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.

Insight into structural stability and helium diffusion behavior of Fe–Cr alloys from first-principles

“…3 The results indicate that there is a main peak at 450-940 K, which shows that most He is desorbed from He m V n , while the dislocation desorption peak is concealed. Sun et al produced 316L austenitic stainless steel by SLM method with He ion irradiation at 450 C. 3 The investigations reveal that the interface provided by subgrain boundaries and nano-oxide inclusions is an effective trapping point for He bubbles and helps to improve its tolerance. 4 Alloy 304 austenitic stainless steel is a standard "18/8 stainless steel", that is, stainless steel is mainly composed of Fe, Cr and Ni, 5 exhibits a face-centered cubic (fcc) austenite phase, [6][7][8] and the content of Cr and Ni is not less than 18% and 8% respectively.…”

“…Gong et al used TDS and DBS to study the behavior of He atoms in high flux and low energy He plasma exposed to 316L stainless steel annealed at 723 K after 10% deformation. 3 The results indicate that there is a main peak at 450–940 K, which shows that most He is desorbed from He m V n , while the dislocation desorption peak is concealed. Sun et al produced 316L austenitic stainless steel by SLM method with He ion irradiation at 450 °C.…”

“…Formulas (9) and (10) are the arithmetic average of Voigt and Reuss bound, which are called Voigt-Reuss-Hill approximations. 34 Combining Table 1 and cubic phase mechanical stability criterion [formula (3)], it is shown that the AFM, AFMD and NM states of pure g-Fe satisfy the stability criteria except for the FM state, and can be stable. From Table 1, it is clear that most of the calculated eigenvalues of the elastic stiffness matrix are positive except for the FM state, which indicates that the state is unstable under elastic deformation.…”

“…Sun et al produced 316L austenitic stainless steel by SLM method with He ion irradiation at 450 °C. 3 The investigations reveal that the interface provided by subgrain boundaries and nano-oxide inclusions is an effective trapping point for He bubbles and helps to improve its tolerance. 4 …”

Recent studies of tungsten-based plasma-facing materials in the linear plasma device STEP

“…Recent research in STEP involves plasma testing of new W-based materials [22][23][24][25], characterizations of H plasmainduced defects [26,27], synergetic effects of high-energy ion implantation and plasma irradiation [28,29], and He behaviours in steels [30,31]. This contribution will first devote one session to the investigation of H plasma-induced defects in pure W to shed light on the fundamental evolution of defects during plasma irradiation.…”