Irradiation-induced shrinkage of highly crystalline SiC fibers

Composites consisting of a SiC matrix prepared by chemical vapor infiltration that was reinforced by Tyranno™ SA^3rd (TSA3) or Hi-Nicalon™ Type S (HNLS) SiC fibers were irradiated with 5.1 MeV Si ions to 100 dpa at 300 °C. It was confirmed that the irradiated microstructure of TSA3 was stable up to 100 dpa. In contrast, the results of surface profilometry and cross-sectional transmission electron microscopy (TEM) showed that HNLS fibers underwent 0.8% shrinkage along the axis and 0.7% radial shrinkage. High-resolution TEM images of the highly damaged regions in the HNLS material revealed the complete loss of carbon ribbons initially distributed at the SiC grain boundaries. Ion-beam-induced diffusion of carbon into the SiC grains was indicated from the observations of the interdiffusion layer formed at the fiber/pyrocarbon interface.