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Volume 71, Issue 2
Displaying 1-29 of 29 articles from this issue
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Yuki Matsuoka, Yasuo Matsunaga, Kiyokazu Nakagawa, Yoshihiro Tsuda, Sh ...2007 Volume 71 Issue 2 Pages 143-150
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSGrowth behavior of coatings formed by AlF3 activated vapor phase aluminizing on a Ni-base superalloy substrate was investigated at 1223-1353 K for up to 4 h using FeAl, FeAl2, Fe2Al5, and FeAl3 pellets as aluminum donors, with an aim at understanding the kinetics under different aluminum activities.
The coatings consist of an outer δ-Ni2Al3 layer, a middle β-NiAl layer, and an inner diffusion layer of γ′-Ni3Al. The amount of aluminum deposition w shows parabolic time dependence at 1353 K, and the parabolic rate constant increases with an increase of the aluminum content of the pellet. The linear relationship is approved between ln (w2) and reciprocal of absolute temperature, 1/T. This implies that aluminum deposition is a thermally activated process. When the Fe2Al5 or FeAl3 pellet is used, the activation energy is similar to those of the aluminum diffusion in the binary Ni-Al alloys. Therefore, the rate of aluminum deposition might be dominantly controlled by the aluminum diffusion in the coating. When the FeAl pellet is used, the activation energy is much smaller. It is supposed that the aluminum supply from the gas phase to the coating surface is smaller than the aluminum diffusion in the coating. In this case, the processes other than the aluminum diffusion in the coating might contribute to the rate-controlling step.
The rate falling occurs in the last stage owing to the phase transformations of FeAl3 → Fe2Al5 → FeAl2 → FeAl caused by the depletion of aluminum in the pellet. When the pellet surface is completely covered by FeAl, the rate-controlling step might change.
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Daizen Watanabe, Koji Higashi, Chihiro Watanabe, Ryoichi Monzen2007 Volume 71 Issue 2 Pages 151-157
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSThe Ostwald ripening of Co particles in a Cu-1 mass%Co alloy during aging at 873, 923, 973 and 998 K has been examined. The average size of Co particles was determined by transmission electron microscopy and the reduction in Co concentration in the Cu matrix with aging time t was determined by electrical resistivity measurements. In the initial stage of aging, the growth rate of particles decreases gradually and, over a time, the growth kinetics of particles obey the t1/3 time law, as predicted by the Lifshitz-Slyozov-Wagner (LSW) theory. Over the same time, the kinetics of the reduction of Co concentration are in accord with the predicted t-1/3 time law. The growth and coarsening of Co particles occur simultaneously before the commencement of coarsening. The change in the growth rate of particles is attributed to the transition from the mixed stage of the growth and coarsening to the coarsening stage. Application of the LSW theory has enabled independent derivation of the Cu/Co interface energy γ and the diffusion coefficient D of Co in Cu during coarsening of particles. The value of γ is estimated as 150 mJm-2, which is much smaller than the values of γ=288-451 mJm-2 previously reported, and is insensitive to the change from the coherent interface of the Co particles to the semi-coherent interface. The estimates of D are in agreement with those for impurity diffusion of Co in Cu.
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Ken-ichi Ikeda, Takeshi Hirota, Kensuke Fujimoto, Youhei Sugimoto, Nao ...2007 Volume 71 Issue 2 Pages 158-163
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSThe formation behavior of polycrystalline silicon thin films during the aluminum induced crystallization (AIC) was investigated by in-situ heating transmission electron microscopy (TEM). The electron dispersive X-ray spectroscopy (EDS) analysis of annealed sample was showed that layer exchange of the a-Si/Al film is occurred during the annealing. Furthermore, from the in-situ heating TEM observation and EDS analysis of as-deposited sample, it was confirmed the co-existence of Si and Al in a-Si/Al film and the lateral growth of crystalline Si grain. The mechanism of AIC and layer exchange were discussed from the experimental results and the phase diagram of Al-Si system.
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Masaaki Kusumoto, Hideyuki Saitoh2007 Volume 71 Issue 2 Pages 164-169
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSWe have investigated a hydrogenation property of Ni coated Mg and Mg-Mg2Ni eutectic alloy made by melting in sealed steel crucible. The hydrogenation kinetics of heat-treated Mg-Mg2Ni specimen at 470°C greatly increased compared with that of the as-cast Mg-Mg2Ni specimen. It is found that the coarsening of the microstructure improves the hydrogenation kinetics, because both of the Mg2Ni phase and Mg phase grow by the heat-treatment in this alloy. The hydrogenation kinetics is considerably improved by Ni coating using hybridization machine for both the pure Mg and Mg-Mg2Ni specimens. It is confirmed that the surface modification by the hybridization method effectively improves the hydrogenation kinetics. This improvement is attributed to the catalytic effect of coated Ni on the dissociation of hydrogen molecules into hydrogen atoms.
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Mikito Kondo, Ryo Morihashi, Chiemi Ishiyama, Masato Sone, Yakichi Hig ...2007 Volume 71 Issue 2 Pages 170-175
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSThe ratio of surface area to volume increases as a material gets smaller. For this reason, the mechanical properties of a micro-sized material are strongly influenced by the surface conditions. To accurately study how the mechanical properties are influenced by the size, we need to test specimens with negligible work-affected layers. However, conventional microfabrication methods are poorly suited for the manufacture of specimens that meet this condition. In order to overcome these problems, we developed a novel method for manufacturing micro-sized tensile specimens with negligible work-affected layers using a precision electrolytic polishing apparatus. A polycrystalline austenitic stainless steel (SUS304) wire with a diameter of 0.5 mm was selected as the material for study. The sample wire (anode) was vertically set at the center of a ring-shaped counter electrode and gripped by a collet chuck. Once the sample was set, a rectangular wave voltage for electrolytic polishing was applied in a flowing electrolytic solution. The apparatus was used to manufacture a tensile specimen with a diameter of 51 μm, i.e., a diameter smaller than the average grain size of the sample. Optical, laser, and scanning electron microscope observations revealed a smooth and mirrored specimen surface. Tensile testing of the specimen by a testing machine for micro-sized materials revealed a clear yield point on a stress-displacement curve. The yield and fracture strength of the specimen were 100 and 180 MPa, respectively, or about the same as those of a single crystal. The specimen deformation observed by scanning electron microscope mainly occurred at single crystal regions placed between grain boundaries.
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Sho Tokui, Kazuhiro Ishikawa, Kiyoshi Aoki2007 Volume 71 Issue 2 Pages 176-180
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSThe relation between microstructure and hydrogen permeability (Φ) of the Nb40Ti30Ni30 alloy after hot-forging and hot-rolling and subsequent annealing treatments has been investigated in order to develop highly hydrogen permeable microstructures. By hot forging and rolling at 1173 K, the primary (Nb, Ti) phase is elongated along the rolling direction (RD), while it is compressively deformed in the normal direction (ND). Thus, anisotropic microstructures can be formed by the hot working technique. Φ673 K of the hot worked sample measured along to RD is 4.4×10-8 [mol H2m-1 s-1 Pa-1/2] at 673 K, which is 2.5 times higher than that of as-cast one. On the other hand, Φ673 K of the hot worked sample measured along to ND is 0.5×10-8 [mol H2m-1 s-1 Pa-1/2], which is 1/3 of that of as-cast one. Φ673 K of the RD sample increases with increasing annealing time and attains to 7.4×10-8 [mol H2m-1 s-1 Pa-1/2] by annealing for 360 ks at 1373 K, which is 3 times higher than that of Pd-25 mass%Ag. Even though fine lamellar eutectic {TiNi+(Nb, Ti)} structure disappears and is replaced by the spherical (Nb, Ti) phase which is embedded in the TiNi matrix, the large resistance to the hydrogen embrittlement is kept. The present work clearly demonstrates that microstructural control of the Nb40Ti30Ni30 alloy using hot working and subsequent heat treatments are effective for development of microstructures showing high Φ without the loss of resistance to the hydrogen embrittlement.
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Masakazu Kobayashi, Hiroyuki Toda, Yuji Kawai, Toshiro Kobayashi, Kent ...2007 Volume 71 Issue 2 Pages 181-186
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSMeasurement of interior strain distribution has been developed based on the synchrotron radiation computed tomography (SR-CT). In metal deformation, local strain distribution differs from macroscopic strain due to microstructural factors such as grains, grain boundaries, particles, pores, voids, and cracks. A model sample, which was made from a copper alloy strengthened with alumina, was prepared containing artificial pores. Tensile loading was applied to the sample step by step. High-resolution tomographic experiment was performed at the third-generation synchrotron radiation facility (SPring-8) in Japan. Gravity center position, volume and surface area in the pores, which were regarded as markers in a tracking procedure, were measured by 3-D digital image analysis in the SR-CT images. The markers before and after the deformation were provided for registration and macroscopic strain correction before the tracking procedure. The marker tracking was carried out by means of matching parameter that was described as functions of distance, volume and surface at markers. The ratio of success tracking was evaluated in order to clarify whether the tracking method developed in this study was reliable. The 3-D strain distribution was represented successfully by the tracking results. A combination of high-resolution SR-CT and tracking of microstructural features is effective to visualize interior strain distribution in materials in 3-D.
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Kazuyoshi Nakashima, Tatsuya Tokunaga, Hiroshi Ohtani, Mitsuhiro Haseb ...2007 Volume 71 Issue 2 Pages 187-189
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSA thermodynamic analysis of the Be-Mo system has been carried out using the CALPHAD method. The formation energies of the four intermetallic phases of this system obtained from first-principles calculations were utilized to compensate for the lack of experimental information on the phase boundaries and thermodynamic properties of this binary system. The optimized thermodynamic parameters reproduced the characteristic features of the phase diagram quite well. Our first-principles calculations show that the stable BeMo3 phase may not have the Cr3Si-type cubic structure reported in a previous study, because of its lower stability. The first-principles calculations also imply that BeMo with a CrB-type orthorhombic structure may be the stable phase in the ground state.
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Eiji Taki, Yuji Kawakami, Masaaki Otsu, Kazuki Takashima2007 Volume 71 Issue 2 Pages 190-194
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSFracture tests have been performed for both macro- and micro-sized specimens prepared from an Fe-3%Si alloy single crystal, and the size effects on fracture behavior have been considered. Micro-sized cantilever beam specimens with dimensions of 10 μm×10 μm×50 μm were prepared by focused ion beam machining. Notches with a depth of 5 μm were introduced into the micro-sized specimens and fatigue pre-crack was also introduced ahead of the notch. Macro-sized three-point bending specimens with dimensions of 2 mm×2 mm×10 mm were also cut from same Fe-3%Si alloy single crystal. Notches with a depth of 1 mm were introduced into the macro-sized specimens, and fatigue pre-crack was also introduced. Notch plane was set to be (100), which is a cleavage plane of this material, and notch direction was set to be [010] for both type of specimens. For macro-sized specimens, cleavage fracture occurred during introducing fatigue pre-crack. In constant, the micro-sized specimens were fractured by ductile manner. A plastic zone was clearly observed on the specimen surface near the crack tip and dimples were found on the fracture surface. The plastic zone size of this material is calculated to be 90 μm. This size is small enough to satisfy small scale yielding for macro-sized specimens, although this size corresponds to large scale yielding in micro-sized specimens. This may cause the size effect on the fracture behavior of this material. The results obtained in this investigation provide important information for designing actual MEMS devices.
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Yuji Kawakami, Takashi Enjoji, Shigeki Mouri, Hiroki Tanaka, Kazuki Ta ...2007 Volume 71 Issue 2 Pages 195-198
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSIn this paper, we describe an experimental study of pulsed current sintered binderless tungsten carbide hard metal. The binderless tungsten carbide is expected to be a highly precious mold material used under high temperature and harsh conditions.
Low temperature and rapid sintering are achieved by the pulsed current sintering method. The developed material has more than 99% of relative density and Rockwell hardness of 96.5[HR30N] without applying hot isostatic press. Due to its rapid sintering, the material has fine microstructure and fine surface roughness. The polished surface roughness (Ra) is less than 3 nm.
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Daiji Kubo, Ryo Nakano, Keisuke Takahashi, Yoshihito Matsumura, Yoshit ...2007 Volume 71 Issue 2 Pages 199-202
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSInfluences of magnetostriction and magnetostrictive susceptibility of composite mover device of Fe-Tb alloy thin film coated with Fe-Pd alloy thin films on one side surface of silicon substrate prepared by DC magnetron sputtering process were investigated. The magnetic field induced the bending motion at 1000 kA/m. The magnetostriction and its susceptibility of the device film approximately corresponds to the average of values of Fe-Tb and Fe-Pd positive magnetostrictive thin films.
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Yoshio Taira, Tsutomu Oikawa, Shingo Masuda, Keisuke Iwata, Akira Tone ...2007 Volume 71 Issue 2 Pages 203-207
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSInfluences of electron beam (EB) irradiation on magnetostriction and its susceptibility of Fe2.6Sm alloy thin films have been investigated. The alloy thin film deposited on a (100) plane of a silicon wafer is prepared by using a direct current magnetron sputtering apparatus. The irradiation enhances compressive magnetostriction and its susceptibility. The large magnetostriction of the irradiated Fe2.6Sm sample occurs, because the irradiation prevents generating the Fe3Sm crystalline with small magnetostriction. On the other hand, the high susceptibility is explained by randomization, induced by EB-irradiation, of Fe2.6Sm amorphous sample, where the magnetic moment rotates easily.
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Fuminori Kobayashi, Naoki Ide, Yoichi Nishino2007 Volume 71 Issue 2 Pages 208-212
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSWe report on the temperature dependence of electrical resistivity and Seebeck coefficient for the p-type (Fe1-xRex)2VAl system with compositions 0≤x≤0.06 in addition to the result of measurements of thermal conductivity at room temperature. While Fe2VAl (x=0) exhibits a semiconductor-like behavior in electrical resistivity, a slight substitution of Re for Fe causes a significant decrease in the low-temperature resistivity and a large enhancement in the Seebeck coefficient, reaching 90 μV/K for x=0.04 at 300 K. The Seebeck coefficient is found to be substantially larger than that for the p-type Fe2(V1-yTiy)Al system. The thermal conductivity decreases more rapidly for the Re substitution than for the Ti substitution, showing that doping of heavier atoms such as Re reduces more effectively the lattice thermal conductivity.
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Yosuke Harai, Masaaki Kai, Kenji Kaneko, Zenji Horita2007 Volume 71 Issue 2 Pages 213-217
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSA magnesium alloy AZ61 was subjected to a process of severe plastic deformation through high pressure torsion (HPT) at room and elevated temperatures. For the HPT process, a pressure of 3 GPa was applied to the alloy with a disk-shaped sample having dimensions of 10 mm in diameter and 0.8 mm in thickness while the lower anvil was rotated with respect to the upper anvil with a rotation speed of 1 rpm for up to 7 turns. Microstructures were observed using optical microscopy and transmission electron microscopy. Hardness was measured across the diameter of the sample to examine any variation with respect to positions from the center of the disk under different HPT conditions. Tensile tests were carried out at 473 K with initial strain rates ranging from 3.3×10-4 s-1 to 3.3×10-2 s-1. Microstructure observations revealed that the average grain size was reduced to 0.52, 0.37, 0.23 and 0.22 μm after 1, 3, 5 and 7 turns, respectively, for HPT performed at 423 K, Superplasticity with an elongation to failure of 620% was attained for the sample processed after 5 turns at 423 K when the tensile specimen was deformed at 473 K with an initial strain rate of 3.3×10-3 s-1.
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Naofumi Sakaguchi, Hiroaki Abe, Yoshio Katano, Takashi Onitsuka, Naoto ...2007 Volume 71 Issue 2 Pages 218-222
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSDefect formation, polymerization and resulting amorphization in C60 under irradiations with electrons and γ-ray were studied by micro-Raman spectroscopy. In the case of electron irradiation, amorphization was induced through accumulation of defects and/or polymerization. Under the electron irradiation above 150 keV, the effect of atomic displacement was evident for amorphization. On the other hand, below 150 keV, the electronic excitation induces amorphization through polymerization. In the case of γ-ray irradiation, polymerization was mainly introduced within the experimental conditions. Although the amorphization was not detected under γ-ray irradiation, the result of Raman spectroscopy indicated that bond opening in intramolecular C-C bondings partially occured implying the preservation of its spherical shape.
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Hitoshi Izuno, Tadaharu Yokokawa, Hiroshi Harada2007 Volume 71 Issue 2 Pages 223-225
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSWe have proposed and developed a new creep constitutive equation for Ni-base superalloys with good reproductibility under the conditions of high temperature low stress and low temperature high stress, good predictivity under the condition of high temperature low stress and middle temperature middle stress. In this paper, an application of a factor analysis for each parameter sets of the equation under the condition of 1100°C/137 MPa, 1000°C/245 MPa, 900°C/392 MPa, 800°C/735 MPa are discussed. In every condition, 2 to 4 factors are got by the analysis, and the tendency of factor loading shows the correspondence of each factor to each creep stage.
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Kyoko Kawagishi, Akihiro Sato, Kazuhide Matsumoto, Toshiharu Kobayashi ...2007 Volume 71 Issue 2 Pages 226-232
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSEQ coating, which is a new and stable bond coat system, suppresses the diffusion of alloying elements between the substrate and coating and the formation of secondary reaction zone (SRZ). In this study, high velocity frame sprayed (HVOF) EQ coatings designed for 2nd generation Ni-base superalloy were deposited on 4th and 5th generation Ni-base superalloys. The stability of microstructure at the interface and creep property of the coating system were investigated. Less than 50 μm-thick of the interdiffusion zone and no SRZ were observed in EQ coating system after 300 h heat treatment at 1100°C, in contrast to beyond 90 μm-thick of diffusion zone and 140 μm-thick of SRZ in the conventional CoNiCrAlY coating system. Creep strength of Al-diffusion and CoNiCrAlY coated 4th generation superalloys showed decrease in thin creep specimens, but EQ coated 4th generation superalloy showed equivalent creep strength for bare material.
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Takanobu Suzuki, Tadaharu Yokokawa, Toshiharu Kobayashi, Yutaka Koizum ...2007 Volume 71 Issue 2 Pages 233-238
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSThe alloying effect of Cobalt (Co) to microstructural parameters and mechanical properties, such as partitioning ratios of alloying elements and creep strength, of Re-bearing Ni-base single crystal superalloys have been investigated. The second generation single crystal superalloys, TMS-82+, Ni-7.8Co-4.9Cr-1.9Mo-8.7W-5.3Al-6.0Ta-2.4Re-0.1Hf, in mass% (8Co) was compared to a Co-free (0Co) and 15 mass% Co (15Co) alloy which had the same chemical composition as TMS-82+ except that Co was changed.
It was shown that the partitioning ratios of alloying elements tend to k(=Xγ/Xγ′)=1, as the content of Co was increased.
Furthermore, it was found that there was suitable content of Co for the creep strength under various temperature-stress conditions.
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Toshiya Nakata, Hiroyasu Tanigawa, Kiyoyuki Shiba, Shin-ichi Komazaki, ...2007 Volume 71 Issue 2 Pages 239-243
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSReduced activation ferritic steels (RAFs) are among the leading candidates for structural materials of fusion reactors. These structural materials are required to have both good fracture toughness and creep properties. In order to attain these properties, Ta is added to RAFs. Ta is not typically present in general heat-resistant steels, however, and Ta behavior in steels has not been clarified in detail. In this study, the basic creep properties of RAFs such as F82H pre-IEA heat, F82H IEA heat, F82H mod3 and JLF-1 HFIR heat were examined with an emphasis on the effects of Ta. Possible effects could include a large prior austenite grain (PAG) size, F82H pre-IEA heat, which has the same major composition as F82H IEA heat but with finer PAGs, or a lower creep strength. In the low-stress range, there was no significant difference in the creep strengths among all of the RAFs. This could be caused by differences on the stress dependence of the minimum creep strain rate, as it did not change at every stress level for the F82H IEA heat but did increase in the low-stress range for the F82H mod3 and JLF-1 HFIR heat. This difference in the F82H IEA heat behavior could be explained by the presence of Ta(C, N), as the XRD analyses on the extraction residue suggested there was no Ta(C, N) formed in the F82H IEA heat.
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Atsushi Sawahata, Hiroyasu Tanigawa, Kiyoyuki Shiba, Masato Enomoto2007 Volume 71 Issue 2 Pages 244-248
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSReduced activation ferritic/martensitic steels (RAFs), such as F82H (Fe-8Cr-2W-0.2V-0.04Ta-0.1C), are the leading candidates for structural materials of fusion reactors, and it is essential for the development of RAFs to assure its good for fusion application. In this study, the influence of Ti on impact property was studied based on microstructural analyses and charpy impact tests which were performed in general-purity F82H (0.004Ti-0.0060N) and high-purity F82H (<0.001Ti-0.0014N). In general-purity F82H, its impact property around DBTT showed both 100% brittle fracture and brittle-ductile, and this tendency did not appear in high-purity F82H. SEM observation on those brittle fracture surfaces of general-purity F82H revealed the presence of Al2O3-Ta(V, Ti)O composite oxides at the fracture initiation point. The size distribution analyses of oxides indicate that the complex oxide in general-purity F82H showed a higher number density than in high-purity F82H. In addition to this, EDS analyses showed that complex oxides in general-purity F82H had a strong peak of Ti, but they were not detected in the oxides in high-purity F82H. These results suggest that Ti has a significant influence on the formation of oxides, which in turn affects impact property.
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Eigo Kakutani, Masahiro Jotoku, Atsushi Yamamoto, Harushige Tsubakino2007 Volume 71 Issue 2 Pages 249-257
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSIt is generally recognized that impurity atoms affect the phenomena of recrystallization. In the present study, we have prepared a low impurity magnesium alloy, then deformation behavior in cold-rolling and corrosion behavior of the alloy were compared with those of a commercial AZ31B magnesium alloy. The low impurity alloy was prepared with using 5N-Al, 4N-Zn and high purity magnesium, the last one was prepared by a vapor deposition technique. Chemical analyses showed that the composition of the alloy was about Mg-3%Al-1%Zn (in mass%). Slices with about 5 mm thickness were cut from an ingot of the alloy, and hot-rolled into 1 mm at 623 K, then solution heat treated at 673 K for 86.4 ks. The specimens were cold-rolled at room temperature with reduction rates of 0~80%. For comparison, a commercial AZ31B alloy with 0.8 mm thickness was used. After cold-rolling, foil specimens for transmission electron microscopy were prepared and microstructures were observed. Recrystallization occurred in the AZ31B alloy by 70% cold-rolling at room temperature. Regions with low dislocation density were frequently observed in heavily cold-rolled specimens, which would show recovery phenomena or early stage of recrystallization. Additionally lowering the impurities resulted in improving a corrosion resistance. Corrosion test using a 1 mass%NaCl solution showed that the low impurity magnesium alloy had a superior corrosion resistance compared with that in the AZ31B alloy. In the AZ31B alloy filiform corrosion occurred after a duration time of 27 minutes, while in the low impurity magnesium alloy, filiform corrosion did not occur for 22 hours but general corrosion occurred.
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Ryota Goto, Yukiko Takahashi, Nobuki Tezuka, Koichiro Inomata, Satoshi ...2007 Volume 71 Issue 2 Pages 258-262
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSWe have investigated the structural, magnetic and barrier properties for Co-ferrite thin films, which have been formed by plasma oxidization of the surface of Co33Fe67(CoFe2) underlayer deposited on MgO(001) single crystal substrates. XRD patterns and cross sectional TEM observation revealed that the Co-ferrite thin films grew epitaxially with the (001) orientations on (001)-oriented CoFe2 underlayer. The saturation magnetization of CoFe2 and Co-ferrite annealed at 523 K were 1.5 Wbm-2 and 0.44 Wbm-2, respectively. Magnetizations of these two layers were rotated simultaneously. Coercivity increased up to near 80 kAm-1 after postannealing. To evaluate barrier properties of Co-ferrite, we have fabricated magnetic tunnel junctions (MTJs) consisting of CoFe2/Co-ferrite/Ta on MgO(001) single crystal substrates through microfabrication technique. These MTJs exhibited the non-linear current density(J)-voltage(V) curves, revealing that Co-ferrite thin films acted as a barrier.
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Regular Articles
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Osami Seri, Takeshi Tadokoro2007 Volume 71 Issue 2 Pages 263-269
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSRecently Japan has a revised regulation (Japanese Industrial Standard, JIS S3200-7) that lead ions in tap water have been restricted to the value of 10 ppb by the 2003 fiscal year. The formal analysis regulated by the above JIS rule has weak points; complicated, expensive and time-consuming procedure to get the value. We have developed an easy and simple method to obtain an reliable criterion for ascertaining the lead ions in tap water. The four kinds of Cu-5%Sn-6%Zn-2%Bi cast specimens containing various lead contents have been electrochemically kept at constant potential of -0.2 V vs. Ag/AgCl in 0.03 mass% acetic acid solution in order to selectively magnify the lead ions. The lead ions extracted into the acetic acid solution was measured by lead-ion-analysis instrument kit in a market. It is found that the value of 100 ppb lead ions by the analysis kit corresponds approximately to the value of the 10 ppb lead ions by the method of JIS S3200-7 procedure.
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Keishi Nakamura, Yasunori Sakagami, Shiomi Kikuchi2007 Volume 71 Issue 2 Pages 270-274
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSResistive materials with resistivity (ρ) of 10.3 to 25.1×10-8 Ωm and temperature coefficient of resistance (TCR) of 540 to 2800×10-6 K-1 were successfully fabricated by using the stacking and rolling of metallic sheets of Cu and Cu-Ni. The Cu-Ni/Cu/Cu-Ni sandwich structure showed changes of electrical characteristics with the conditions of heat treatment. The TCR values of the specimens decreased with increase of diffusion layer thickness at the interface of Cu and Cu-Ni layers by heat treatment. This process allows the electrical characteristics to be controlled as required, and the preparation of a precise resistor for current detection.
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Kenya Nagahisa, Yasuhiro Shimojo, Gen Sasaki, Makoto Yoshida2007 Volume 71 Issue 2 Pages 275-283
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSAs a potential material for high temperature services, unidirectional sintered SiC fiber reinforced SiO2-30 mol%Al2O3 composite with BN interphase was synthesized by liquid state hot pressing. The obtained composite had dense structure, and both the mullite and glassy SiO2 phases were found in the matrix. No chemical reaction among the constituents was observed.
The composites were exposed to air at 1573 K up to 3600 ks and then oxidation behavior was investigated. Three-point flexural test was performed at room temperature after each exposure. Flexural strength decreased with an increase in the exposure time and then leveled off in 360 ks. This tendency corresponds to the crystallization of SiO2 glass in the matrix. Change in the stress field which is caused by the crystallization and phase transformation of SiO2 would lead to the reduction of the strength. It was confirmed that oxidation progressed along the fibers and the oxidized depth was limited within approximately 200 μm independent of exposure time (3.6∼3600 ks). The oxide layer with approximately 10 μm thickness including silicon, aluminum and oxygen was found on the surface of the composites. This layer will prevent the inner oxidation within 200 μm.
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II. Tensile Strength and Charpy Impact Value at Room TemperatureMasami Taguchi, Hidehiko Sumitomo, Ryo Ishibashi, Yasuhisa Aono2007 Volume 71 Issue 2 Pages 284-290
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSIn the previous paper, authors reported the material processing of ultra-fine crystalline 12%Cr ferritic stainless steels. The micro-structure was composed of Zr oxide particles and grain that was 0.1 to 0.6 μm in diameter. Mechanical properties of ultra-fine grained ferritic stainless steels were investigated from aspects of tensile properties and toughness in this study.
The properties obtained are as follows. In the developed stainless steels, the Hall-Petch relation was established between 0.2% proof stress and inverse of square root of grain size at room temperature. The slope was nearly equal to that of pure iron. On the one hand, an addition of Zr and ZrO2 (>0.08%), or only of ZrO2 to the steel led to the brittle property in Charpy impact tests. The low toughness may be caused by the presence of large amount of oxygen. In the steels to which Zr, or Zr and small amount of ZrO2 were added, on the other hand, the Charpy impact values at room temperature were above about 3 MJ/m2 up to tensile strength of 1500 MPa. These values were twice to three times as large as those of conventional ferritic stainless steel SUS410 or those of other precipitation-strengthened steels at the same level of tensile strength. It was found out that the developed steels possess excellent mechanical properties. From details of fracture surface observation it is guessed that the cracks propergate along boundaries between MA powders sintered, for steels with lower impact values. The boundaries may have a brittle region in strength. Therefore, an improvement of boundary property is expected to contribute to strengthening and toughening.
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Kentaro Onaka, Masami Mayuzumi, Yoshihiro Mizutani, Junichi Tani2007 Volume 71 Issue 2 Pages 291-294
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSRecently, stress corrosion cracking (SCC) was observed in L-grade (low carbon) stainless steel (SS) components such as core shrouds and primary loop recirculation pipes in boiling water reactors (BWR). Since a shroud was fabricated from several parts machined from thick plates and connected by welding process, both the hot rolled surface and the cross section were exposed to the high temperature water environment. Hence, SCC susceptibility should be examined after considering the hot rolling direction during the production process of SS thick plates. Creviced bent beam test was conducted on type 316L and type 316 SS plate specimens machined from the longitudinal/transverse (LT), the transverse/short-transverse (TS) and the longitudinal/short-transverse (LS) planes. Each specimen was cold rolled by 10% to 30% just before machining to the final shape. After exposure to the test environment for 1000 h, each specimen was observed by a scanning electron microscope to measure SCC length on the surface.
SCC susceptibility was higher in the LS and TS planes than the LT plane for both type 316L and type 316 SS, although the susceptibility of type 316L SS was much lower than type 316 SS. The SCC length conformed to the log-normal distribution irrespective of the cold rolling ratio and, hence, a statistical analysis could be applied by assuming the distribution when a life prediction of SS components would be necessary.
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Masahiro Kitada2007 Volume 71 Issue 2 Pages 295-303
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSThe microstructures and optical properties of niiro-colored Cu-20 mass%Ag eutectic alloy (shibuichi in Japanese) have been investigated. Specimens are fabricated by a traditional Japanese metal-craft technique. An aqueous solution containing cupric sulfate, alum and artificial verdigris is used to color the alloy sheet at 373 K (100°C). A transmission electron microscope, X-ray diffractometer, EPMA, XPS, AES and spectrophotometer are used to determine the physical properties of the coloring layer. The αCu areas in the eutectic structure is preferentially strongly colored bluish black. Although the color change of αAg areas is less, the areas around αAg are a light yellowish orange and brown. The colored layer consists of crystalline and amorphous Cu2O, and Ag nanograins of various shapes distributed in the Cu2O matrix. The large Ag grains are nonoxidized αAg grains in a Cu-Ag eutectic structure. The Ag nanograins precipitate when the αCu grains are oxidized. The elements Cl and S are detected in the colored surface by EPMA and the compounds CuS, CuCl2 and CuSO4 are detected by XPS. Ag2S is detected near Ag grains by lattice image analysis. The reflectance of the specimen decreases with increasing coloring time. In conclusion, the Cu2O film and Ag nanograins in Cu2O mainly contribute to the color change.
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Tomohiro Okumura, Mitsuo Saitoh, Kazutaka Nishikawa, Akio Furusawa, Ke ...2007 Volume 71 Issue 2 Pages 304-311
Published: 2007
Released on J-STAGE: February 01, 2007
JOURNAL FREE ACCESSThere has been an intensive effort in the industries in recent years to replace leaded solder with lead-free process in order to minimize the emission of toxic materials. However, leaded solder is still used in many cases where no alternative lead-free process is currently available. Leaded soldering of the wire terminals is one of the worst examples as it causes cross contamination of lead into the lead-free solder bath during the successive process. To avoid this problem, it is important to develop a new process of successfully removing polymer film coated on a copper wire. We have investigated the use of atmospheric pressure plasma as a solution for the polymer removal in conjunction with lead-free solder plating. The atmospheric plasma technology has some unique advantages compared with the conventional low pressure plasma processes such as low cost operation and high speed processing as the chemical reaction tends to be more enhanced at higher pressure. An atmospheric micro-plasma source was thus developed for this purpose and its high etching rate of more than 100 μm/min with fluorine gas mixture was demonstrated. Furthermore, it was found that the copper wires processed by this plasma could be readily plated with lead-free solder at low temperature of 250°C without any use of fluxes even at 168 hours after removing the polymer film.
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