The effects of co-implanting strontium (Sr) and helium (He) into SiC at temperatures exceeding the critical amorphization temperature and annealing above 1000 °C

Abstract

The structural evolution and migration behaviour of strontium (Sr) in polycrystalline silicon carbide (SiC) co-implanted with helium (He) exceeding 300 °C were investigated at temperatures above 1000 °C. Sr ions were implanted into SiC at 600 °C (denoted as Sr-SiC-600) and co-implanted with He ions at 350 °C (denoted as Sr + He-SiC-600). Both samples were subsequently isochronally annealed at 1100 °C, 1200 °C, and 1300 °C for 5 h. Both as-implanted and annealed were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Rutherford backscattering spectrometry (RBS). Implantation at 600 °C resulted in a defective layer embedded in the crystalline SiC. Co-implantation led to the formation of He platelets in the defective layer, as well as blisters and large voids on the surface accompanied by slight migration of Sr. Annealing the Sr-SiC-600 samples up to 1300 °C resulted in formation of Sr precipitates accompanied by neither migration nor loss. Contrary annealing Sr + He-SiC-600 samples up to 1300 °C resulted in the formation of Sr precipitates accompanied by some loss of Sr. These results indicate trapping of Sr in both samples. This trapping was influenced by thermally activated cavities in the Sr-SiC-600 samples and by He induced cavities in the Sr + He-SiC-600 samples. These findings have significant implications for the design and performance of TRISO fuel particles.