• Tribology and Lubricants
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• v.14 no.4
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• pp.114-120
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• 1998

The T-curve, wear and erosion behaviors of two different silicon carbides, i.e., the fine grained SiC and the in situ-toughened SiC(IST-SiC). Both materials exhibited an increasing T-curve behavior, although the T-curve of IST-SiC was steeper than that of fine grained SiC. The fracture toughness of IST-SiC was larger than that of fine grained SiC at long crack regime, whereas an opposite tendency occurred at short crack regime. The rate of material removal during wear and erosion tests was higher in IST-SiC compared to fine grained SiC. The difference between the material removal rates of two materials was discussed in the light of their R-curve behaviors.

• Journal of the Korean Ceramic Society
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• v.44 no.4 s.299
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• pp.189-193
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• 2007

Effect of additive composition on fracture toughness of in situ-toughened $SiC-Si_3N_4$ composites was investigated for five different additive compositions. The highest toughness $(6.4MPa{\cdot}m^{1/2})\;in\;SiC-Si_3N_4$ composites investigated herein was obtained when an Y-Mg-Si-Al-O-N oxynitride glass was used as a sintering additive. The improvement in fracture toughness was produced by enhanced bridging and deflection by $Si_3N_4$ grains.

• Proceedings of the Korean Ceranic Society Conference
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• 2000.04a
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• pp.44.1-44.1
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• 2000

• Journal of the Korean Ceramic Society
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• v.38 no.12
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• pp.1075-1079
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• 2001

The R-curve for in situ-toughened SiC-30 wt% TiC composites was estimated by the indentation-strength method and compared to that of monolithic SiC with toughened microstructure. Both materials exhibited rising R-curve behavior. The SiC-TiC composites, however, displayed better damage tolerance and higher resistance to crack growth. Total volume fractions of SiC key grains, which take part in toughening mechanisms such as crack bridging and crack deflection, were 0.607 for monolithic SiC ceramics and 0.614 for SiC-TiC composites. From the microstructural characterization and the residual stress calculation, it was inferred that this superior performance of SiC-TiC composites can be attributed to stress-induced microcracking at heterophase (SiC/TiC) boundaries and some contribution from carck deflection by TiC grains.

• Proceedings of the Korean Ceranic Society Conference
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• 2000.04a
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• pp.43.2-43.2
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• 2000

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.04a
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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.

• Proceedings of the Korean Ceranic Society Conference
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• 2000.04a
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• pp.45.1-45.1
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• 2000

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.10a
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• pp.386-391
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• 2000

It is known that Si$_3$N$_4$ceramic insert has less hardness than A1$_2$O$_3$ceramic insert. But Si$_3$N$_4$ceramic insert has not only high toughness and strength but also low thermal expansion coefficient, which makes it has longer tool life under thermal stress condition. In this study, commercial Si$_3$N$_4$ ceramic insert and home-made SiC-Si$_3$N$_4$ceramic insert which has different sintering time and chemical composition is tested under various cutting conditions. The experimental result is compared in terms of tool life and cutting force. Generally, As the cutting speed and the feed rate increased, the cutting force and the flank wear increased too. The performance of SiC-Si$_3$N$_4$ceramic insert shows the possibility to be a new ceramic tool.

• The Korean Journal of Ceramics
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• v.2 no.3
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• pp.152-156
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• 1996

Fine (~0.09 $\mu$m) $\beta$-SiC Powders with 3.3wt% of large (~0.44$\mu$m) $\alpha$-SiC of $\beta$-SiC particles (seeds) added were hotpressed at 175$0^{\circ}C$ using $Y_2O_3$, $Al_2O_3$ and CaO as sintering aids and then annealed at 185$0^{\circ}C$ for 4 h to enhance grain growth. The resultant microstructure and polytypes were analyzed by high resolution electron microscopy (HREM).Growth of $\beta$-SiC with high density of microtwins and formation of ${\alpha}/{\beta}$ composite grains consisting of $\alpha$-SiC domain sandwiched between $\beta$-SiC domains were found in both specimens. When large $\alpha$-SiC (mostly 6H) seeds were added, the $\beta$-SiC transformend preferentially to the 6H polytype. In contrast, when large $\beta$-SiC (3C) seeds were added, the fine $\beta$-SiC transformed preferentially to the 4H polytype. Such results suggested that the polytype formation in SiC was influenced by crystalline form of seeds added as well as the chemistry of sintering aids. The ${\alpha}/{\beta}$ interface played and important role in the formation of elongated grains as evidenced by presence of ${\alpha}/{\beta}$ composite grains with high aspect ratio.

• Journal of Korean Ophthalmic Optics Society
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• v.5 no.2
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• pp.207-210
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• 2000

The SiC-TiC composites materials for glasses lens cutting were fabricated by hot-pressing and annealing. The amount of TiC was 0, 10, 20, 30wt% in the mixture of ${\beta}-SiC$. The microstructure of materials for glasses lens cutting was very dependent on the TiC amount. The introduction of larger amount of TiC improved fracture toughness, optical microscope and XRD analysis of the surface of samples were carried out. An in situ-toughened microstructure, consisted of distributed elongated SiC, matrix like TiC grains was developed by using ${\beta}-SiC$. Typical hardness and fracture toughness of materials for spectacle lens cutting were 14.9 GPa and $5.7MPa{\cdot}m^{1/2}$, respectively.