Helium implantation effects on mechanical properties of SiCf/SiC composites

Helium effects on mechanical properties of SiC/SiC composites were studied to apply the composites on structural materials of a fusion reactor. Two types of 2D-SiC/SiC composites were examined in this work. Helium was implanted using 36 MeV alpha particles with an energy degrader system to obtain a uniform helium depth distribution in the specimen. The implantation temperature was 400-800 degrees C and the helium concentration after implantation was about 150-170 appm. Three-point bending test was carried out at room temperature. Results of bending test showed that a small decrease of bend strength was observed in the composite which had the higher bend strength before implantation. Helium implantation effect was not clearly observed in the lower bend strength composite. SEM observation results on the fracture surface gave no evidence for fiber coating failure. The decrease of bend strength after helium implantation may be attributed to a degradation of mechanical properties of the fibers by implanted helium. (C) 1998 Elsevier Science B.V.