Effect of the addition of Cu on irradiation induced defects and hardening in Zr-Nb alloys

Highlights: • Irradiation defects were characterized in both α and β phases in two Zr-Nb alloys with and without Cu addition. • The alloying element redistribution and second phase precipitation under irradiation were analyzed. • The irradiation hardening was measured by nanoindentation; the relationship between damage and hardening was established. • The contributions of various hardening mechanisms were discussed, and the impact of the presence of Cu demonstrated. - Abstract: The irradiation hardening, growth, and creep of Zr alloys are strongly influenced by the presence of alloying elements. Cu is added to some Zr alloys due to its ability to form second phase particles which can cause strengthening. However, how the addition of Cu affects the microstructure and mechanical properties under irradiation remains unclear. In the current study, two Zr alloys, Zr-2.5Nb and Zr-2.5Nb-0.5Cu were selected and irradiated to 0.5 dpa and 5 dpa at 573 K with 5 MeV self-ions. The evolution of microstructure and hardness were characterized by Transmission Electron Microscopy and nanoindentation. Results show that the existence of Cu in the Zr alloys significantly altered the irradiated microstructure and resultant hardness. The addition of Cu resulted in a slight reduction of the irradiation loop size and density in both α and β phases, and its presence in β-Zr notably delayed the precipitation of ω phase. The redistribution of Fe from β phase to α phase was also slower in Zr-2.5Nb-0.5Cu than in Zr-2.5Nb. Irradiation caused hardening in both alloys, however, the hardening in Zr-2.5Nb-0.5Cu was not as significant as in Zr-2.5Nb due to the delayed ω precipitation.