quenched condition can possess high-strength and high-ductility as well as moderate corrosion resistance.

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A New Austenitic FeMnAlCrC Alloy with High-Strength, High-Ductility, and Moderate Corrosion Resistance

Effects of Organic Additive during Thermal Reduction of Platinum Electrodes for Dye-Sensitized Solar Cells

Min-Hye Kim, Young-Uk Kwon

pp. 2322-2324

Abstract

We report on a method to prepare Pt electrodes with homogeneously dispersed Pt nanoparticles on fluorine-doped tin oxide substrates by adding an organic additive, hydroxypropyl cellulose (HPC), in the Pt precursor solution for thermal decomposition on the substrates. The Pt electrodes prepared with various amounts of added HPC are characterized electrochemically by cyclovoltammetry and electrochemical impedance spectroscopy. The addition of HPC increases the surface area of the Pt electrode and, hence, the electrocatalytic activity. The overall conversion efficiency of a dye-sensitized solar cell is increased by 12.7% by using such a Pt electrode as a cathode.

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Effects of Organic Additive during Thermal Reduction of Platinum Electrodes for Dye-Sensitized Solar Cells

Microstructure and Strain Rate Sensitivity of Mg-11Li-3Al-1Ca Alloy

L. R. Cheng, Z. Y. Cao, Y. B. Liu, L. Zhang, T. Q. Li, G. H. Su

pp. 2325-2328

Abstract

As-cast and extruded Mg-11Li-3Al-1Ca alloys were successfully prepared. The microstructure of specimens was analyzed with OM, SEM, EDS and XRD. It was found that as-cast specimens were composed of β phase (Lithium), small pieces of divorced eutectic α phase (Magnesium), MgLi2Al and Al2Ca compounds. During the extrusion process, the microstructure was refined and partial recrystallization was observed. Uniaxial tension tests were carried out under different strain rate. The ultimate intensities were obviously higher than common β phase Mg-Li alloys to compare with past studies. Deformation capacity of the extruded specimen at room temperature was estimated by strain-rate sensitivity exponent (m value), which was 0.071. Serrated flows were apparent through out the deformation history and the phenomenon was interpreted through the competition between dynamic strain aging (DSA) of solute atoms and shearing of precipitates by dislocations.

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Microstructure and Strain Rate Sensitivity of Mg-11Li-3Al-1Ca Alloy

Characteristics of Isotropically Conductive Adhesive (ICA) Filled with Carbon Nanotubes (CNTs) and Low-Melting-Point Alloy Fillers

Byung-Seung Yim, Jong-Min Kim

pp. 2329-2331

Abstract

A new class of isotropic conductive adhesive (ICA) using a carbon nanotubes (CNTs) and a low-melting-point alloy (LMPA) fillers has been developed. We investigated the fundamental materials characteristics including curing behavior and temperature-dependant viscous property of ICA. In addition, the morphology of conduction paths in each ICA was investigated using X-ray inspection systems and an optical microscope. Mechanical and electrical characteristics of formulated ICAs were determined and compared with those of three kinds of conventional ICAs filled with Ag flakes. The CNT-filled solderable ICA formed good metallurgical interconnection between upper and corresponding lower electrode. In addition, the results indicated that the CNT-filled ICA exhibit lower electrical resistance and higher mechanical strength, as compared with those of conventional ICAs.

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Characteristics of Isotropically Conductive Adhesive (ICA) Filled with Carbon Nanotubes (CNTs) and Low-Melting-Point Alloy Fillers

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