Effects of helium irradiation on fine grained β-SiC synthesized by spark plasma sintering

Silicon carbide has a high resistance to irradiation making it a material of choice for use in the nuclear reactors. In this work, we focus on experiments involving implantation of 30 key He-3 ions at room temperature (RT) in sintered beta-SiC. Helium is produced in large quantities in fission and fusion reactors, and its accumulation in materials can lead to the formation of bubbles. The irradiation induces structural modifications within the material that can be coupled with changes in composition, especially at high fluence. Three ion fluencies are used here: 5 x 10(15), 1 x 10(17) and 1 x 10(18) at. cm(-2). Structural damages are studied by electron microscopy and helium profiles are measured by nuclear reaction analysis (NRA). At 1 x 10(18) at. cm(-2), helium bubbles are formed in the implanted zone, which also undergoes strong oxidation. Surface blisters are also observed and helium concentration threshold for bubble formation is estimated to about 4 at. % by correlating the MET observations with the results obtained by ion beam analysis. For the highest fluence, a residual concentration of 3.6 x 10(17) at. cm(-2) was measured just after implantation (instead of 1 x 10(18) at. cm(-2)), which indicates a significant release of helium by the material during the process. The link between the microstructural evolution of the material, its progressive oxidation under beam and the release of helium is discussed. The very likely role played by the porosity on the oxidation of the material under irradiation at RT is underlined. Finally, the results obtained here on silicon carbide are compared with those obtained on another ceramic (TiC) which does not amorphize in similar conditions.