Effect of neutron irradiation on tensile properties of unidirectional silicon carbide composites

Tensile properties of unidirectionally reinforced Hi-Nicalon™ Type S SiC fiber, chemically vapor-infiltrated (CVI) SiC-matrix composites, with either pyrolytic carbon (PyC) or multilayered PyC/SiC interphase, were characterized following neutron irradiations to the maximum fluence of 7.7 × 1025 n/m2 at 380 and 800 °C. The stress–strain behavior of the multilayered interphase composites remained unmodified after irradiation. The PyC interphase composite increased in ultimate tensile stress and strain to failure following neutron irradiation, whereas the proportional limit stress exhibited a slight decrease. Potential mechanisms for these changes include accommodation of misfit stress through irradiation creep, reduced interfacial friction, and differential swelling among individual composite constituents.