A micro-Raman investigation of the SCS-6 SiC fiber

The microstructure of the SCS-6 SiC fiber, a fiber widely studied as a reinforcement in metal matrix and ceramic matrix composites, was characterized by spatially resolved Raman spectroscopy. Cross sections of as-received fibers and fibers annealed at 1640 °C were characterized in the backscattering geometry with the 514.5 nm line of an Ar+ laser. Characteristic graphitic peaks were observed in the several regions of the SCS-6 fiber, including the inner SiC region. The SiC transverse optical phonon mode was observed in the outer SiC region as a double peak, suggesting the presence of multiple polytypes in this region. Spectra of the outer SiC layer of this fiber in the zircon-matrix composite also showed a distinct Si peak. Silicon in this fiber is believed to be responsible for the observed anomalous thermal expansion behavior of the fiber between 1300 and 1400 °C.