IN-SITU OBSERVATION OF MICROSTRUCTURAL DEVELOPMENT IN FE-CR-NI ALLOYS UNDER DUAL-BEAM IRRADIATION

To investigate the effect of gaseous elements on point defect cluster formation, such as dislocation loops and cavities, in-situ observation of dual-beam irradiation has been carried out for Ni and commercial stainless steels by using 1300 kV HVEM and 300 kV ion-accelerator facility. During dual-beam irradiation to Ni, small cavities nucleated at only compression side of faulted interstitial loops. From the loop growth experiment in both of Ni and stainless steels, it was confirmed that injected He can increase the migration energy of vacancies, which means He has a strong binding energy to vacancies. Therefore, He atoms and vacancies can move to the compression side of dislocations. In commercial 316 steels the cavity nucleation was strongly enhanced by the dual-beam irradiation, and the bi-modal distribution in cavity size was developed at higher He concentration. From the dual-beam irradiation with different He injection rate, it was clarified that the cavity formation with small size is needed to accumulate some amount of He in the matrix. These suggest that injected He atoms can be stored in the internal sinks.