EFFECTS OF NEUTRON-IRRADIATION AND SUBSEQUENT ANNEALING ON STRENGTH AND TOUGHNESS OF SIC CERAMICS

Three kinds of SiC fabricated with different sintering aids were neutron-irradiated to fluences from 8.0 × 1023 to 6.0 × 1024 n/m2 (E > 1 MeV) in the Japan Materials Testing Reactor (JMTR). Neutron irradiation increased bending strength of hot-pressed SiC containing about 1% BeO by 10%, while it decreased that of reaction-bonded (about 9% free Si) and pressureless-sintered (about 1% B and C) SiC by 30 and 20%, respectively. Correspondingly, fracture toughness of hot-pressed SiC measured by the Vickers indentation method was raised by irradiation. The subsequent annealing led to a decrease in fracture toughness and a macroscopic length with increasing annealing temperature. These results are discussed in terms of localized plastic deformation, through the dislocation channeling around tips of cracks. © 1990.