Study of the Ion-Irradiation Behavior of Advanced SiC Fibers by Raman Spectroscopy and Transmission Electron Microscopy

6H-SiC single crystals and two types of SiC fibers, Hi-Nicalon type S and Tyranno SA3, have been irradiated with 4-MeV Au3+ up to 2x10(15)cm(-2) (4dpa) at room temperature, 100 degrees C and 200 degrees C. These fibers are composed of highly faulted 3C-SiC grains and free intergranular C. Stacking fault linear density and grain size estimations yield, respectively, 0.29nm(-1) and 26-36nm for the Hi-Nicalon type S fibers and 0.18nm(-1) and 141-210nm for the Tyranno SA3 fibers. Both transmission electron microscopy and surface micro-Raman spectroscopy reveal the complete amorphization of all the samples when irradiated at room temperature and 100 degrees C and a remaining crystallinity when irradiated at 200 degrees C. The latter observations reveal a multi-band irradiated layer consisting in a partially amorphized band near the surface and an in-depth amorphous band. Also, nanocrystalline SiC grains with high stacking fault densities can be found embedded in amorphous SiC at the maximum damage zone of the Hi-Nicalon type S fibers irradiated at 200 degrees C.