Cavity Formation Study in SiC/SiC Composites Irradiated with Multiple-ion Beam at Elevated Temperatures

J.-J. Kai (Sp), H.T. Keng, Z.H. Zeng, F.R. Chen, National Tsing Hua University, Hsinchu (Taiwan) 
 
Silicon carbide fiber-reinforced silicon carbide composites are the major canditates as the advanced structural materials for the fusion power reactor due to their low induced radioactivity, high specific strength at elevated temperatures and reasonable mechanical toughness. One of the main concerns to use these materials in the fusion reactor environment is the radiation stability of the microstructure in advanced SiC/SiC composites which in turn will affect their high temperature mechanical strength and toughness. In this study, we irradiated two types SiC/SiC/ composites made with advanced SiC fibers: Tyranno-SA and Hi-Nicalon Type-S, respectively, by using dual-ion beam (6 MeV Si-ion and 1.13 MeV He-ion) at a dose rate of 4x10-6 dpa/s and 150 appm He/dpa. The experiments were performed at 600 to 1000oC and under high vacuum (1x10-5 Pa). The microstructural analysis is done by using HRTEM with XEDS and ELLS.

In the experiments for 10 dpa at 600oC, there was no cavity or bubble found in both materials, neither in the matrix nor in the fibers. For the case of 100 dpa at 800oC, we found bubbles in the SiC matrix of both composites, and also in the fiber of Tyranno-SA/SiC composite, but not in the fiber of Hi-Nicalon Type-S/SiC composite. It is believed that due to the grain size of Hi-Nicalon Type-S fiber is much smaller (few nm) than that of Tyranno-SA fiber. In the 100 dpa a 1000oC experiment, we found bubbles in both matrix and fiber in the two types of composites and in some areas we also found large cavities co-existed with smaller bubbles (bi-model). The bubbles are mostly located along grain boundaries and unevenly distributed.

We have completed the triple-ion beam irradiation facility recentle and the triple-ion irradiation experiments are underway and we will have more results at the symposium.