Revealing the synergistic effect of invisible helium clusters in helium irradiation hardening in tungsten

Irradiation hardening caused by helium (He) ion bombardment is directly related to the pinning effect of He-related defects on dislocation glide in metals. Taking tungsten as an example, we have systematically investigated the pinning effect of different size He-related defects on the 1/2<111> dislocation glide by molecular dynamics simulations. Interestingly, it is found that not only the nanoscale He bubbles, but also the invisible He clusters play a critical role in He-irradiation hardening. Under the multiple invisible He clusters synergy, the critical resolved shear stress (CRSS, t) will linearly increase with the increasing of He cluster number (m), following the equation τ_CRSS=τ_dis+m·Δτ_Hen−Vi. Accordingly, the CRSS of the multiple invisible He clusters is easy to catch up or even surpass that for nanoscale He bubbles. Consequently, the synergistic effect of invisible He clusters must be considered for He-irradiation hardening in metals.