Longitudinal dilation behavior of ion-irradiated Tyranno™-SA SiC fibers at elevated-temperatures

Advanced SiC fibers with low oxygen content, nearly-stoichiometric composition and high crystallinity, are envisaged as reinforcement in SiCf/SiC composites for next generation nuclear reactors. In this study, we performed ion-irradiation experiments at GANIL (Caen, France) on the advanced fiber, Tyranno™-SA grade-3, with 95 MeV Xe ions at room-temperature. To prevent the damage gradient in fiber, the fibers were irradiated on two sides with two fluence levels (2.46 × 1014 ions/cm2 for the first side +2.52 × 1014 ions/cm2 for the opposite side and 9.89 × 1014 ions/cm2 for the first side +1.02 × 1015 ions/cm2 for the opposite side). According to TRIM-code calculation, the ion irradiation damages in the fibers affected the entire volume of the fibers, with estimations of 0.05 and 0.2 dpa. The structural evolution under the ion irradiation was studied by transmission electron microscopy (TEM) and Raman spectroscopy. The results did not reveal a complete amorphization. The gradual transition in physical properties, such as deformation and coefficient of thermal expansion (CTE) and electrical conductivity, during heating and cooling up to 1800 °C were monitored by longitudinal dilation test of a single fiber. These physical property changes (or recoveries) of the ion-irradiated fibers were categorized in the following temperature regions (1st stage: <200 °C (no recovering), 2nd stage: 200–1400 °C (recovering) and 3rd stage: >1400 °C (almost completely recovered)). In particular, a linear recovery in the medium range of 800–1400 °C during heating had very limited property changes.