• Title, Summary, Keyword: $Si_3N_4$ Ceramics

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High Temperature Properties of $Si_3N_4-Re$Silicon Oxynitride (Re=Y, Yb, Er, La) Ceramics

  • Park, Heon-Jin;Lee, June-Gunn;Kim, Young-Wook;Cho, Kyeong-Sik
    • The Korean Journal of Ceramics
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    • v.5 no.3
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    • pp.211-216
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    • 1999
  • Four different $\beta-Si_3N_4$ ceramics with silicon oxynitrides $[Y_10(SiO_4)_6N_2, Yb_4Si_2N_2O_7, Er_2Si_3N_4O_3, \;and La_{10}(SiO_4)_6N_2$, respectivley] as secondary phases have been fabricated by hot-pressing the $Si_3N_4-Re_4Si_2N_2O_7$ (Re=Y, Yb, Er, and La) compositions at $1820^{\circ}C$ for 2h under a pressure of 25 MPa. The high temperature strength and oxidation behavior of the hot-pressed ceramics were characterized and compared with those of the ceramics fabricated from $Si_3N_4-Si_2O_7$ compositions. The $Si_3N_4-Re_4Si_2N_2O_7$composition investigated herein showed comparable high temperature strength to those from $Si_3N_4-Re_2Si_2O_7$ compositions. Si3N4 ceramics from a $Si_3N_4-Y_4Si_2N_2O_7$ composition showed the highest strength of 877 MPa at $1200^{\circ}C$ among the compositions. All $Si_3N_4$ ceramics investigated herein showed a parabolic weight gain with oxidation time at $1400^{\circ}C$ and the oxidation products of the ceramics were $SiO_2$ and $Re_2Si_2O_7$. The $Si_3N_4-Re_4Si_2N_2O_7$ compositions showed inferior oxidation resistance to those from $Si_3n_4-Re_2Si_2O_7$ compositions, owing to the incompatibility of the secondary crystalline phases of those ceramics with $SiO_2$, the oxidation product of Si3N4.Si3N4 ceramics from a $Si_3N_4-Er_4Si_2N_2O_7$ composition showed the best oxidation resistance of 0.375mg/$\textrm{cm}^2$ after oxidation at $1400^{\circ}C$ for 102 h in air among the compositions.

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Fabrication and Characterization of Electrical Discharge Machinable $Si_3N_4$-TiN Composites

  • Park, Heon-Jin;Kim, Young-Wook;Lee, June-Gunn;Lee, Soo W.;Chung, Soon-Kil
    • The Korean Journal of Ceramics
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    • v.1 no.2
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    • pp.101-105
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    • 1995
  • Electrical discharge machinable $Si_3N_4$ was fabricated with the addtion of 20-60 vol% TiN by gas pressure sintering. Their sinterability, microstructure, mechanical and electrical properties were characterized as a function of the TiN content. The addition of TiN up to 20 vol% increased the flexural strength and fracture toughness as compared with those of the monolithic Si3N4. For the TiN content higher than 40 vol%, the electrical resistivity was lower than $1062\Omega$.cm. The $Si_3N_4$ with the addition of 40 vol% of TiN appears to have the optimum considerable sinterability, mechanical and electrical properties, and machinability. A microstructural analysis showed that the enhanced toughening was due to the crack deflection.

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Mechanical Properties and Microstructures of Self-toughened Silicon Nitride Cermic Prepared by Microstructural Control (미세구조 제어에 의해 제조한 자체 강인화 질화규소 세라믹의 기계적 성질과 미세조직)

  • 김완중;이영규;조원승;최상욱
    • Journal of the Korean Ceramic Society
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    • v.36 no.4
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    • pp.432-443
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    • 1999
  • The self-toughened Si3N4 ceramics where needle-like coarse ${\beta}$-Si3N4 grains were dispersed within fine-grain-ed matrix were prepared via hot-prssing at 1730$^{\circ}C$ for 2 h using 5 vol% ${\beta}$-Si3N4 whiskers as a seed. In this study the microstructures and mechanical properties of self-toughened Si3N4 ceramics were investigated. The flexural strength of self-toughened Si3N4 ceramics was increased from 600-800 MPa of the Si3N4 monolith to 830-1025 MPa. The KIC was also increased from 4.0-5.0MPa$.$m1/2 of the Si3N4 monolith to 5.8-6.5MPa$.$m1/2$.$The needle-like coarse Si3N4 grains in self-toughened ceramics were considered to induce various toughening mechanisms including the crack deflection pull-out and bridging and to contribute to KIC improvement. In ad-dition to toughening mechanisms the KIC improvement was considered to be partially indebted also to the orien-tation of large ${\beta}$-Si3N4 grains and to the promoting effect of ${\beta}$-Si3N4 whiskers on the ${\alpha}$ to ${\beta}$ transtion.

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Effect of Yttria and Ceria on Mechanical Properties and Oxidation Behaviors of $\alpha$-Sialon Ceramics ($\alpha$-Sialon 세라믹스의 역학적 성질과 산화거동에 미치는 $Y_2O_3$$CeO_2$의 첨가영향)

  • 이은복;이홍림;조덕호;박원철
    • Journal of the Korean Ceramic Society
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    • v.30 no.11
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    • pp.941-948
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    • 1993
  • The powder mixture of Si3N4-AlN-Y2O3, Si3N4-AlN-CeO2 and Si3N4-AlN-Y2O3-CeO2 system was hot-pressed at 175$0^{\circ}C$ for 2h in N2 to prepare $\alpha$-Sialon ceramics. The mechanical property and oxidation behaviour of the prepared $\alpha$-Sialon ceramics were investigated. At 120$0^{\circ}C$, oxidation resistance was best for the Y2O3 added $\alpha$-Sialon ceramics and oxidation rate increased when the amount of CeO2 increased. But when the mixture of Y2O3 and CeO2 added $\alpha$-Sialon ceramics showed a good oxidation resistance. Fracture toughness of (Y2O3+CeO2) added $\alpha$-Sialon ceramics was higher than Y2O3 added $\alpha$-Sialon ceramics.

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High-Temperature Strength of the Hot-Pressed Partially Stabilized $\alpha$-Sialon Ceramics Having the Composition of Y0.1(Si, Al)12(N, O)16 ($Y_{0.1}$(Si, Al)$_12$(N, O)$_16$의 조성을 갖는 부분안정화 $\alpha$-Sialon 열간가압소결체의 고온강도)

  • 조덕호;이형복
    • Journal of the Korean Ceramic Society
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    • v.29 no.5
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    • pp.410-418
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    • 1992
  • Si3N4, AlN and Y2O3 powder mixtures of the Y0.1(Si, Al)12(N, O)16 composition were hot-pressed at 1900℃ for 0 to 60 min under 30 MPa in order to fabricate the partially-stabilized α-Sialon ceramics (X=0.1). Room and high temperature flexural strengths of the specimens were compared with those of Si3N4-5 wt%Y2O3, Si3N4-5 wt%Y2O3-2 wt%Al2O3, and β-Sialon (Z=0.5) ceramics. The flexural strength of the α-Sialon ceramics which was hot-pressed for 15 min showed the highest value of 820 MPa at 1400℃ that is relatively higher temperature. It is guessed that a little amount of glassy phase existed in grain boundary because Y2O3 and AlN components were incoperated in Si3N4 grains, or transient liquid phase sintering, and microstructure with the smaller grain size and the interlocked grains of α'-and β-Si3N4 was obtained by the hot-pressing at high temperature of 1900℃ for the short time (15 min).

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The Effect of Si3N4 Addition on Nitriding and Post-Sintering Behavior of Silicon Powder Mixtures

  • Park, Young-Jo;Ko, Jae-Woong;Lee, Jae-Wook;Kim, Hai-Doo
    • Journal of the Korean Ceramic Society
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    • v.49 no.4
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    • pp.363-368
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    • 2012
  • Nitriding and post-sintering behavior of powder mixture compacts were investigated. As mixture compacts are different from simple Si compacts, the fabrication of a sintered body with a mixture composition has engineering implications. In this research, in specimens without a pore former, the extent of nitridation increased with $Si_3N_4$ content, while the highest extent of nitridation was measured in $Si_3N_4$-free composition when a pore former was added. Large pores made from the thermal decomposition of the pore former collapsed, and they were filled with a reaction product, reaction-bonded silicon nitride (RBSN) in the $Si_3N_4$-free specimen. On the other hand, pores from the decomposed pore former were retained in the $Si_3N_4$-added specimen. Introduction of small $Si_3N_4$ particles ($d_{50}=0.3{\mu}m$) into a powder compact consisting of large silicon particles ($d_{50}=7{\mu}m$) promoted close packing in the green body compact, and resulted in a stable strut structure after decomposition of the pore former. The local packing density of the strut structure depends on silicon to $Si_3N_4$ size ratio and affected both nitriding reaction kinetics and microstructure in the post-sintered body.

A Study on the Micro Hole Drilling Characteristics of $Si_3N_4$-BN Based Machinable Ceramics ($Si_3N_4$-BN계 가공성 세라믹스의 마이크로 홀 가공특성에 관한 연구)

  • 김동우;조명우;조원승;이응숙;이재형
    • Journal of the Korean Society for Precision Engineering
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    • v.21 no.4
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    • pp.48-56
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    • 2004
  • Ceramics are very difficult-to-cut materials because of its high strength and hardness. Their machining mechanism is characterized by cracking and brittle fracture. In this paper, to give good machinability to the ceramics, h-BN powders are added to $Si_3N_4$, by volume of 20, 25 and 30%. And the machinability of the produced ceramics is tested using micro drilling system. Through required experimental works, it is shown that the micro drilling machinability is varied along with the volumetric percentage of h-BN powders. Also, it is verified that the obtained results can be used to develop new machinable ceramics of good material properties and machinability.

Corrosive Degradation of MgO/Al2O3-Added Si3N4 Ceramics under a Hydrothermal Condition (MgO/Al2O3가 소결조제로 첨가된 Si3N4 세라믹스의 수열 조건에서의 부식열화 거동)

  • Kim, Weon-Ju;Kang, Seok-Min;Park, Ji-Yeon
    • Korean Journal of Materials Research
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    • v.17 no.7
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    • pp.366-370
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    • 2007
  • Silicon nitride ($Si_3N_4$) ceramics have been considered for various components of nuclear power plants such as the mechanical seal of a reactor coolant pump (RCP), the guide roller for a control rod drive mechanism (CRDM), and a seal support, etc. Corrosion behavior of $Si_3N_4$ ceramics in a high-temperature and high-pressure water must be elucidated before they can be considered as components for nuclear power plants. In this study, the corrosion behaviors of $Si_3N_4$ ceramics containing MgO and $Al_2O_3$ as sintering aids were investigated at a hydrothermal condition ($300^{\circ}C$, 9.0 MPa) in pure water and 35 ppm LiOH solution. The corrosion reactions were controlled by a diffusion of the reactive species and/or products through the corroded layer. The grain-boundary phase was preferentially corroded in pure water whereas the $Si_3N_4$ grain seemed to be corroded at a similar rate to the grain-boundary phase in LiOH solution. Flexural strengths of the $Si_3N_4$ ceramics were significantly degraded due to the corrosion reaction. Results of this study imply that a variation of the sintering aids and/or a control (e.g., crystallization) of the grain-boundary phase are necessary to increase the corrosion resistance of $Si_3N_4$ ceramics in a high-temperature water.

The Effect of Oxygen Introduction on Oxidation Resistance and Cutting Performance of Silicon Nitride Ceramics

  • Nagano, Mituyoshi;Sano, Hideaki;Sakaguchi, Shigeya;Zheng, Guo Bin;Uchiyama, Yasuo
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • pp.857-858
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    • 2006
  • In order to clarify the wear resistance as cutting tools, the effect of oxygen addition on oxidation behavior of the ${\beta}-Si_3N_4$ ceramics with 5 mass% $Y_2O_3$ and 2 or 4 mass% $Al_2O_3$ was investigated by performing oxidation tests in air at $1300^{\circ}$ to $1400^{\circ}C$ and cutting performance tests. From test results, we could conclude that the mechanical properties of ${\beta}-Si_3N_4$ ceramics depending on oxygen introduction are much effective on cutting performance improvements of ${\beta}-Si_3N_4$ ceramics.

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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 Korean Powder Metallurgy Institute
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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.