Evaluation of irradiation hardening in proton-irradiated [formula omitted]-zirconium hydride and Zr2.5Nb

Abstract

A sample with a δ-zirconium hydride rim grown on a Zr2.5Nb pressure tube was proton irradiated to different damage levels and its mechanical properties were probed using nanoindentation. Irradiations were also carried out on non-hydrided Zr2.5Nb as a reference. A numerical model proposed by Dao et al. and developed by Wang et al. was used to calculate the yield strength and the work hardening exponent. The samples were subjected to 0.2, 0.4, and 0.8 displacements per atom (dpa), with the irradiation temperature kept below 100 ∘C. To account for the indentation size effect, the Nix-Gao model was used to calculate the true hardness (H0) of both materials. Both hydrided and non-hydrided samples show an increase in the true hardness and in the yield strength due to the irradiation hardening. The true hardness of the δ-zirconium hydride increased from 3 GPa at 0 dpa to 4.31 at 0.8 dpa. Similarly, the H0 of the Zr2.5Nb increased from 2.53 at 0 dpa to 3.03 at 0.8 dpa. Additionally based on the model analysis, the yield strength increased from 731 MPa to 1146 MPa for the δ-zirconium hydride, and 662 MPa to 850 MPa for the Zr2.5Nb, with the latter in good agreement with literature values for Zr2.5Nb. Lastly, evaluation of the work hardening exponent with the different dpa levels suggests the defects density evolves differently with irradiation in the two materials. These novel results demonstrate a clear change in mechanical properties of the δ-zirconium hydride with irradiation.