MICROSTRUCTURE OF AL2O3 AND MGAL2O4 IRRADIATED AT LOW-TEMPERATURES

Polycrystalline specimens of aluminum oxide (99.9% purity) and stoichi ometric magnesium aluminate spinel (MgAl2O4) were irradiated with 4 Me V Ar+ ions at 200 and 300 K to doses of 0.1 to 10 displacements per at om (dpa). Volumetric swelling was determined from step-height and latt ice parameter measurements. The step-height swelling increased with de creasing irradiation temperature, with values of similar to 4.5% and s imilar to 0.8% in Al2O3 and MgAl2O4, after similar to 10 and 5 dpa at 200 K, respectively. Faulted interstitial dislocation loops lying on { 111} planes were observed in spinel irradiated at 200 and 300 K, indic ating the presence of significant interstitial mobility at both temper atures. Dislocation loops and network dislocations were observed in al umina following irradiation at 300 K, but resolvable defect clusters d id not form at 200 K. Amorphization was not observed in any of the spe cimens. The critical temperature for amorphization is predicted to be slightly below 200 K for alumina irradiated at similar to 10(-4) dpa/s . Due to the higher defect mobility in spinel compared to alumina, the critical temperature for amorphization in spinel is expected to he si gnificantly lower than that of alumina. (C) 1998 Elsevier Science B.V.