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Volume 69, Issue 9
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Hayato Kita, Masanari Kimoto, Takeo Kudo2005 Volume 69 Issue 9 Pages 805-809
Published: 2005
Released on J-STAGE: October 12, 2005
JOURNAL FREE ACCESSInfluence of Al content on corrosion resistance of Mg-Al-Zn alloys containing 1 to 9 mass%Al was investigated in chloride environments. The corrosion rate decreased with increasing the Al content in the alloys regardless of the testing methods such as salt immersion test (SIT) and salt spray test (SST). The immersion tests in buffered solutions at constant pH also clarified that the effect of the Al content on the corrosion resistance is largest around pH 10, and diminished when pH is raised up to 12, where Mg-Al-Zn alloys are passivated by the formation of Mg-hydroxide on the surface. XPS analysis revealed that Al was concentrated in the surface film, especially around pH 10, and its concentration was increased with the Al content in the alloys. The high corrosion resistance of Mg-Al-Zn alloys with high Al can be attributed to the formation of the Al-rich surface film in chloride environments.
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Kosei Kominato, Hirofumi Homma, Hideyuki Saitoh2005 Volume 69 Issue 9 Pages 810-814
Published: 2005
Released on J-STAGE: October 12, 2005
JOURNAL FREE ACCESSWe investigated the relation between hydrogenation property and eutectic structure of a Mg-Mg2Ni two-phase alloy that is made by melting Mg and Ni in a sealed steel crucible. Both the hydrogen content and the plateau pressure increase with the rise of the measurement temperature of PCT (Pressure-Composition-Temperature) curve for both the furnace cooled and water cooled specimens. In these specimens, the maximum hydrogen contents increase up to 5.6 mass% as the increase of the cycle number of PCT measurement at 400°C. On the other hand, the maximum hydrogen content of the heat treated specimen does not depend on the PCT cycle number, and maintains a higher value of about 5.6 mass%. The eutectic structures are fine for both the furnace cooled and water cooled specimens, and coarse for the heat-treated specimen. The hydrogenation behavior depends on the morphology of the eutectic structure, that is, the coarsening of the eutectic structure causes the acceleration of hydrogenation.
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Shinsuke Nakano, Shunsuke Muto, Tetsuo Tanabe2005 Volume 69 Issue 9 Pages 815-824
Published: 2005
Released on J-STAGE: October 12, 2005
JOURNAL FREE ACCESSChanges in hardness of several representative ceramics and semiconductors associated with ion irradiation were systematically studied, using a combined method of nanoindentation and finite element analysis. We established a new method for precisely extracting hardness of the embedded damaged layer of ion-irradiated samples. The method was applied to silicon carbide, α-quartz, silica glass and silicon. To semi-quantitatively discuss their mechanical properties changed by irradiation, we introduced a phenomenological model expressed by a set of kinetic equations, and extracted material parameters by fitting the experimental data with the theoretical model. Finally we propose a new atomistic mechanism for plastic deformations of covalent amorphous materials. The present results would give a standard framework to discuss the mechanical property changes of ceramics irradiated with energetic particle.
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Yoshiyasu Itoh, Shoko Suyama, Hideyasu Andoh, Takahiko Shindoh2005 Volume 69 Issue 9 Pages 825-830
Published: 2005
Released on J-STAGE: October 12, 2005
JOURNAL FREE ACCESSTungsten/copper coatings had been developed by using a plasma spraying process for the electric arc resistance. However, the heat resistant properties, such as the delamination of tungsten/copper coatings, were not clarified. In this study, a plasma heating apparatus with a cooling function of specimen is newly developed for the evaluation of heat resistant of tungsten/copper coatings, which are sprayed by a low pressure plasma spraying process. As a result, it is verified using the plasma heating apparatus that the delamination lives of tungsten/copper coatings can be evaluated by the thermal cycle test under gradient temperature distribution. Also, it is confirmed by stress analyses that the delamination of tungsten/copper coatings is mainly caused by the stress singularity at the edge of coating interface. Consequently, the reduction of stress singularity at the edge of tungsten/copper coatings is effective for lengthening of the delamination lives.
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Hidehiro Yoshida, Kenji Nakatani, Hitoshi Nagayama, Takahisa Yamamoto, ...2005 Volume 69 Issue 9 Pages 831-834
Published: 2005
Released on J-STAGE: October 12, 2005
JOURNAL FREE ACCESSSuperplastic behavior in a fine-grained, GeO2-doped 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) with the dopant level of 0.2 to 3 mol% was examined at 1400°C under an initial strain rate of 1.3×10-4 s-1. Microstructure and chemical composition at the grain boundaries were examined by high-resolution transmission electron microscopy (HRTEM) combined with an X-ray energy dispersive spectrometer (EDS). No secondary phase was observed along the grain boundaries, though EDS analysis indicated the segregation of Ge cations along the grain boundaries. The Ge content at the grain boundaries tends to increase with increasing the total amount of GeO2 addition, but saturate over the doping level of 2 mol%. Dependence of flow stress reduction on the total amount of GeO2 addition has a good correlation with Ge content at the grain boundaries. This fact indicates that the GeO2-doping effect on the flow stress in 3Y-TZP is caused mainly from the grain boundary segregation of Ge cations.
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Hidehiro Yoshida, Hitoshi Nagayama, Akihide Kuwabara, Taketo Sakuma2005 Volume 69 Issue 9 Pages 835-840
Published: 2005
Released on J-STAGE: October 12, 2005
JOURNAL FREE ACCESSTemperature and strain rate dependence on high temperature elongation to failure in fine-grained ceramics is phenomenologically explained from grain growth behavior during deformation and the superplastic flow behavior. The elongation to failure at temperatures between 1573 and 1773 K was analyzed for 2 mol%TiO2 and 2 mol%GeO2 co-doped tetragonal zirconia polycrystal (TZP), which exhibits excellent high temperature ductility. The improvement in the high temperature ductility in TZP is attributed to dopant cation segregation in the vicinity of the grain boundaries. The phenomenological analysis revealed that co-doping of Ti and Ge cations increases the grain size at the time of failure, as a parameter to describe a limit of an accommodation process for superplastic flow. The parameter of the critical grain size at the time of failure correlates well with the value of overlap population in cation-doped TZP model cluster obtained from a first-principle molecular orbital calculation. The covalent bond at the grain boundaries plays a critical role in the high temperature tensile ductility of TZP.
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Tomonori Nambu, Nobue Shimizu, Hisakazu Ezaki, Hiroshi Yukawa, Masahik ...2005 Volume 69 Issue 9 Pages 841-847
Published: 2005
Released on J-STAGE: October 12, 2005
JOURNAL FREE ACCESSThe hydrogen permeation through pure niobium metal was investigated using a gas permeation technique, focusing mainly on the measurements in a highly soluble hydrogen state. The hydrogen diffusion was found to be the rate-determining step for the hydrogen permeation reaction. However, the Sieverts law that the hydrogen solubility in a metal is proportional to the square root of hydrogen pressure, was no longer satisfied in the experimental condition of the temperatures of 473 K to 673 K and the applied pressures of 260 kPa at the inlet and 60 kPa at the outlet for hydrogen. This was mainly due to the presence of a large amount of soluble hydrogen in the metal under this condition. As a result, the measured apparent hydrogen permeability decreased monotonously with decreasing temperature in pure niobium. This was completely the reverse of the temperature dependence of the hydrogen permeability in the low solubility state where the Sieverts law was satisfied. It was stressed here that the permeation measurement of hydrogen in the high solubility state was indeed necessary for getting some performance data of metal membranes in practical use.
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Hidekazu Sueyoshi, Harunori Odo, Shinji Mizokuchi, Shigeru Abe, Kazuya ...2005 Volume 69 Issue 9 Pages 848-854
Published: 2005
Released on J-STAGE: October 12, 2005
JOURNAL FREE ACCESSThe consumption of soldering iron was examined using Pb-free solder and the solder/soldering iron reaction was discussed in connection with the kinetics. The consumption of soldering iron increased with an increase in solder/soldering iron contact time. When the fused solder was removed by compressed air cleaning, no thick reaction layer was observed at the solder/soldering iron interface. When the fused solder remained on the surface of the soldering iron after such cleaning, a thick reaction layer was observed. As fused solder was held for a long time on the surface of the soldering iron, a thick FeSn2 reaction layer of was formed at the solder/soldering iron interface. The rate of formation of the reaction layer seemed to be controlled by the diffusion of iron through the reaction layer. The reaction layer was relatively hard (Hv 378) and had many voids. It was possible to remove the reaction layer by compressed air cleaning. On the basis of these results, it is clear that the soldering iron consumption due to Pb-free solder occurs according to the mechanism of the formation of a reaction layer of about 30 nm thickness through one soldering process, followed by flaking away with compressed air cleaning.
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