Carbon fiber/ceramic matrix composites: processing, oxidation and mechanical properties
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Ceramic matrix composites (CMC) have been considered in the last two decades to be alternative materials for highly demanding thermo-structural applications. Pre-ceramic polymers offer significant advantages for manufacturing these composites by the polymer impregnation method. In the present work, carbon fiber/silicon oxycarbide (C/SiCxOy) composites were obtained by controlled pyrolysis of carbon fiber/bridge polysilsesquioxane composites (COMPOSITE 1) followed by infiltration/pyrolysis cycles with a polycyclic silicone network. The polysilsesquioxane showed high wettability and adhesion on the carbon fiber surface. An improvement of the thermo-oxidation resistance and a reduction of the porosity as a function of the number of polycyclic silicone infiltration cycles were observed. An extra improvement in the thermo-oxidation protection was found when the C/SiCxOy composite was coated with a poly(phenylsilsesquioxane) layer (COMPOSITE 2). Shear properties for the composites showed a dependence on the nature of the matrix. The average in-plane shear strength and the shear modulus were 44.2 ± 1.9 MPa and 2.2 ± 0.5 GPa for the polymeric matrix composite (COMPOSITE 1), respectively. For the ceramic matrix composite (COMPOSITE 2) the values were 14.2 ± 4.1 MPa and 15.0 ± 2.0 GPa, respectively. The properties of the latter composite were also governed by the microstructure of the ceramic matrix.
KeywordsCarbon Fiber Pyrolysis Temperature Ceramic Matrix Composite Polymeric Matrix Composite Ceramic Phase
We gratefully acknowledge financial support from CNPq and FAPESP (Process 00/06882-5).
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