Helium implantation damage resistance in nanocrystalline W-Ta-V-Cr high entropy alloys

Abstract

Nanocrystalline W-Ta-Cr-V high entropy alloys have shown promising properties as nuclear fusion materials with enhanced radiation resistance to heavy ion irradiation and negligible radiation hardening. In this work, we investigate the performance of the alloy under low energy helium (He) implantation up to a fluence of 1.25 × 1017 cm−2 at 1223 K. We observe a uniform high density of very small (~2–3 nm) bubbles grown at a slow rate along with enhanced He bubble damage resistance, further marked by no preferential bubble formation on the grain boundaries, even at much higher fluences compared to previously implanted tungsten grades. First principle calculations of He formation and migration energies in this alloy indicate deep energetic wells on the potential landscape and low diffusivity of He compared to pure W. The results imply higher overall (considering both grain matrices and grain boundaries) implantation resistance due to slow He diffusion and accumulation, and confirm the enhanced vacancy-self interstitial recombination argument in these alloys.