Electron-beam induced dissociation of dislocation loops in magnesia–alumina ceramics

Abstract

Kinetics of interstitial-type dislocation loops in α-Al 2O 3 and MgO·Al 2O 3, which were induced by 6 keV Ar + ions at 300 K, has been investigated under electron irradiation at 300–870 K by transmission electron microscopy. Dislocation loops disappeared during electron irradiation at energies of 100, 150 and 200 keV, where displacement damage is hardly induced in α-Al 2O 3 and MgO·Al 2O 3 with those electron energies. The disappearing rate of dislocation loops increases with decreasing electron energy and with decreasing irradiation temperature. Further, a portion of dislocation loops in α-Al 2O 3 has been found to grow under the subthreshold-energy electron irradiation, and the average size of the surviving dislocation loops decreases with irradiation at 300 K but increases at 370, 420 and 570 K. We have reached a conclusion that dislocation loops in α-Al 2O 3 and MgO·Al 2O 3 dissociate into isolated interstitials through ionizing radiation. The generated interstitial has been found to mostly recombine with radiation-induced vacancies at lower irradiation temperature (300 K) but to be absorbed to the surviving dislocation loops at higher temperature (370–570 K). The disappearing rate of loops is discussed in terms of a balance between the dissociation process by ionizing radiation and the diffusion process of the generated interstitials.