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

In order to characterize the microstructural evolution of the iron sol id solution under irradiation, two pressure vessel steels irradiated i n service conditions and, for comparison, low copper model alloys irra diated with neutrons and electrons have been studied. The characteriza tion has been carried out mainly thanks to small angle neutron scatter ing and atom probe experiments. Both techniques lead to the conclusion that clusters develop with irradiations. In Fe-Cu model alloys, coppe r clusters are formed. These clusters do not appear to be pure copper. Nevertheless, their actual shape and composition are still a matter o f investigation. In the low copper industrial steels, the feature is m ore complex. Solute atoms like Ni, Mn and Si, sometimes associated wit h Cu, segregate as clusters. These Si, Ni, Mn associations, may facili tate the copper segregation although the initial iron matrix contains a low copper concentration.