Tungsten
displays high strength in extreme temperature and radiation
environments and is considered a promising plasma facing material
for fusion nuclear reactors. Unlike other metals, it experiences substantial
irradiation hardening, which limits service life and presents safety
concerns. The origin of ultrahigh-irradiation hardening in tungsten
cannot be well-explained by conventional strengthening theories. Here,
we demonstrate that irradiation leads to near 3-fold increases in
strength, while the usual defects that are generated only contribute
less than one-third of the hardening. An analysis of the distribution
of tagged atom–helium ions reveals that more than 87% of vacancies
and helium atoms are unaccounted for. A large fraction of helium–vacancy
complexes are frozen in the lattice due to high vacancy migration
energies. Through a combination of in situ nanomechanical tests and
atomistic calculations, we provide evidence that irradiation hardening
mainly originates from high densities of atomic-scale hidden point-defect
complexes.
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