Role of Helium Bubbles and Voids on the Property of Nanocrystalline Tungsten

Abstract

This manuscript embarks on an inquiry into the influence of helium implantation on nanocrystalline tungsten, a contender for plasma-facing components (PFCs) in nuclear fusion reactors. The study underscores the inevitability of helium retention in tungsten due to the anticipated high flux of helium atoms from D-T fusion reactions in future reactors such as ITER and DEMO. This retention, potentially culminating in surface blistering and grain boundary embrittlement, propels an investigation into the helium's preferential substitutional configuration over interstitial within tungsten's lattice, leading to cavity and bubble formation. Atomistic tensile testing simulations, exploiting a helium-specific interatomic potential, dissect the ramifications of helium concentration and voids on tungsten's mechanical properties across grain sizes of 10nm and 15nm. The presence of helium at grain boundaries instigates detachment, influencing structural behaviors under strain. Notably, the study reveals a dichotomy in helium's effect: benign at concentrations up to the critical point, beyond which significant embrittlement and elastic softening occur, corroborating with theoretical predictions on helium-induced grain boundary embrittlement. This nuanced exploration delineates the intricate dance between helium implantation levels, grain size, and the ensuing mechanical property alterations in nanocrystalline tungsten, casting light on its viability and endurance as a PFC material under the rigorous conditions forecasted in fusion reactors.