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Volume 76, Issue 8
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Regular Articles
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Keisuke Narita, Toshiyuki Koyama, Yuhki Tsukada2012 Volume 76 Issue 8 Pages 475-481
Published: 2012
Released on J-STAGE: August 01, 2012
JOURNAL FREE ACCESSIt has been proposed that the long-period stacking ordered (LPSO) structure in Mg-Zn-Re (Re: the rare-earth elements) alloys establishes the excellent mechanical properties among Mg-based light metals. In this study, the phase separation of metastable hcp phase in Mg-Y-Zn system is simulated on the basis of the phase-field method in order to understand the stability and formation mechanism of the LPSO structure. The obtained results are as follows. The metastable spinodal decomposition is observed near the Mg corner in Mg-Y-Zn ternary system before the conventional spinodal decomposition in accordance with the miscibility gap of the hcp phase. That is the supersaturated solid solution of Mg-7 at%Y-7 at%Zn alloy separates into two phases; Mg-12 at%Y and Mg-17 at%Zn. The morphology of the microstructure is lamellae structure elongated along the [0001] direction of hcp phase, and the wavelength of the lamellae structure is about 7nm. These results suggest that the metastable spinodal decomposition might be correlated with the stability of the LPSO structure.
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Yuya Sumino, Hideo Watanabe, Naoaki Yoshida2012 Volume 76 Issue 8 Pages 482-488
Published: 2012
Released on J-STAGE: August 01, 2012
JOURNAL FREE ACCESSIn order to investigate the effect of periodic temperature irradiation on pure copper, heavy ion irradiation under constant temperature and periodic temperature were performed. Specimens were irradiated up to 10 dpa in the temperature range of 373-673 K. The formation and growth of voids were suppressed by the periodic temperature irradiation. In comparison with the constant temperature irradiation at 673 K, number density of void decreased by the periodic temperature irradiation. This result was explained by the disappearance of small vacancy-type clusters (formed at 673 K) during successive irradiation at 473 K.
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Microstructure of Japanese Matchlock Gun Fabricated by a Kunitomo Gunsmith in the Edo Genroku PeriodManako Tanaka, Masahiro Kitada2012 Volume 76 Issue 8 Pages 489-495
Published: 2012
Released on J-STAGE: August 01, 2012
JOURNAL FREE ACCESSThe microstructure and mechanical properties of the steel barrel of a Japanese matchlock gun fabricated by the gunsmith Kunitomo Tokudayuu in the Edo Genroku period have been investigated. The purpose of this work is to obtain modern materials-science data for a Japanese matchlock gun fabricated by a noted Kunitomo gunsmith and to study the manufacturing technique of the steel barrel. Specimens are cut from the center, the muzzle, and the screw of the barrel. The carbon concentration is determined by chemical analysis. The microstructure and nonmetallic inclusions of the specimens are observed with an optical microscope and a scanning electron microscope (SEM). To evaluate the hardness, Vickers hardness (Hv) is used. The inner structure of the screw is observed by X-ray radiography. The carbon concentration is 0.007 mass% in the center of the barrel and 0.07-0.3 mass% in the muzzle. The distribution of nonmetallic inclusions in the center of the barrel indicates that the barrel was fabricated by joining two long edges of a steel sheet, a technique that is called Udonbari (seamed steel pipe in Japanese). The muzzle was reinforced with steel having a higher carbon content than that of the center of the barrel by rolling the steel over the Udonbari barrel. The female screw of the barrel was made of clad steel. Both male and female screws of the barrel were made by a cutting technique.
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Satoshi Semboshi, Satoshi Yamauchi, Hiroshi Numakura2012 Volume 76 Issue 8 Pages 496-503
Published: 2012
Released on J-STAGE: August 01, 2012
JOURNAL FREE ACCESSWe have investigated the specific contributions of titanium-hydride precipitates to the improvement of electrical conductivity and strength for Cu-0.36 mol% Ti alloys aged in a hydrogen atmosphere at 773 K, where Cu4Ti phase is not to appear. During the aging, titanium-hydride particles, which have a composition of H/Ti=2, are formed by reaction of solute titanium with hydrogen diffused into the alloy. The particles have an octahedral shape with facets parallel to {111} of the matrix. The size and volume fraction of the hydride particles increase with aging time, and then level off after aging for 100 h, while the number density exhibits a maximum at 24 h. The precipitation reduces the concentration of solute titanium in the matrix and leads to significant improvement of the electrical conductivity, to the level comparable to pure copper. The dispersed TiH2 particles gives rise to strengthening with the Orowan mechanism, of approximately 40 MPa at a maximum in yield strength.
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Masaaki Shuto, Ken Kurosaki, Yuji Ohishi, Hiroaki Muta, Shinsuke Yaman ...2012 Volume 76 Issue 8 Pages 504-507
Published: 2012
Released on J-STAGE: August 01, 2012
JOURNAL FREE ACCESSThe efficiency of thermoelectric device is determined by the material's thermoelectric figure of merit ZT=S2σT/κ. Therefore, low thermal conductivity κ is essential to achieve high ZT value. Here we show the high-temperature thermoelectric properties of α-Ag9GaTe6. Polycrystalline high-density bulk samples of α-Ag9GaTe6 were prepared. The sample showed quite low thermal conductivity to be 0.25 W m−1 K−1 at room temperature, corresponding to the mean free path of phonons of around 0.4 nm. α-Ag9GaTe6 exhibited relatively high ZT value of ~0.36, mainly due to the low thermal conductivity.
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Katsuhiro Sagara, Yun Lu, Yusuke Matsuda2012 Volume 76 Issue 8 Pages 508-514
Published: 2012
Released on J-STAGE: August 01, 2012
JOURNAL FREE ACCESSThe addition of metal into thermoelectric materials has been used as one method to improve thermoelectric performance. Although the electrical resistivity of thermoelectric materials can be decreased largely by the metal composition, it is always accompanied with some negative effects such as the thermal conductivity increase. Therefore, it seems necessary to investigate the composite effects and their influence on thermoelectric properties.
In the present work, analysis models of finite element method with series and random distribution for thermoelectric composites were proposed and established. Thermoelectric properties including electrical resistivity, Seebeck coefficient and thermal conductivity of thermoelectric composites were investigated by the proposed models. Thermoelectric properties calculated by the models were compared with those obtained by the experiments and theories of the rule of mixture and the general effective medium equation (GEM).
The results revealed that the values of thermoelectric properties calculated from the proposed models were consistent with those from the experiments and the rule of mixture in the series model. In addition, the results calculated by the random distribution model showed a similar tendency with those from the experiments and GEM. The proposed analysis models are suitable to discuss the thermoelectric properties of thermoelectric composites.
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Atsushi Yamaguchi, Kohji Gotoh, Tomoki Tomita, Shinji Fukumoto2012 Volume 76 Issue 8 Pages 515-520
Published: 2012
Released on J-STAGE: August 01, 2012
JOURNAL FREE ACCESSA manufacturing technique for the modeling of titanium powder by indirect selective laser sintering (SLS) and magnesium infiltration was developed. The modeling powder used for the indirect SLS was prepared by coating 1.1 mass% nylon with titanium powder particles and then mixing 1.9 mass% phenol resin powder (<10 µm). The hardness of the modeling powder at 477 K was greater than that of A90 (durometer type A), and it was suitable for indirect SLS modeling. While the amounts of resin (nylon and phenol) were equal in both methods, unlike the use of nylon coating and phenol resin powder, which resulted in the formation of a sufficiently hard titanium powder, the use of nylon resin powder and phenol resin powder resulted in the formation of an insufficiently hard titanium powder.
The titanium powder preform and a magnesium ingot were then heated at 973 K, and the dense composite, consisting of titanium particles and infiltrated magnesium, was fabricated by the self-activation of the infiltrated molten magnesium. Microstructure analyses of the composites titanium, magnesium, and titanium-carbide (TiC) were conducted by XRD. We concluded that the formation of TiC was attributed to the formation of titanium and carbon during the decomposition of the phenol resin.
The density, hardness, and tensile strength of the obtained composites are 3.2, 60 HRB, and 241 MPa, respectively. The tensile strengths of the composites are significantly higher than those of the cast magnesium (106 MPa). We believe that a large increase in the tensile strength after infiltration was due to the sintered behavior of the titanium powder and the densification of magnesium infiltration. Thus, the infiltration of magnesium into the titanium powder preform can be considered as an effective method for manufacturing lightweight composites.
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