• Title/Summary/Keyword: SiC-AlN ceramics

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The Effects of Sliding Speed and Load on Tribological Behavior of Ceramics in Line-contact Sliding (선접촉시 세라믹의 마찰 및 마멸 특성에 미치는 속도와 하중의 영향)

  • 김영호;이영제
    • Tribology and Lubricants
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    • v.11 no.4
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    • pp.35-44
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    • 1995
  • Within the practical ranges of speed and load, the formation of transfer films and the consequent effects on the friction and wear behavior of ceramic materials during repeated pass sliding contact were studied. These tests were done using $Al_{2}O_{3}$, SiC and $Si_{3}N_{4}$ with the cylinder-on-flat test configuration. The three pairings behaved differently, even if some wear mechanisms were common to the three systems. The $Al_{2}O_{3}$ pair showed the least wear in overall conditions, followed by the $Si_{3}N_{4}$ pair in harder sliding conditions. The wear of SiC was very high at severe loading. In case of $AL_{2}O_{3}$ and $Si_{3}N_{4}$, the transfer film, whenever formed, is strongly attached, enough to resist being wiped off by the slider. As a consequence, the formation of this f'fim leads to a decrease in the wear rate because of the protecting role of the film. The presence of the film at the contact interface also results in high friction. Also, the wear rate of each ceramics is related to the frictional power provided by load, speed and friction.

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.

Fractographic Analysis of Ceramic Composites by Transmission Electron Microscopy using Surface Replication Technique (표면복제법을 이용한 세라믹 복합재료 파괴현상의 투과전자현미경 분석)

  • Jun, Hyeung-Woo;Kim, Gyeung-Ho;Kim, Byung-Ho
    • Applied Microscopy
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    • v.26 no.4
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    • pp.447-456
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    • 1996
  • Fracture surfaces of materials contain useful information ranging from crack path to the mechanism of fracture. Since limitation of electron transparency requires a sample in the form of thin foil for TEM observations, it is impossible to extract such information directly from the fracture surfaces. In this study, the method of surface replication from the ceramic fracture surface is employed to characterize the process of crack propagation in ceramic matrix composites using TEM analysis. The surface replica from the fracture surface in ceramic materials provides detailed surface morphology and more importantly, loosened particles on the fracture surface are collected. Electron diffraction and chemical composition analyses of these particles reveal crack path in the specimen. Furthermore, one can determine the mode of fracture by observing the fracture surface morphology from the image of replica. Two examples are given to illustrate the potential of the surface replication technique. In the first example, apparent toughness increase in $B_{4}C-Al$ composites at high strain rate is investigated by surface replication to elucidate the mechanism of fracture at different strain rates. The polytypes of SiC formed during the sintering of SiC-AlN composite and their effect on the fracture behavior of SiC-AlN composite are analyzed in the second example.

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Microstructure, Mechanical and Wear Properties of Hot-pressed $Si_3N_4-TiC$ Composites

  • Hyun Jin Kim;Soo Whon Lee;Tadachika Nakayama;Koichi Niihara
    • The Korean Journal of Ceramics
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    • v.5 no.4
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    • pp.317-323
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    • 1999
  • Si3N4-TiC composites have been known as electrically conductive ceramics. $Si_3N_4-TiC$ composites with 2 wt% $Al_2O_3$ and 4 wt% $Y_2O_3$ were hot pressed in $N_2$ environment. The mechanical properties including hardness, fracture toughness, and flexural strength and tribological properties were investigated as a function of TiC content. $Si_3N_4-40$ vol% TiC composite was hot pressed at $1,750^{\circ}C$, $1,800^{\circ}C$, and $1,850^{\circ}C$ for 1, 3 and 5 hours in $N_2$ gas. Mechanical and tribolgical properties depended on microstructures, which were controlled by hte TiC content, hot press temperature, and hot press holding time. However, mechanical properties and tribological behaviors were degraded by the chemical reaction between TiC and N. The chemically reacted products such as TiCN, SiC, and $SiO_2$ were detered by the X-ray diffraction analysis.

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Effect of Additive Composition on Mechanical Properties of Silicon Carbide Sintered with Aluminum Nitride and Erbium Oxide

  • Lee, Sung-Hee;Kim, Young-Wook
    • Journal of the Korean Ceramic Society
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    • v.42 no.1
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    • pp.16-21
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    • 2005
  • The effect of additive composition, using AlN and $Er_{2}O_{3}$ as sintering additives, on the mechanical properties of liquid-phase-sintered, and subsequently annealed SiC ceramics was investigated. The microstructures developed were quantitatively analyzed by image analysis. The average thickness of SiC grains increased with increasing the $Er_{2}O_{3}/(AlN + Er_{2}O_{3})$ ratio in the additives whereas the aspect ratio decreased with increasing the ratio. The mechanical properties versus $Er_{2}O_{3}/(AlN + Er_{2}O_{3})$ ratio curve had a maximum; i.e., there was a small composition range at which optimum mechanical properties were realized. The best results were obtained when the ratio ranged from 0.4 to 0.6. The flexural strength and fracture toughness of the SiC ceramics were $550\~650\;MPa$ and $5.5\~6.5$ MPa${\cdot}m^{1/2}$, respectively.

Synthesis of $\alpha$-Sialon Ceramics from an Alkoxide and Their Mechanical Properties(II) (알콕사이드로 부터 $\alpha$-Sialon 세라믹스의 제조 및 기계적 성질(II))

  • 이홍림;윤창현
    • Journal of the Korean Ceramic Society
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    • v.28 no.3
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    • pp.189-196
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    • 1991
  • Si(OC2H5)4, commercial AlN and Y2O3 powder were used as the precusor of Si3N4, AlN, Y2O3, respectively. After Si3N4 powder was synthesized by carbothermal reduction and nitridation at 135$0^{\circ}C$ for 13h in N2 atmosphere, characteristics of synthesized powder and the ceramics sintered at 178$0^{\circ}C$ for 1h under 30MPa were investigated. In order to evaluate the reliability of sintered body, Weibull modulus was investigated. Premixing of carbon black as a reduction agent had no effect on Si(OH)4 formation, and Si3N4 powder synthesized from Si(OC2H5)4 was $\alpha$-Si3N4 single phase. Mechanical properties of sintered body were measured as follows : flexural strength ; 750MPa, fracture toughness ; 3.71Mn/3/2, hardness : 17.4GPa, thermal shock resistence temperature ; $600^{\circ}C$. Flexural strength at room temperature was 750MPa and was retained up to 110$0^{\circ}C$. The Weibull modulus of sintered body was 10.7.

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Sintering Behavior and Thermal Conductivity of Aluminum Nitride Ceramics with MgO-CaO-Al2O3-SiO2 Nano-glass Additive (나노 MgO-CaO-Al2O3-SiO2 glass 첨가제를 가진 AlN의 소결거동 및 열전도도)

  • Baik, Su-Hyun;Kim, Kyung Min;Ryu, Sung-Soo
    • Journal of Powder Materials
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    • v.25 no.5
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    • pp.426-434
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    • 2018
  • In this study, $MgO-CaO-Al_2O_3-SiO_2$ (MCAS) nanocomposite glass powder having a mean particle size of 50 nm and a specific surface area of $40m^2/g$ is used as a sintering additive for AlN ceramics. Densification behaviors and thermal properties of AlN with 5 wt% MCAS nano-glass additive are investigated. Dilatometric analysis and isothermal sintering of AlN-5wt% MCAS compact demonstrates that the shrinkage of the AlN specimen increases significantly above $1,300^{\circ}C$ via liquid phase sintering of MCAS additive, and complete densification could be achieved after sintering at $1,600^{\circ}C$, which is a reduction in sintering temperature by $200^{\circ}C$ compared to conventional $AlN-Y_2O_3$ systems. The MCAS glass phase is satisfactorily distributed between AlN particles after sintering at $1,600^{\circ}C$, existing as an amorphous secondary phase. The AlN specimen attained a thermal conductivity of $82.6W/m{\cdot}K$ at $1,600^{\circ}C$.

Effect of SiC Filler Content on Microstructure and Flexural Strength of Highly Porous SiC Ceramics Fabricated from Carbon-Filled Polysiloxane (SiC 필러 함량이 탄소 함유 Polysiloxane으로부터 제조된 고기공률 탄화규소 세라믹스의 미세조직과 꺾임강도에 미치는 영향)

  • Eom, Jung-Hye;Kim, Young-Wook;Song, In-Hyuck
    • Journal of the Korean Ceramic Society
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    • v.49 no.6
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    • pp.625-630
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    • 2012
  • Highly porous silicon carbide (SiC) ceramics were fabricated from polysiloxane, SiC and carbon black fillers, AlN-$Y_2O_3$ additives, and poly (ether-co-octene) (PEOc) and expandable microsphere templates. Powder mixtures with a fixed PEOc content (30 wt%) and varying SiC filler contents from 0-21 wt% were compression-molded. During the pyrolysis process, the polysiloxane was converted to SiOC, the PEOc generated a considerable degree of interconnected porosity, and the expandable microspheres generated fine cells. The polysiloxane-derived SiOC and carbon black reacted and synthesized nano-sized SiC with a carbothermal reduction during a heat-treatment. Subsequent sintering of the compacts in a nitrogen atmosphere produced highly porous SiC ceramics with porosities ranging from 78 % to 82 % and a flexura lstrength of up to ~7 MPa.

Thermoelectric Conversion Characteristics of SiC Ceramics Fabricated from 6H-SiC Powder (6H-SiC로부터 제작한 SiC 세라믹스의 열전변환 특성)

  • ;Kunihito Koumoto;Hiroaki Yanagida
    • Journal of the Korean Ceramic Society
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    • v.27 no.3
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    • pp.412-422
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    • 1990
  • Porous SiC ceramics were proposed to be promising materials for high-temperature thermoelectric energy conversion. Throughthe thermoelectric property measurements and microstructure observations on the porous alpha SiC and the mixture of $\alpha$-and $\beta$-SiC, it was experimentally clarified that elimination of stacking faults and twin boundaries by grain growth is effective to increase the seebeck coefficient and increasing content of $\alpha$-SiC gives rise to lower electrical conductivity. Furthermore, the effects of additives on the thermoelectric properties of 6H-SiC ceramics were also studied. The electrical conductivity and the seebeck coefficient were measured at 35$0^{\circ}C$ to 105$0^{\circ}C$ in argon atmospehre. The thermoelectric conversion efficiency of $\alpha$-SiC ceramics was lower than that of $\beta$-SiC ceramics. The phase homogeneity would be needed to improve the seebeck coefficient and electrical conductivity decreased with increasing the content of $\alpha$-phase. In the case of B addition, XRD analysis showed that the phase transformation did not occur during sintering. On the other hand, AlN addiiton enhanced the reverse phase transformation from 6H-SiC to 4H-SiC, and this phenomenon had a great effect upon the electrical conductivity.

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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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    • 2006.09b
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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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