Evaluation of neutron irradiated silicon carbide and silicon carbide composites

The effects of fast neutron irradiation on SiC and SiC composites have been studied. The materials used were chemical vapor deposition (CVD) SiC and SiC/SiC composites reinforced with either Hi-NicalonTM Type-S, Hi-NicalonTM or SylramicTM fibers fabricated by chemical vapor infiltration. A statistically significant population of flexural samples were irradiated up to 4.6 x 1025 n/m2 (E > 0.1 MeV) at 300, 500, and 800 deg. C in the High Flux Isotope Reactor at Oak Ridge National Laboratory. Dimensions and weights of the flexural bars were measured before and after the neutron irradiation. Mechanical properties were evaluated by four point flexural testing. Volume increase was seen for all bend bars following neutron irradiation. The magnitude of swelling depended on irradiation temperature and material, while it was nearly independent of irradiation fluence over the fluence range studied. Flexural strength of CVD SiC increased following irradiation depending on irradiation temperature. Over the temperature range studied, no significant degradation in mechanical properties was seen for composites fabricated with Hi-NicalonTM Type-S, while composites reinforced with Hi-NicalonTM or Sylramic fibers showed significant degradation. The effects of irradiation on the Weibull failure statistics are also presented suggesting a reduction in the Weibull modulus upon irradiation. The cause of this potential reduction is not known