Irradiation damage and hardening in pure Zr and Zr-Nb alloys at 573 K from self-ion irradiation

Abstract

Zr-ion irradiation was performed on pure Zr, Zr-2.5Nb, and Zr-5Nb to a dose of 0.5 or 5 dpa at 573 K. The irradiation induced defects, alloying element redistribution, precipitation, and hardening were analyzed by Transmission Electron Microscopy and nanoindentation. In all the samples, irradiation induced the formation of ⟨a⟩ and ⟨c⟩ component loops in the α phase, and ½〈111〉 and 〈100〉 loops in the β phase. The presence of Nb in the α phase enhanced the formation of ⟨a⟩ component loops. As irradiation dose increased from 0.5 to 5 dpa, there is an apparent increase of the ⟨c⟩ component loop fraction with a corresponding decrease in ⟨a⟩ loops in the α phase. The Nb and Fe were observed to be redistributed from β to α phase. Irradiation significantly refined the size and increased the density of ω precipitates compared to thermal treatment alone. Irradiation caused noticeable hardening; compared with the defects in the α and β phase, the ω precipitates had a much more significant effect on hardening. This study suggests that decreasing the fraction of β phase in Zr-Nb alloys reduces the irradiation hardening.