Experimental simulation of the effect of transmuted helium on the mechanical properties of silicon carbide

Experimental results simulating the effects of transmuted helium on the mechanical properties of SiC are presented. High-purity, stoichiometric chemically vapor-deposited SiC bend bars were cyclotron implanted using 37.7 MeV α particles at 590 °C. A uniform implantation to 100 and 1000 appm was carried out, with a maximum implantation depth of ≃0.46 mm. Samples were then neutron irradiated to a dose of ≃8 dpa at 800 °C, thereby simulating atomic displacements at dose rates and temperatures similar to those of a fusion blanket, while in the presence of high helium levels of (≃125 appm He/dpa). Results on as-implanted SiC yield statistically significant changes in bend strength, indent fracture toughness and density. It is clear that these changes are in part due to the ≃0.1 dpa dose coincident with the helium implantation. Following neutron irradiation a larger change in properties occurs, though the difference between the helium pre-injected SiC, and the irradiated control samples was not statistically significant.