On the shrinkage of neutron irradiation-induced cavities in Eurofer97 steel upon heating

By employing in situ transmission electron microscopy (TEM) observation and cluster dynamics (CD) simulations, we studied the annealing behaviours of neutron irradiation-induced cavities in reduced activation ferritic/martensitic (RAFM) steel Eurofer97 subjected to heating up to 550 degrees C. Experimental results showed that the cavities behaved differently from the general coarsening behaviours of cavities formed by ion implantations. Rapid shrinkage of some cavities was observed when heating temperatures exceeded 500 degrees C. Three types of cavity annealing behaviours were identified: (i) cavity remained stable; (ii) cavity shrank to a smaller size and then kept stable; (iii) cavity shrank and eventually disappeared. The CD simulations, which were based on the rate theory, well reproduced these experimental observations. It was revealed that the shrinkage course can be terminated by the dramatic rise of helium density (helium/vacancy ratio) inside the shrinking cavity. Cavity stopping shrinkage and being stable at high temperatures, without being annealed out, potentially suggests the modification in cavity coarsening kinetics driven by the conventional Ostwald ripening mechanism.