Microstructure evolution and hardening behavior in FCC Ni under ion irradiation: Influence of dose rate

The dose rate-dependent microstructure evolution and hardening of FCC-Ni was investigated. Irradiations were conducted using 6 MeV I3+ ions at a temperature of 723 K, across four distinct dose rates. TEM analyses revealed that with increasing dose rate, the size of dislocation loops decreased while their density increased. In contrast, both the size and density of voids exhibited a declining trend. The defect dynamics were considered to elucidate the underlying mechanisms of these findings. Nano-indentation test was utilized to evaluate the depth-dependent hardness, revealing a pronounced irradiation hardening effect that diminished as the dose rate increased. A mechanistic model was developed, incorporating the hardening contributions of irradiation-induced voids and loops, along with the role of dislocation networks. The model provided an analysis of microstructure parameters and strengthening coefficients with respect to dose rate, identifying the dominant hardening mechanisms at various depths and highlighting their evolution with dose rate.