Effect of differential swelling between fiber and matrix on the strength of irradiated SiC/SiC composites

Mechanical properties of silicon carbide (SiC)-fiber-reinforced SiC matrix (SiC/SiC) composites are sensitive to residual stresses induced during the fabrication process. Differential swelling between individual SiC fibers and the SiC matrix due to irradiation modifies the residual stresses, thereby affecting the strength of the irradiated composites. To understand the effect of irradiation on the strength of SiC/SiC composites, the swelling of the fibers and matrix was evaluated following 5.1 MeV Si²⁺ ion irradiation corresponding to a dose of ∼3 dpa at 873-1273 K. The magnitude of swelling in Tyranno™-SA3 SiC fiber and a chemical-vapor-infiltrated SiC matrix was similar. The magnitude of swelling of the matrix was larger than that of the SA3 fibers by 0.2-0.5% in nano-infiltrated and transient eutectic phase (NITE) SiC/SiC composites at 873-1273 K to 3 dpa. This swelling mismatch can reduce the residual tensile stress in the NITE-SiC matrix and in turn improve the proportional limit stress of NITE SiC/SiC composites after neutron irradiation.