The evolution of micro defects in He+ irradiated FeCrNi alloy during isochronal annealing

In order to study the microstructural evolution of the He+ irradiated FeCrNi model alloy, 140 keV He+ ions were implanted into the specimen with the fluence of 1 × 1015 ions/cm2 at room temperature. Positron annihilation spectroscopy was used to characterize the evolution of micro defects during isochronal annealing between 423 and 873 K. The decrease of the S parameter between 573 and 623 K has been associated to the annihilation of vacancy clusters, which were not trapped by helium atom. While the decline of the S parameter between 773 and 823 K in the damage region might be caused by the dissociation of HenVm clusters. The dissociated vacancy clusters were unstable and annihilated rapidly, which decreases the concentration of vacancy defects.