Abstract
Pure and O-doped Nb have been irradiated to 50 atom displacements per atom with 3.0-MeV 58Ni + ions at successive temperatures of 1050, 1230, 1050 or 770 K. The effects of these temperatures changes on the void diameter and void number density in the irradiated Nb have been examined by transmission electron microscopy. The void volume resulting from these successive temperature changes is significantly lower than the combined void volume expected from separate isothermal irradiations. The lower void volume is due to irradiation- and thermal-induced shrinkage of voids with the more pronounced effect occurring in O-doped Nb. Shrinkage effects occur with a change of irradiation temperature from 1230 to 1050 or 770 K as well as from 1050 to 1230 K. In addition to these void-shrinkage effects, anomalous growth of some voids was observed for a change of irradiation temperature from 1230 to 1050 or 770 K. Mechanisms based on the segregation of 0 impurity to the vicinity of void surfaces are presented to explain these void shrinkage and growth effects.
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