+Insights into the helium bubbles coarsening behavior in the post irradiated annealing 304L stainless steel processed by laser powder bed fusion

350 keV He + ions were injected into laser powder bed fusion (LPBF) processed 304L stainless steel andtraditional rolled 304L stainless steel with a flux of 1 × 10 17 ions/cm 2 at room temperature and followed byannealing at 750 °C for 10 and 100 h and 300h, respectively. The results showed that the material swellingdue to helium bubbles coarsening was almost not observed in both the LPBF and rolled samples after 10 hoursof annealing duration. A rapid coarsening and swelling of bubbles occurred in rolled samples but only moderate bubbles growth in the LPBF sample after annealing for 100 hours. After annealing for 300h, the heliumbubbles of both samples tend to grow steadily. For 10 hours of annealing, the irradiated samples were in disequilibrium state and the apparent activation energy (E act ) calculated by Arrhenius model determines that heliumatoms tended to diffuse through the displacement mechanism, and helium bubbles grew under the migration andcoalescence (MC) mechanism. With the annealing time over 100 hours, the high-density dislocations and thenano-oxide particles in LPBF sample still had a strong trapping effect on helium bubbles moving and growth.After annealing for 300 hours, the cellular subgrains in the LPBF sample decomposed, and the nano oxide particles had no trapping effect on the helium bubbles. At this time, the dislocation structure played the primary rolein suppressing the helium bubbles growth, and the radiation resistance of the LPBF sample remained superiorto that of rolled samples.