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- The effect of helium (He), silver (Ag) and strontium (Sr) ions implantation and annealing on the surface and structural properties of SiC as well as the migration of Ag and Sr was investigated in this study. Ag and Sr were sequentially implanted at 360 keV and 280 keV, respectively, each to a fluence of 2 × 1016 cm−2 at 600 °C. Some dual implanted (Ag + Sr-SiC) samples were additionally implanted with He of 17 keV to a 1 × 1017 cm−2 at 350 °C, forming triple-implanted samples (Ag + Sr + He-SiC). Both dual and triple implanted samples underwent isochronal annealing at 1100, 1200, and 1300 °C for 5 h. Ag, Sr and He implantation introduced defects in both dual and triple implanted samples. However, triple-implanted samples developed surface blisters and holes due to the migration of He bubbles. At 1100 °C, partial recovery of structural damage was observed in both dual- and triple-implanted samples, but graphite formed in the latter, and holes persisted. At higher temperatures (i.e., 1200 and 1300 °C), dual-implanted samples showed significant structural recovery, whereas the graphite in triple-implanted samples impeded the healing of defects. Depth profiling revealed minimal changes in Ag and Sr distributions and concentrations in dual-implanted samples post-annealing up to 1300 °C. However, triple-implanted samples lost ∼20 % of Ag and Sr at 1100 °C due to sublimation via holes. At 1200 and 1300 °C, no further losses occurred, but Ag and Sr migrated toward the surface. These findings suggest that He implantation promotes the formation of holes in SiC, facilitating the loss of Ag and Sr at 1100 °C. Additionally, He-induced defects enhance the migration of Ag and Sr toward the surface during annealing at 1200 and 1300 °C.
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- 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.
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