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Detailed Program
Paper Number : ST-P01
Time Frame : 12:00~13:30
Presentation Date : Friday, 28, November
Session Name : Structural Ceramics
Session Chair 1# : -
Session Chair 2# : -
Properties of SiC Precursors for the precursor impregnation and pyrolysis (PIP) process
Prof. Seahoon Lee
Korea Institute of Materials Science
Seven polycarbosilane (PCS)-based precursors provided by American, Chinese and Korean companies were evaluated for the fabrication of SiC/SiC composites by precursor-impregnation and pyrolysis (PIP) process. Tyrano-SA grade 3 woven fabrics with PyC coating were used for the fabrication of the ceramic matrix composites (CMC). The ceramic yields of the American PCS were higher (67 - 80%) than those of the Chinese and Korean ones (50 - 63%). The softening of the solid type precursors mostly occurred at 280-320oC except the American product (175oC). The relative density of the CMC made with the Chinese precursor was the highest among the tested systems after 7 PIP cycles (90%). The CMCs from the American and the Korean precursors showed elegant fracture behavior with relatively low strength (200 - 240 MPa), while those from the Chinese precursor were more brittle and strong (310 MPa). The CMCs made with the Chinese precursor suffered from strong deterioration at 1500oC although the Si/C ratio of the precursor-derived ceramics (PDC, 0.864) was more close to the stoichiometric value than those of the other PDCs (0.475-0.823). Thanks to the fiber pull-out mechanism during fracture, the stress-strain curves displayed a jagged failure behavior. Maximum flexural strength of 305 MPa was obtained from the CMC made with the NaBond precursor, but this CMC showed rather brittle fracture behavior. Several evidences were given to reveal the high temperature strength deterioration of the NaBond-CMC material at 1500oC in Ar atmosphere. For gaining a deeper understanding of the strength degradation of NaBnond-CMC at 1500oC, the high temperature thermal behavior as well as the corresponding phase characterization of NaBond precursor after pyrolysis was further analyzed. Although a major mass loss was completed before 1400oC, a further mass loss in the temperature range of 1400oC to 1500oC was still detected (from 63.6% to 63.0%, as seen in the inset figure). This mass loss may possibly induce voids and cracks, which acted as a negative role as described above. The comparison of crystallization degree for NaBond pyrolyzed at different temperatures indicated that ongoing crystallization after 1400oC occurred and density increase with accompanying the generation of cracks, which would therefore decrease the bending strength.
Acknowledgements :