Effects of External Stress on Defect Annihilation and Bubble Swelling During Annealing of Neutron‐Irradiated Silicon Carbide

Silicon carbide ceramics fabricated by three different methods were neutron‐irradiated in the Japan Materials Testing Reactor and were subsequently annealed free from stresses or under compressive external stresses. The macroscopic length monotonically decreased with annealing above the irradiation temperature, when annealing was performed below ∼1300°C. This decrease was not affected by the external stresses. However, annealing above ∼1300°C led to an increase in length in B‐containing SiC. The expansion was caused by the formation and growth of He bubbles at grain boundaries. The growth occurred by flow of vacancies into bubbles. The compressive stress retarded the expansion along the loading direction. This retardation was compensated by a length incrase along the lateral direction. The effect of external stresses was discussed by considering differently oriented He bubbles. One bubble was stress favored and the other stress unfavored. The stress determined the diffusional flow of vacancy‐He atom complexes between the favored and unfavored bubbles which were caused by anisotropic expansion under a directional stress.