STRENGTH-DEGRADING MECHANISMS FOR CHEMICALLY-VAPOR-DEPOSITED SCS-6 SILICON-CARBIDE FIBERS IN AN ARGON ENVIRONMENT

The room-temperature tensile strengths of chemically-vapor-deposited S CS-6 silicon carbide fibers were measured after 1 to 400 h heat treatm ents in 0.1 MPa of argon at temperatures up to 2100 degrees C. The fib ers heat-treated for 1 h above 1400 degrees C and those heat-treated f or 400 h above 1300 degrees C showed strength degradation. Scanning an d transmission electron microscopic examination of the degraded fibers showed formation of a recrystallization region within the outer zone of the SiC sheath and the growth of SiC particles in the carbon-rich s urface coating. The activation energy for the growth of the recrystall ization region was similar to 370 kJ/mol. The tensile strength of the fibers was found to vary as an inverse function of the recrystallized zone thickness.