Post-irradiation annealing of neutron-irradiated EUROFER97

Abstract Recent post-irradiation annealing (PIA) investigations on the neutron-irradiated reduced-activation ferritic-martensitic (RAFM) steel EUROFER97 have led to an almost complete recovery of the mechanical properties. To identify responsible microstructural processes, transmission electron microscopy (TEM) investigations on neutron-irradiated (330 °C, 15 dpa) and subsequently annealed (550 °C, 3 h) EUROFER97 samples have been carried out. It is observed that PIA results in a reduction of dislocation loops density with a simultaneous increase in their mean size and formation of dislocation lines/networks. Additionally, a reduction of cavities density with increment in their mean size was observed. The loops’ annealing behaviour appears to be vacancy/interstitial diffusion driven and is situated between the two extremes of isolated loops shrinkage/annihilation and their coarsening. Out of the two phenomena, the one that transpires depend on the presence or absence of the external sources and sinks in the loops neighbourhood. These competing mechanisms define the overall loops size distribution evolution upon PIA. Additionally, vacancy or their cluster migration and coalescence could be the main mechanism for cavities coarsening. The observed microstructural recovery upon PIA explains the recovery of mechanical properties by healing of irradiation induced defects.