Dislocation and void segregation in copper during neutron irradiation

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Abstract
High-purity (99·999%) and fully annealed copper specimens have been irradiated in the DR-3 reactor at Ris⊘ to doses of 1 × 1022 and 5 × 1022 neutrons (fast)m−2 (2 × 10−3 dpa and 1 × 10−2 dpa, respectively); the irradiation experiments were carried out at 250°C. The irradiated specimens were examined by transmission electron microscopy. At both doses, the irradiation-induced structure was found to be highly segregated; the dislocation loops and segments were present in the form of irregular walls and the voids were distributed between these walls. The dislocation walls were practically free of voids and generally had a void-denuded zone along them. The density of dislocations (loops and segments) was very low in the region containing voids (i.e. between the dislocation walls). Even with this low dislocation density, the void swelling rate was very high (∼2·5% per dpa). The implications of the segregated distribution of sinks for void formation and growth are briefly discussed. It is pointed out that the present observations cannot be understood in terms of the conventional bias-driven swelling mechanism.