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The literature on radiation-induced swelling and hardening in copper and its alloys is reviewed. Void formation does not occur during irradiation of copper unless suitable impurity atoms such as oxygen or helium are present. Void formation occurs for neutron irradiation temperatures of 180 to 550°C, with peak swelling occurring at ˜320°C for irradiation at a damage rate of 2 × 10-7 dpa/s. The posttransient swelling rate has been measured to be ˜0.5%/dpa at temperatures near 400°C. Dispersion-strengthened copper has been found to be very resistant to void swelling due to the high sink density associated with the dispersion-stabilized dislocation structure.
Irradiation of copper at temperatures below 400°C generally causes an increase in strength due to the formation of defect clusters which inhibit dislocation motion. The radiation hardening can be adequately described by Seeger's dispersed barrier model, with a barrier strength for small defect clusters of α ≈0.2. The radiation hardening apparently saturates for fluences greater than ˜ 1024 n/m2 (˜0.1 dpa) during irradiation at room temperature due to a saturation of the defect cluster density. Grain boundaries can modify the hardening behavior by blocking the transmission of dislocation slip bands, leading to a radiation-modified Hall-Petch relation between yield strength and grain size. Radiation-enhanced recrystallization can lead to softening of cold-worked copper alloys at temperatures above 300°C.
neutron, ion, irradiation, microstructure, tensile properties, void formation, radiation hardening, copper, copper alloys
Research staff member, Oak Ridge National Laboratory, Oak Ridge, TN