Mechanical properties and thermal stability of carbon fiber cloth reinforced sol-derived mullite composites
For the wide application as thermal protection materials, it is very necessary for mullite ceramics to improve fracture toughness. In this paper, the laminated and stitched carbon fiber cloth preform reinforced mullite (C/mullite) composites were prepared through the route of sol impregnation and heat treatment using the Al2O3—SiO2 sol with a high solid content as raw materials. The C/mullite composites showed a flexural strength of 228.9 MPa that was comparable to that of dense monolithic mullite although the total porosity reached 13.4%. Especially, a fracture toughness of 11.2 MPa·m1/2 that was 4–5 times that of dense monolithic mullite was obtained. Strength deterioration due to the carbothermal reduction between carbon fiber and the residual SiO2 in matrix was found above 1200 °C. A pyrolytic C (PyC) coating was deposited on carbon fibers as interfacial coating. The chemical damage to carbon fibers was obviously alleviated by the sacrifice of PyC coating. Accordingly, the C/PyC/mullite composites kept strength unchanged up to 1500 °C, and showed much higher strength retention ratio than C/mullite composites after annealing at 1600 °C.
Keywordscarbon fiber reinforced mullite composite sol mechanical property thermal stability
This work was supported by the Open Foundation of Science and Technology on Thermostructural Composite Materials Laboratory (Grant No. 614291102010117), the Science Innovation Foundation of Shanghai Academy of Spaceflight Technology (Grant No. SAST2015043), and the National Natural Science Foundation of China (Grant No. 11572277).
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