DEFECT FORMATION IN ION-IRRADIATED AL2O3 AND MGAL2O4 - EFFECTS OF GRAIN-BOUNDARIES AND FUSION TRANSMUTATION PRODUCTS

Polycrystalline alumina (Al2O3) and spinel (MgAl2O4) were preimplanted with H, He and C, and irradiated with Ar+ ions at temperatures of 260 to 810-degrees-C in order to examine the effects of displacement damage and transmutation products on cavity and dislocation loop formation. In alumina, cavities were formed in all the Ar+ irradiated specimens for both the unimplanted and preimplanted H, He and C cases. Larger cavities occur preferentially near grain boundaries after high dose irradiation at elevated temperatures. This preference depends on grain orientation, and appears to be related to the anisotropy of the hexagonal crystal structure. In contrast, cavity formation in spinel was only observed in preimplanted specimens irradiated with Ar+ ions at relatively high temperatures or high doses. Wide defect-free regions adjacent to grain boundaries were observed in spinel for certain irradiation conditions.