  Refractory High-Entropy Alloys (RHEAs) hold promising potential to be used as
structural materials in future nuclear fusion reactors, where W and its alloys
are currently leading candidates. Fusion materials must be able to withstand
extreme conditions, such as (i) severe radiation-damage arising from
highly-energetic neutrons, (ii) embrittlement caused by implantation of H and
He ions, and (iii) exposure to extreme high-temperatures and thermal gradients.
Recent research demonstrated that two RHEAs - the WTaCrV and WTaCrVHf - can
outperform both coarse-grained and nanocrystalline W in terms of its radiation
response and microstructural stability. Chemical complexity and
nanocrystallinity enhance the radiation tolerance of these new RHEAs, but their
multi-element nature, including low-melting Cr, complicates bulk fabrication
and limits practical applications. We demonstrate that reducing the number of
alloying elements and yet retain high-radiation tolerance is possible within
the ternary system W-Ta-V via synthesis of two novel nanocrystalline refractory
medium-entropy alloys (RMEAs): the W$_{53}$Ta$_{44}$V$_{3}$ and
W$_{53}$Ta$_{42}$V$_{5}$ (in at.\%). We experimentally show that the radiation
response of the W-Ta-V system can be tailored by small additions of V, and such
experimental result was validated with theoretical analysis of chemical
short-range orders (CSRO) from combined ab-initio atomistic Monte-Carlo
modeling. It is predicted from computational analysis that a small change in V
concentration has a significant effect on the Ta-V CRSO between
W$_{53}$Ta$_{44}$V$_{3}$ and W$_{53}$Ta$_{42}$V$_{5}$ leading to
radiation-resistant microstructures in these RMEAs from chemistry stand-point
of views. We deviate from the original high-entropy alloy concept to show that
high radiation resistance can be achieved in systems with simplified chemical
complexity.
