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Volume 73, Issue 7
Displaying 1-10 of 10 articles from this issue
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Takashi Ueda, Chinatsu Okamura, Kazuhiro Hasezaki2009 Volume 73 Issue 7 Pages 487-490
Published: 2009
Released on J-STAGE: July 01, 2009
JOURNAL FREE ACCESSSingle phase β-Zn4Sb3 was prepared by applying a two-stage heat treatment and the carrier concentration of β-Zn4Sb3 was controlled by doping with doping elements. The undoped and doped samples were prepared by direct melting followed by two-stage heat treatment at 723 and 673 K after solidification of the samples in sealed quartz ampoules. Impurity doping of the samples was performed by adding one atomic percent of Se, In, Pb, Te or Bi. The resulting samples were characterized by X-ray diffraction, differential thermal analysis (DTA), optical microscopy, electron probe micro-analysis (EPMA) and their Seebeck coefficients determined at room temperature. The undoped samples were shown by X-ray diffraction and DTA to comprise of single phase β-Zn4Sb3, while the doped samples contained multiple phases. From the measurements of the Seebeck coefficient, all samples were found to be of the p-type and all found to have almost the same values. These results indicate that β-Zn4Sb3 has limited solubility for these doping elements for controlling carrier concentration.
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Takashi Hamachiyo, Maki Ashida, Kazuhiro Hasezaki2009 Volume 73 Issue 7 Pages 491-494
Published: 2009
Released on J-STAGE: July 01, 2009
JOURNAL FREE ACCESSThe (Bi0.5Sb1.5)Te3 samples were prepared by mechanical alloying followed by hot pressing. Grain sizes were controlled in a range from 1 to 10 μm by controlling the sintering temperature in a range from 623 to 773 K. A fine measurement system was constructed for thermal conductivity based on the static comparison method. The thermal conductivity of the sample was 1.397 W/mK. The system has an accuracy of less than 1% for 1.411 W/mK of the reference quartz. The thermal conductivity was 0.89 W/mK for the sample sintered at 623 K, where the grain size of 1.75 μm was measured by scanning electron microscopy (SEM). The thermal conductivity increased on the sample sintered at 673 K because of grain growth and decreased on those sintered at the temperatures from 673 to 773 K because the increase of pore size caused to decrease thermal conductivity. The increase of thermal conductivity for the samples sintered at temperatures above 773 K was affected by the increase of carrier concentration.
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Zhao Fang, Yamaguchi Tomiko, Ikeda Hideyuki, Nishio Kazumasa2009 Volume 73 Issue 7 Pages 495-501
Published: 2009
Released on J-STAGE: July 01, 2009
JOURNAL FREE ACCESSThe γ→α transformation during continuous cooling was simulated by Monte Carlo method on conditions of ten stages of cooling rate and nine stages of austenite grain sizes. The authors have investigated effects of cooling rate and initial austenite grain size on γ→α transformation and ferrite grain growth. Main results obtained are as follows. The relationship between ferrite grain sizes and cooling rate showed that the ferrite grain sizes hyperbolically decreased against the cooling rate until 500°C/s and then the ferrite grain refinement hardly occurred. The ferrite grain sizes were decreased with an decrease of the initial austenite grain sizes. γ→α transformation rate was increased with the refinement of initial austenite grain. A linear relationship between initial austenite grain sizes and final ferrite grain sizes was obtained by simulation of continuous cooling.
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Shigeo Fukumoto, Sukeharu Nomoto2009 Volume 73 Issue 7 Pages 502-508
Published: 2009
Released on J-STAGE: July 01, 2009
JOURNAL FREE ACCESSThe numerical methodology for multi-phase field model has been presented in association with calculation of phase diagram. Calculations for FA-mode solidification of stainless steel were performed in conditions of multi-component and multi-phase alloy. It was confirmed that differences of residual δ-phase contents between several cooling rate conditions were in agreement with experimental measurements.
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Masao Morishita, Hiroaki Yamamoto2009 Volume 73 Issue 7 Pages 509-517
Published: 2009
Released on J-STAGE: July 01, 2009
JOURNAL FREE ACCESSIsobaric heat capacities, Cp, of La0.207Co0.207O0.586, La0.179Sr0.032Co0.210O0.579 and La0.109Sr0.109Co0.218O0.564 from near absolute zero Kelvin (2 K) to high temperature (1340 K) were measured by a relaxation method and differential scanning calorimetry. In the Cp values for La0.207Co0.207O0.586, two peaks at 628 K and 788 K were observed, consistent with the phase transition of from semi-conductor to metal and the phase transition at which magnetic moment increased as a function of temperature, respectively. Also, in the Cp values for La0.179Sr0.032Co0.210O0.579, such two-kinds of the phase transitions, that is the phase transition of semi-conductor to metal and the phase transition increasing the magnetic moment, were observed in the lower temperature ranges than in La0.207Co0.207O0.586. The phase transition from ferromagnetic- to paramagnetic-metal was caused at 239 K in La0.109Sr0.109Co0.218O0.564, while such two kinds of phase transitions observed in La0.207Co0.207O0.586 and La0.179Sr0.032Co0.210O0.579 were disappeared. The Debye temperature, ΘD, of La0.207Co0.207O0.586 was determined from the measured Cp values below 10 K. Its isochoric heat capacity, CV, was calculated by inserting ΘD into the Debye function, and the isochoric entropies of vibration, Δ0TSV, was determined, followed by calculating the entropy of vibration of oxygen vacancy, ΔfSTvib.V(Vö), by differentiation of Δ0TSV with the Vö content. The ΔfSTvib.V(Vö) obtained at 298 K and 800 K were 42.86 J·K-1·mol-1 and 44.00 J·K-1·mol-1, respectively. Such a large ΔfSTvib.V(Vö) appears to be one of important reason for foming Vö.
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Ayaka Kawagishi, Shohei Kawano, Minoru Obata, Yoshiyuki Kawaharada2009 Volume 73 Issue 7 Pages 518-526
Published: 2009
Released on J-STAGE: July 01, 2009
JOURNAL FREE ACCESSThe radiation induced segregation (RIS) at grain boundary (GB) in neutron irradiated type 316 stainless steel (SS) under boiling water reactor (BWR) condition was simulated by using the Fe-Cr-Ni-Si-Mo system model in which vacancy and interstitial mechanisms were considered for solute migration. The material constants used in the model were fixed to fit the experimental results on RIS at GB. The calculated depth and width of concentration profiles near GB in type 316 SS were comparable to the reported experimental results. The degrees of GB segregation were enhanced at lower neutron flux, and the tendency of flux dependence was similar to experimental results. The theoretical model is applicable to predict the RIS at GB to type 316 SS irradiated in BWR.
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Yong-Jai Kwon, Ichinori Shigematsu, Naobumi Saito2009 Volume 73 Issue 7 Pages 527-532
Published: 2009
Released on J-STAGE: July 01, 2009
JOURNAL FREE ACCESSThe surface region of the aluminum foams (trade name ALPORAS) was modified through the friction stir processing (FSP) which was performed by using friction phenomena with a high-speed rotating tool. The tool was rotated at speeds ranging from 820 to 2400 rpm, and plunged from the top surface of the aluminum foam, and then traversed at speeds ranging from 50 to 300 mm/min. The surface-modified zone (SMZ) had considerably smoother surface in comparison to the unprocessed zone (UZ). Especially for 1390 rpm and 150 mm/min, the smoothest surface was obtained, which was attributed to the smaller amount of pores in the SMZ. In addition, a very dense layer was formed near the surface of the SMZ through the localized collapse and densification of the cell structure near the surface region, which was attributed to the friction phenomena with the high-speed rotating tool. The mechanical properties of the aluminum foams were significantly improved through the FSP. Especially for 1390 rpm and 150 mm/min, the SMZ exhibited the highest average maximum indentation strength and energy absorption ability, which were equivalent to about 2.2 times the values of the UZ. The tool rotation speed and the tool traverse speed were very important parameters not only in controlling the surface morphology, but also in improving the mechanical properties of the aluminum foams. The FSP was a very effective technology for the remarkable improvement in the mechanical properties through the cell structure control of the surface region of the aluminum foams, without any dense skin materials.
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Jun Shinozaki, Izumi Muto, Hiroshi Ogawa, Nobuyoshi Hara2009 Volume 73 Issue 7 Pages 533-541
Published: 2009
Released on J-STAGE: July 01, 2009
JOURNAL FREE ACCESSThe effects of third element addition on the atmospheric corrosion resistance of zinc die-cast alloys were investigated by using the cyclic wet and dry test which simulated a diurnal change in specimen temperature and relative humidity in an actual outdoor environment with a constant dew point of 301 K. The amount of chloride ion deposition on the specimen surface was adjusted to 1.0×10-3 g·m-2 by the formation of a uniform layer of diluted synthetic sea water. The addition of magnesium (Mg) improved the corrosion resistance of zinc alloys, while the addition of nickel (Ni) degraded the corrosion resistance. X-ray photoelectron spectroscopy measurements indicated that corrosion products formed on Mg-added alloys contained Mg compounds such as oxide, hydroxide, and carbonate. Electrochemical polarization curves of as-polished specimens indicated that the addition of Mg has little effect on anodic and cathodic reaction rates. On the contrary, the addition of Ni or Ti promoted cathodic reaction. The polarization curves measured on specimens after 1 cycle of the cyclic corrosion test indicated that the corrosion products formed on Mg-containing alloys leaded to anodic passivation and inhibited cathodic reaction, while those on Ni-containing alloys accelerated cathodic reaction. Scanning electron microscopic observation on specimens after 1 cycle of the cyclic corrosion test showed that Mg-containing alloys had smooth and uniform surfaces with dense corrosion products, while Ni- or Ti-containing alloys had rough surfaces. It is concluded that the formation of thin and dense corrosion product layer is responsible for the high corrosion resistance of Mg-containing alloys.
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Akira Shimamoto, Hiroshi Ohkawara, Sung-mo Yang, Dae-kue Choi, Satoshi ...2009 Volume 73 Issue 7 Pages 542-547
Published: 2009
Released on J-STAGE: July 01, 2009
JOURNAL FREE ACCESSVarious stainless steels were investigated to examine the new NDE technique. The new NDE technique did not depend on either magnetization or demagnetization of materials. The magnetic flux caused by stress concentration in stainless steels was examined with the ultra sensitive magnetic flux density meter. Tensile and biaxial fatigue tests were conducted to observe the magnetic flux leakage. Results from biaxial fatigue tests indicated that the measured magnetic flux curves had local periodical cycles with global increasing tendencies. The defect evaluation would be possible by comparing the flux density value at the stress concentration regions with that of other areas.
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Errata
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Michiharu Ogawa, Toshiharu Noda, Masato Ueda, Masahiko Ikeda2009 Volume 73 Issue 7 Pages 548
Published: 2009
Released on J-STAGE: July 01, 2009
JOURNAL FREE ACCESSDownload PDF (62K)
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