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The Effect of Excess Carbon on the Crystallographic, Microstructural, and Mechanical Properties of CVD Silicon Carbide FibersABSTRACTSilicon carbide (SiC) fibers made by chemical vapor deposition (CVD) are of interest for organic, ceramic, and metal matrix composite materials due their high strength, high elastic modulus, and retention of mechanical properties at elevated processing and operating temperatures. The properties of SCS-6™ silicon carbide fibers, which are made by a commercial process and consist largely of stoichiometric SiC, were compared with an experimental carbon rich CVD SiC fiber, to which excess carbon was added during the CVD process. The concentration, homogeneity, and distribution of carbon were measured using energy dispersive x-ray spectroscopy (SEM/EDS). The effect of excess carbon on the tensile strength, elastic modulus, and the crystallographic and microstructural properties of CVD silicon carbide fibers was investigated using tensile testing, x-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM).Key Words CVD SiC fiber Silicon carbide (SiC) fibers SEM/EDS Crystallographic and microstructural properties retention of mechanical properties at elevated processing and operating temperatures Si/C compositional ratio Pyrolytic graphite coating Alkylchlorosilanes Compositionally graded coating Electron energy loss spectroscopy (EELS) analysis ACKNOWLEDGEMENTSThis work was performed under the auspices of the United States Dept. of Energy by the University of California, Lawrence Livermore National Laboratories under contract of No. W-7405-Eng-48. UCRL-ABS-222155.REFERENCES1. R.J. Suplinskas and J.V. Marzik, in Handbook of Reinforcements for Plastics, edited by J.V. Milewski and H.S. Katz (New York: Van Nostrand Reinhold Co., 1987) pp. 340-363. 2. X.J. Ning and P. Pirouz, J. Amer. Ceram. Soc. 76, 2033 (1993). 3. X.J. Ning and P. Pirouz, J. Mater. Res. 6, 2234 (1991). |
