Concentration dependence of the retarding effect on tungsten recrystallization under high-dose helium ion implantation

Recrystallization, a critical issue that weakens the strength and thermal shock resistance of tungsten-based plasma-facing material in fusion devices, is effectively retarded by helium. In this study, the retarding effect of helium on recrystallization was studied using tungsten samples implanted by high-dose helium ions with doses ranging from 5 × 10²¹m⁻² to 1 × 10²³ m⁻² at two temperatures (room temperature and 673 K), and followed by annealing temperatures ranging from 1573 K to 2073 K. The results show that helium in all six samples exhibits retarding effect, with recrystallization beginning until 1773 K. Notably, the sample implanted at 673 K with a dose of 5 × 10²¹ m⁻² demonstrates the lowest recrystallization fraction of 13% at the annealing temperature of 1873 K, suggesting that the retarding effect weakens once the helium ion concentration exceeds a certain threshold. The hardness of high-dose helium ion-implanted tungsten samples exhibits distinct temperature-dependent patterns, different from the monotonic decline typically observed in previous helium-implanted tungsten samples. Additionally, the recovery of pinholes, created by the rupture of helium bubble, on {100} planes was observed to be the slowest, explained through molecular dynamics simulations. This work offers valuable insights into maintaining the retarding effect on recrystallization by tuning helium concentration in tungsten.