Fig. 1 Basic diffusion methods of He atoms [7]

Fig. 2 Molecular dynamics (MD) simulation of the bcc Fe system with randomly distributed He (0.1% concentration) at 1 ns and 5 ns [22]

Fig. 3 Schematic map of the loop punching mechanism described by the pressure-driven model [20,62]

Fig. 4 a Structure of a He4V cluster and a SIA. b He and defect distributions for the case of 125 He atoms. c He and defect distributions after inserting 250 He at 0.6 ns. The insets in b and c are the detailed arrangements of a He-SIA cluster and a He cluster-SIA loop complex, respectively [21]

Fig. 5 Schematic illustration of bubble growth mechanisms: a MC mechanism, b OR mechanism [7]

Fig. 6 Bright field kinematical micrographs of the He-implanted plates with 1000 appm in grain interior in 316L austenitic stainless steel: a as implanted (focal image), b annealed at 650 °C (under-focal image), c annealed at 750 °C (under-focal image), d annealed at 850 °C (under-focal image) and, e annealed at 900 °C (under-focal image), f annealed at 1000 °C grain interior (under-focal image) [69]

Fig. 7 A sequence of video frames which shows a profile of bubble motion at 750 °C in Fe [16]

Fig. 8 TEM micrographs of the He-implanted sample following thermal treatment of 750 °C for 100 h of low magnification a; and higher magnification b [78]. The images were recorded in under focus conditions, with a defocus of ~ − 1000 nm

Fig. 9 Swelling curve as a function of dose in W irradiated with 25 keV He ions [87]

Fig. 10 Temperature dependence of swelling in HT9 irradiated with 5 MeV Fe++ at 188 dpa: 10 appm He [18]

Fig. 11 Typical swelling versus dpa curves for standard 316 AuSS (316SS), a swelling-resistant AuSS (PCA), and various ferritic-martensitic steels (HT9, 9C-1Mo, and 21/4C-1Mo) [19]

Fig. 12 CRSS (critical resolved shear stress) for edge dislocation to release from void and helium bubbles with different He/V ratios, both with different sizes, at temperature of 10 K and strain rate of 108/s [100]

Fig. 13 CRSS (critical resolved shear stress) for edge dislocation to release from 2 nm helium bubbles with different He/V ratios and 2 nm void at different temperatures and same strain rate [100]

Fig. 14 Hardening behavior of unirradiated and 1.2 MeV He ion-irradiated UNS N10003 alloys at 650 °C [79]

Fig. 15 Radiation hardening ratio as a function of irradiation temperature [88]

Fig. 16 a Intergranular fracture surface induced by the tritium exposure treatment [117]; b porous structure observed on intergranular fractured facets of “in-beam” ruptured titanium modified (DIN 1.4970) cold work (CW) [119]

Fig. 17 Ratio of intergranular (IG) fracture surface by SSRT test a and He concentration b as function of radiation dose in PWR and fast breeder reactors (FBR) [134]

Fig. 18 a Comparison of radiation depth dependent He bubble density (scattered data point) distributions in irradiated 49 nm, 96 nm Fe films and bulk Fe. b Evolution of indentation hardness (as-deposited, irradiated, hardness change) as a function of d−1/2, where d stands for average grain size [158]

Fig. 19 The higher spatial resolution of Atom probe tomography a shows a grain boundary edge on and b is in an orthogonal orientation [149]

Fig. 20 TEM images of bubbles on a larger Ti (N, C) precipitates, b dislocations, and c grain boundaries, respectively [149]

Fig. 21 Effect of initial sink strength on the radiation hardening of steels following fission neutron irradiation near 300 °C to damage levels of 1.5-78 displacements per atom (dpa) [144]

Fig. 22 Effect of sink strength on the volumetric void swelling of ion-irradiated (4-MeV Ni and 200-400-keV He) and fission neutron-irradiated Fe-Cr-Ni austenitic alloys [144]

Fig. 23 Energy barrier for the upcoming interstitial He in bcc Fe to enter the Ce (blue circles) cage to join the encapsulated He (red, gray and blue circles represent He, Fe and Ce respectively) [154]

Fig. 24 Average bubble size and bubble density in W and W-5Ta alloy at 800 °C as a function of damage level [153]

Fig. 25 Optical micrographs of SLMed 304L stainless steel: a columnar grains, and b equiaxed grains. Bright field TEM images of c cellular sub-grain structures with dislocation tangles as the cell wall, d δ-ferrite, and e σ phase identified by EDS chemical composition [178]

Fig. 26 TEM images of irradiated SLM 316L SS: a cellular sub-grain structures, b nano-inclusions. c Schematic diagram of the effects of sub-grain boundaries and inclusions to radiation defects and He bubbles [188]

Fig. 27 Effects of grain size and oxide inclusions on the sink strengths in the as-built laser powder bed fusion (LPBF), the solution-annealed LPBF, and the rolled 304L stainless steel [189]

Fig. 28 Number density and size of helium bubbles in four samples of comparison S1 (As-built, implanted), S2 (As-built, implanted, PIA at 600 °C for 1 h), S3 (As-built, implanted, PIA at 600 °C for 1 h) and S4 (Solution-annealed, im-planted, PIA at 600 °C for 1 h) [190]