• Journal of the Korean Ceramic Society
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• v.37 no.11
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• pp.1091-1096
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• 2000

본 연구에서는 기상 반응법을 이용하여 TMS(Tetramethylsilane:Si($CH_3$)$_4$)와 NH$_3$그리고 H$_2$의 혼합기체로부터 반응 온도 1000~120$0^{\circ}C$ 및 입력비(NH$_3$/Si($CH_3$)$_4$) 1~3의 조건에서 초미분의 SiC-Si$_3$N$_4$복합 분말을 합성하였다. 합성되어진 복합 분말들의 결정상의 변화와 평균 입경을 알아보기 위해 XRD와 TEM 분석을 행한 결과, 구형의 비정질 분말이 형성되었으며, 입자의 크기는 약 70~130nm이었다. 입자의 크기는 입력비에 관계없이 거의 일정하였으나 반응 온도가 증가함에 따라서 감소하였다. FT-IR과 EA 분석 결과, 합성되어진 분말은 Si, N, C, 그리고 H로 이루어진 화합물임을 확인할 수 있었다. 또한 입력비가 다른 조건에서 합성되어진 분말을 $N_2$분위기 하에서 155$0^{\circ}C$로 2시간 열처리를 행한 결과, 낮은 입력비인 경우 $\beta$-SiC, $\alpha$-Si$_3$N$_4$와 $\beta$-Si$_3$N$_4$의 결정상들이 혼재하였으나, 높은 입력비인 경우는 결정화 후 $\alpha$-Si$_3$N$_4$상만이 존재하였다.

• Journal of the Korean Ceramic Society
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• v.36 no.10
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• pp.1102-1107
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• 1999

SiC-Si3N4 composites were prepared by mixing $\alpha$-Si3N4 powder to $\alpha$-SiC powder in the range of 10 to 30 vol% with 10vol% interval. 6wg% Al2O3 and 6wt% Y2O3 were respectively added as sintering aids. Hot pressing was performed at 1,80$0^{\circ}C$ for 1 hour with 25 MPa pressure. In the case of adding 20vol% of $\alpha$-Si3N4 powder the relative density to theoretical value and the flexural strength were 99.1% and 34,420 MPa respectively and the worn amount was 2.09$\times$10-3 mm2 which were the highest values in the all range of he composition. Although the composite containig 10 vol% of $\alpha$-Si3N4 powder showed the highest fracture toughness(KIC) of 4.65MN/m3/2 the reduction of the wear resistance in this composite is likely to be affected by the homogeneity and the uniformity of the grain coalescence and growth during the sintering process.

• Journal of the Korean Ceramic Society
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• v.36 no.8
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• pp.799-804
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• 1999

Composites of SiC-Si3N4 consisted of uniformly distributed elongated $\beta$-Si3N4 grains and equiaxed $\beta$-SiC grains were fabricated with $\beta$-SiC,. $\alpha$-Si3N4 Al2O3 and Y2O3 powders. By hot-pressing and subsequent annelaing elongated $\beta$-Si3N4 grains were grown via$\alpha$longrightarrow$\beta$ phase transformation and equiaxed $\beta$-Si3N4 composites increased with increasing the Si3N4 content owing to the reduced defect size and enhanced crack deflection by elongated $\beta$-Si3N4 grains and the grain boundary strengthening by nitrogen incorporation. Typical flexural strength and fracture toughness of SiC-40 wt% Si3N4 composites were 783 MPa and 4.2 MPa.m1/2 respectively.

• 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.

• Journal of the Korean Ceramic Society
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• v.30 no.12
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• pp.999-1006
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• 1993

Si3N4(p)-SiC(p) composites were prepared by gas pressure sintering at 190$0^{\circ}C$ for 1 hour. $\alpha$-SiC with average particle size of 0.48${\mu}{\textrm}{m}$ were dispersed from zero to 50vol% in $\alpha$-Si3N4 with average particle size of 0.5${\mu}{\textrm}{m}$. Y2O3-Al2O3 system was used as sintering aids. When 10vol% of SiC was added to Si3N4, optimum mechanical properties were observed; relative density of 98.8%, flextural strength of 930MPa, fracture toughness of 5.9MPa.m1/2 and hardness value of 1429kg/$\textrm{mm}^2$. Grain growth of $\beta$-Si3N4 was inhibited as the amount of added SiC was increased. SiC particles were found inside the $\beta$-Si3N4 intragrains in case of 10, 20 and 30vol%SiC added composites.

• Journal of the Korean Ceramic Society
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• v.36 no.5
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• pp.547-554
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• 1999

The self-reinforced Si3N4 ceramics were prepared by pressureless-sintering using ${\beta}$-Si3N4 whiskers as a seed. Effects of ${\beta}$-Si3N4 whiskers on microstructure and mechanical properties and the ${\alpha}$ to ${\beta}$ phase transition of Si3N4 were investigated. The self-reinforced Si3N4 ceramics were densified(relative density$\geq$98%) by pressureless-sintering (1800$^{\circ}C$ 2h) using 8mol% Y2O3 and 6mol% Al2O3 as sintering aids and 5 vol% ${\beta}$-Si3N4 whiskers within self-reinforced Si3N4 ceramic seemed to hinder the densification owing to their acicular shapes but accelerated the ${\alpha}$ to ${\beta}$ phase transition because they acted as pre-existing nuclei. It was found that the more ${\beta}$-Si3N4 nucei the faster ${\alpha}$ to ${\beta}$ phase transition.

• Journal of the Korean Ceramic Society
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• v.25 no.2
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• pp.143-153
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• 1988

In order to synthesize the partially stabilized $\alpha$-Sialon, A1N and Y2O3 were added to synthesized $\alpha$-Si3N4. The phase composition, mechanical properties, micro structure, etc, of the synthesized $\alpha$-Sialon were investigated. Partially stabilized $\alpha$-Sialon ceramics could be synthesized from the composition which was a little deviated from x=0.4, x=0.6 composition along the Si3N4.0.1Y2O3:0.9AlN tie line at 1750-180$0^{\circ}C$ for 2 hrs in N2 atmosphere. It is assumed that A1N is more closely related than Y2O3 to the formation of $\alpha$-Sialon, and that A1N is more easily dissolved into $\alpha$-structure than into $\beta$-structure. In Ya2O3-rich phase mechanical properties were observed to be poor because of formation of mellilite, grain growth, and thermal decomposition of $\alpha$-Sialon. The maximum values of M.O.R, KIC and hardness are 723 MPa, 4.5MN/㎥/2 and 19.3 GPa, respectively, and they were observed for the $\alpha$-Sialon ceramics sintered at 178$0^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.25 no.4
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• pp.380-384
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• 1988

This investigation includes nitridation phenomena of silicon powder compacts in air. Nitridation reaction condition has been provided with using silicon nitride bed and active carbon additive. Reaction products are Oxynitride, $\alpha$-Si3N4, and $\beta$-Si3N4, Oxynitride(Si2N2O) phase in formed at outer surface layer ofsilicon powder compacts. $\alpha$-Si3N4, and $\beta$-Si3N4 are formed at inner region of powder compacts. Microstructural observation indicates that nitridation mechanism in this work is the same as conventional nitridation mechanism nitrogen gas.

• Journal of Powder Materials
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• v.5 no.1
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• pp.15-21
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• 1998

The effect of $\alpha$/$\beta$ phase on the mechanical properties and contact damage of silicon nitrides $Si_3N_4$) was investigated. Silicon nitride materials were prepared from two starting powders, at selective increasing hot-pressing temperatures to coarsen the microstructures: (i) from relatively coarse $\alpha$-phase powder, essentially equiaxed $\alpha$-$Si_3N_4$ grains, with limited, slow transformation to $\beta$-$Si_3N_4$ grain; (ii) from relatively fine $\alpha$-phase powder, a more rapid transformation to $\beta$-$Si_3N_4$, with attendant grain elongation. The resulting micro-structure thereby provided a spectrum of $\alpha$/$\beta$ phase ratios, grain sizes, and grain shapes. Fracture strength, hardness, and toughness were measured, and contact damage and strength degradation after indentation were investigated by Hertzian indentation using spherical indenter. A brittle to ductile transition in $Si_3N_4$ depended on $\alpha$/$\beta$ phase ratio as well as grain size. Silicon nitride with elongated $\beta$ grains showed a superior, contact damage resistance.

• Journal of the Korean Ceramic Society
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• v.30 no.10
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• pp.785-790
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• 1993

Sialon ceramics are presently seen as promising materials with high hardness, strength, fracture toughness and corrosion resistance for friction and wear applications. The objective of present work is to improve of mechanical properties and wear resistance of $\alpha$-Sialon(x=0.4) by addition of SiC whisker. $\alpha$-sialon(x=0.4)/SiC whisker composites were obtained by hot-isostatic pressing at 173$0^{\circ}C$ for 1 hour under 1757Kg/$\textrm{cm}^2$ N2 pressure after pressureless sintering the mixture of Si3N4, Y2O3, AlN at 1780~180$0^{\circ}C$ for 3~5 hours in N2 atmosphere. As the amount of SiC whisker content increased, relative density and hardness were decreased, however fracture toughness, bending strength and tribological properties were improved. Tribological properties of $\alpha$-Sialon/15 vol% SiC whisker composite were improved in spite of its low mechanical properties.