Positron Annihilation Doppler Broadening Study of the Helium-implanted (ODS) EUROFER

Positron annihilation Doppler broadening spectroscopy (DBS) measurements were conducted to investigate the evolution of radiation-induced open-volume defects in Eurofer97 steel and its ODS variant. Helium-implanted samples have been investigated by slow positron beam technique. With this approach, we were able to obtain a significant amount of positron lifetime and Doppler broadening data and evaluate them with respect to the dpa and helium concentration effects. The results of the experiment confirm a more pronounced creation of growing helium-vacancy agglomerations for the Eurofer steel, comparing to its ODS variant. The bubble-to-void transformation was indicated by the change in the trend of the S-parameter vs. dpa plot of the Eurofer sample. In the case of the ODS Eurofer, the coalescence of helium bubbles, accompanied by saturation of the S-parameter, was not so evident. The present study provides the first experimental DBS data, showing a retarded formation of cavities, caused by the presence of oxide dispersoids in the ODS steel.