In-situ TEM investigations of dislocation loop annealing kinetics in neutron-irradiated 9%Cr RAFM steel

Post-irradiation annealing (PIA) is beneficial in recovering degraded mechanical properties of irradiated materials due to the evolution of irradiation-induced defects. To understand the underlying responsible mechanisms, isothermal PIA experiments were carried out in this work on a neutron-irradiated 9%Cr reduced-activation ferritic-martensitic steel (EUROFER97) using in-situ transmission electron microscopy. In general, PIA at 600 °C led to an appreciable reduction of the dislocation loop density and increment in the loops mean size. This is found mainly associated with the vacancy-mediated loops shrinkage phenomenon. The driving force for this process is loop's curvature force. Nevertheless, the spontaneous evolution of the loops neighboring microstructure substantially alters their annealing kinetics. Therefore, in this study, loops’ annealing kinetics in EUROFER97 is discussed in terms of various scenarios originating in terms of the presence or absence of the local external sources and sinks. In addition, influence of loops type, alloying elements segregation and free surface are also discussed.