All issues
Volume 74, Issue 2
Displaying 1-12 of 12 articles from this issue
- |<
- <
- 1
- >
- >|
Regular Articles
-
Hiroshi Suzuki, Daisuke Kobayashi, Nobuko Hanada, Kenichi Takai, Yukit ...2010 Volume 74 Issue 2 Pages 65-71
Published: 2010
Released on J-STAGE: February 01, 2010
JOURNAL FREE ACCESSHydrogen is introduced in commercial (99% pure) aluminum by electrochemical charging to study the existing state of hydrogen and its effect on the mechanical properties of aluminum. Electrochemical charging is conducted in an aqueous solution of H2SO4 with 0.1 mass% NH4SCN as a hydrogen recombination poison. The potential and pH during the charging are chosen from the immune, passive, and corrosive regions on Pourbaix diagram to determine the optimum conditions for the charging. The maximum amount of hydrogen absorbed is obtained in the immune region. The amount of hydrogen and its existing state are examined using hydrogen desorption curves, which are obtained by thermal desorption spectroscopy. The curves show distinctive peaks that correspond to trapping sites of hydrogen in the material. One of the peaks is observed at approximately 100°C and it corresponds to vacancies and dislocations in the material; another peak is observed at approximately 400°C and it corresponds to molecular hydrogen in blisters. It is presumed that charged hydrogen diffuses into the bulk of the material to form hydrogen-vacancy pairs, and then these pairs cluster to form blisters. The fracture strain of charged aluminum in the immune region decreased with a slower strain rate, showing an inverse dependence on the fracture strain of the uncharged material. This phenomenon is considered to be caused by the transport of hydrogen by dislocations through the interaction between hydrogen and the dislocations. The phenomenon is further confirmed by the observation of hydrogen release during tensile deformation, where the amount of hydrogen is higher in the strain rate region where the interaction between the dislocations and hydrogen is more prominent.
View full abstractDownload PDF (2633K) -
Makoto Takagi, Hiroyuki Nakayama, Akihito Matsumuro2010 Volume 74 Issue 2 Pages 72-76
Published: 2010
Released on J-STAGE: February 01, 2010
JOURNAL FREE ACCESSThree-dimensional micro structures fabricated by focused ion beam chemical vapor deposition (FIB-CVD) are expected to be used as structural materials for MEMS/NEMS. In this research, the square micro structures were fabricated by FIB-CVD using probe currents of 48, 200, 1300 and 5200 pA, and Vickers hardness tests of the micro structures were carried out. The Vickers tests revealed that the hardness of the micro structures depends on the probe current density. The cross-sectional TEM observations indicated that the micro structure has an amorphous phase. The results show that the consistent fabrication process of the micrometer-scale beam with both ends fixed by the FIB-CVD method was established. Mechanical properties of the micro structure with beam shape were investigated by three-point bending tests. Using a nano-indentation apparatus, the bending tests showed that Young's modulus of a beam-shaped structure was 20±2 GPa and the fracture stress was 2.2±0.1 GPa. Furthermore, SEM observation of the cleavage surface on a beam-shaped structure after failure showed brittle fracture. SEM-EDS images revealed that a homogeneous composition distribution of 94 at% carbon and 6 at% gallium over the entire micro structure.
View full abstractDownload PDF (3307K) -
Tokiko Nakagawa, Ryousuke Sumi, Hiroyuki Kaneko2010 Volume 74 Issue 2 Pages 77-84
Published: 2010
Released on J-STAGE: February 01, 2010
JOURNAL FREE ACCESSElectrochemical characteristics of a Fe-Zn galvanic couple were studied under O2-CO2 mixtures of 2 MPa in a 3 mass% NaCl solution at 423 K for 14.4 ks. In 100% O2 and in 10% CO2+90% O2, both the galvanic corrosion current and corrosion potential of the couple remarkably changed after a certain period. Then, the polarities of the galvanic corrosion currents of the couple were reversed, indicating that Fe was not protected any more and rather corroded at an accelerated rate. On the other hand, the polarities of the current of the couple in 20% CO2+80% O2 and in 100% CO2 were not changed during the immersion time, indicating that Fe was still protected, although the galvanic currents were very low in 100% CO2. The galvanic corrosion potentials were always close to the corresponding cathodic potentials, indicating that the corrosion is governed by cathodic control. In 10% CO2+90% O2 and in 100% O2, the polarization characteristics of Zn specimen before and after the immersion test drastically changed, indicating that the galvanic couple of Zn anode and Fe cathode before the test changed to the couple of Fe anode and Zn cathode after the test. But, in 20% CO2+80% O2 and in 100% CO2, the galvanic couple of Zn anode and Fe cathode was hold during the immersion time. As CO2 ratio decreased, the corrosion products on the surface of Zn changed in the sequence: ZnCO3→Zn5(CO3)2(OH)6→Zn5Cl2(OH)8→ZnO. Above results show that Zn specimen in a Fe-Zn couple acts as a cathode due to the formation of ZnO on Zn. Therefore, whether Zn acts as a sacrificial anode or not, depends on the possibility of the formation of ZnO on Zn.
View full abstractDownload PDF (1621K) -
Takeshi Terajima, Kazuhiro Nakata, Hisamichi Kimura, Akihisa Inoue2010 Volume 74 Issue 2 Pages 85-88
Published: 2010
Released on J-STAGE: February 01, 2010
JOURNAL FREE ACCESSIn order to improve the mechanical properties of Zr55Al10Ni5Cu30 metallic glass, tungsten-reinforced Zr55Al10Ni5Cu30 was developed. Tungsten particles with a diameter φ=100 μm were uniformly distributed into the matrix, exhibiting good wettability with the Zr55Al10Ni5Cu30 metallic glass matrix. Due to the extremely high melting temperature of tungsten, the tungsten particles coexisted with amorphous Zr55Al10Ni5Cu30, although a reaction layer of ZrW2 and a crystallized matrix formed to a certain extent depending on the sample. Nevertheless, the total amount of crystallization in both the matrix and the reaction phases remained small. As the volume fraction of W was increased from 0 to 8.7%, the compressive plastic strain increased from 0 to 1.3%, and the compressive fracture strength increased from 1480 MPa to 1870 MPa. The coefficient of thermal expansion of monolithic Zr55Al10Ni5Cu30 decreased from 10.4×10-6/K to 8.2×10-6/K in the case of the composite containing 30% W powder.
View full abstractDownload PDF (1192K) -
Shingo Watanabe, Sei-ichi Akutagawa, Ken Sawada, Tatsuo Iwasa, Yuhei S ...2010 Volume 74 Issue 2 Pages 89-93
Published: 2010
Released on J-STAGE: February 01, 2010
JOURNAL FREE ACCESSIn order to analyze the magnetic behaviors of iron complexes biologically synthesized in magnetic bacteria MS-1, we performed FMR (Ferromagnetic Resonance) measurements for each fraction of the cell. We observed FMR spectra from the ferric iron (Fe3+) compounds distributed in each fraction of the MS-1 cell. In particular, the MS fraction yielded an anisotropic FMR signal, whereas other fractions were simple FMR spectra of Gaussian type.
Upon counting the numbers of spins in various cell fractions, we compared them with the iron population as determined by the 1.10-phenanthroline method. We found a good correlation between the number of spins and the iron population in several cell fractions. We concluded that the cell fractions other than those fractions containing magnetite, consist mostly of ferric irons rather than ferrous irons.
View full abstractDownload PDF (590K) -
Atsushi Yamaguchi, Yoshihiro Mitsutani, Kohji Gotoh, Tomoki Tomita, Sh ...2010 Volume 74 Issue 2 Pages 94-100
Published: 2010
Released on J-STAGE: February 01, 2010
JOURNAL FREE ACCESSThe infiltration process of Cu-Sn alloy into indirect selective laser sintered (SLS) stainless steel preforms was investigated. The heating rate for the infiltration process was 0.17 K/s and the holding temperature was varied from 1293 to 1473 K for 3.6 ks. The process was carried out in an inert gas atmosphere. Although the volume of the preforms without infiltration decreased with increasing sintering temperature, the volume of the infiltrated parts remained constant at approximately -5%. The stainless steel particles were coarsened by the increasing holding temperature during infiltration; however, the area ratio of stainless steel particles remained constant at approximately 60% regardless of the holding temperature. The tensile strength and elongation of the infiltrated parts were approximately 540 MPa and 10%, respectively, regardless of the holding temperature.
View full abstractDownload PDF (3824K) -
Yoshiko Takamatsu, Hisao Esaka, Kei Shinozuka2010 Volume 74 Issue 2 Pages 101-109
Published: 2010
Released on J-STAGE: February 01, 2010
JOURNAL FREE ACCESSNear-ternary eutectic Sn-Ag-Cu alloys are leading candidates for Pb-free solders. These alloys have three solid phases: β-Sn, Ag3Sn and Cu6Sn5. In order to reveal the solidification process of the alloy, the technique for quenching samples during freezing was used to evaluate the freezing characteristics of near eutectic ternary Ag-Cu-Sn alloys. In the present study, Sn-3.5Ag-0.5Cu and Sn-3.5Ag-1.5Cu (mass%) samples were investigated. These samples were subjected to the thermal program to give a cooling rate of about 0.05°C/s.
In the case of Sn-3.5Ag-0.5Cu alloy, the solidification structure almost corresponded with the estimation from equilibrium phase diagram, though the solidification process was different. In this study the Sn-Ag3Sn eutectic nucleated immediately after primary β-Sn solidified. On the other hand, eutectic Cu6Sn5 did not nucleate easily, though the temperature of the specimen indicated at 217°C (ternary eutectic temperature).
In the case of Sn-3.5Ag-1.5Cu alloy, the solidification structure as well as solidification process were quite distinct from the estimation of equilibrium phase diagram. Primary Cu6Sn5 was the first phase formed in the liquid. This was followed by the nucleation and growth of psud-primary Ag3Sn. The recalescence was observed when β-Sn nucleated and grew as a halo. The ternary eutectic structure emerged after Sn-Ag3Sn binary eutectic solidification.
View full abstractDownload PDF (14701K) -
Takashi Ueda, Chinatsu Okamura, Yasutoshi Noda, Kazuhiro Hasezaki2010 Volume 74 Issue 2 Pages 110-113
Published: 2010
Released on J-STAGE: February 01, 2010
JOURNAL FREE ACCESSn-type tellurium doped ZnSb was prepared by direct melting at 923 K after which it was quenched in water within an evacuated quartz ampoule. All the ingots were heat treated at 723 K for 100 h. The resultant samples were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA) and by measurement of their Seebeck and Hall coefficients. XRD and DTA indicated that the solubility limit of tellurium in ZnSb was less than 3 at%. The samples with 0, 1 and 3 at% tellurium were p-type while those with 1.90 and 2.06 at% tellurium were n-type. These results indicated that n-type ZnSb samples can be obtained by the proper doping of tellurium. Excess doping with tellurium resulted in precipitation of the ZnTe phase and a change in conduction from n- to p-type. The maximum power factor for the 2.06 at% tellurium doped n-type sample was found to be 0.84×10-3 Wm-1 K-2 at 573 K.
View full abstractDownload PDF (1450K) -
Sei Miura, Takuro Mimaki, Shinji Moriwaki, Nagato Ono2010 Volume 74 Issue 2 Pages 114-118
Published: 2010
Released on J-STAGE: February 01, 2010
JOURNAL FREE ACCESSThe present paper describes the variations in mechanical properties of Al-Zn-Mg-Cu alloy single crystals with various aging times. The cylindrical single crystals of 7475 aluminum alloys were produced at 1033 K by the Bridgman method, where the composition of initial material and the shape of carbon mold were modified for the growth of quaternary crystals. Specimens appropriate for tensile and hardness testing were obtained from the single crystal rod homogenized at 823 K for 900 ks using a spark-cutting method. Subsequently, they were aged at 393 K for 3.6, 86.4, 900 and 2880 ks after quenching in ice water from 773 K. In the stress-strain curves of the alloy single crystals, the yield stress increased remarkably with the increase of aging time. Also, a decrease of elongation for the aged specimens was seen accompanying a decrease in the rate of work hardening after yielding. Moreover, some serrations occurred particularly in the final plastic stage on the curves. Hardness of the alloy single crystals agreed with those of polycrystals due to the occurrence of multiple slips during loading. However, the alloy single crystals exhibited a marked decrease in yield strength in comparison to the polycrystals. In single crystals, a single glide was found to occur. If we compare the increase of critical resolved shear stress (CRSS) derived from two different theories of precipitation hardening with the experimental value, the present results were roughly in agreement with the theoretical values except for the specimen aged for 3.6 ks. This fact indicated that the maximum strength of Al-Zn-Mg-Cu alloy single crystals was achieved in the transition from the mechanism in which dislocations cut through the precipitated particles to the bypass mechanism of Orowan with the growth in particle size.
View full abstractDownload PDF (1206K) -
Shunji Kajikawa, Yasuaki Isobe, Masazumi Okido2010 Volume 74 Issue 2 Pages 119-126
Published: 2010
Released on J-STAGE: February 01, 2010
JOURNAL FREE ACCESSThe purpose of this study is to investigate the effect of amount of adhered chloride and applied stress on crevice corrosion cracking of high strength type-304 stainless steel. The cold worked type-304 stainless steel pipe with shot peening were applied for this study. A crevice was created between the outside of the pipe and an O-ring. A press fitting part was inserted inside the pipe to apply a tensile stress to outer surface of the pipe. Specimens were provided in a wet/dry cyclic corrosion test after one spray of artificial seawater.
The crack generation time decreased as amount of adhered chloride increased. It was found that negative correlation between the crack generation time and the logarithm of the chloride amount. This result seemed to be related to the fact that the pit growth rate was proportional to the logarithm of the chloride amount. This respect was verified by cyclic corrosion test and electrochemical measurements such as ER, CREV.
The effect of applied stress was evaluated by changing the size of press fitting part inserted in the pipe. The crack generation time decreased as the applied stress increased.
View full abstractDownload PDF (5222K) -
Tatsuya Yamamoto, Shinichiro Nanba, Yoshihide Ebihara, Yoshitake Nishi2010 Volume 74 Issue 2 Pages 127-130
Published: 2010
Released on J-STAGE: February 01, 2010
JOURNAL FREE ACCESSImpact values of sandwich structural composites (CFRP/ABS/CFRP and CFRP/PMMA/CFRP) of both acrylonitrile butadiene styrene (ABS) and poly methyl methacrylate (PMMA) resins cores covered with carbon fiber reinforced polymer (CFRP) sheets at both side surfaces were obtained. The impact value of CFRP/ABS/CFRP, which approximately corresponded to that of CFRP composite, was more than two times higher than that of CFRP/PMMA/CFRP. Both the Weibull coefficient (n) exhibiting reproducibly and the lowest impact value (as) for safety design were determined as indicators of reliability. Both values of CFRP/ABS/CFRP and CFRP were higher than those of the CFRP/PMMA/CFRP. Thus, the use of ABS resin as the core enhanced the reproducibly and design safety. In addition, since the price of CFRP was higher than that of ABS resin, the sandwich structural composites of CFRP/ABS/CFRP could be used for articles of daily.
View full abstractDownload PDF (1664K)
Letters to the Editor
-
Yoshihiko Hangai, Shinji Koyama, Takao Utsunomiya, Makoto Hasegawa2010 Volume 74 Issue 2 Pages 131-133
Published: 2010
Released on J-STAGE: February 01, 2010
JOURNAL FREE ACCESSA composite structural material with an “A1050 porous aluminum/SS400 dense steel plate” is fabricated by friction stir welding (FSW), which is used both for mixing blowing agent powder with aluminum plates and for lap joining aluminum and steel plates in the same process. It is shown that, after the aluminum plates are foamed, diffusion bonding is realized and an Fe-Al intermetallic compound is formed at the interface of porous aluminum and dense steel. This is because new surfaces of aluminum and steel plates are formed by FSW, and thus bonding is realized at the interface of these plates immediately after FSW.
View full abstractDownload PDF (1016K)
- |<
- <
- 1
- >
- >|