All issues
Volume 45, Issue 12
Displaying 1-20 of 20 articles from this issue
- |<
- <
- 1
- >
- >|
-
Yasuki Miyakoshi, Kohji Takazawa, Kohsuke Tagashira, Kamota Shuichi, H ...1998 Volume 45 Issue 12 Pages 1111-1115
Published: December 15, 1998
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSThe applicability of sintered WC-Fe alloys as stress relief layer materials for the sinter-bonding method of cemented carbide and carbon steel has been basically discussed. The structure and mechanical properties of sintered WC-(20-40mass%)Fe alloy compacts were investigated. These WC-Fe alloys compacts sintered at 1553K or higher showed complete densification. η phase (Fe3W3C) particles which were coarser than the tungsten carbides particles were formed in the sintered compacts, and also fine pearlite structure were formed in binder metal parts. Though the hardness of sintered compacts were almost independent of sintering temperature being higher than 1553K, the fourpoint bending strength decreases with the increase of sintering temperature. It may be caused by coarsening of rl phase particles. Therefore the restraint in growth of rl phase particles in the WC-Fe alloys is effective for the high bonding strength. Coefficient of thermal expansion α (K-1) between 303 and 973K for the compacts sintered at 1553K was given by α=(0.093VFe+4.12)×10-6, where VFe is volume percent of iron powder.View full abstractDownload PDF (4311K) -
Norimitsu Hirose, Junichi Asami, Toshiyuki Tanaki, Makoto Yuasa, Isao ...1998 Volume 45 Issue 12 Pages 1116-1121
Published: December 15, 1998
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSIn this study, the effects of porosity on sound properties, elastic moduli (Young's modulus, shear modulus and Poisson's ratio) and tensile strength of sintered compacts were investigated. The sound velocities were obtained by an acoustic pulse method.
At the same porosity, the elastic moduli increased with increasing of sintering temperature. In the case that the longitudinal wave velocity and sintering temperature were known, the porosity of measurement area (partial porosity) was able to calculated.
In addition, the prediction of fractured position with an acoustic microscope and the calculation of partial porosity of fractured position from measurement of the longitudinal wave velocity were carried out, we obtained the relationships between elastic moduli, tensile strength and porosity of fractured position. From the results, since the partial porosity of fractured position were larger than the average porosity, the elastic moduli and the tensile strength against average porosity were underestimated in comparison with that against partial porosity of fractured position.View full abstractDownload PDF (3256K) -
Hiroyuki Y. Suzuki, Kenji Shinozaki, Masato Murai, Hidenori Kuroki1998 Volume 45 Issue 12 Pages 1122-1130
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSAn overall development of microstructure during sintering of high purity sub-micron alumina is investigated. The alumina is compacted by the High-Speed Centrifugal Compaction Process (HCP alumina). An alumina powder with a purity of 99.99 mass% and mean particle size of 0.22μm is dispersed in 25 mass% of ion-exchanged water, compacted applying a centrifugal force of 10, 000-20, 000 g for 3 ks, and sintered at 1473-1623 K for 0-172.8 ks in air.
The microstructure of sintered HCP alumina has particular combination of its density and grain size in each sintering condition, and they make single grain-size/relative-density trajectory. The location of the trajectory shifts toward smaller in grain size and higher in density compared to previously reported ones.
The grain-size/relative-density trajectory is divided into three stages as the microstructure morphology changes. In the stage I, the microstructure is composed of open pore network, and its trajectory shows a straight line with low gradient. In the stage II, the microstructure has closed pores and the trajectory curves upward. After the density almost reaches uppermost limit, the morphological development enters to stage III, and steep straight trajectory is observed.
The sintered compact at the boundary of stage II and III shows the highest strength. The microstructure of that body has a density of about 99 % and homogeneous fine grains with equi axed isolated pores located at the four-grain corners.View full abstractDownload PDF (4832K) -
Etsuro Sugimata, Syouichi Nasu, Kentaro Ohhashi1998 Volume 45 Issue 12 Pages 1131-1135
Published: December 15, 1998
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSWe prepared Bi2Sr2CaCu2Oy polycrystalline superconductor by partially melting method in HNO3 or solid state method and investigated the influence of precursor condition and quench temperature upon the critical current density. The best starting temperatures of quench were 650°C in HNO3 method and 500°C in solid state method. In these conditions, critical current densities were 198A/cm2 in the former and 102A/cm2 in the latter. We found that starting temperature of quench influences the break of junctions between grains by thermal contraction and condition of precursor influences the occuring defect and grain growth in melting process.
It is important to select the best conditions of quench and precursor to prepare Bi2Sr2CaCu2Oy polycrystalline superconductor with high critical temperature and density by partially melting and quench method.View full abstractDownload PDF (5216K) -
Takahiro Yamada, Zenji Hiroi, Mikio Takano, Minoru Nohara, Hidenori Ta ...1998 Volume 45 Issue 12 Pages 1136-1141
Published: December 15, 1998
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSPolycrystals of Cu2GeO4 have been synthesized under high pressure (4 GPa) and high temperature (900°C) conditions. It has the tetragonally distorted spinel structure with CuO6 octahedra elongated along the c axis due to the Jahn-Teller effect. The crystal structure is apparently three-dimensional, but the major superexchange path is assumed to be one-dimensional along the edge sharing chains. In fact, the magnetic susceptibility of Cu2GeO4 shows a broad maximum around 100 K and is well described as that of the S=1/2 Heisenberg antiferromagnetic chains with interaction J of 135 K. A small jump in the susceptibility curve is observed at 33 K, which is considered to be a sign of antiferromagnetic ordering. Moreover, specific heat measurements show a large sharp peak at the same temperature, suggesting a first-order phase transition. The effects of Mg substitution for Cu and Si substitution for Ge are also reported.View full abstractDownload PDF (466K) -
Hiroyuki Kawamura, Kimikazu Moritani, Yasuhiko Ito1998 Volume 45 Issue 12 Pages 1142-1147
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSA stationary discharge was generated in molten chloride by simple apparatus and successfully applied at electrolysis. Fine nickel particles were obtained using a LiCl-KCl-NiCl2 melt under atmospheric argon gas. From the grading analysis which was estimated through the SEM observation of fine nickel particles, the particles were almost spherical, and the particle sizes were found to depend on the concentration of NiCl2 and the charge. For the growth of fine nickel particles, the particle sizes were compared with numerical solutions of a Brownian collision-coalescence in colloidal suspensions.View full abstractDownload PDF (3434K) -
[in Japanese]1998 Volume 45 Issue 12 Pages 1150
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSDownload PDF (99K) -
Junichi Hojo1998 Volume 45 Issue 12 Pages 1151-1156
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSMany kinds of ceramic composites have been studied to improve the mechanical properties of ceramics. Among them, recently, much attention has been paid to nanocomposites, in which fine particles of the second phase are dispersed in the matrix. In order to realize such a nanostructure, it is important to control the particle structure of starting powder. One of the promising approaches is the use of fine composite particles. In this paper, the preparation and application of fine composite particles were reviewed with emphasis on SiC and Si3N4-base composite particles obtained by a vapor phase reaction method and a fluidized-bed CVD method.
It was found that the nanocomposites of SiC-BN and Si3N4-BN systems had an excellent thermal-shock resistance due to fine dispersion of h-BN particles.View full abstractDownload PDF (5279K) -
Noriyuki Maeda, Masaru Yoshinaka, Ken Hirota, Osamu Yamaguchi1998 Volume 45 Issue 12 Pages 1157-1161
Published: December 15, 1998
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSReactive Snot powders have been prepared by the hydrazine method. Their individual particles tend toward a hexagonal morphology with increasing temperature. Well-densified SnO2 ceramics (99.8% of theoretical) with an average grain size of 0.9μm have been fabricated by hot isostatic pressing for 2 h at 900°C and 196 MPa. Their Vickers hardness and bending strength are -14.4 GPa and -200 MPa, respectively. They exhibit an electrical conductivity of -5 × 10-3 S⋅cm-1 at room temperature.View full abstractDownload PDF (6615K) -
Masayoshi Miyamoto, Makoto Sasaki, Ken-ichi Mukaida1998 Volume 45 Issue 12 Pages 1162-1165
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSTo develop high-temperature heat elements with a small temperature-coefficient electrical conductivity, small-grained MoSi2-SiC ceramics were prepared by reaction sintering ceramic precursor with molybdenum powder. By second sintering at 1773 K for 10 h, two phases of MoSi2 and β-SiC were formed. The average grain size of both MoSi2 and SiC ranges several tens nanometers. Electrical conductivity measurement revealed that conductive behavior changed from semiconductive to metallic with increasing molybdenum disilicide content. 54.3 wt% MoSi2/β-SiC composite showed an almost constant temperature coefficent in the temperature range at around to 600-850 K.View full abstractDownload PDF (388K) -
Masato Uehara, Hirofumi Ogata, Hideaki Maeda, Junichi Hojo1998 Volume 45 Issue 12 Pages 1166-1171
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSFine SiC powder and SiC-TiC composite powder were prepared by vapor phase reactions using Si(CH3)4 and TiCl4. The particle size was about 200nm. They were hot-pressed at 2000°C in Ar with a sintering aid of Al2O3 or Y2O3-Al2O3 system. The sintered bodies were densified to 98-99% of theoretical. Rod-like grains were observed in monolithic SiC with both Al2O3 and Y2O3-Al2O3 system, and the higher fracture toughness was observed in Y2O3-Al2O3 system. The fracture toughness was increased by TiC inclusions although the growth of rod-like SiC grains tended to be retarded. The growth of SiC grains was exaggerated in SiC-TiC composite powder with a large amount of Y2O3-Al2O3 sintering aid, leading to more improved fracture toughness. The present results suggest that the improvement of fracture toughness can be enhanced by combination of rod-like SiC grain growth and TiC inclusion with Y2O3-Al2O3 sintering aid.View full abstractDownload PDF (6774K) -
Jian-Feng Yang, Yong-Ho Choa, Tohru Sekino, Koichi Niihara1998 Volume 45 Issue 12 Pages 1172-1177
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSTo meet the practical application, a kind of commercially available Si3N4 powder by direct Si nitridation was used to fabricate dense Si3N4/SiC nanocomposite by pressureless sintering method. The price of this kind of powder is much lower than that of powder by imide decomposition. 5-30 vol% of SiC powder (average particle size: 80 nm) were added in the composite to investigate the effect of SiC particle. Totally 15 wt% of MgAl2O4 and ZrO2 (50 wt% each) were used as sihtering additives. With increasing SiC content, the densities of the composites decreased. α-β Si3N4 phase transformation was enhanced at low temperatures, but prohibited at high temperatures for large SiC content. The sample with larger SiC content gave a relatively smaller Si3N4 grain size because SiC particles limit the Si3N4 grain growth by pinning and prohibiting the grain boundary movement. An improvement of Young's modulus, flexural strength and hardness by the SiC addition was found. Further increase in SiC content resulted in a decrease of these properties because of the decreasing density for the samples sintered at low temperatures. With an intermediate sintering temperature, the samples with 20 vol% SiC reached to high flexural strength as 1050 MPa as a result of good density and relatively fine grain size structure. The decreased fracture toughness with increasing the SiC content was observed by the refinement of Si3N4 grain. However, it was improved with the increasing sintering temperature. The result of this study provided an economic way to fabricate the Si3N4/SiC nanocomposite with a strength higher than 1 GPa and appropriate fracture toughness.View full abstractDownload PDF (5041K) -
Junzo Tanaka1998 Volume 45 Issue 12 Pages 1178-1185
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSAuger electron spectroscopy and transmission electron microscopy were applied to understand the grain boundary phenomena of ZnO and SrTiO3. The interface structure of SrTiO3 bicrystals was analyzed by molecular dynamics method; peculiar local configurations around the interfaces and their electronic states were investigated in relation to the formation of interfacial states. Regards ZnO grain boundaries, molecular orbital calculation was adopted for the elucidation of chemical bonding state and frontier electron state.View full abstractDownload PDF (2176K) -
Yoshio Sakka, Tohru S. Suzuki, Keishi Nakano, Keijiro Hiraga1998 Volume 45 Issue 12 Pages 1186-1195
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSSuperplasticity provides the possibility of high-temperature deformation processing of dense ceramics that has advantages of greater shape formability with better dimensional accuracy. To enhance the tensile ductility, microstructural design is required to get a fine grain size that is stable against coarsening during deformation at hightemperatures. Zirconia particle dispersed alumina is known to be effective in suppressing grain growth but the initial grain size of alumina reaches about 1μm using a conventional dry processing. In the present study, zirconia dispersed alumina composites were produced by colloidal process. Well-dispersed slurries consisting of α-Al2O3 and ZrO2 fine powders were prepared by adjusting the pH value or adding appropriate amounts of polyelectrolyte. The slurries were consolidated by slip casting, followed by isostatic pressing (CIP). The consolidated bodies have small pore size and narrow pore size distribution, which enabled sintering at low-temperature of 1400°C and resulted in the desired fine-grained microstructure. It is demonstrated that large tensile elongation exceeding 550% can be obtained for the colloidally processed samples owing to dense, fine-grained and homogeneous microstructure.View full abstractDownload PDF (6823K) -
Koichi Kugimiya1998 Volume 45 Issue 12 Pages 1196-1201
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe development of magnetic heads used in the VTR's has been studied for over 30 years. The development coincided with the sharp rise and the present stagnant growth of our industry, electric and electronic market in Japan. The prominent growth has been observed at the time of a newly launched compact home use VTR just after the first oil shock. This rapid growth had been realized by the intense R&D of heads and tapes with never ending endeavor and eagerness for the very high density recording. One of the key technologies was the intrigued application and combination of anisotropic properties of crystalline materials, besides the drastic improvement of magnetic tapes and the steady advancement of a tape/head interface. Although the markets is slow these days, the technologies are still advancing to realize even higher densities. The DVC with ME tape is here and renewed efforts have been intensively paid for a drastic improvement of HDD technologies. A new materials, GMR, has been recently introduced. The renewed effort will be expected to open new gigantic AV & C markets over the next century.View full abstractDownload PDF (2396K) -
Cheng Zhou, Tatsuhiko Aizawa, Kiyohiko Tatsuzawa1998 Volume 45 Issue 12 Pages 1202-1206
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSNano-granulation process of Cu/Co system is investigated on the route of bulk mechanical alloying. Using the bulk mechanical alloying, the super-satu rated solid solution of Cu-20mol%Co has been prepared. Through the further h eat treatment, the Co nano-precipitated from the super-saturated solid solut ion in the copper matrix, resulting in appearance of the giant magneto-resis tance. In the present study, the nano-precipitation of Co and the Co-particu late size is investigated by XRD, VSM and TEM. The relationship between the magneto-resistance ratio and the nano-precipitation process of Co is investi gated. This relation depends on both the nucleation rate of Co-cluster preci pitate and the growth rate of Co-cluster. The change of the magneto-resistan ce ratio with the Co-cluster size is also obtained: Co precipitate size mus t be 1-3 nm to attain higher magneto-resistance ratio than 10%.View full abstractDownload PDF (1770K) -
Tadachika Nakayama, Yong-Ho Choa, Takao A. Yamamoto, Koichi Niihara1998 Volume 45 Issue 12 Pages 1207-1210
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe iron oxide nanocrystalline were manufactured by a Inert Gas Condensation - Pulse Electric Current Sintering (IGC-PECS) process. The IGC method involves condensation of vapors of metallic or nonmetallic powders with a controlled residence time in a low pressure environment. The particle size was controlled by pressure of inert gas (He). The smallest average size of powders, 8 nm and the largest average size of powders, 28 nm, were used as a starting precursors for PECS. The smallest average grain size of sintered pellets is 33 nm under the condition at 1073 K with applied pressure of 100 MPa.View full abstractDownload PDF (2362K) -
Akihiro Matsumoto, Keizo Kobayashi, Makoto Takagi, Toru Imura1998 Volume 45 Issue 12 Pages 1211-1215
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSTi-37.5at%Si powder mixtures were mechanically alloyed in a-planetary ball mill under an Ar atmosphere. The powder prepared by milling for 50 hr, consisted of amorphous and nano-sized Si grains, was consolidated using a cubic type anvil apparatus under a high hydrostatic pressure of 5.4GPa. The compact consolidated at 623K was fully densified with the retention of non-equilibrium structures. The compressive strength of the compact at room temperature was about 2.5GPa.View full abstractDownload PDF (4587K) -
Masami Ikeyama, Setsuo Nakao, Soji Miyagawa, Yoshiko Miyagawa, Hiroaki ...1998 Volume 45 Issue 12 Pages 1216-1219
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSUsing double ion species implantation of metal and oxygen ions, we have examined the possibility of synthesis of metal-oxide fine particles in glass or sapphire surface. Characteristics of ion implanted silica glass and sapphire were examined by RBS, XRD and optical (absorption and photo-luminescence) measurements. 1.8 MeV 1×1017 Cu+/cm2 implantation into silica glass and a successive heat treatment of 1000°, 1h in the air can make Cu fine particles. 1.8 MeV 1×1017 Cu+/cm2 and 1.0 MeV 1×1017 O+/cm2 implantation into silica glass and the successive heat treatment can synthesis Cu2O fine particles of about 8 nm in radius. 1.8 MeV 5×1016 Ti+/cm2 and 1.0 MeV 1×1017 O+/cm2 into sapphire and the successive heat treatment can synthesis Ti02 fine particles of about 10 nm in radius. The TiO2 particles were rutile-type with (200) orientation, which may be related to the (0001) orientation of sapphire substrate. Luminescence from defects in sapphire substrate was observed, but luminescence from the particles could not be detected.View full abstractDownload PDF (308K) -
Masanobu Nunogaki1998 Volume 45 Issue 12 Pages 1220-1223
Published: December 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThis experimental study is concerned with the fabrication of "cermets" at a sub-surface layer of metal by reactive plasma processing at high temperatures. Samples of Ti and Zr were carbonized or nitrided with use of CH4 gas or a gas mixture of N2 and H2, respectively. Experiments were done below 1300°C for less than 3h. Thickness and hardness of modified layers were increased with the modifying time and temperature, especially, at temperature over 900°C. The maximum Vicker's hardness of TiC based cermet was about 5000Hv (kg/mm2) and the maximum thickness of ZrN reached about 50μm for only 2h, both at 1300°C. For the next step aiming to decrease the activation energy of atomic diffusion and the modifying temperature, the effects of pre-irradiation processing before the main processing were reviewed for the nitriding of pure aluminium. In addition, relating to the application of ion implantation to the fabrication of cermets by sintering, "a powder/granular material holder" was newly designed.View full abstractDownload PDF (1359K)
- |<
- <
- 1
- >
- >|