• Journal of Ocean Engineering and Technology
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• v.23 no.5
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• pp.32-38
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• 2009

Silicon nitride samples with aligned whisker seeds were prepared with different amounts of yttria and alumina as the sintering additives. Their sintering behaviors and the microstructural developments between $1850^{\circ}C$ and $2050^{\circ}C$ were examined. The sample with larger amount of the sintering additives showed faster densification and grain growth. Even though addition of the aligned whisker seeds slightly retarded densification of silicon nitride, it improved the flexural strength and the fracture toughness. Both the flexural strength and the fracture toughness of silicon nitride with the aligned whisker seeds were increased as the amount of the sintering additives was increased.

• Journal of the Korean Ceramic Society
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• v.39 no.8
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• pp.715-720
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• 2002

Silicon nitride samples with aligned whisker seeds were prepared with different amounts of yttria and alumina as the sintering additives. Their sintering behaviors and the microstructural developments between 2123K and 2323K were examined. The sample with larger amount of the sintering additives showed faster densification and grain growth. Even though addition of the aligned whisker seeds slightly retarded densification of silicon nitride, it improved the flexural strength and the fracture toughness. Both the flexural strength and the fracture toughness of silicon nitride with the aligned whisker seeds were increased as the amount of the sintering additives was increased.

• Journal of Ocean Engineering and Technology
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• v.27 no.2
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• pp.8-12
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• 2013

Four kinds of silicon nitride composites with tri-laminate structure were prepared by stacking tapes with aligned ${\beta}-Si_3N_4$ whisker seeds. The composites were fabricated using a modified tape casting method for enhanced alignment of the whisker seeds. The relative densities of all four samples reached 99% at room temperature. The three-point flexural strengths of the samples according to the stacking sequences were measured at both room temperature and 1723 K. The high temperature strength of sample WWW was $457{\pm}14$ MPa. The fracture of sample WWW occurred mainly along the grain boundary. The room temperature strengths of samples OOO, OWO, WOW, and WWW were $430{\pm}32$ MPa, $470{\pm}19$ MPa, $700{\pm}14$MPa, and $940{\pm}14$ MPa, respectively.

• Proceedings of the Korean Ceranic Society Conference
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• 2000.04a
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• pp.100.1-100.1
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• 2000

• Proceedings of the Korean Ceranic Society Conference
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• 2003.10a
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• pp.62.1-62
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• 2003

• Proceedings of the Korean Ceranic Society Conference
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• 2002.10a
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• pp.177.2-177
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• 2002

• Journal of the Korean Ceramic Society
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• v.40 no.10
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• pp.931-935
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• 2003

A complex-shaped part was successfully fabricated by Laminate Object Manufacturing (LOM) technique using silicon nitride tape with aligned silicon nitride whisker seeds. The ceramic tape was cut using a commercial cutting plotter according to the cross section drafts generated by slicing a 3-D model, and then the tapes were stacked sequentially. In order to improve adhesion between the tapes, stacking was performed under vacuum. After binder burnout, the part was encapsulated using latex emulsion and was cold isostaically pressed under 250 ㎫. It was sintered to 98.5% TD at 2148 K for 4 h under 2 ㎫ nitrogen pressure.

• Journal of the Korean Ceramic Society
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• v.43 no.3 s.286
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• pp.152-155
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• 2006

Silicon carbide ceramics seeded with 10-30 wt% SiC whiskers are fabricated by hot pressing and annealing. A quantitative texture analysis including calculation of the Orientation Distribution Function (ODF) is used for obtaining the degrees of preferred orientation of the fabricated samples. The microstructure and crystallographic texture are discussed with respect to the effect of ${\beta}-SiC$ whisker seeds on the resulting fracture toughness values. The SEM microstructures and the texture data reveal a correlation between texture and fracture toughness anisotropy.

• The Korean Journal of Ceramics
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• v.5 no.2
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• pp.119-124
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• 1999

Silicon nitride ceramics with highly oriented microstructure were prepared by tape casting a slurry containing 5 wt% of the silicon nitride whiskers. The whiskers were aligned in the casting direction and worked as seeds for the grain growth. The anisotropy was observed from the sintering shrinkage, Vickers indentation crack lengths, and XRD patterns. The cracks were much longer on the surface normal to the aligned grains than on the tape casting surface where the lateral cracks were also observed. The effect of sintering additives and the annealing treatment on the indentation crack length was examined. The sample with higher silica content had longer cracks than the one with lower silica content. The crack length anisotropy increased after annealing at 2123K.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.3
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• pp.473-480
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• 1997

$\beta-SiC$powder with or without the addition of 1-3 wt% of $\beta-SiC$ whiskers (seeds) was hot-pressed at $1850^{\circ}C$ for 1 h using $Al_2O_3$ and $Y_2O_3$ as sintering aids. The hot-pressed materials were subsequently annealed at $1950^{\circ}C$ to enhance grain growth. The introduction of $\beta-SiC$ whiskers into $\beta-SiC$ does not affect the microstructure as well as mechanical properties significantly because the whiskers are not viable in the presence of liquid phase during hot-pressing. The strengths and fracture toughnesses of the hot-pressed and subsequently 5 h-annealed materials with 1 wt% $\beta-SiC$ whiskers and without $\beta-SiC$ whiskers were 465 MPa and 5.8 MPaㆍ$m^{1/2}$, and 451 MPa and 5.5 MPaㆍ$m^{1/2}$, respectively.