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Volume 67, Issue 8
Displaying 1-8 of 8 articles from this issue
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Ayumu Ibe, Minoru Itai, Norio Yamaguchi, Osamu Ohashi2003 Volume 67 Issue 8 Pages 369-373
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn order to elucidate the optimum microstructure in an Fe-Si alloy for a phase transformation to FeSi2(β-phase), electrical resistivity, microstructure and phases were observed after carrying out the annealing heat treatment of Fe2Si5(α-phase)-FeSi(ε-phase) eutectic alloy compacts with different grain sizes and phase distributions. The activation energy of the ε-phase transformation reaction was also investigated. For compacts with fine, uniform crystal grains, the electrical resistivity changed rapidly and the activation energy was small. However, in compacts where the ε-phase crystal grain size and distribution was not uniform, changes in electrical resistivity were slower than that of compacts with a fine, uniform ε-phase, and the activation energy was large. We concluded that the quantity of crystal grain boundary acting as the diffusion course and Si attainment frequency to the ε-phase influenced the changes in electrical resistivity and activation energy. In the materials with fine crystal grains, Si mainly diffused along grain boundaries, and the time taken for Si to reach the ε-phase was short. In the materials where the ε-phase exhibited uniform crystal grains, the frequency of Si reaching the ε-phase, was high, and transformation into β-phase was quick. The optimum microstructure for a phase transformation to β-phase in the Fe-Si alloy consists of a fine and uniform ε-phase.View full abstractDownload PDF (858K) -
Yoshiei Kato, Yasuo Kishimoto2003 Volume 67 Issue 8 Pages 374-378
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSNumerical analysis and experiments on gas flow rate through a submerged tuyere versus pressure in a tank were carried out to design an optimal flow pattern of bottom-blown gas in a refining furnace. The gas flow in the tuyere was formulated as an isentropic flow with friction. When the Mach number reached unity at the tuyere front, the mass flow rate was proportional to the pressure in the tank. The calculated results for compressed gas flow under high pressure in the tank agreed well with those of the experiments. The pressure in the tank increased with the increase in pulverized lime injection rate under the same gas flow rate. Regarding the gas flow pattern at the final refining stage to minimize iron oxide, the gas flow rate is decreased in a bottom-blown converter, whereas the submerged gas flow rate is increased in a top- and bottom-blown converter. A region of allowable gas flow rate and pressure control range was shown where neither drilling of gas jet through the bath nor leakage of steel melt in a tuyere occurs.View full abstractDownload PDF (351K) -
Yoshiei Kato, Koji Yamaguchi, Yasuo Kishimoto2003 Volume 67 Issue 8 Pages 379-384
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSGas behavior in water, splash amount and mass transfer rate between gas and liquid of a helical tuyere in which swirl flows formed were investigated, and compared with those of a conventional circular tuyere. Three kinds of helical tuyere were used for the experiments: 1) a tuyere divided by a twisted sheet inside a circular tube to form two partitions, 2) a tuyere clogging one of the two partitions of 1), and 3) a tuyere comprising three twist-bundled circular tubes.
The back attack phenomenon was diminished or its frequency was decreased when gases were injected into water through multiple holes with different jet angles because of increased shear stress at the interface of the gas cavity into the tuyere.
The diameters of both the formed and rising gas bubbles in the helical tuyere were smaller than those in the circular one, for the same reason as discussed above in the back attack phenomenon. Gas through the helical tuyere spread in the transverse direction, whereas gas injected by the circular tuyere was concentrated in the middle of the vessel.
The splash amounts of the helical tuyere were less than those of the circular one because vertical momentum and rising gas velocity were small.
The increase in interface area between gas and liquid resulting from the smaller bubble diameter and rising gas velocity of the helical tuyere enhances the mass transfer rate between gas and liquid, compared with the circular tuyere.View full abstractDownload PDF (500K) -
Hisao Tanaka, Won-Yong Kim, Masakuni Fujikura, Ryohei Tanaka, Yoshinao ...2003 Volume 67 Issue 8 Pages 385-390
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe high-temperature tensile creep rupture properties of the Nb solid solution in-situ composites (Nbss)/Nb5Si3 and Nbss/Nb5Si3/(Nb, Hf) C have been studied in relation to their chemical compositions and microstructures. The samples were prepared by arc melting. Nbss/Nb5Si3 in-situ composites alloyed with Mo and W have a maze-like structure. Small dispersed carbide regions were mainly observed in Nb solid solution and phase boundary in the Nbss/Nb5Si3/(Nb, Hf) C in-situ composites. Additionally, carbides precipitated inside the silicide region after the creep rupture test. High-temperature tensile creep tests were conducted at 1773 K under argon over a stress range from 20 to 200 MPa. We found that Nb-16Si-5Mo-15W-5Hf-5 C has a high creep rupture strength, with a time-to-rupture of 477 h at 1773 K under a stress 100 MPa. Addition of W is more effective than Mo to increase on creep strength at 1773 K, and the rupture time was prolonged at lower stress in Nb-20Si-5Mo-5Hf-5C tri-phase alloy with a dispersion of (Nb, Hf) C carbide particles.View full abstractDownload PDF (1189K) -
Yoshinori Ono, Tetsumi Yuri, Hideshi Sumiyoshi, Saburo Matsuoka, Toshi ...2003 Volume 67 Issue 8 Pages 391-397
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSHigh-cycle fatigue properties and crack initiation behavior were investigated in Ti-5%Al-2.5%Sn ELI alloy with a mean alpha grain size of 80 μm, which had been prepared using the same manufacturing process as the material employed for the liquid hydrogen turbo-pump of H-II launch vehicle No. 8. The 0.2% proof stress and the ultimate tensile strength of this alloy increased with decreasing temperature. Fatigue strength in the longer-life region did not increase in response to increments in tensile strength at cryogenic temperatures. This is attributable to the temperature dependence of crack initiation behavior, and indicates that fatigue cracks tend to initiate earlier at lower temperatures. Fatigue cracks initiated in the specimen interior independently of the test temperatures of 4 K, 77 K and 293 K and formed large crack initiation sites consisting of several crystallographic facet-like structures at cryogenic temperatures. Each facet-like structure was formed through transgranular initiation and growth of micro cracks along slip bands. These sub-surface micro cracks initiated separately in the thinner part of the hourglass-type test piece, and propagated to adjacent grains or combined with each other to form a fatigue crack initiation site. On the other hand, there were no facets that could be clearly identified as the crack initiation sites at 293 K.View full abstractDownload PDF (1848K) -
Yoshihiro Matsubara, Hideo Saito, Hideyuki Okada, Toshiyuki Fujii, Sus ...2003 Volume 67 Issue 8 Pages 398-403
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe effects of grain-boundary orientation on plastic deformation and recrystallization are investigated using a copper double cylindrical bicrystal. This consists of cylindrical inside crystal with a second crystal wrapped around its the curved side surface. Tensile testing is performed on specimens cut from this bicrystal. In addition to slip lines caused by the operation of primary slip systems, slip lines from operation of secondary slip systems with certain orientations are observed preferentially near the grain boundary. Following the testing, specimens are annealed and recrystallized grains are formed preferentially near the grain boundary where secondary slip lines were observed. Compatibility of plastic deformation at the grain boundary is discussed in terms of energy and the idea of “incompatibility factor” is proposed. The orientation dependence of the grain-boundary phenomena is well explained using the incompatibility factor.View full abstractDownload PDF (438K) -
Rongguang Wang, Mitsuo Kido, Tarou Tokuda, Kouji Kato, Suketsugu Nakan ...2003 Volume 67 Issue 8 Pages 404-409
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe wetting behavior of micro-droplets (distilled water and lubrication oil) on natural mica and silicon nitride (Si3N4) surfaces was observed and evaluated using an atomic force microscope (AFM). The wetting contact angle changes with droplet size, which is discussed.
Micro-droplets of water and oil were successfully observed with the AC non-contact mode of the AFM. The micro-droplets of oil were applied to mica and Si3N4 surfaces by the cantilever of the AFM. The wetting evaluation showed that wetting contact angles for micro-droplets on mica and Si3N4 surfaces were lower than those of macro-ones, and the values were lower for smaller micro-droplets.View full abstractDownload PDF (643K) -
Yukihiro Isoda, Yoshio Imai, Yoshikazu Shinohara2003 Volume 67 Issue 8 Pages 410-415
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe effects of crystal grain sizes on the thermoelectric properties were investigated for sintered β-FeSi2 doped with Mn or Co. Sintered materials of β-FeSi2 doped with Mn or Co were prepared by the cold-pressing and sintering technique.
The mean powder size, sintered grain size Cs and annealed grain size Ca decreased exponentially with increasing ball-milling duration. The mean crystal grain sizes (Cs and Ca) of FeSi2 doped with Mn were larger than that of Co-doped specimen after sintered and annealing. The Seebeck coefficient α and electrical resistivity ρ of Mn-doped p-type FeSi2 increases with Ca. On the other hand, α of Co-doped n-type FeSi2 is independent of Ca, while ρ decreases with increasing Ca. The Hall mobilities of p- and n-type FeSi2 specimens were approximately independent of Ca. For p-type FeSi2, the carrier concentration nH decreased with increasing Ca, whereas nH of n-type FeSi2 increased with Ca. This result shows that the Ca dependence of the α and ρ is similar to the nH dependence. For p-type FeSi2, the increase in nH with decreasing Ca is due to the holes formed in grain boundaries. For n-type FeSi2, the decrease in nH with decreasing Ca is due to the carrier compensation. Thermal conductivity of p- and n-type FeSi2 specimens decrease with decreasing Ca, because the phonons are scattered in grain boundaries. The effective maximum power (Pef) at the temperature difference 800 K for p-type Fe0.93Mn0.07Si2 decreases with Ca. On the other hand, and Pef for n-type Fe0.985Co0.015Si2 increases with Ca. It was found that p- and n-type FeSi2 showed high thermoelectric performance at ball-milled powder sizes of 1.10 μm and 2.12 μm, respectively.View full abstractDownload PDF (844K)
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