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Volume 68, Issue 4
Displaying 1-9 of 9 articles from this issue
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Naoki Omura, Makoto Kobashi, Naoyuki Kanetake2004 Volume 68 Issue 4 Pages 211-215
Published: 2004
Released on J-STAGE: June 24, 2005
JOURNAL FREE ACCESSTitanium carbide (TiC) reinforced 6061 aluminum alloy composites were fabricated by the combination process of combustion reaction and vortex technique. Titanium, carbon and 6061Al powders were blended and consolidated. When the consolidated powder blend was heated, combustion reaction occurred near the melting point of aluminum and, as a result, TiC particles were formed in 6061Al matrix (base composite). The in situ formed TiC particles were spherical shape with 2-5 μm in diameter. The combustion synthesized TiC/6061Al base composite was then added into molten 6061Al to control the volume fraction of TiC particle (5, 10 and 15 vol%TiC). Regardless of the volume fraction, TiC particles in the base composite were easily incorporated and dispersed uniformly in the 6061Al matrix within 300 seconds stirring. On the other hand, when the commercial TiC powders were directly added in molten 6061Al alloy, 1800 seconds or longer stirring time was necessary to achieve incorporation (more than 95%) and uniform dispersion of TiC. The mechanical properties of the composites fabricated using the base composite were roughly equal to those using commercial TiC powder.View full abstractDownload PDF (3089K) -
Masao Hayakawa, Koji Yamaguchi, Megumi Kimura, Kazuo Kobayashi2004 Volume 68 Issue 4 Pages 216-222
Published: 2004
Released on J-STAGE: June 24, 2005
JOURNAL FREE ACCESSMicrostructural analyses by FE-SEM and TEM were performed for a ferritic heat-resisting steel that contained 12 mass% chromium and 2 mass% tungsten to characterize a multiscale structure consisting of prior austenite grains, packets, blocks and subgrains. The size distributions of the blocks, precipitates and subgrains were quantitatively evaluated before and after a creep-fatigue testing, respectively, to relate the creep-fatigue property. As the results, it was shown that the occupancy of precipitates on prior austenite grain boundaries increased markedly and subgrains became coarse during the creep-fatigue testing, while the size of blocks did not change. It is suggested that the growth of the grain boundary precipitates and subgrains plays an important role of the creep-fatigue fracture mechanism.View full abstractDownload PDF (1359K) -
Naoki Okada, Ryota Genma, Yoshitake Nishi, Haru-Hisa Uchida2004 Volume 68 Issue 4 Pages 223-227
Published: 2004
Released on J-STAGE: June 24, 2005
JOURNAL FREE ACCESSIn the hydrogen energy system, hydrogen storage materials become important from view points of both hydrogen storage and transportation. Alkaline hydrogen storage materials are much attractive for their high hydrogen storage capacity, while the hydrogen reaction rates are too small at lower temperatures. In this paper, improved reaction kinetics is reported for an alkaline hydrogen storage material (Na2LiAlH6) with rare earth oxides mixed by mechanical alloying.View full abstractDownload PDF (2186K) -
Long yun Piao, Tetsuichi Motegi2004 Volume 68 Issue 4 Pages 228-231
Published: 2004
Released on J-STAGE: June 24, 2005
JOURNAL FREE ACCESSIn our continuous casting of semisolid aluminum alloys and magnesium alloys using an inclined cooling plate, we have succeeded to cast billets consisting of granular grains. The cooling plate generates crystal in these alloys with small solid fraction. We coated the cooling plate with BN to prevent the formation of a solid shell. The number of grains was influenced by the thickness of the BN coating. Therefore, we investigated the influence of the BN coating thickness on the number of crystals, solid fraction, relation between isothermal holding time, and heat flux. The optimal BN coating thickness for obtaining the largest number of grain was 30 μm. In this case, the largest degree of supercooling in the molten alloy occurred on the cooling plate and the largest heat flux was obtained. The solid fraction in the semisolid slurry was 2.6% just below the cooling plate and it became more than 40% in the tundish held at 60 seconds.View full abstractDownload PDF (2727K) -
Atsushi Hibino2004 Volume 68 Issue 4 Pages 232-239
Published: 2004
Released on J-STAGE: June 24, 2005
JOURNAL FREE ACCESSThe combustion synthesis of the TiAl intermetallic compound was investigated. The raw Ti/Al powder was prepared from elemental Ti and Al powder with controlling of the Ti/Al ratio. The Ni/Al (Ni/Al ratio = 1) was added to the raw Ti/Al powder as the sintering additive. The compacts made from the mixed powder were reacted by the thermal explosion combustion synthesis. The mechanical properties of the synthesized products were measured in the range of the Ti/Al ratio from 0.67 to 9.00.
The measurements of the density, the phases, the microstructure and the size accuracy of the products revealed that a good performance with high density and fine micro structures was obtainable when the Ti/Al ratio was in the range from 1.00 to 1.22. Effect of the quantity of the Ni/Al additive on the density of the products was also examined.View full abstractDownload PDF (1616K) -
Naoki Takata, Ken-ichi Ikeda, Fuyuki Yoshida, Hideharu Nakashima, Hiro ...2004 Volume 68 Issue 4 Pages 240-246
Published: 2004
Released on J-STAGE: June 24, 2005
JOURNAL FREE ACCESSIn order to clarify the correlation between the grain boundary energy and its atomic structure in copper, energy and atomic structure of ‹110› symmetric tilt boundaries in copper were simulated by molecular dynamics method. From the calculations, it was revealed that the grain boundary energy of ‹110› symmetric tilt boundaries strongly depended on misorientation and that there are deep energy cusps at the misorientation angles which correspond to (111)Σ3 and (113)Σ11 symmetric tilt boundaries. It was found that the atomic structure of each ‹110› symmetric tilt boundary was described by three kinds of structural units which constitute (331)Σ19, (111)Σ3 and (113)Σ11 symmetric tilt boundaries respectively, and by (110) and (001) single crystal units. The volume expansion of each grain boundary was evaluated and compared with the grain boundary energy. As a result, it was elucidated that the grain boundary energy depends on the excess free volume of symmetric tilt boundaries.View full abstractDownload PDF (2292K) -
Jae Sik Yoon, Hyeoung Ho Park, In Sung Bae, Shoji Goto, Byung Il Kim2004 Volume 68 Issue 4 Pages 247-251
Published: 2004
Released on J-STAGE: June 24, 2005
JOURNAL FREE ACCESSIn order to produce high-quality tantalum powder of spherical shape with a uniform particle size and a high purity using metalothermic reduction process, it is important to control the reaction temperature and reaction rate.
In this study, we developed a metallothermic reduction method using the system supplying materials continuously from the external unit where the feed material of K2TaF7 and Na as a reductant were continuously supplied into the reaction furnace and the reaction rate was controlled.
The characteristics of tantalum powder produced by the continuous supply system were compared with those of the powder produced by a batch system that the whole amount of the feed material and reductant were supplied all together into the reaction furnace at one time.
We could get tantalum powder with spherical shape and uniform particlesize with the diameter of 2∼3 μm because we used the external continuous supply system where the reaction temperature and reaction rate could be well controlled.
After deoxidation, dehydration, and heat treatments, the purity of the tantalum power reached to 99.5 mass% level of the reagent grade. The yield of tantalum powder increased from 80% in the batch system to 90% in the external continuous supply systemView full abstractDownload PDF (3523K) -
Effect of Pressure on the Magnetization of Fe-Ni and Fe-Ni-Cu Alloys Prepared by Mechanical AlloyingTakashi Yamagata, Hiromitsu Ino, Masaki Yamada, Tsuneaki Goto2004 Volume 68 Issue 4 Pages 252-256
Published: 2004
Released on J-STAGE: June 24, 2005
JOURNAL FREE ACCESSMagnetic properties of Fe-Ni and Fe-Ni-Cu alloys prepared by milling were investigated in relation to the Invar effect. By the mechanical alloying preparation of Fe-Ni binary alloys, FCC single phase was obtained in Fe0.65Ni0.35 and exclusively BCC phase in Fe0.80Ni0.20. Between these two compositions, FCC and BCC mixed phase appeared. The atomic volume of the FCC phase decreases with increasing Fe concentration.
Fe0.67Ni0.33, (Fe0.75Ni0.25)0.9Cu0.1, Fe0.68Ni0.32 and Fe0.69Ni0.31 with high concentrations of iron, where the FCC phase is almost unstable, show large pressure coefficients of the magnetization (dMs/dP)/Ms (0) at 4.2 K, about −2.5×10-2 GPa-1. In contrast, (Fe0.65Ni0.35)0.9Cu0.1 and (Fe0.67Ni0.33)0.9Cu0.1 with lower concentrations of iron show much smaller values of about −0.02×10-2GPa-1 at 4.2 K. The estimated pressure coefficient of the magnetization of the FCC phase in Fe0.69Ni0.31 after subtracting the contribution of the BCC phase in the alloy is as large as −11.9×10-2GPa-1.View full abstractDownload PDF (724K) -
Yosiki Suematsu, Soong-Keun Hyun, Hideo Nakajima2004 Volume 68 Issue 4 Pages 257-261
Published: 2004
Released on J-STAGE: June 24, 2005
JOURNAL FREE ACCESSLotus-type porous nickel was successfully fabricated by unidirectional solidification using the molybdenum-sheet mould coated by Al2O3-Na2SiO3 in an argon atmosphere. During solidification, the moisture absorbed in Al2O3-Na2SiO3 at atmospheric temperature is dissolved into the melt and then the gas pores are formed at the solid-liquid interface. The pore size and porosity were controlled by the pressure of argon gas as well as the amount of moisture in the mould, while the pore growth direction was controlled by the freezing direction. By increasing the pressure of argon gas the pore formation is suppressed, since the pressure and the density of the gas in the growing pore are increased with the total pressure of the atmosphere. The pore diameter ranges from 50 μm to 1 mm and the maximum porosity is about 60%.View full abstractDownload PDF (4719K)
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