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Volume 48, Issue 6
Displaying 1-14 of 14 articles from this issue
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Se-Hyun Ko, Bong-Gyu Park, Hitoshi Hashimoto, Toshihiko Abe, Shuji Han ...2001 Volume 48 Issue 6 Pages 481-487
Published: June 15, 2001
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSAn in-situ composite consisting of titanium carbide and iron aluminide was synthesized by mechanical alloying of the powder mixture of titanium, carbon iron and aluminum followed by pulse discharge sintering. Nominal composition of milled powders was (Fe-28at%Al)-9.6at%Ti-9at%C. Milling up to 50 h causes the X-ray peak broadening of elemental powders due to the fragmentation of the crystallites. The variation of the lattice parameter during milling suggests that the formation of iron solid solution starts at 100h and is completed at 150h. Mechanical alloying also leads to the extension of solid solubility. After milling for 1h to 400h, pulse discharge sintering was carried out at 1273 K, 1373 K and 1473 K, respectively. Fe3Al and TiC precipitate from the supersaturated iron solid solution containing aluminum, titanium and carbon by sintering. The microstructures of the composites consist of large TiC particles of about 5μm in diameter, iron aluminide regions containing TiC particles with sub-micron sizes and the regions of particle-free iron aluminide at all sintering conditions.View full abstractDownload PDF (7954K) -
Akinori Hashimoto, Munetake Satoh, Tomohiro Iwasaki2001 Volume 48 Issue 6 Pages 488-493
Published: June 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSSpring-back and compression properties of two kinds of mixtures including rubber powder were examined by uni-axial compression. One was a mixture with fine powder (calcium carbonate) and another was a mixture with fibrous material (aramid fiber pulp) and fine powder (calcium carbonate).
Spring-back behaviors of rubber powder mixtures are characterized by the ratio of maximum spring-back and the pressure at which the spring-back of mixture began. Effects of volume fraction of rubber powder on deformation behavior of rubber particles are evaluated by using Cooper's equation, which expresses powder consolidation process in terms of two mechanisms, i.e., rearrangement of particles in powder bed and deformation of rubber particles.View full abstractDownload PDF (3566K) -
Novi Granito, Hideyuki Kuwahara, Tatsukiko Aizawa2001 Volume 48 Issue 6 Pages 494-500
Published: June 15, 2001
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSFe-Cr alloys have been nitrided by plasma process in the temperature range of 773 to 893 K to develop a controlled nitrided microstructure. Typical microstructures of nitriding layers were observed on the cross section of specimens plasma nitrided at temperature below 823 K. A novel nitriding layer of stripe pattern was observed on the cross section of Fe-13Cr alloy, which was plasma nitrided at 873 K for 176.4 ks. This microstructure consisted of sub-layers, which seems to have different dissolved chromium content each other. Also it was observed that the hardness gradually increased from the specimen surface toward the nitriding front before changed sharply to the same level as matrix hardness. Such phenomena can not be explained only by nitrogen diffusion process during the nitriding, but also diffusion of alloying elements i.e. Cr should be considered to contribute significantly to the stripe-pattern microstructure. A series of frictional wear examination result showed that such nitrided layer properties should be a good candidate for improving wear resistance.View full abstractDownload PDF (3601K) -
Nobuto Taniguchi, Koji Hayashi2001 Volume 48 Issue 6 Pages 501-511
Published: June 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe peritectoid reactions of FeSi(ε-phase: core)+Fe2Si5 (α-phase: matrix)→3FeSi2 (β-phase: rim) and ε(core)+ Si(matrix)→β(rim) in Mn-doped Fe-66.7at%Si thermoelectric alloy is known to be extremely slow. We have already proposed the following new hypothesis of "Exhaustion of diffusion-contributable vacancy in core/rim structure" for the mechanism of such slow rate of peritectoid reactions: (1) for the progressing of the peritectoid reactions, Si atoms in the matrix of α or, β+Si (Si-source) need to diffuse to the closed interface of ε-core/β-rim (reaction site) via β-rim, and at the same time the atomic-vacancies in ε-core should diffuse in counter-wise direction to the matrix via the closed interface and β-rim, and (2) such mutual counter-wise diffusions strongly suppress vacancies in the matrix to diffuse into ε-core and thus causes "the exhaustion of diffusion-contributable vacancy in ε-core and β-rim", which leads to the extremely slow rate of the peritectoid reactions.
In this study, we succeeded in getting the following one experimental evidence for the above new hypothesis: the β-formation rate was extremely fast for ε-grains contacting with test-piece surface acting as vacancy-source, compared with that for ε-grains in test-piece inside. This conclusion also suggested that general diffusion data obtained by diffusion-couple experiments can not be directly applied to the diffusion-related phenomena which occur at a closed interface and the reactant atoms or ions diffuse from the outside of the closed interface to the interface via the product, i.e., rim, etc..View full abstractDownload PDF (7190K) -
Akinori Katsui, Kazutoshi Iwamoto, Hiroaki Matsushita2001 Volume 48 Issue 6 Pages 512-516
Published: June 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe sol-gel-derived diopside gels of the composition 25mol%CaO-25mol%MgO-50mol%SiO2 are prepared adding hydrochloric acid of 1 to 4 mol/dm3 concentration in the basic step, and the crystallization behavior of the gels during heating is investigated using thermal differential analysis (DTA-TG), X-ray diffraction and Fourier transform infrared spectroscopy. The results show, that the addition of hydrochloric acid leads to lower temperatures of glass formation and crystallization, due to the ristriction of calcium carbonate formation, and that the suitable concentration for the single phase crystallization is 3 mol/dm3.View full abstractDownload PDF (315K) -
Shinichi Kikkawa, Akio Kijima, Ken Hirota, Osamu Yamaguchi2001 Volume 48 Issue 6 Pages 517-522
Published: June 15, 2001
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSMicrogravity was applied for 4.5 seconds using dropping facility to freezing of various kinds of mixed aqueous solutions such as ZrOCl2⋅8H2O-MCl3⋅6H2O(M=Yor Al). The precipitates were freeze dried and then fired to 1000°C. Both good crystallinity and well mixing of the metal salts were observed when the microgravity was applied just before the freezing of the aqueous solution.View full abstractDownload PDF (1801K) -
Noriaki Sakurai, Junjiro Takekawa2001 Volume 48 Issue 6 Pages 523-527
Published: June 15, 2001
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSIn order to obtain Ti-Mo alloy having high density and strength by sintering at temperature as low as possible, the effects of a slight amount of additive as Carbon (C), Nickel (Ni), Cobalt (Co) were investigated.
A Ti-12Mo alloy, in which β phase is stable, was selected as test material because of its high corrosion resistance and strength.
In this work, a slight amount of additives such as C, Ni, Co were added to the Ti-12Mo premixed powder before sintering. It was shown that Co was much effective on the strengthening: The tensile strength of Ti-12Mo sintered compacts containing 1.0 mass%Co was 1150 MPa, being more than 17% higher than the compacts without the additive. The density was also increased with increasing Co, though the maximum density was less than 95% of theoretical density. C also increased the densify of Ti-Mo compacts, however it lowered the strength because it made the pores irregular by precipitating the TiC particles in them. Ni improved neither the densifying nor the strengthening.View full abstractDownload PDF (3843K) -
[in Japanese]2001 Volume 48 Issue 6 Pages 530
Published: June 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSDownload PDF (108K) -
Takekazu Nagae, Masaru Yokota, Masateru Nose2001 Volume 48 Issue 6 Pages 531-538
Published: June 15, 2001
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSThe Pulsed Current Pressure Sintering (PCPS) is well known as rapid sintering process. This is a kind of hot pressing which employs the pulsed electric current to heat materials. It is suggested to be characterized by four major advantages over the conventional consolidation techniques, i.e.: (1) preservation of original microstructures after consolidation, (2) high density consolidation in a short time, (3) removal of adsorbed materials on the powder surface, (4) improved mechanical properties resulted from these (1)-(3) items. We employed the PCPS process to consolidate the aluminum alloy powder and attained the high strength sintered specimen. Furthermore, a hollow shaped compact was formed by PCPS using core materials.View full abstractDownload PDF (5428K) -
Hisashi Kuwano, Hiroki Takeda, Satoshi Kawamura, Siro Takahashi, Hisas ...2001 Volume 48 Issue 6 Pages 539-545
Published: June 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSPure iron powders were mechanically milled for 6kmin (100h) to produce nanocrystals with the grain diameter of 13 nm that was measured by X-ray diffraction. The nano-structured iron powders were sintered at temperatures between 556 to 807 °C under an applied pressure of 50 to 79 MPa to form a disc having a diameter of 50 mm. The mean grain size of the compacted discs characterized by transmission electron microscope grows from 90 to 310 nm with increasing sintering temperature. A maximum Vickers hardness and a maximum fracture stress obtained in the present study were 356 Hv and 630 MPa, respectively. The results are discussed in conjunction with the result of warm pressing study performed by Malow and Koch.View full abstractDownload PDF (5200K) -
Keizo Kobayashi, Akihiro Matsumoto, Toshiyuki Nishio, Kimihiro Ozaki, ...2001 Volume 48 Issue 6 Pages 546-550
Published: June 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe effect of a pulsed current on heating in a pulsed current sintering (PCS) was examined. When a graphite mold was used for the PCS, the heating rate of the mold did not depend on a frequency of a pulsed current. The heating rate of graphite applying pulsed current was larger than that of graphite applying direct current, because of the difference of the input of energy between pulsed current and direct current.
The heating rate of the mold in a PCS was determined by a mold material. The hard metal with free carbon was heated more quickly than a usual hard metal in the PCS. Moreover, the cast iron including the precipitation of carbon was obtained higher heating rate by applying pulsed current. The heating rate of cast iron was almost unchanged by the morphology of the carbon, such as nodular graphite cast iron and gray cast iron.
The metal mold including carbon is suitable for the near net forming of the powder in the PCS because of its machinability.View full abstractDownload PDF (3548K) -
Toshiyuki Ueno, Yukio Makino, Shoji Miyake, Saburo Sano, Hidenori Sait ...2001 Volume 48 Issue 6 Pages 551-557
Published: June 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSNew sintering aids based on ytterbia-alumina system were developed for the sintering of silicon nitride with 28GHz millimeter-wave (mm-wave) heating. Sinterability was examined in silicon nitrides with 5wt%Yb2O3-3wt%Al2O3 (5Yb-3Al) and 5wt%Y2O3-3wt%Al2O3 (5Y-3Al). It was found that fully densified silicon nitride with 5Yb-3Al aid was obtained at 1600°C in mm-wave heating, and 1850°C in conventional heating. On the other hand, nearly same densified silicon nitride with 5Y-3Al aid was obtained at 1700°C in mm-wave heating, and 1750°C in conventional heating. For the silicon nitride with ytterbia-alumina system, it was indicated that their densification temperatures strongly depended on the ratio of Yb2O3 to Al2O3. In the mm-wave sintering, the temperature necessary for densifying up to 96% theoretical density showed a quite similar tendency to the liquidus temperature in the ytterbia-alumina system. While, the densification temperatures for the same silicon nitrides in the conventional sintering were rather higher than those in the mm-wave sintering and monotonously decreased with increasing the content of alumina in the aid. Because of lower sintering temperatures in the mm-wave heating, finer microstructures were obtained in the mm-wave sintered silicon nitrides, compared with those sintered by the conventional heating.View full abstractDownload PDF (1589K) -
Yurii Bykov, Vladislav Holoptsev, Yukio Makino, Shoji Miyake, Ivan Plo ...2001 Volume 48 Issue 6 Pages 558-564
Published: June 15, 2001
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSSintering of Si3N4-based ceramics using microwave power at frequencies of 28 and 30GHz has been studied. Sintering of materials with various oxide additives, 3 wt% Al2O3+5 wt% Y2O3 and 3 wt% Al2O3+5 wt% Yb2O3, and small amount of 1.5 wt% Al2O3+2.5 wt% Yb2O3 additives has been investigated. A comparison of the results obtained at different rates of heating, from 5°C/min to 90°C/min, shows that the apparent activation energy for sintering in the materials with large amount of additives decreases with an increase of the microwave power absorbed per unit volume of material. The rate of densification depends strongly on the rate of the α-to β-phase transformation at the initial stage of sintering. The results show that microwaves do not affect directly the rate of the α-to β-phase transformation. Therefore, pressureless sintering of the Si3N4 ceramics with low content of additives and low rate of phase transformation can not be enhanced by an increase in the specific microwave absorbed power.View full abstractDownload PDF (556K) -
Yoichi Murakoshi, Masaharu Takahashi, Kotaro Hanada, Toshio Sano, Hide ...2001 Volume 48 Issue 6 Pages 565-570
Published: June 15, 2001
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSHollow cylinder product has been made from aluminum powder by a dynamic compaction method that electromagnetic force shrinks an aluminum tube named as a sheath and utilises deformation of the sheath to compact the aluminum powder. A female screw and a taper can be formed inside of the product by this method. The electromagnetic force appears between the sheath and a solenoid coil according to Flemming's left hand law and can be controlled by discharge energy of a power supply. By using a cylindrical core with high stiffness the sheath shrinks uniformly without wrinkles and the aluminum powder can be compacted uniformly. The compacted powder compact, which was sintered at 893 K for 1 hour in a vacuum furnace, has shown about 2.0g/cm3 of density and 50MPa of compression failure strength. The density and strength increase with an increase in the discharge energy. However, the strength has decreased due to applying the same electromagnetic force on the sheath repeatedly.View full abstractDownload PDF (7723K)
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