Neutron Irradiation Effects of Oxide Sintering Additives for SiCf/SiC Composites

Silicon carbide fiber-reinforced silicon carbide matrix composites (SiCf/SiC) are considered as one of the candidates for blanket materials in future fusion reactors. Generally, densification of SiC needs sintering additives due to the covalent nature of Si-C bonding, and sintering additives such as Al2O3, Y2O3, and YAG are frequently added to SiC. However, neutron irradiation effects of sintering additives on SiCf/SiC composite properties are still unclear. In this study, oxide sintering additives such as Al2O3, Y2O3, YAG and an Al2O3-Y2O3-CaO mixture (abbreviated as AYC), were irradiated up to the neutron fluency of 2.0∼2.5×1024 n/m2 (E>0.1MeV) at 333∼363K in the BR2 reactor. Macroscopic swelling and change in lattice parameter due to the irradiation were measured. Length changes of the Y2O3 and Al2O3 specimens were ∼0.2% but that of YAG specimen was very large, 3.86%. Macroscopic length swelling of the AYC was at the midpoint of both figures. Crystallinity of the YAG specimen was greatly reduced and many micro cracks were observed after the irradiation. Lattice parameter change of the YAG specimen was large (1.41%), however it was still smaller than the macroscopic length change. The relative correlation of macroscopic length increase and those of lattice parameters of the Y2O3 and Al2O3 specimens was high.