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Volume 34, Issue 2
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[in Japanese]1987 Volume 34 Issue 2 Pages 51-59
Published: February 25, 1987
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSDownload PDF (612K) -
Kohmei Halada, Tohru Takeda, Kazumi Minagawa1987 Volume 34 Issue 2 Pages 60-65
Published: February 25, 1987
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSDilatometric examination was used to investigate the sintering of the higher-pressure water atomized Ni-20%Cr super fines. It was confirmed that sinterability of the super fines was superior to alloy powders atomized with the ordinary water pressures. Sintering in hydrogen atmosphere improved the sinterability of the Ni-20%Cr super fines, which was due to the fact that the main sintering mechanism of Ni-20%Cr super fines in hydrogen atmosphere was volume diffusion while grainboundary diffusion was the main mechanism in both argon and vacuum atmosphere.View full abstractDownload PDF (3999K) -
Katsuhiko Homma, Tsuneo Tatsuno, Hiroshi Okada1987 Volume 34 Issue 2 Pages 66-72
Published: February 25, 1987
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSα-SiC and β-SiC starting powders mixed with 1 wt% B and 1 wt% C as densification aids, were pressed and normally sintered at 2000-2200°C. These sintered compacts and commercial sintered compacts (Kyo-sera, SC201) were HIP'ed without capsule using in 100 MPa Ar gas and N2 gas at 1700°C.
Weight change, density and flexural strength were investigated, and the results obtained were summarized as follows:
(1)The amount of weight gain during N2-HIP treatment which was remarkably large in case of low temperature sintered compacts (about 15%), was caused by the reaction between high pressure N2 gas and SiC.
(2)The density of all specimens increased by HIP treatments, and the density of N2-HIP'ed compacts was increased with the weight gain.
(3) The flexural strength of sintered a-SiC and commercial SiC compacts increased by HIP treatments, and the higher strength was obtained in case of N2-HIP treatment. It was considered that the flaw size in SiC compacts was apparently decreased by the rod like Si3N4 crystal which was formed y the reaction between N2 gas and SiC.View full abstractDownload PDF (3721K) -
Katsuhiko Homma, Tsuneo Tatsuno, Hiroshi Okada1987 Volume 34 Issue 2 Pages 73-77
Published: February 25, 1987
Released on J-STAGE: July 12, 2010
JOURNAL FREE ACCESSSi3N4 powders mixed with 6wt%Y2O3-2-6wt%Al2O3 and 6wt%Y2O3-1.5wt%MgO as sintering aids, were pressed and normally sintered at 1600°C. The sintered compacts were HIP'ed without capsule using in 100 MPa nitrogen gas at 1700°C. Density, weight change, a to β phase transformation and flexural strength were studied, and the results obtained were summarized as follows:
(1) The amount of weight loss during sintering was relatively small in case of Y2O3-Al2O3 series, so that the sinterability was better than in Y2O3-MgO series.
(2) In case of both the series, the amount of a to β transformation in sintered compacts was decreased compared with the compacts which contained 6 wt%Y2O3 only, and the tendency in Y2O3-Al2O3 series was more remarkable than in Y2O3-M90 series.
(3) The mean strength of Y2O3-Al2O3 series was improved from 340 to 700 MPa by HIP treatment. It was found that the improvement of strength depended on not only density, but also a toβ transformation and fibrous structure formation in Si3N4 during HIP treatment.View full abstractDownload PDF (3216K) -
Masahiro Yoshimura, Kazuo Suzuki, Shigeyuki Somiya1987 Volume 34 Issue 2 Pages 78-84
Published: February 25, 1987
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSTitanium and zirconium powders did not yield nitrides effectively by the treatment in pressurized ammonia of 1 MPa and above, at 700°C for 3 h. The addition of NH4Cl was effective for the nitridation of Ti and Zr. Reactions of titanium powder (99.1 % up) mixed with 10 wt% (9.2 mol%) ammonium chloride have been studied at 300-700°C under 0.1 or 1 MPa NH3 (initial pressure) for 3 h. Ti and NH4CI did not react at 300°C, but formed TiH1.924 at 400°C, and then TiH1.924 changed into TiN above 500°C. When the sample of Ti-10 wt% NH4Cl was heated at 300-600°C under 0.4 MPa Ar gas for 3 h, TiH1.924 was produced at 400°C and above, but TiN was not produced.
When the sample of Zr-10 mol% (6 wt%) NH4Cl was heated under 0.1 or 1 MPa NH3, ZrN was formed above 600°C through the formation of ZrH and ZrH2 above 400°C. A small amount of β-ZrNCI was also produced at 700°C under the same conditions.View full abstractDownload PDF (3133K) -
Nobuyuki Yamamoto1987 Volume 34 Issue 2 Pages 85-90
Published: February 25, 1987
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSRelations between PTC effect and reactions observed in DTA were investigated in the temperature range of 25 to 1400°C on the specimens prepared by adding SiO2 or Si3N4 to Y-doped BaTiO3. Two kinds of eutectic reactions were observed in DTA, i.e. reaction A at 1184-1238°C, and B at 1290-1327°C. Resistivity was measured on the specimens quenched before and after these reactions took place. Compared to the specimen quenched after reaction A, remarkable reduction in PTC effect was observed in the specimen quenched before reaction A. Quenching from much higher temperature, i.e. above reaction B temperature, however, gave a larger PTC effect. Microstructures of boundary phases suggested that Ti-rich phase (Ba6Ti17O40) played an important role on the appearance of PTC effect.View full abstractDownload PDF (2171K) -
Nobuyuki Tamari, Isao Kondo, Makoto Kinoshita1987 Volume 34 Issue 2 Pages 91-94
Published: February 25, 1987
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSAddition effects of some fluorides, NaF, MgF2, CaF2 and AIF3, on the densification and the mechanical properties (Bending strength, fracture toughness) of hydroxyapatite were investigated. Sintering treatments were performed by hot-pressing under 10 min-20 MPa. An addition amount of each fluoride was fixed at 2.5 wt%. Of above fluorides added, calcium fluoride brought on extremely good results for the sintering of hydroxyapatite. The sintered compacts having relative densities more than 98% were obtained from 900°C in the case of adding calcium fluoride. On the other hand, the hydroxyapatite single compacts were fully densified above 1200°C. Moreover, the hydroxyapatite compacts containing calcium fluoride had a little higher bending strengths and fracture toughnesses than the hydroxyapatite single compacts because of the difference of their fine structures or grain sizes. Addition of other fluorides, on the contrary, obstructed the densification of hydroxyapatite.View full abstractDownload PDF (1520K)
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