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Volume 74, Issue 5
Displaying 1-8 of 8 articles from this issue
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Yutaka Aikawa, Katsuhiko Fujii2010 Volume 74 Issue 5 Pages 289-293
Published: 2010
Released on J-STAGE: May 01, 2010
JOURNAL FREE ACCESSThe melting temperature Tm of cubic metals is reevaluated using the variation method, which takes into consideration the anharmonicity of both the trial potential and the crystal potential. The value of Tm is proportional to the dissociation energy D. It is also proportional to the number of interactions between atoms, which is accurately estimated by using normal coordinates instead of each atomic displacement. The obtained results are consistent with the trend observed in the experiments; accordingly, the slope of the straight line obtained for the Tm vs. D plot is higher for body-centered cubic metals than for face-centered cubic metals.
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Jun-ichi Echigoya, Yosuke Adachi2010 Volume 74 Issue 5 Pages 294-298
Published: 2010
Released on J-STAGE: May 01, 2010
JOURNAL FREE ACCESSThe real substrate temperature during sputtering was estimated by adopting a phase separation system of cobalt-indium tin oxide thin film. The nanostructure, consisting of Co fibers in an In2O3-SnO2 (ITO) matrix was formed during sputtering through surface diffusion. The increase of the substrate surface temperature was determined based on sputtering time and substrate temperature dependence of the Co fiber diameter. The activation energy of mutual surface diffusion was determined as being 0.57 eV using values of the real substrate temperature. The increase of real substrate temperature due to the increase of power density was also estimated.
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Tatsuo Kumagai2010 Volume 74 Issue 5 Pages 299-306
Published: 2010
Released on J-STAGE: May 01, 2010
JOURNAL FREE ACCESSThe influence of an applied stress (σ) on densification behaviors of a mechanically milled 3Y-TZP ceramic powder by pulse current pressure sintering (PCPS) has been investigated. The densification rate vs temperature (ρ−T) and densification rate vs relative density (ρ−ρ) curves at the constant heating rates (HR=0.1, 0.3, 1.0 and 2.0 K/s) could be described using data points (T, ρ and ρ) selected from all the results of PCPS conducted at the various electric currents in the range of 700 to 1000 A. Although the ρ values increase with increasing HR, the T and ρ values corresponding to the peaks of ρ (ρmax) show almost the constant values of 1300 K and 0.8 (at σ=90.5 MPa) respectively, irrespective of HR. By the increase of σ, moreover, the T value corresponding to ρmax shifts to the lower T side, however the ρ value corresponding to ρmax remains unchanged. Although the stress exponent (n) values, which are the gradient of the ln ρ vs ln σeff lines (σeff: effective stress), increase continuously with increasing T, but the re-estimated n values from the ln ρ vs ln (σeff−σ0) lines (σ0: threshold stress) show almost the constant value of 1.85 to 1.97. Also, the apparent activation energy (Q) estimated from the Arrhenius plot of ln (σeff−σ0) vs 1/T is 521.14±18.43 kJ/mol. The obtained n and Q values suggest that densification of the 3Y-TZP powder compacts by PCPS proceeds by grain boundary sliding affected by the threshold stress as well as the creep deformation in the middle stress region, and rate-determined by lattice diffusion of the solute Zr4+ ions.
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Naotsugu Yamamoto, Jinsun Liao, Kazuhiro Nakata2010 Volume 74 Issue 5 Pages 307-313
Published: 2010
Released on J-STAGE: May 01, 2010
JOURNAL FREE ACCESSFriction stir spot welding (FSSW) and resistance spot welding (RSW) were applied to join a noncombustible AMX602 magnesium alloy, and the microstructures and mechanical properties of the joints at various welding parameters were investigated in detail. In the FSSW at a tool rotating speed of 1750 rpm, the defect free joints were obtained at welding time of 3 to 14 s, and the tensile shear load of the joint increased with the welding time. The Vickers hardness in the SZ was higher than that in the base metal because of the formation of fine-grained microstructures in the SZ, which resulted from dynamic recrystallization. In the RSW, the defect free joint was not obtained at all welding conditions in the present study; however, the tensile shear load of the joint increased with the welding time and/or welding current. The Vickers hardness in the nugget was higher than that in the base metal because of the formation of net-like intermetallic compound of Al2Ca along the sub-grain boundaries of dendritic microstructures in the nugget. For both the FSSW and RSW, the tensile shear load of the joint increased with joining area. It was found that the tensile shear strength of the joints of FSSW and RSW was almost identical, and the tensile shear load of the joint was dependent on the joining area, irrespective of whether FSSW or RSW was employed in the present study.
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Ryosuke Suzuki, Koichi Kitazono2010 Volume 74 Issue 5 Pages 314-320
Published: 2010
Released on J-STAGE: May 01, 2010
JOURNAL FREE ACCESSThe anisotropic foaming behavior of the aluminum precursor manufactured by powder metallurgical process was investigated quantitatively. The precursor was manufactured using the uniaxial hot pressing and compressed parallel and perpendicular to hot pressing direction at room temperature. Foaming tests were carried out using the cubic specimen cut from the precursor. In order to evaluate expansion anisotropy, the deviatoric strain tensor was defined using the expansion strain tensor. The absolute values of three diagonal components of deviatoric strain tensor increase with increasing the prestrain. The anisotropic pore shape was also evaluated using the mean pore aspect ratio and the pore orientation. It is found that the prestrain plays an important role during the foaming of the precursor.
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Chinatsu Okamura, Takashi Ueda, Kazuhiro Hasezaki2010 Volume 74 Issue 5 Pages 321-324
Published: 2010
Released on J-STAGE: May 01, 2010
JOURNAL FREE ACCESSSingle phase β-Zn4Sb3 was prepared by mechanical grinding (MG). Source materials for the Zn4Sb3 ingots were prepared using three different processes after the direct melting of constituent elements. The ingot was obtained by quenching the melt in water within an evacuated quartz ampoule and heat-treated for a total of 200 h in two stages at 723 K and 673 K. The resultant ingots were mechanically ground and sintered at 623 K by hot pressing. The sintered materials were obtained as crack-free single phase β-Zn4Sb3 and characterized by X-ray diffraction, differential thermal analysis (DTA) and thermoelectric property measurements. The thermal conductivity of the sintered materials was 0.88 Wm−1 K−1 at room temperature and this value was slightly lower than that reported for the materials prepared by a conventional powder metallurgy method. Results indicate that the β-Zn4Sb3 single phase of the dimensionless figure of merit ranged from 1.06-1.31 at 573 K.
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K. Nomura, Y. Miwa, Y. Shimada, C. Watanabe, R. Monzen2010 Volume 74 Issue 5 Pages 325-330
Published: 2010
Released on J-STAGE: May 01, 2010
JOURNAL FREE ACCESSThe effects of addition of 0.1 mass%Mg and 0.1 mass%Fe on the strength and stress relaxation property of a precipitation-hardenable Cu-0.52 mass%Ni-0.19 mass%P alloy aged at 450°C have been investigated. Precipitation of Ni2P, Ni12P5, both Ni2P and Ni5P4, and both Ni12P5 and Ni5P4 phases was observed to occur on aging the Cu-Ni-P, Cu-Ni-P-Fe, Cu-Ni-P-Mg, and Cu-Ni-P-Fe-Mg alloys, respectively. The needle-like Ni5P4 phase was first found to be precipitated in the Cu matrix. In the peak-aging stage, the yield strength of the four alloys is controlled by the Orowan mechanism. The addition of Mg to the Cu-Ni-P alloy enhanced the strength of the alloy, but the Fe addition did not significantly affect the strength. The strength of the Cu-Ni-P-Mg alloy was nearly identical to that of the Cu-Ni-P-Fe-Mg alloy. The increase in strength by the addition of Mg is ascribed to the decrease in inter-precipitate spacing of precipitates. The Cu-Ni-P-Fe alloy exhibited better stress relaxation property than the Cu-Ni-P alloy, probably because atoms caused by pairs of Fe and P chemical bonding are dragged by moving dislocations. Adding Mg to the Cu-Ni-P alloys did not essentially change the stress relaxation property. This may be as a result of the combination of the increase in stress relaxation resistance caused by the Mg-atom-drag effect on dislocation motion and of the decrease in that due to the decrease in the amount of P atoms in the Cu matrix by adding Mg.
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Hirofumi Tokunaga, Shinichiro Haruki, Sohei Sukenaga, Noritaka Saito, ...2010 Volume 74 Issue 5 Pages 331-336
Published: 2010
Released on J-STAGE: May 01, 2010
JOURNAL FREE ACCESSWe measured the viscosity and the refractive index of the binary tellurite glasses and melts, (M2O-TeO2 M=Li, Na and K), and investigated the thermal and compositional dependences of the properties.
It was found that the viscosity and the refractive index of the binary tellurite melts decreased with increasing temperature, M2O content, and the radius of added cation. It was attributed to the structural change of melt from TeO4 trigonal bipyramid to TeO4 − trigonal bipyramid and TeO3 trigonal pyramid with increasing temperature and M2O content.
In an attempt to determine the change of tellurite structural units (TeO4, TeO4 − and TeO3) with temperature and M2O content, the fraction of structural units in the melts was calculated from the refractive index of melts on the basis of the relationship between the refractive index and the structural units of tellurite glasses. It was found that the fraction of TeO3 increased with increasing temperature and M2O content, which was corresponded to the thermal and compositional dependences of the viscosity and refractive index measurements.
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