MICROSTRUCTURAL CHARACTERIZATION OF ATOM CLUSTERS IN IRRADIATED PRESSURE-VESSEL STEELS AND MODEL ALLOYS

In order to characterize the microstructural evolution of the iron solid solution under irradiation, two pressure vessel steels irradiated in service conditions and, for comparison, low copper model alloys irradiated with neutrons and electrons have been studied. The characterization has been carried out mainly thanks to small angle neutron scattering and atom probe experiments. Both techniques lead to the conclusion that clusters develop with irradiations. In Fe-Cu model alloys, copper clusters are formed. These clusters do not appear to be pure copper. Nevertheless, their actual shape and composition are still a matter of investigation. In the low copper industrial steels, the feature is more complex. Solute atoms like Ni, Mn and Si, sometimes associated with Cu, segregate as clusters. These Si, Ni, Mn associations, may facilitate the copper segregation although the initial iron matrix contains a low copper concentration.