The formation of helium bubbles in 316L stainless steel irradiated with 2.5 MeV He+ ions

Specimens of 316L stainless steel are irradiated with 2.5 MeV He+ ions at temperatures of 400, 500 and 550 degree C, respectively. For each implantation the dose and dose rate are separately 2.5 x 1021 ion/m2 and (3.2-3.8) x 1016 ion/m2s-1. Bubble structures are investigated with cross-sectional transmission electron microscopy (XTEM). The measured apparent activation energies provide evidence that the formation of bubbles is controlled by He diffusion via the self-interstitial/He replacement mechanism. Good agreement is found between these results and other low-dose experimental data, indicating that the underlying mechanism holds constant for different implantation conditions. The pre-implantation cold-working enhances significantly the nucleation of bubbles, and the dislocations are favorable sites for bubble nucleation in the investigated temperature range