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 degrees 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 tiber is believed to be responsible for the observed anomalous thermal expansion behavior of the fiber between 1300 and 1400 degrees C. (C) 1997 American Institute of Physics.