Evolution of structures and internal stress of ZrC-SiC composite under He ion irradiation and post-annealing

Abstract

Composite ceramics show great potential for utilization in nuclear systems. However, the component phases therein may exhibit large variations in structural response to the ion irradiation including degree of lattice expansion, ability to maintain the crystallinity, types and density of as-formed defects, etc. Such discrepancy may result in the evolution of internal stress and consequently more complicated interactions with respect to the irradiation behavior, which remains less understood. In this study, a ZrC–30 vol% SiC composite is chosen to study the irradiation and helium retention behavior under 540 keV He ion irradiation with a fluence of 1 × 1017/cm2 and subsequent annealing at 1000 °C and 1500 °C. Irradiation-induced volume dilation of ZrC lattice and especially from an amorphization process of SiC leads to a maximum compressive stress of ∼66 GPa at a certain irradiation depth, at which horizontal cracks are generated but only in ZrC grains. During high-temperature annealing, migration of defects, diffusion and coalesce of helium species, growth of He bubbles, recovery of crystal lattices and formation of dislocations are found to be closely correlated to the irradiation-induced gradient of helium retention concentration, lattice damage and internal stress along the irradiation depth along with the recrystallization process of amorphous SiC. The as-observed irradiation behavior and structural evolution during annealing are discussed by theoretical consideration of internal stress in the composite using the COMSOL Multiphysics package.