  A novel W-based refractory high entropy alloy with outstanding radiation
resistance has been developed. The alloy was grown as thin films showing a
bimodal grain size distribution in the nanocrystalline and ultrafine regimes
and a unique 4 nm lamella-like structure revealed by atom probe tomography
(APT). Transmission electron microscopy (TEM) and X-ray diffraction show an
underlying body-centered cubic crystalline structure with certain black spots
appearing after thermal annealing at elevated temperatures. Thorough analysis
based on TEM and APT correlated the black spots with second phase particles
rich in Cr and V. After both in situ and ex situ irradiation, these
precipitates evolve to quasi-spherical particles with no sign of
irradiation-created dislocation loops even after 8 dpa at either room
temperature or 1073 K. Furthermore, nanomechanical testing shows a large
hardness of 14 GPa in the as-deposited samples, with a slight increase after
thermal annealing and almost negligible irradiation hardening. Theoretical
modeling based on ab initio methodologies combined with Monte Carlo techniques
predicts the formation of Cr and V rich second phase particles and points at
equal mobilities of point defects as the origin of the exceptional radiation
tolerance. The fact that these alloys are suitable for bulk production coupled
with the exceptional radiation and mechanical properties makes them ideal
structural materials for applications requiring extreme conditions.
