Growth inertia of irradiation defects and its governing role in microstructural evolution in Mo-Re alloys

Microstructural evolution under temperature fluctuations during irradiation is strongly history-dependent. Early-stage irradiation defects can act as sinks that bias later evolution, but the conditions that let these sinks remain dominant are unclear, limiting reliable prediction of defect evolution under realistic service conditions. Here, by combining in-situ temperature-varying irradiation with object kinetic Monte Carlo (OKMC) simulations, this study identifies a growth-inertia effect of early-formed defects, in which irradiation defects tend to inherit their prior growth behavior even under drastic temperature reduction. Two critical thresholds define the stability of this inertial regime: a critical failure temperature T_c (∼400–500 °C, ∼450 °C as an estimate for Mo-5Re-0.5Nb) and a critical initial dose D_c (∼0.015 dpa). When the temperature falls below T_c and/or the initiation dose is below D_c, growth inertia breaks down, leading to substantial defect re-nucleation. A dimensionless kinetic descriptor, termed inertia potential Q, was derived from defect kinetics to quantify the underlying mechanisms. The generality of growth inertia was examined in both Mo-based alloys and pure Mo, with pure Mo exhibiting a lower T_c (∼300–400 °C), consistent with OKMC simulation predictions that Q decreases with increasing Re content. Furthermore, when a sufficient initiation dose (above D_c) is provided, high-temperature pre-irradiation suppresses subsequent nucleation at lower temperatures, yielding a sparse large-loop microstructure with reduced irradiation hardening. These findings establish defect initiation as a governing factor in irradiation evolution and provide a quantitative framework for predicting microstructural stability under variable-temperature irradiation conditions.