Irradiation hardening of FeCrAl ODS alloys with Zr/Hf addition after high-energy self-ions irradiation

FeCrAl ODS steel is the promising candidate cladding material for the accident tolerant fuel (ATF) of the light water reactors (LWR), due to the formation of Al2O3 in alloys which could suppress the oxidation reaction with hot steam. In the present work, change in microstructures and the corresponding irradiation hardening of two kinds of FeCrAl ODS alloys (15.5Cr-4Al), with 0.6 wt% Zr (denoted as P1) or 0.8 wt% Hf addition (denoted as P2), were investigated. Electron backscattered diffraction (EBSD) and transmitted electron microscopy (TEM) were used to characterize grains and dispersion morphology of oxides, respectively. Compared to P1, P2 has finer and denser oxides. 56Fe17+ ions with kinetic energy of 352.8 MeV were used to produce a quasi-uniformly distributed damage region from the near-surface to a depth of 24 μm in the specimens by using an energy degrader. A damage level of 0.8 dpa (displacement per atom) was attained in the specimens of both alloys simultaneously at 200℃. The Vickers hardness test shows that both specimens exhibited an apparent irradiation hardening. The extent of hardening of P2 (6 %) is significantly lower than P1 (12 %). TEM results show that irradiation-induced dislocation loops occur in both specimens but with a relatively smaller average size in P2. The results demonstrate that compared to the 0.6 wt% Zr addition, the 0.8 wt% Hf addition improves more significantly the hardening resistance, which was discussed in terms of the calculated sink strength originating from the oxides/matrix interface.