PNNL

Abstract

Post-irradiation annealing experiments were conducted on neutron-irradiated pure copper (from 0.01 to 0.3 dpa at 100 degrees C) to explore the possibility of mitigating the effects of radiation hardening on the strength and ductility. The post-irradiation annealing (PIA) condition of 300 degrees C for 50 hours yielded mixed results and did not completely remove the effects of irradiation. However, there were changes brought about in the microstructure that led to the removal of the yield point phenomenon and restored some of the unirradiated ductility and work hardening. The true stress-strain curves have been calculated for both the as-irradiated and the PI annealed Cu and compared to that of the unirradiated pure copper. The true stresses at which the as-irradiated samples begin to neck (based on the engineering stress-strain curves) are similar for the 0.1 to 0.3 dpa samples and are similar to that of the unirradiated copper. On the other hand, the as-irradiated 0.01 dpa condition and all of the post-annealed conditions begin necking at lower stresses, but at similar strains. The work hardening rate in the as-irradiated copper (0.1 to 0.3 dpa), when compared on Kocks-Mecking plots, shows that after a few percent strain, the macroscopic work hardening behavior mimics that of the unirradiated pure copper in the latter stages of work hardening. The PI annealing does little to restore the elongation compared to the as-irradiated state, yet lowers the yield strength, removes the yield point phenomenon and causes the material to begin necking at a lower stress. Further work is needed to understand the dislocation interactions (annihilation and storage of dislocations during plastic deformation, sweeping of the defects introduced during irradiation) that produce a situation where the PIA samples neck at similar strains but lower stresses than that of the as-irradiated.