• Title/Summary/Keyword: Gas pressure sintering

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Environmental Influences on Gas pressure Sintering of $Si_3N_4$ (질화규소의 가스압 소결에 미치는 환경 영향)

  • 김인섭;이경희;이병하
    • Journal of the Korean Ceramic Society
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    • v.30 no.4
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    • pp.309-315
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    • 1993
  • Gas pressure sintering is a promising process in various densification methods of high strength Si3N4 ceramics. Environmental influences on gas pressure sintering of Si3N4 was investigated with the variationof packing powder, specimen container and N2 gas pressure. The specimens had higher density, larger weight loss and inhomogeneous color in graphite specimen container than in SN26 crucible. The variations of sintering densities in various packing powders (Si3N4, SN26, AlN, BN) were very small but SiC powder was synthesised in graphite crucible with Si3N4 packing powder, aluminium oxynitride compounds were synthesised in SN26 crucible with AlN packing power. Also N2 gas pressure over 20kg/$\textrm{cm}^2$ reduced the densification of Si3N4 in one step-gas pressure sintering. As the result of two step-gas pressure sintering at 700kg/$\textrm{cm}^2$ for 15min., relative density of 99.9% and 3-point bending strength of 1090MPa and dense microstructure of 3~4${\mu}{\textrm}{m}$ grain size were obtained.

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Densification of $Si_3N_4$ Cera,ocs by Two Step Gas Pressure Sintering (2단계 가스압 소결에 의한 질화규소의 치밀화)

  • 이상호
    • Journal of the Korean Ceramic Society
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    • v.35 no.7
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    • pp.659-664
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    • 1998
  • Densification behavior of $Si_3N_4$ ceramics by two step gas pressure sintering was compared with pres-sureless sintering one step gas pressure sintering or hot isostatic pressing. While it was difficult to get the highly interlocked ${\beta}-Si_3N_4$ microstructure during the pressureless sintering due to decomposition above $1800^{\circ}C$ gas pressure sintering could solve this problem by increasing the densification temperature 2MPa of nitrogen pressure was enough to inhibit the decomposition up to $1890^{\circ}C$ and especially two step gas pres-sure sintering applying comparatively low pressure(2MPa) until the closed pore stage and then high pres-sure(10MPa) after pore closure could increase the hardness and the toughness.

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Wear Behavior of Silicon Nitride Depending on Gas Pressure Sintering Conditions

  • Kim, Sung-Ho;Lee, Soo-Wohn;Park, Yong-Kap
    • The Korean Journal of Ceramics
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    • v.6 no.3
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    • pp.193-200
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    • 2000
  • Si$_3$N$_4$powder with 2 wt% $Al_2$O$_3$and 6 wt% $Y_2$O$_3$additives was sintered by the gas pressure sintering (GPS) technique. The unlubricated wear behavior depending on sintering conditions such as sintering temperature, pressure, and sintering time was investigated. When the sintering temperature and time increased, the larger elongated grains were formed and the microstructural heterogeneity increased. When sintering pressure increased, grain growth, however, was impeded. Also, the wear properties depended on microstructure and friction coefficient were related to grain size. Based on the experimental results, the wear properties were associated with initial friction coefficients as well as mechanical properties including fracture toughness and flexural strength.

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A Study on Machinability of Silicon Nitride Ball Sintered by Various Gas Pressure Sintering(GPS) Conditions (가스압 소결조건에 따른 질화규소볼의 가공성에 대한 연구)

  • 이수완;김성호;정용선
    • Journal of the Korean Ceramic Society
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    • v.35 no.2
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    • pp.115-122
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    • 1998
  • The effect of sintering conditions on the sinterability for silicon nitride has been studied by many in-vestigators. However the effect of sintering conditions on the machinability which is the major barrier to the field applications of the ceramic components has not been fully studied. In this study the sintering con-ditions such as temperature gas pressure and time in silicon nitride were varied. The physical and mechan-ical properties of the gas pressure sintered (GPS) silicon nitride were measured. The optimum mi-crostructure of silicon nitride with the excellent machinability was investigated by MFG(magnetic-fluid grinding) technique. An attempt was made to figure out how the mechanical properties influence upon the machinability of silicon nitride ball.

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Phase Formation and Physical Properties of SiAlON Ceramics Fabricated by Gas-Pressure Reactive Sintering (가스압 반응소결로 제조된 SiAlON 세라믹스의 상형성과 물리적 특성)

  • Lee, Soyul;Choi, Jae-Hyeong;Han, Yoonsoo;Lee, Sung-Min;Kim, Seongwon
    • Journal of Powder Materials
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    • v.24 no.6
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    • pp.431-436
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    • 2017
  • SiAlON-based ceramics are some of the most typical oxynitride ceramic materials, which can be used as cutting tools for heat-resistant super-alloys (HRSA). SiAlON can be fabricated by using gas-pressure reactive sintering from the raw materials, nitrides and oxides such as $Si_3N_4$, AlN, $Al_2O_3$, and $Yb_2O_3$. In this study, we fabricate $Yb_{m/3}Si_{12-(m+n)}Al_{m+n}O_nN_{16-n}$ (m=0.3, n=1.9, 2.3, 2.7) ceramics by using gas-pressure sintering at different sintering temperatures. Then, the densification behavior, phase formation, microstructure, and hardness of the sintered specimens are characterized. We obtain a fully densified specimen with ${\beta}$-SiAlON after gas-pressure sintering at $1820^{\circ}C$ for 90 min. under 10 atm $N_2$ pressure. These SiAlON ceramic materials exhibited hardness values of ~92.9 HRA. The potential of these SiAlON ceramics for cutting tool application is also discussed.

Influence of Sintering Condition on Characteristics of $\alpha$-SiC Ceramics ($\alpha$-SiC 소결체의 특성에 미치는 소성조건의 영향)

  • 정두화;김인술;김효준
    • Journal of the Korean Ceramic Society
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    • v.28 no.10
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    • pp.824-830
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    • 1991
  • $\alpha$-SiC(B; 0.4 wt, C; 3 wt%) was sintered in Ar atmosphere from 205$0^{\circ}C$ to 220$0^{\circ}C$ by means of pressureless sintering and gas pressure sintering in order to find optimum sintering condition of $\alpha$-SiC. Mechanical properties and microstructures of sintered bodies were investigated according to sintering method. The effect of sintering condition on sinterability of $\alpha$-SiC was also examined by using the dilatometer. 97.5% and 98.8% of theoretical density were obtained from pressureless sintering and gas pressure sintering of $\alpha$-SiC powder, respectively. And modulus of rupture was measured as 270~350 MPa and 420 MPa respectively.

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Effects of the Whisker Orientation and Sintering Temperature on Mechanical Properties of the Si$_3$N$_4$ based Composites (Si$_3$N$_4$ Whisker의 배열방향과 소결온도가 Si$_3$N$_4$ 복합체의 기계적 성질에 미치는 영향)

  • 김창원;박동수
    • Journal of the Korean Ceramic Society
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    • v.36 no.5
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    • pp.483-489
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    • 1999
  • Gas pressure sintered silicon nitride based composites with 3 wt% $\beta$-Si3N4 whiskers were prepared and change of properties according to the whisker orientation and sintering temperature was studied. The tapes with whiskers were fabricated by two different method ; conventional tape casting and a modified tape casting by using guide pins,. Orientations of the whiskers were controlled by different stacking sequences of the sheets cut from the tape. Samples were fully densified by gas pressure sintering at 2148-2273K. As the sintering temperature increased size of the large elongated grains increased. In case of unidirectional samples sintering shrinkage normal to the whisker alignment direction was larger than that of parallel to the direction and the shrinkage anisotropy increased slightly as sintering temperature increased. As sintering temperature increased the crack length parallel to whisker alignment direction became shorter but that normal to the direction did not depend on sintering temperature. In case of cross-plied samples the anisotropy of mechanical properties disappeared.

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Effects of gas pressure sintering (GPS) conditions on the mechanical properties of silicon nitride (가스압 소결(GPS) 조건이 질화규소의 기계적 특성에 미치는 영향)

  • 이수완;김성호;정용선
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.7 no.4
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    • pp.619-625
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    • 1997
  • $Si_3N_4$ powder with 2 wt% $Al_2O_3$ and 6 wt% $Y_2O_3$additives was gas pressure sintered (GPS). Characterization of the mechanical properties was compared with sintering conditions (temperature, pressure, time). Based on experimental result , the optimal condition of gas pressure sintering was found at $1900^{\circ}C$, 3 MPa for 1 hour. It is assumed that mechanical properties were degraded due to the grain coasening effects with increasing temperature or holding time. However, the grain size was decreased with increasing pressure, resulted in better strength, but lower fracture toughness. Present results suggested that optimization of processing parameters was impotant for better mechanical properties of $Si_3N_4$.

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Gas Pressure Sintering of SiC(p)-TiC(p) Composites (분위기 가압소결에 의한 SiC$_{(P)}$-TiC$_{(P)}$ 복합체 제조)

  • 김인술;김병수;장윤식;박홍채;오기동
    • Journal of the Korean Ceramic Society
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    • v.29 no.10
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    • pp.791-796
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    • 1992
  • SiC(p)-TiC(p) composites were prepared by gas pressure sintering technique. B4C powder and phenolic resin were added as sintering aids by 0.3 wt%-B and 3 wt%-C, TiC powder were dispersed in SiC by 0, 10, 20, 30 and 50 vol%. Flextural strength, fracture toughness and theoretical density of 70 vol% SiC-30 vol% TiC composite sintered at 220$0^{\circ}C$ by gas pressing were 540 MPa, 5.5 MPa.m1/2 and 98.8% respectively.

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High Temperature Erosion Properties of Silicon Nitride Fabricated by GPS and HP Method (GPS와 HP법으로 제조된 질화규소의 고온 Erosion 특성)

  • 최현주;안정욱;임대순;박동수
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2000.11a
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    • pp.304-309
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    • 2000
  • Si$_3$N$_4$-6wt%Y$_2$O$_3$-lwt%Al$_2$O$_3$was prepared by hot pressed and gas pressure sintering to investigate the effect of microstructure on erosion behaviors. Hardness and fracture toughness were measured with prepared specimens to study the high temperature erosion properties. A gas blast type erosion tester was used In examine erosion behavior of the specimens up to 700$^{\circ}C$. In case of GPS silicon nitride, the erosion rate increases up to 500$^{\circ}C$ and decreases over 500$^{\circ}C$. Maximum erosion rate was observed at 300$^{\circ}C$ for HP silicon nitride. The principal factors affecting the high temperature erosive wear of brittle materials are largely dependent on high temperature properties of grain boundaries.

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