Impact of sub-grain structure on radiation resistance in additively manufactured 316L stainless steels: An atomic insight into the mechanism

Laser-based additive manufacturing (AM) provides a new pathway for rapid manufacturing of radiation-resistant materials used in the nuclear engineering system. Ultrafine sub-grain boundary (SGB) structure in AM materials plays an important role in enhancing radiation resistance of materials. Here, we combined experimental and molecular dynamics simulation methods to investigate the interaction between cellular SGBs in AM 316L stainless steel (SS) and irradiation-induced defects. Experimental results prove that the laser powder-bed-fusion (L-PBF) 316L SS presents a more uniform distribution of the defect sizes and the mean defect size is smaller after irradiation compared with cold-rolled (CR) 316L SS. The energetics and dynamics simulation results show that the SGB structure is an efficient sinking site for interstitial atoms. Density of dislocation network on SGBs exerted a significant effect on the reduction of interstitial atom formation energy near SGBs. After irradiation, the evident increase of SGB volume ratio fails to improve the defect self-healing performance but reduces the dislocation density on the SGB, thereby impairing the radiation resistance of the material. This work provides an insight into better understanding of the AM radiation enhanced materials from the combination of atomic simulation and irradiation experiments.