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Volume 45, Issue 11
Displaying 1-18 of 18 articles from this issue
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Akira Tsukuda, Kozo Yokota, Hisakazu Tomino, Yoshihito Kondo1998 Volume 45 Issue 11 Pages 1013-1017
Published: November 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSSeveral kinds of zirconia toughened alumina ceramics (ZTA ceramics) with the different amount of monoclinic zirconia were produced by a slip casting and a normal sintering using fine powders. Grinding force was adopted as a criterion of grindarbility, and fracture toughness, bending strength and tetragonal zirconia contents were also measured as properties related to toughened mechanisms. The results are summarized as follows:
1) ZTA ceramics with the addition 10vol% of monoclinic zirconia indicated the maximum fracture toughness and tetragonal zirconia content.
2) The grinding force was the maximum value at the addition 10vol% of monoclinic zirconia. The grindarbility of ZTA ceramics was dominated by fracture toughness.
3) The toughened mechanism of ZTA ceramics in this study was closely connected with tetragonal zirconia contents.View full abstractDownload PDF (2199K) -
Kozo Yokota, Akira Tsukuda, Yoshihito Kondo1998 Volume 45 Issue 11 Pages 1018-1023
Published: November 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSEffect of addition of MgO on growth behavior of platelike grains in alumina sintered bodies was investigated and also their mechanical properties were investigated. The growth of platelike grains in the direction of long axis were restrained by addition of MgO, so the aspect ratio of the grains decreased with increasing amount of MgO. However, platelike grain growth mechanism with any amount of MgO up to 0.1mass% was considered to be similar, because the slopes of growth isotherms in log-log plot of platelike grain size of long axis versus sintering time were nearly equivalent. Although the bending strength of alumina sintered bodies with 20-30vol% platelike grains was almost. the same in comparison with the bodies which did not contain platelike grains, the fracture toughness of the former bodies were about 10-40% larger than the latter bodies. The mechanism of increasing fracture toughness in this study was considered to be the crack deflection process. The fracture toughness increased with aspect ratio of platelike grains in sintered bodies.View full abstractDownload PDF (6829K) -
Hiroyuki Tsudo, Hideto Yoshida, Hiromasa Shimojima1998 Volume 45 Issue 11 Pages 1024-1027
Published: November 15, 1998
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSThe chemical composition of an Al alloy will influence the properties of Al alloy matrix composites. In this paper, Al2O3 particles / Al alloy metal matrix composites were made by high pressure infiltration, and the influence of Al alloy chemical composition, especially Si content, on the mechanical properties (strength and toughness) of the Al alloy matrix composites was studied. The Si content of the Al alloy was changed, and other elements were added to examine their influence on the mechanical properties. The results obtained were as follows: when Cu and Ni were added to the Al alloy, the bending strength of the composites was improved at high temperature. Increasing the alumina volume fraction also improved the bending strength. However increasing the Si content decreased the fracture toughness. The possibility of improving heat-resistance of Al2O3 particles reinforced Al composite was found.View full abstractDownload PDF (2830K) -
Tetsuji Hoshika, Yutaka Hiraoka1998 Volume 45 Issue 11 Pages 1028-1033
Published: November 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSIn order to evaluate the strength and ductility of a material whose size and shape are limited, it is quite valid to apply the bend tests by using miniaturized specimens. In this study bend tests and tensile tests were performed for doped molybdenum with an elongated grain structure. Then influence of specimen thickness and test method on the low-temperature strength and ductility was discussed. In this study the fracture strength and ductility particularly at low temperatures were represented by two parameters, critical stress and critical temperature respectively.
Results are summarized as follows. First, influence of specimen thickness ranging 0.5-1.0mm on the critical stress and critical temperature was not recognized for doped molybdenum with an elongated grain structure. Secondly, relationship between yield strength (σyt) by tensile tests and that (σyb) by bend tests was σyt=σyb/1.74 for doped molybdenum with an elongated and very large grain structure.View full abstractDownload PDF (2454K) -
Daisuke Akahoshi, Akihiko Hayashi, Yutaka Ueda1998 Volume 45 Issue 11 Pages 1034-1035
Published: November 15, 1998
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSThe high Tc superconductor YBa2Cu3Oy (YBCO) is an oxygen non-stoichiometric compound and its oxygen content y changes from 6.0 to 7.0 under various conditions (temperature and oxygen partial pressure). At around room temperature, the crystal structure of YBCO is tetragonal in 6.0<y<6.4 and orthorhombic in 6.4<y<7.0. The relation between oxygen content and ortho-tetra transition at y>6.6 has been unknown because of the restriction of experimental methods. In this experiments, using the newly developed TG-DTA making it possible to measure under high pressures, we have investigated oxygen non-stoichiometry of YBCO under high oxygen pressure (>1atm). In results, we obtained new knowledge of the dependence of O-T transition temperature on oxygen content y (>6.6).View full abstractDownload PDF (173K) -
Yoshihisa Kishimoto, Masami Ueda, Osamu Yamashita1998 Volume 45 Issue 11 Pages 1036-1041
Published: November 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe iron-silicon-aluminum alloys (especially Sendust) have been widely used for the application requiring high saturation flux density, low coercive force and high electric resistivity. For this reason they have been appreciated for magnetic thin film heads, however, they are too hard and brittle to be made into thin film by rolling or three dimensional complex shaped products by mechanical work or conventional powder metallurgy process. The reduction in the size and weight of apparatus that can be accomplished by its use has had an important effect on technical developments. In this report, magnetic characteristics of Sendust ring samples produced by the powder metallurgy process with spray drying method were investigated. After gas atomized Sendust powders were mixed with paraffin compounds, these powders were granulated by spray drying method using organic binder consisting of poly (vinyl alcohol) (PVA) and plasticizer in the range from 0.1wt% to 0.5wt% of PVA, in order to improve the powder flowability and mechanical strength of green bodies. Results show that the present method is an excellent process for producing near-net-shape parts with high performance and high precision in dimension after sintering.View full abstractDownload PDF (3690K) -
[in Japanese]1998 Volume 45 Issue 11 Pages 1044
Published: November 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSDownload PDF (90K) -
Shoji Miyake1998 Volume 45 Issue 11 Pages 1045-1049
Published: November 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSResearch on ceramics sintering by milimeter-wave range microwaves is briefly reviewed in conjunction with that by pulsed high current supply. Unique features of mm-wave sintering are demonstrated in comparison with sintering by electrical furnaces as well as by 2.45 GHz radiation. Studies on mm-wave sinterig of Al2O3+ZrO2 composite and Si3N4, as well as of TiN+Cr2N composite, which has been conducted at JWRI, Osaka University, are described. Sintering mechanism of mm-wave radiation and pulsed high current supply is discussed based on the electromagnetic phenomena within the powder particles and grain boundaries.View full abstractDownload PDF (2338K) -
Hiroshi Kimura1998 Volume 45 Issue 11 Pages 1050-1054
Published: November 15, 1998
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSThis overview describes the fundamentals of the electric discharge consolidation which provide a route to the design and development of advanced materials. The proposed intelligent sintering consists of the pulse electric discharge system, combined with the process control methodologies and the microstruture control techniques. The process control and/or model is set up for the formation of the neck between spherical amorphous particles via feeding rectangular pulses and the full densification of amorphous ceramic compact under electric field. Furthermore, the electric field controlled technique can synthesize fully dense nanograined ceramics having the plastic strain rate of 3.10-2s-1 around 1350 K.View full abstractDownload PDF (1580K) -
Mamoru Omori1998 Volume 45 Issue 11 Pages 1055-1060
Published: November 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSSpark plasma system (SPS) has been called spark plasma sintering (SPS) or plasma activated sintering (PAS). This system is characterized by generation of spark plasma. The plasma has not been identified directly. There are several unique phenomena which are considered to be resulted from the effect of plasma. The following examples are described. Aluminum metal is sintered. Pure tungsten carbide becomes a dense body. Discharged pattern is obtained on the surface of insulator. Organic fibers are etched. Carbon is solidified. Thermosetting polyimide is consolidated. Structure of insoluble polymonomethylsilane is rearranged into soluble one.View full abstractDownload PDF (3829K) -
Yusuke Goto, Mokoto Sasaki, Ken-ichi Mukaida, Mamoru Omori, Akira Okub ...1998 Volume 45 Issue 11 Pages 1061-1064
Published: November 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSBCN ceramic powder was prepared from pyridine-borane complex as starting material and spark plasma sintering (SPS) of the powder was performed on the condition at 2073 K for 10 min in a vacuum (heating rate: 90 K h-1, pressure: 39 MPa, diameter: 10 mm). Crystallization of layered BCN ceramics was progressed by SPS. The interlayer spacings were 0.341 nm after SPS and 0.347 nm before SPS. The density was 2.43 mg m-3 after SPS and 2.40 mg m-3 before SPS. The hardness of Hv=65 was obtained by SPS. The electrical conductivity in the direction parallel to the pressing direction was about 100 S m-1 and that in the direction perpendicular to the pressing direction was about 200 S m-1 at room temperature.View full abstractDownload PDF (1994K) -
Shigeaki Sugiyama, Mitsuhiko Kimura, Koichi Asari, Toru Yoshida, Taro ...1998 Volume 45 Issue 11 Pages 1065-1070
Published: November 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSA composite of TiB2 and TiC was synthesized from B4C and Ti powders by spark plasma sintering accompanied with the solid-state displacement reaction of them. In the early stages of the reaction, TiB, TiB2, Ti3B4, and TiC were formed as reaction. products, and finally they were changed completely into TiB2 and TiC. Relative density of composites reached more than 99 % at 1800°C and above. At 1800°C and below the composites had unique microstructure; TiB2 phases formed networks surrounding TiC phases. The network structure disappeared at higher temperatures, and TiB2 phases were dispersed more homogeneously in TiC phases. The composites obtained at 2000°C had mechanical properties of Young's modulus 514 GPa, Poisson's ratio 0.18, Vickers hardness 2090 and fracture toughness 3.8 MPa m0.5View full abstractDownload PDF (2916K) -
Shin-ichi Sumi, Yoshiki Mizutani, Toshihiko Abe1998 Volume 45 Issue 11 Pages 1071-1075
Published: November 15, 1998
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSFunctionally graded materials (FGM), composed of zirconia and nickel system, were sintered from laminated mixtures by the pulse discharge sintering method (PDS). The partially stabilized zirconia (Y2O3-3mol%, size; 0.8μm) and nickel (size; 5μm) were mixed at 90, 80, 60, 40vol%PSZ in a ceramic ball mill for 2 hours with ethanol. These mixtures and two pure materials were laminated in a mold made of graphite. The designed thickness of each layer varies from 0.2mm to 2mm. The different thickness FGM specimens were sintered. These were evaluated by the ultrasonic imaging, and also observed by the optical microscope at the cross section. By the microscope, it was found that the matrix of the FGM specimens consisted of zirconia and very fine nickel particles dispersed in the matrix. In some FGM, ultrasonic images showed no clear defect in all interfaces at just after sintering, however after about 2 weeks, slight defect images were recognized, then the defect changed to the crack image after about 2 months. To know the mechanism of the change, 3 kinds of 2 layers sintered samples (90/80, 80/60, 90/60vol%PSZ) were fabricated, these samples were examined by ultrasonic imaging after each thermal treatment. As the results, it was observed that some of defects gradually propagated to inside, then finally changed to large cracks or a delamination.View full abstractDownload PDF (3698K) -
Kimihiro Ozaki, Keizo Kobayashi, Akira Sugiyama, Toshiyuki Nishio1998 Volume 45 Issue 11 Pages 1076-1080
Published: November 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSAn Al-Cr amorphous powder prepared by mechanically grinding a rapidly solidified ribbon was consolidated by pulsed current sintering at lower temperature than the crystallization temperature. The rapidly solidified Al100-xCrx(x=5-15) ribbons were prepared by single roll method. The quasicrystalline phase existed in the 7-13at%Cr ribbons. By mechanically grinding, the amorphous phase was formed in the powder of 10-15at%Cr. The analysis by XRD and DSC revealed that the mechanically ground Al87Cr13 and Al85Cr13 powders were a single amorphous phase. Al90Cr10 powder consisted of the Al phase and the amorphous phase. A disk specimen of 10mm in diameter was prepared by sintering at 500MPa pressure at 573K with a hard metal die. The consolidated Al90Cr10 had the porosity of 3.3%, while Al87Cr13 had the porosity of 20.7%. The marked difference between them is resulted from the mass flow of the Al in the Al90Cr10 sample to the triple points among the particles.View full abstractDownload PDF (4568K) -
Norio Matsui, Keizo Kobayashi, Akira Sugiyama, Kimihiro Ozaki1998 Volume 45 Issue 11 Pages 1081-1085
Published: November 15, 1998
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSFe-48at%Cr alloy powders were synthesized by mechanical alloying (MA) of Fe powder and Cr powder using a planetary ball milling for 180ks under 1.33kPa argon gas atomosphere. In order to consolidate the MA powder at a lower temperature, 0.5-5.0mass%Al powders were mixed with the MA powder for 36ks by a planetary ball mill. The results of DSC indicated that Al powders were not reacted with mechanical alloyed powders and remained as primary powders. The obtained mixed powders were consolidated by spark plasma sintering (SPS) apparatus.
By the addition of Al, the starting temperature of the shrinkage of mixed powders during SPS was reduced to lower of 100-150K than that of mechanical alloyed powders. However, the sintered bodies containing more than 2.5mass%Al were brittle because of the formation of FeAl intermetallic compound during a sintering process. The sintered body which contained 0.5mass%Al had fine microstructure and the hardness of 350-370Hv.View full abstractDownload PDF (2975K) -
Masanori Ae, Kazuo Ichii, Toshio Oishi, Nobuhiro Yoshida, Mamoru Ozawa1998 Volume 45 Issue 11 Pages 1086-1091
Published: November 15, 1998
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSFe0.95Co0.05Si2 (n-type) and Fe0.91Cr0.09Si2 (p-type) water-atomized powders were sintered by using SPS (Spark Plasma Sintering) system in the conditions of the temperature at 973, 1023, and 1073K, the holding time for 60, 300, 600, 1200, 2400 and 3600s and the applied pressure 49MPa. The differences in temperature being caused by current, as Peltier effect, through the thermoelectric element of βFeSi2 were measured.
The maximum differences in temperature of about 0.4K, and the maximum figure of merit Z about 8×10-6K-1 in case of thermoelectric cooling were obtained for the element produced by the conditions of the apparent temperature 1023K, holding time 3600s and applied pressure 49MPa.
It was found that the optimum conditions in producing βFeSi2 elements can be estimated by measuring the differences in temperature by Peltier effect, and more, that the powder of n-type is superior to that of p-type in sintering characteristic, however this phenomenon should be still being studied in detail.View full abstractDownload PDF (5193K) -
Takekazu Nagae, Masaru Yokata, Nasateru Nose1998 Volume 45 Issue 11 Pages 1092-1097
Published: November 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe ceramics cores were applied for the Pulse Current Pressure Sintering (PCPS) method in order to consolidate the hollow shaped compact of the Al-12mass% Si powder. In this process, the aluminum alloy powder was densified due to the shrinking of the core and plastic flow of the aluminum alloy powder itself. After sintering of hollow compact under the most suitable condition, the density was reached to 2.65g/m3 which is the 99% of relative density for the Al-12mass%Si alloy.
We tried to use various kinds of ceramics for the core material. As a result, we found that the h-BN had best characteristics for the core, because it was easy to be compressed and broken down to be removed after sintering treatment.View full abstractDownload PDF (6627K) -
Tomohiro Takida, Tadashi Igarashi, Yoshiharu Doi, Takekazu Nagae, Yuta ...1998 Volume 45 Issue 11 Pages 1098-1104
Published: November 15, 1998
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSIn order to improve both fracture strength and ductility at low temperature, fine-grained sintered molybdenum alloys dispersed with 0.8mol% TaC or 1.6mol% TiC were prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The mixtures of fine molybdenum powder with grains measuring 20nm in diameter and carbide particles which were prepared by MA, were sintered at 1870K for 300s under 49MPa by SPS. The sintered alloys had relative densities of over 99% and grain sizes of approximately 2-5μm. The low-temperature fracture strength and ductility were evaluated by a three-point bending test at 77K to 360K. The results were compared with those for sintered alloys dispersed with 0.4-1.6mol% TaC or TiC which were prepared by MA and hot isostatic pressing (HIP). The following results were obtained.
(1) Both low-temperature fracture strength and ductility increased by dispersion of carbides. This result was the same as those obtained from sintered alloys prepared by MA and HIP.
(2) The alloy dispersed with TaC had a low dutile-to-brittle transiton temperature of 157K and a high fracture strength of 1860MPa at the temperature.
(3) High fracture strength of the present alloy was attributed to both carbide dispersion and grain refining, though the former effect was much effective.
(4) The alloy dispersed with TaC exhibited mostly intergranular fracture mode. The intergranular fracture area comprised 70% of the total fracture area. In contrast, the alloy dispersed with TiC exhibited a mixed mode of intergranular and transgranular fracture. The intergranular fracture area comprised 50%.View full abstractDownload PDF (4532K)
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