CONTINUOUS FABRICATION OF SILICON-CARBIDE FIBER TOWS BY CHEMICAL-VAPOR-DEPOSITION

The feasibility of preparing small-diameter, high-strength, thermally stable silicon carbide fiber toms by the continuous chemical vapor dep osition (CVD) of SIC onto carbon fiber tows was experimentally evaluat ed. Calculations of bending stresses and stresses caused by thermal ex pansion mismatch between the substrate and coating were used to evalua te the influence of coating thickness and substrate fiber diameter and type. Statistically designed and analyzed processing studies quantita tively showed the influence of key CVD process variables (temperature, pressure, and how rates of CH3SiCl3 and H-2) on fiber attributes such as coating thickness and uniformity, surface roughness, percent agglo meration, and strength. Emphasis was given to conceiving and evaluatin g various fiber spreading devices in order to enhance coating uniformi ty and to minimize filament agglomeration within a tow. Uniform coatin gs and fiber tensile strengths as high as 3 GPa were achieved.