Mechanical- and physical-property changes of neutron-irradiated chemical-vapor-deposited silicon carbide

Indentation and density measurements have revealed important changes in the mechanical and physical properties of silicon carbide (SiC) due to neutron irradiation. Specifically, the changes in the elastic modulus, hardness, fracture toughness, and density with irradiation have provided an understanding of the expected performance of SiC and SiC composites in nuclear applications. After the accumulated damage has saturated, these mechanical properties were affected primarily by the irradiation temperature. Chemical-vapor-deposited (CVD) SiC was irradiated above the saturation fluence and yielded volumetric swelling of 2.6% and 1.3% for irradiation temperatures of 100°-150°C and 500°-550°C, respectively. At the same respective temperatures, the elastic modulus decreased from an unirradiated value of 503 GPa to approx. 420 and 450 GPa. Conversely, the hardness increased from 36 GPa for the unirradiated CVD SiC to 38 and 40 GPa for the samples irradiated at 100°-150°C and 500°-550°C, respectively. Interestingly, these two independent properties approached almost-constant levels after exposure to a fluence of 0.5 × 10²⁵ n/m², E > 0.1 MeV. Indentation fracture toughness measurements, which were within the range of values in the literature for conventional fracture toughness procedures for SiC, increased from approx. 2.8 MPa·m ^1/2 for the unirradiated samples to 3.7 and 4.2 MPa·m ^1/2 for the samples that were irradiated at 100°-150°C and 500°-550°C, respectively.