Helium self-trapping and diffusion behaviors in deformed 316L stainless steel exposed to high flux and low energy helium plasma

Abstract

A large number of dislocation networks were introduced in to 316L stainless steel by cold rolling. Subsequently, low energy (40 eV) helium ions were implanted by exposing the steel to helium plasma. Thermal desorption and positron annihilation spectroscopy were used to study the behavior of helium in the presence of dislocations, with emphasis on helium self-trapping and migration behaviors. Helium desorption behaviour from different helium trapping states was measured by the thermal desorption spectroscopy. Most of the helium desorbed from the HemVn clusters, and the corresponding desorption peak is located at ~650 K. The desorption peak from helium-dislocation clusters (HemD) is at approximately 805 K. The effect of annealing on the defect evolution was investigated by positron annihilation spectroscopy. For the specimen exposed to helium plasma without displacement damage, the increment of S parameter meant the existence of helium self-trapping behavior (HemVn). Helium atoms could diffuse two to three orders of magnitude deeper than the implantation depth calculated by SRIM. The diffusing helium atoms were gradually trapped by dislocation lines and formed HemD. Elevated temperatures enhance the self-trapping behavior and cause helium atoms to dissociate/desorb from the HemVn clusters, increasing the S parameters at 473–673 K. The gradual recovery of vacancies in the HemVn clusters decreased the S parameter above 673 K.