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Volume 36, Issue 4
Displaying 1-16 of 16 articles from this issue
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Tohru Kohno1989 Volume 36 Issue 4 Pages 345-351
Published: June 25, 1989
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSIt was known in the first fundamental study that in the light load and very high speed revolution region (2-6 kg/cm2, above 20, 000 rpm), sintered bearings could be driven under hydrodynamic lubrication after achieving sufficiently good conformity. In the actual applications, however, the state of the lubrication at the start-up becomes a severe boundary owing to insufficient conformity, consequently a large amount of wear occurs or the bearings may seize.
On the basis of the above-mentioned study, a new Cu-Sn-P-MoS2 type bearing has been developed, which showed excellent performance under both boundary and hydrodynamic conditions. The distinctive features of the bearing are as follows; the thin layer of the reaction product (phosphorus compound) formed around the MoS2 particles in the sintered structure acted as a kind of binder between the matrix and the MoS2 particles, thus preventing the solid lubricant (MoS2) from mixing into the lubricant oil, which causes the increase in the apparent viscosity of the oil and consequently the coefficient of friction and the bearing temperature under the hydrodynamic conditions.View full abstractDownload PDF (2989K) -
Hiroyuki Ichinose, Hitoshi Igarashi1989 Volume 36 Issue 4 Pages 352-356
Published: June 25, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSThe sintering mechanisms of gamma iron had been examined from the neck growth experiment on spool model compacts by Fischmeister and Zahn, and Matsumura, respectively. Both groups found that the neck growth exponent changes from 5 at high sintering temperature to 7 at low temperature and concluded that volume diffusion mechanism prevails at high temperature and surface diffusion controls the process at low temnerature.
In the sintering experiment of nickel on various model compacts, however, Ichinose and Igarashi found that the neck grain-boundaries in spool model compact are not effective sink for vacancies, which may be attributed to strong restriction to shrinkage in this model compact.
From this point of view, a sintering experiment of gamma iron was conducted on 3 wire model compact, in which neck growth and shrinkage were observed as a function of time at 1300°, 1200°, 1100° and 1000°C. The corresponding exponents were 5, 5.5, 6.2 and 7, respectively. Shrinkage was observed in the sintering at high temperatures, but not observed at 1000°C, except long time side. The volume diffusion coefficients obtained from neck growth and shrinkage at 1300°C coincide with each other and are in fairly good agree-ment with tracer results. The surface diffusion coefficient obtained from neck growth at 1000°C was in fairly good agreement with Matsumura's result. Thus, in this three wire model compact, volume diffusion with vacancy sink at neck grain-boundaries prevailed at high temperature and surface diffusion did at low temperature.View full abstractDownload PDF (1560K) -
Hideshi Miura, Tadatoshi Honda, Youichi Tokunaga1989 Volume 36 Issue 4 Pages 357-364
Published: June 25, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSEffects of several types of carbon and graphite powders on the compressibility, sinterbility and carburization of the iron-carbon compacts were investigated by studying microstructures, and further mechanical properties of these sintered materials were determined. Carbon powders used in the present study were amorphous carbon such as coals, cokes and carbon blacks together with natural, artificial and kish graphites.
Addition of amorphous carbon powders to iron powder generally led to lower compressibility and carburization than that of graphites. However, material using petroleum coak (green) powder showed good carburization and strength near to those produced using natural graphite powder, and material using kish graphite powder (particle size: 10μm) showed the most superior properties. In conclusion, the refining of carbon or graphite particles improved the properties of sintered materials. This was effective even for the amorphous carbon powders such as smokeless coal and petroleum coke which were usually considered to be poorly reactive.
It was concluded that required properties for the additive carbon powder were high degree of graphi-tization, flaky shape and fine particle size about 10μm.View full abstractDownload PDF (7680K) -
Tadahiko Watanabe1989 Volume 36 Issue 4 Pages 365-370
Published: June 25, 1989
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSIt was difficult to produce dense and high strength TiB2 ceramics by using hot pressing. This paper described densification and strengthening mechanisms by using of three kinds of additives. First additives are CoB, FeB, Ni4B3 and NiB. Each additive makes dense TiB2 ceramics. The densification mechanism is explained as activated sintering and pressure effects. The ceramics which have higher transverse rupture strengths and lower porosities can be produced by adding the second each additive of VB2, NbB2, TaB2, CrB2, MnB2, MoB2, Mo2B5 and W2B5. The higher transverse rupture strength has been caused mainly by suppressing grain growth of TiB2 with the solid solution between TiB2 and the hexagonal boride such as TaB2, and caused secondarily by the lattice strain of TiB2.
Hence, it is expected that TiB2 ceramics having the higher mechanical shock resistance can be made from the raw materials with smaller particle size of TiB2. However, fine raw powders gave more pores, because of oxidizing during mixing. Final additives are cubic carbides such as TiC, ZrC and HfC. When the each additive adds to TiB2-1%CoB-6%TaB2 mixed powder, the ceramics have the smaller particle size and the lower porosity.
This lower porosity, for example, may be formed by a solid solution of M(C, O) and deoxidation of the raw TiB2 powder.View full abstractDownload PDF (1310K) -
Mitsuo Ueki, Takeshi Saito, Hisashi Suzuki1989 Volume 36 Issue 4 Pages 371-373
Published: June 25, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSThe reason why the sinterability of nitrogen contained cermet became lower with increasing nitrogen content, was studied. The TiC-(0-40)mass%TiN-15mass%Mo2C-lOmass%Ni cermets sintered in vacuum were used as specimens. It was found that TiN particles were denitrified and carburized during rising temperature to sintering temperature and subsequently during sintering under liquid phase. Therefore, the reason was considered to be in the fact that the amount of liquid phase at a fixed sintering temperature decreased as the mixed powder behaved like low carbon alloy, and on the other hand, micropores due to nitrogen gas generation formed during sintering.View full abstractDownload PDF (3245K) -
Nobujiro Tsuchiya, Osamu Terada, Akira Sasaki, Hisashi Suzuki1989 Volume 36 Issue 4 Pages 374-378
Published: June 25, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSIt was found by the present authors that Co pools generally formed in the microstructure of WC-Co alloy. Then, the influence of Go pools on the strength of the alloy and the cause of formation of Co pools were examined. The following results were obtained.
(1) The formation of Co pools resulted from the flaky powder, that is, Co rich WC-Co agglomerates which appear in the mixed powder during ball-milling. The flaky powder often formed, when the mixture was ball-milled by using stainless-steel pot. Then, the mechanism of formation of flaky powder was discussed. (2) The strength of usual alloy having Co pools in the structure was always lower than that of the alloy free from Co pools. The lower strength of usual alloy was owing to the fact that Co pools were apt to act as a fracture source.View full abstractDownload PDF (3947K) -
Keiichi Kobori, Mitsuo Ueki, Tsuyoshi Saito, Hisashi Suzuki1989 Volume 36 Issue 4 Pages 379-384
Published: June 25, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSIt was recently found by the present authors that, when WC-βt-Co alloy (βt=WC/TiC/TaC s.s.) was sintered by using Co powder and βt powder supersaturated with WC (named βt(E) powder), sheet-like WC phases crystallized in the structure during sintering. The βt(E)-Co mixed powder was sintered and then hot-pressed to get anisotropic WC-βt-8mass%Co alloy specimens having the stratified structure of sheet-like WC. Some properties such as mechanical properties, cutring performance, etc. of the above alloy were investigated.
The sheet of WC, its surface orientation being coincided with (0001) planes of WC, became parallel to the specimen surface perpendicular to the hot-pressing direction with increasing reduction in thickness. The surface hardness and transverse-rupture strength of specimen were higher than those of usually isotropic alloy. The crack propagation across the sheet-like WC was greatly checked. The edge strength of cutting tools was improved considerably. The phenomena above mentioned were discussed in detail.View full abstractDownload PDF (5266K) -
Keiichi Kobori, Mitsuo Ueki, Atsushi Fukawa, Hisashi Suzuki1989 Volume 36 Issue 4 Pages 385-389
Published: June 25, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSThe strength of three sorts of cemented carbides coated with TiC by CVD process was studied mainly relating to the carbide grain size. It was found that the strength of coated alloys was almost not influenced by the carbide grain size, in contrast to that of substrates which decreased with increasing the grain size. It was also found that whether the substrate was HIP-treated or not, had no relation to the strength of coated alloys. The result of milling test for the coated P30 alloy showed that the resistance to fracture of cutting edge was greatly improved with increasing the carbide grain size, the tendency being different from that of the strength of coated alloys.
The above phenomena as well as the decrease in strength generally observed in coated alloys were discussed in detail.View full abstractDownload PDF (3092K) -
Ken-ichi Takagi, Masao Komai1989 Volume 36 Issue 4 Pages 390-396
Published: June 25, 1989
Released on J-STAGE: July 12, 2010
JOURNAL FREE ACCESSThe effects of Mo/B atomic ratio on the mechanical properties and the phase formation in Fe-5B-5Cr-xMo alloys were studied. The effects on alloy partitioning, lattice parameters and the morphology of Mo2FeB2 type complex boride in the alloys were also studied.
The transverse rupture strength (TRS) and hardness of the iron-molybdenum complex boride base hard alloys depend strongly on their Mo/B atomic ratio (Mo content), the type of ferrous binder and the morphology of the Mo2FeB2 type complex boride. The best combination of TRS and hardness is obtained at an optimal Mo/B atomic ratio of 1.0 where very little third phase exists such as M6C (M: metal) other than Mo2FeB2 type complex boride and a martensitic binder, and the small grain size boride phase are also present.View full abstractDownload PDF (6962K) -
Akifumi Ueno1989 Volume 36 Issue 4 Pages 397-403
Published: June 25, 1989
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSControl of a radial concentration of nickel metal partioles in an alumina sphere was achieved by impregnating the spheres with a solution composed of nickel nitrate dissolved in ethylene glycol, ethyl silicate, and a small amount of nitric acid. The position of the nickel narrowband from the center of the sphere was well controlled merely by the impregnating time. The nickel loading in the catalyst was intentionally varied with the nickel concentration in the impregnating solution. The external surface of the catalyst prepared was covered with thin SiO2 films resulting from the gelling of ethyl silicate over the alumina sphere. The micropores observed in the thin SiO2 films were sharply sized around 20 Å.View full abstractDownload PDF (2945K) -
Teruo Takahashi, Hashimoto Hashimoto, Koichiro Koyama1989 Volume 36 Issue 4 Pages 404-410
Published: June 25, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSA new process is proposed and tested in order to prepare an Al2O3-dispersion-strengthened copper, combining the mechanical alloying and following heat-treatment. The mechanical alloying was carried out with an attritor using powders of electrolytic pure Cu, gas-atomized Cu-8 mass% Al master alloy and Cu2O as starting materials. By mechanical alloying for 72.0 ks, homogeneous Cu-Al-O solid solutions or nanometer order mixtures of each starting material substances were obtained. These powders were then converted to the A12O3-dispersion-strengthened copper by heating, in vacuum, below the temperature of 1273 K. The dispersed particles precipitated by heat-treatment were γ-Al2O3 under the temperature of 1073 K, and γ-Al2O3 and small amount of α-Al2O3 at 1173 K for 3.6 ks, and α-Al2O3, γ-Al2O3 and Fe(Al, Cr)2O4 at 1273 K for 3.6 ks. These dispersed particles have a tendency to aggregate. The hardness value of Al2O3-dispersion-strengthened copper corresponding to 4.13 oxide vol%, heat treated below the temperature of 973 K, showed the highest value among the samples studied in the present work. The Al2O3-dispersion-strengthened copper powders obtained in this study had tendency to sweat pure Cu at the powder particle surface by heat-treatment. The occurrence of sweating resulted in a marked decrease in the hardness values of Al2O3-dispersion-strengthened alloys.View full abstractDownload PDF (8306K) -
Junichi Hojo, Blaise Champagne, Serge Dallaire1989 Volume 36 Issue 4 Pages 411-417
Published: June 25, 1989
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSCeramics particles of Al2O3 and SiC (mean diameter:'40-770μm) were coated with fine metal particles of Al, Ni, Co, Mo and W (mean diameter: 5-10μm) by the agglomeration coating technique in which ceramics particles containing polyethylene glycol as binder were mixed with metal particles in a rotating cylinder and heated above the melting point of polyethylene glycol so that metal particles were fixed on the surface of ceramics particles by the molten binder. The quantity of metal coating reached a maximum of about 60 vol%. Coarser ceramics particles attained a larger quantity of metal coating. The addition of Al-stearate to metal particles was effective to disperse metal particles and increase the surface coverage of the coating.View full abstractDownload PDF (3232K) -
Masaru Yokota, Takahiro Fujii, Hiroshi Nagai, Keiichiro Shoji1989 Volume 36 Issue 4 Pages 418-425
Published: June 25, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSWettability of sintered Al2O3 plates by Al and Al-Ti alloys containing up to 5 mass% Ti was studied by means of sessile drop method in considering various oxygen partial pressures (Po2) in ambient atmosphere. Results obtained are summarized as follows:
(1) Wetting angle between pure Al and sintered Al2O3 plates at 1373 K in vacuum (Po2=1.4×10-1-1.7×10-4 Pa), decreased with the increase of holding time. This corresponds to the primary spreading process, i.e., dissolution of Al2O3 in liquid Al determines the time-dependent wetting between pure Al and sintered Al2O3 plates.
(2) Surface tension of liquid pure Al increased with the increase of Po2 in atmosphere. On the contrary, interface energy between liquid pure Al and solid sintered Al2O3 plates decreased with the increase of Po2. No influence of Po2 on wetting angle was found.
(3) Addition of Ti to liquid Al did not change it's surface tension, however, a slight decrease in work of adhesion of liquid Al-Ti alloy to sintered Al2O3 plates, with Ti content up to 3 mass%Ti, and an increase at 5 mass% Ti were observed.
(4) Fine granular oxide (Al2TiO5) was found to form at the interfaces between Al-Ti alloys and sintered Al2O3 plates, but did not alter the wettability in this system.View full abstractDownload PDF (4222K) -
Tamotsu Ueyama, Takashi Yamamoto, Kiyoshi Okazaki1989 Volume 36 Issue 4 Pages 426-433
Published: June 25, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSWe studied the effects of alumina particle diameter and flux specific surface area on the sinterability of alumina substrate in relation with the powder packing density.
Alumina particle diameter and flux specific surface area were varied within the ranges from 0.5 to 3.6μm and from 1 to 100 m2/g, respectively. The larger the alumina particle diameter, the higher became the minimum sintering temperature. The minimum sintering temperature of alumina substrate decreased by about 50°C when agglomerated particles were pulverized and packing density was improved. On the other hand, the effect of flux specific surface area was insignificant on minimum sintering temperature. Saturated sintered density remained almost unchanged when the alumina particle diameter was varied.
However, it became higher when agglomerated alumina particles were pulverized. Surface smoothness was improved significantly when agglomerated particles were pulverized and hence the green sheet packing density increased.View full abstractDownload PDF (2309K) -
Shinjiro Tashiro, Kenichi Gotoh, Hideji Igarashi1989 Volume 36 Issue 4 Pages 434-438
Published: June 25, 1989
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSTwo kinds of lead-based relaxor materials which are different in sintering temperature, (Pb, Sr) (Mg, Zn, Nb, Ti)O3 [H-material] and Pb(Zn, Nb, Fe, W)O3 [L-material], for multilayer ceramic capacitor were synthesized from oxide powders by calcination at 1170°C and 800°C in H-material and L-material, respectively. Each material was ground by ball-milling into two kinds of powders with different particle size [H (C), L (C), H (F) and L (F) powder], respectively. Average particle sizes of H (C), L (C), H (F) and L (F) powders were 0.73, 1.31, 0.25 and 0.22μm, respectively. These four kinds of powders were mixed in four kinds of conbination of H (C)-L (C), H (F)-L (C), H (C)-L (F) and H (F)-L (F) with various ratios. Microstructure and dielectric properties of ceramics sintered from their mixed powders were experimentally investigated focusing on the 2-phase structure of H-and L-material. The densification of their mixed powders was mainly dependent on the particle size of L-material. The densification of H (F)-L (F) powder was achieved at the lowest temperature in four kinds of mixed powder, and dense ceramics were obtained from H (F)-L (F) powder with a ratio of 1 : 2 at firing temperature of 900°C. It was concluded, that the microstructure consists partially of 2-phase structure of H-and L-materials. (from the SEM observation and their dielectric properties)View full abstractDownload PDF (1971K) -
Noboru Taguchi, Takaho Otomo1989 Volume 36 Issue 4 Pages 439-443
Published: June 25, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSThe immersion of sintered product into CaCl2, CaBr2 aqueous solution and CaF2 suspended solution at room temperature in vacuum and subsequent drying have been carried out. The halide concentration of solution was changed from 0.5 wt% to 10.0 wt%. The effect of immersion treatment on the reducibility index (RI) and reduction degradation index (RDI) of sintered product have been studied.
The main results obtained are as follows:
(1) On the immersion into CaCl2 aqueous solution, RI was slightly decreased and RDI remarkably im-proved.
(2) On the immersion into CaBr2 aqueous solution, RI was maintained in the value of original sintered product and RDI was more improved than in the case of CaCl2 solution.
(3) On the immersion into CaF2 and Ca(OH)2 suspended solution, the effect of immersion treatment on RI and RDI was scarcely seen.
(4) Improvement of RDI was caused by the delay of the reduction rate due to CaCl2 and CaBr2 layer adhered inside of the pore and resultant decrease of the amount of cracked magnetite particles.View full abstractDownload PDF (2792K)
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