Evaluation of fiber/matrix interfacial strength of neutron irradiated SiC/SiC composites using hysteresis loop analysis of tensile test

Advanced SiC/SiC composites composed of highly-crystalline and near-stoichiometric SiC fibers, SiC matrix by CVI method, and PyC interphase were irradiated up to 1.0 × 10 ²⁵ n/m ² (E > 0.1 MeV, ∼1 dpa) at 1273K. Unload/reload cyclic tensile test and hysteresis loop analysis were carried out in order to identify neutron irradiation effects on interfacial properties of advanced SiC/SiC. The composites exhibited good irradiation resistance in ultimate tensile strength (∼10% increase), but there were slight reduction of elastic modulus and proportional limit stress (PLS) (∼10%). Wider hysteresis loops and lower gradient of the curves beyond PLS from the strain-stress curves, and longer pullouts of fiber from the SEM observation were observed, which imply weaker F/M interactions after neutron irradiation. From the hysteresis loop analysis, degradation of interfacial sliding stress and negative increment of misfit stress after neutron irradiation were obtained.