  Radiation-enhanced precipitation of Cr-rich {\alpha}' in irradiated Fe-Cr
alloys, which results in hardening and embrittlement, depends on the
irradiating particle and the displacement per atom (dpa) rate. Here, we utilize
a Cahn-Hilliard phase-field based approach, that includes simple models for
nucleation, irradiating particle and rate dependent radiation-enhanced
diffusion and cascade mixing to simulate {\alpha}' evolution under neutrons,
heavy ions, and electron irradiations. Different irradiating particles manifest
very different cascade mixing efficiencies. The model was calibrated using
neutron data. For cascade inducing neutron/heavy-ion dpa rates at 300 {\deg}C
between 10^-^8 and 10^-^6 dpa/s the model predicts approximately constant
number density, decreasing radius, decreasing {\alpha}' Cr composition, and
lower {\alpha}' volume fraction. The model then predicts a dramatic transition
to no {\alpha}' formation above approximately 10^-^5 dpa/s, while electron
irradiation, with weak mixing, had little effect at dpa rates up to 10^-^3
dpa/s. These model predictions are consistent with experiments. We explain the
results in terms of the flux dependence of the radiation enhanced diffusion,
cascade mixing, and their ratio, which all vary significantly in relevant flux
ranges for neutron and cascade inducing ion irradiations. These results show
that both cascade mixing and radiation enhanced diffusion must be accounted for
when attempting to emulate neutron-irradiation effects using accelerated ion
irradiations.

Materials Science