• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1998년도 제27회 춘계학술대회
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• pp.139-145
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• 1998

This paper addresses the R-curve properties, wear resistance, and erosion resistance of the two silicon carbide ceramics with different microstructures, i.e. , fine grained SiC and in situ-toughened SiC(IST SIC). Fine grained SiC exhibits a relatively flat R-curve behavior whereas the IST SiC exhibits a increasing R-curve behavior. The increasing R-curve behavior in IST SiC is attributed to relatively weak grain boundaries. The rate of material removal during wear tests and erosion tests was higher for IST SiC than that for fine grained SiC. This is attributed to the weaker grain boundaries in IST SiC than that in fine grained SiC. It is implied that fracture toughness in short crack regime should be taken into consideration in the interpretation of the microscopical material removal process. We show that the higher the strength of grain boundaries is, the higher wear and erosion resistances are.

• The Korean Journal of Ceramics
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• 제5권3호
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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.

• 한국세라믹학회지
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• 제43권8호
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• pp.458-462
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• 2006

A simple pressing process using a SiC powder, $Al_2O_3-Y_2O_3$ sintering additive, and polymer microbeads for fabricating cellular SiC ceramics is demonstrated. The strategy for making the cellular ceramics involves: (i) forming certain shapes using a mixture of a SiC powder, $Al_2O_3-Y_2O_3$ sintering additive, and polymer microbeads by pressing; (ii) heat-treatment of the formed body to burn-out the microbeads; and (iii) sintering the body. By controlling the microsphere content and sintering temperature, it was possible to adjust the porosity in a range of 16% to 69%. The flexural and compressive strengths of cellular SiC ceramics with $\sim$40% porosity were $\sim$60 MPa and $\sim$160 MPa, respectively.

• 한국분말재료학회지
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• 제1권1호
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• pp.15-20
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• 1994

The effect of SiC addition on sintering behaviors and microstructures of TiB2 ceramics were studied. The sintering of TiB2 was limited due to the surface diffusion and rapid grain growth at high temperature. However the addition of SiC to TiB2 ceramics improved the densification to above 99% of the theoretical density. The sintering of TiB2-SiC composite starts at 120$0^{\circ}C$ with the melting of the oxides in particle surface as impurities. After the reduction of the oxide by additional cabon at above 140$0^{\circ}C$, the grain boundary diffusion through the interface of TiB2-SiC play an important role. TEM observation showed neither chemical reactions nor other phases formed at the TiB2-SiC interfaces but the microcracks were observed due to the mismatch of thermal expansion between TiB2-SiC.

• 한국세라믹학회지
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• 제47권6호
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• pp.578-582
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• 2010

$ZrB_2$ has a melting point of $3245^{\circ}C$ and a relatively low density of $6.1\;g/cm^3$, which makes this a candidate for application to ultrahigh temperature environments over $2000^{\circ}C$. Beside these properties, $ZrB_2$ is known to have excellent resistance to thermal shock and oxidation compared with other non-oxide engineering ceramics. In order to enhance such oxidation resistance, SiC was frequently added to $ZrB_2$-based systems. Due to nonsinterability of $ZrB_2$-based ceramics, research on the sintering aids such as $B_4C$ or $MoSi_2$ becomes popular recently. In this study, densification and high-temperature properties of $ZrB_2$-SiC ceramics especially with $B_4C$ are investigated. $ZrB_2$-20 vol% SiC system was selected as a basic composition and $B_4C$ or C was added to this system in some extents. Mixed powders were sintered using hot pressing (HP). With sintered bodies, densification behavior and high-temperature (up to $1400^{\circ}C$) properties such as flexural strength, hardness, and so on were examined.

• 한국세라믹학회지
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• 제48권4호
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• pp.312-315
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• 2011

The effect of slurry composition and wafer flatness on a material removal rate (MRR) and resulting surface roughness which are evaluation parameters to determine the CMP characteristics of the on-axis 6H-SiC substrate were systematically investigated. 2-inch SiC wafers were fabricated from the ingot grown by a conventional physical vapor transport (PVT) method were used for this study. The SiC substrate after the CMP process using slurry added oxidizers into slurry consisted of KOH-based colloidal silica and nano-size diamond particle exhibited the significant MRR value and a fine surface without any surface damages. SiC wafers with high bow value after the CMP process exhibited large variation in surface roughness value compared to wafer with low bow value. The CMPprocessed SiC wafer having a low bow value of 1im was observed to result in the Root-mean-square height (RMS) value of 2.747 A and the mean height (Ra) value of 2.147 A.

• 대한기계학회논문집A
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• 제31권4호
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• pp.425-431
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• 2007

[ $Al_2O_3/SiC$ ]composite ceramics were sintered to evaluate the bending strength and elastic wave characteristics. The three-point bending test was carried out under room temperature. The elastic wave was detected by fracture wave detector. The crack healing behavior was investigated from 1373 K to 1723 K. The bending strength of $Al_2O_3/SiC$ composite by nanocomposite is higher than that of $Al_2O_3$ monolithic. Crack-healing behavior depended on an amount of additive powder $Y_2O_3$. In $Al_2O_3/SiC$ composite ceramics with 3 wt. % $Y_2O_3$ for additive powder, the bending strength at 1573 K is about 100% increase than that of the smooth specimens. From the result of wavelet analysis of elastic wave signal, the smooth specimen and heat treated specimen of $Al_2O_3$ monolithic and $Al_2O_3/SiC$ composite ceramics showed characteristics of frequency about 58 kHz. The strength of $Al_2O_3/SiC$ composite ceramics was a little higher than those of $Al_2O_3$ monolithic. The dominant frequencies were high with increasing of $Y_2O_3$ for additive powder. The dominant frequencies had direct connection with the bending strength.

• 대한금속재료학회지
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• 제50권11호
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• pp.839-845
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• 2012

The effect of an AlN additive on the thermoelectric properties of SiC ceramics was studied. Porous SiC ceramics with 48-54% relative density were fabricated by sintering the pressed ${\alpha}-SiC$ powder compacts with AlN at $2100-2200^{\circ}C$ for 3 h in an Ar atmosphere. In the undoped specimens, the Seebeck coefficients were positive (p-type semiconducting) possibly due to a dominant effect of the acceptor impurities (Al, Fe) contained in the starting powder. With AlN addition, the reverse phase transformation of 6H-SiC to 4H-SiC was observed during the sintering process. The electrical conductivity of the AlN doped specimen was larger than that of the undoped specimen under the same conditions, which might be due to a reverse phase trans-formation. The Seebeck coefficient of the AlN doped specimen was also larger than that of the undoped specimen. The density of specimen and the amount of addition had significant effects on the thermoelectric properties.

• 동력기계공학회지
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• 제15권6호
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• pp.67-72
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• 2011

In the present study, crack healing effect and residual stress of $Al_2O_3$ ceramics were investigated by changing the sintering temperature and heat treatment conditions. And also it was investigated that the influence of different filler loadings of nano-sized SiC particles on the crack healing behavior of $Al_2O_3$ ceramics. The test samples were characterized by three point bend flexural tests to evaluate their mechanical properties. The morphological changes were studied by FE-SEM and EDS. The test results indicated that the $Al_2O_3$ with nano-sized SiC ceramics sintered at $1800^{\circ}C$ were showed highest density. Sintering temperature at $1800^{\circ}C$, the bending strength of heat treatment in air atmosphere specimens showed about 42 % increment in comparison to the un-heat treated specimens. The cracked specimens can be healed by heat treatment in vacuum atmosphere but the crack healing effect of $Al_2O_3$ ceramics, which is heat treated in air atmosphere was higher than that of heat treated in vacuum atmosphere. $Al_2O_3$ with 30 wt% of SiC ceramics indicated higher crack healing ability than that with 15 wt% of SiC ceramics. The FE-SEM images showed that the median cracks and pores were disappeared after heat treatment in air.

• 한국세라믹학회지
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• 제39권10호
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• pp.948-954
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• 2002

차세대 발전 시스템에서 사용되는 고온 가스 필터용 지지층 소재를 제조하기 위하여 용융 Si 침윤 방법으로 기공율이 32∼36%, 주기공 크기가 37∼90 ${\mu}m$ 범위를 갖는 고강도 다공질 반응소결 탄화규소(RBSC)를 개발하였다. 반응소결 탄화규소 다공체의, 최대 파괴강도는 120MPa이었으며, 용융 Si 침윤 방법으로 제조된 반응소결 탄화규소 다공체에서는 SiC 입자 사이에 SiC/Si로 이루어진 기지상이 형성되어 있기 때문에 파괴 강도 및 열충격 특성이 점토 결합 탄화규소 다공체 보다 우수하였다. 반응소결 탄화규소 다공체의 기공율 및 기공 크기는 잔류 Si의 양 및 성형체에 사용한 SiC 입자 크기에 따라 다르게 나타났다.