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Volume 71, Issue 3
Displaying 1-10 of 10 articles from this issue
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Kyoko Kawagishi, Akihiro Sato, Toshiharu Kobayashi, Hiroshi Harada2007 Volume 71 Issue 3 Pages 313-319
Published: 2007
Released on J-STAGE: March 01, 2007
JOURNAL FREE ACCESSThe oxidation properties of the 2nd-5th generation Ni-base superalloys were investigated. Isothermal oxidation examination was performed at 1023, 1173 and 1373 K in air for up to 3.6×106 s and the oxides were identified by using XRD analysis and SEM cross section observation.
The 3rd, 4th generation superalloys and 5th generation superalloy TMS-173 formed thick NiO layers at the surface caused by the outward diffusion of Ni at 1023 K. These alloys showed poor oxidation resistance at 1173 and 1373 K due to the spinel formation, except for the oxidation resistances of the 3rd generation superalloys at 1373 K which were slightly improved by forming Al2O3 layers under the spinel layers. The 2nd generation superalloy and 5th generation superalloy TMS-196 show excellent oxidation resistance at all temperatures examined in this study, forming Al2O3 protective layers. These favorable results were caused by their high Cr content.
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Akihiro Sato, Yasuhiro Aoki, Mikiya Arai, Hiroshi Harada2007 Volume 71 Issue 3 Pages 320-325
Published: 2007
Released on J-STAGE: March 01, 2007
JOURNAL FREE ACCESSThis article compares the creep rupture responses of aluminide coated samples with uncoated ones to elucidate the effect of diffusion layers on resistance against creep. Three Ni-base single crystal superalloys, CMSX-4, TMS-75 and TMS-138, were chosen for present study. Creep specimens had thicknesses ranged from 1 mm to 4 mm to simulate the varying dimensions across the actual turbine blade. Creep conditions were set at 1060°C-137 MPa and 1100°C-137 MPa. Experimental results indicated that the creep-rupture lives of coated specimens were shorter than those of the bare samples. In particular, the coated TMS-138 specimen with 1 mm thickness had an 86% reduction in creep rupture life. Microstructural observations on coated samples indicated the formation of diffusion zones beneath the coating; a creep life model was then developed to taken account the reduction in load bearing cross sectional area. In conclusions, the creep-rupture lives predicted by the model have shown good agreement with the experimental values.
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Baolong Shen, Masahiro Akiba, Akihisa Inoue2007 Volume 71 Issue 3 Pages 326-329
Published: 2007
Released on J-STAGE: March 01, 2007
JOURNAL FREE ACCESSThe addition of 2 at%Mo combined with 2 at%Si was found to be effective for the extension of the supercooled liquid region (ΔTx) and approaching alloy to a eutectic point in the Fe77-xMoxGa3P10C4B4Si2 alloy system. The ΔTx value is 33 K for the Fe77Ga3P12C4B4 glassy alloy, and increases to 60 K for the Fe75Mo2Ga3P10C4B4Si2 glassy alloy. Besides, this glassy alloy exhibits a high reduced glass transition temperature (Tg/Tl) of 0.6. The large ΔTx and high Tg/Tl enabled us to prepare the Fe75Mo2Ga3P10C4B4Si2 bulk glassy alloy successfully with a diameter of 2 mm and high saturation magnetization (Is) of 1.27 T. The Fe75Mo2Ga3P10C4B4Si2 glassy alloy also exhibits good soft magnetic properties, i.e., high effective permeability at 1 kHz of 1.1×104 and low coercive force of 5 A/m.
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Tarou Tokuda, Fumihiro Suzumura, Kozo Ohtani, Kimitoshi Sato, Mitsuo K ...2007 Volume 71 Issue 3 Pages 330-335
Published: 2007
Released on J-STAGE: March 01, 2007
JOURNAL FREE ACCESSRecently, the use of Pb-free solder has caused early deterioration and decreased lifetime of the soldering iron tip. Therefore, it is critical to find a solution to this problem.
In this study, the changes in the properties of a ceramics/metal composite (Al2O3/Ni) were investigated. The resistance of solder erosion and thermal conductivity were also investigated in the composites. The possibility of using that composite as the soldering iron tip was considered. The ceramics/metal composite did not have the anisotropic mechanical properties and solder wettability, while those properties did not vary with changes in the pressure area of HP sintering. The test temperatures (503 K and 623 K) and environments (air and N2 gas) also did not influence those properties of the composite. The changes in those properties of an Al2O3/Ni composite were caused by the generation of columnar or equi-axied grains with the addition of Ni and by changes in the relative density and the surface energy. Although the thermal conductivity was lower in the Al2O3/Ni composite compared with Cu, erosion by molten solder could be controlled in the composite.
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Hideo Abe, Takahiro Matsuura, Hiromi Shimazaki, Takeshi Tanaka, Tohru ...2007 Volume 71 Issue 3 Pages 336-341
Published: 2007
Released on J-STAGE: March 01, 2007
JOURNAL FREE ACCESSIn a previous study, the properties and mechanism of peeling on nickel electroforming were investigated by changing the activation treatment and the surface roughness of the plate and varying the treatment conditions (concentration, time, and temperature) of potassium dichromate solution. In this study, the chromate treatment was carried out on noble metals, base metals, and Cu-Zn alloy. It was found that chromate films can be formed on noble metal plates. The thickness of chromate film was different on the noble metal and base metal plates, and was less than about 15 nm on noble metal plates, but was in the order of the standard electrode potential (SEP) on base metal plates. It was found that the chromate films formed on all metal plates contained metal elements of that plate.
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Kensuke Kuroda, Shinji Nakamoto, Yoshihiro Miyashita, Ryoichi Ichino, ...2007 Volume 71 Issue 3 Pages 342-345
Published: 2007
Released on J-STAGE: March 01, 2007
JOURNAL FREE ACCESSThe aim of this study was to investigate the in vivo performance of implants coated with hydroxyapatite (HAp) with different surface morphologies. HAp coatings were formed on commercially pure titanium rods (2 mm in diameter, 5 mm in length) by the thermal substrate method in an aqueous solution that included Ca(H2PO4)2 and CaCl2. The coating experiments were conducted at 40-140°C and pH=8 for 15 or 30 min. All the specimens were covered with HAp, which had different morphologies such as net-like, plate-like, and needle-like. The coated rods were implanted in the tibiae of 10-week-old male rats. Noncoated titanium rods were used as the control in this study. The constructs were retrieved 14, 28, and 56 days postimplantation and examined for new bone formation and tissue response in the cancellous and cortical bone, respectively. After 14 days implantation, new bone formed on both the HAp-coated and noncoated titanium rods in the cancellous and cortical bone. However, the bone-implant contact ratio, which was used for the evaluation of new bone formation, was significantly dependlnt on the surface morphology of the HAp, and the results demonstrated that the needle-like coating appears to promote rapid bone formation.
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Shuichi Hara, Masato Yamashita, Takayuki Kamimura, Masugu Sato2007 Volume 71 Issue 3 Pages 346-353
Published: 2007
Released on J-STAGE: March 01, 2007
JOURNAL FREE ACCESSThe detail structure of heavy rust layers with large swelling and laminated layers formed on weathering steel bridges have been investigated by optical microscope and laboratory powder X-Ray diffraction (XRD) and synchrotron XRD in SPring-8. Some large gaps (inter-layer) and many linearly arrayed voids (LAV) were found along layers. The mass ratio of spinel-type iron oxide [mainly Magnetite (Fe3O4)] in average composition of the whole layer was 30-40 mass%. In contrast the mass ratio of spinel in its local parts, i.e. outer layer, inter-layer and inner layer position was not higher in common but mass ratio of β-FeOOH was higher. Thus we propose a multilayer model structure for these unique rust layers which are made of Spinel Poor, Rich and Poor unit cell structure (SPRaP-cell) compartmentalized by LAV.
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Takashi Ando, Nobuo Itoh, Kenichiro Togoe, Yoshio Harada2007 Volume 71 Issue 3 Pages 354-360
Published: 2007
Released on J-STAGE: March 01, 2007
JOURNAL FREE ACCESSIn order to improve the adhesion of 75 mass% Cr-Fe alloy plasma spray coatings, which provide sulfide corrosion resistance for the inner surface of NAS battery high-temperature type Al cylinders, the Al substrate temperature and the flattering behavior of the plasma spray particles were studied. Also, experiments were conducted to study how changes in the preheating temperature of the Al cylinder affected the spray coating's adhesion. The splat morphology of the spray particles changed significantly in relation to the preheating temperature of the Al substrate, from splash shaped to disk shaped as the preheating temperature increased. It was especially evident that the splat morphology of the particles changed sharply at over 433 K, forming disk shaped with excellent adhesion splats to the substrate. In addition, as the preheating temperature was increased, fewer coating defects such as blisters and peeling were seen on the spray coating. A good correlation was found between the flatness of the spray particles and the adhesion of the coating formed by changing the preheating temperature of the Al cylinder. When the preheating temperature was set at over 433 K, coating with good adhesion were formed. It was therefore shown that by studying the flattening behavior of the plasma spray particles, could be found an effective method for improving the adhesion of plasma spray coating.
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Takayoshi Fujino, Teppei Matzuda2007 Volume 71 Issue 3 Pages 361-367
Published: 2007
Released on J-STAGE: March 01, 2007
JOURNAL FREE ACCESSTitanium dioxide (TiO2) coatings were prepared by chemical conversion treatment of magnesium in (NH4)2[TiO(C2O4)2] with H2O2, then, anatase type TiO2 coatings were prepared by sintering. To identify the coating structure, coating analysis was carried out using an infrared absorption spectrum analyzer. Based on the infrared absorption results, a component of the coating was found in the hydrolysis product of peroxo-titanium compound. Furthermore, the coating analysis was carried out using X-ray diffractometry (XRD), and non-sintered coating was amorphous; however, the coating sintered at more than 573 K was anatase-type titanium dioxide.
In the forming process of the conversion treatment in (NH4)2[TiO(C2O4)2] with H2O2, first, the magnesium was dissolved to H+ in the bath and then, hydrogen ions on the magnesium surface were consumed to generated hydrogen gas. Thus, the pH of the interface became alkali. The hydrolysis of the peroxo-titanium compound was deposited on the magnesium because pH increased on the surface. From the XPS results and the TG-DTA results, a component of the coating is a hydrolyzation product of a peroxo-titanium compound and Mg(OH)2. Because Mg(OH)2 is generates in pH more than 11, it is considered that the pH on the magnesium surface is more than 11.
The coating sintered at 573 K had the highest photocatalytic activity. The photocatalytic activity of the coating sintered at 623 K was lower than the coating heated at 573 K, which is attributed to growth of TiO2 particle. This forming process of the coating is low cost because of the useless electrolytic decomposition process and increasing the speed of the treatment. It is possible to treat complicated form of the substrate metal, so this method can be expected to use in various fields. Therefore this method is expected to practical use for environmental purification.
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Hiroyuki Toda, Toshiro Kobayashi, Masakazu Kobayashi, Junpei Sawamura, ...2007 Volume 71 Issue 3 Pages 368-377
Published: 2007
Released on J-STAGE: March 01, 2007
JOURNAL FREE ACCESSThe present authors have proposed in-situ composites in which cold working was applied to the cutting chip mixture of dissimilar materials. The composites have exhibited superior strength together with ultra-fine grain structure. In this study, such composite materials are produced by combining 6061 aluminum alloy and IF steel chips. Microstructural evolution processes are visualized by means of the microtomography as well as the TEM observation. It has been clarified that ultra-fine grains with a large fraction of high angle boundaries are obtained due to the effects of severe plastic deformation during cutting. Grain size of the matrix aluminum alloy is reduced to about 220 nm by applying swaging strain of only 1.9. It should be noted that the significant strain hardening of the chips occurs during initial deformation stage where strain applied by swaging seems to be consumed mostly for consolidation. The chips gradually change their orientation in the material at this stage. It can be inferred that the rapid development of ultra-fine structure in the matrix is also attributed to gradual change in deformation axis thereby realizing effective multi-axial deformation. Overall, the utilization of chips is identified as a highly effective way of grain refining compared to the other uni- and multi-axial deformation processes.
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