Effect of elevated-temperature neutron irradiation on fracture toughness of ceramics

Single-crystal forms of MgAl2O4, Y3/Al5O12, and Al2O3 were irradiated in the EBR-II fast fission reactor to a fluence of 0.3 x 1026 n/m2 at 10150K, and to -1 to 2 x 1026 n/m2 at 925 and 11000K. Fracture toughness was subsequently measured at room temperature by an indentation technique, and radiation-induced defect aggregates were characterized by transmission electron microscopy. A slight increase in toughness of MgAl2O4 was observed, and attributed to interaction of cracks with strain fields around dislocation loops. No significant change was noted for Y3Al5O12, despite the presence of a high concentration of unresolved defect clusters. Fracture toughness of Al2O3 was markedly increased, with the enhancement apparently attributable in large part to impedance of crack propagation by interaction with the irradiation-induced void lattice