STRUCTURE AND PROPERTIES OF SYLRAMIC~(?) SILICON CARBIDE FIBER_A POLYCRYSTALLINE, STOICHIOMETRIC beta-SiC COMPOSITION

摘要

SYLRAMIC~(? )silicon carbide fiber is a stoichiometric, submicrometer polycrystalline beta-SiC fiber in tow form, which also contains 3 wt percent crystalline titanium diboride. The approx 0.05 mu m TiB_2 crystallites are found primarily at triple points of the 0.1 to 0.5 mu rn beta-SiC crystallites. The latter contain considerable twinning and stacking faults, leading to an apparent (beta-SiC crystallite size of 40-60 nm by Scherrer X-ray line broadening. The (3-SiC crystallites appear to be free of intergranular phases. Because of its crystalline structure, the 10 mu m diameter fiber exhibits low creep, high modulus and high thermal and oxidative resistance as well as high strength. The presence of Ti does not adversely affect parabolic oxidation kinetics at 1200 deg C in air (k_p=1.6 X l0~(-18)m~2/s) since a boron-sintered, alpha-SiC monolithic material shows similar oxidation kinetics. Properties of this fiber are compared to HI-NICALON~(? ), another small diameter, commercially-available, high performance SiC ceramic product. The SYLRAMIC fiber is found to have a higher temperature capability (approx 1400 deg C) than HI-NICALON ceramic fiber (approx 1200 deg C). SYLRAMIC fiber is available on spools in tow form and as a 5 HS woven cloth.