In recent years, the stability of alloy-phase structures under irradiation has become a major concern in materials for advanced nuclear systems. A number of studies have indicated that the irradiation response of an alloy's phase distribution can be controlled by several competing mechanisms and can therefore be a complex function of its preirradiation processing and the irradiation conditions.

The present experiments were performed to investigate the effect of a factor of 100 difference in damage dose rate on γ′-precipitates in Ni-6.84Al. Prior to irradiation, the alloy was solution-treated and aged to produce γ′-precipitates with a mean cube edge of 33.7 nm. Specimens were examined by transmission electron microscopy following irradiation with 2.8 MeV ⁵⁸Ni⁺ ions to peak damage doses of 0.81, 2.5 and 8.1 displacements per atom (dpa) at an irradiation temperature of 725°C for damage dose rates of 4.4 × 10⁻² and 4.4 × 10⁻⁴ dpa/s. Following irradiation at the lower dose rate, the precipitates developed complex contrast features, which appeared to be some combination of internal dislocations and antiphase boundaries. The precipitates, however, retained their preirradiation size and shape. Following the high-dose-rate irradiation, the preirradiation precipitates developed a ragged appearance at low irradiation dose, and additional γ′-precipitation appeared in the matrix, producing a bimodal size distribution. At 8.1 dpa, the original precipitates had completely dissolved, and the size distribution of the precipitates was unimodal, with a mean size of approximately 5.0 nm.

Analysis of the observed behavior by existing theories in the literature indicated that all of the effects just noted could not be explained by any single, currently available theory. Satisfactory agreement was found with a treatment based on a combination of several previously proposed growth, dissolution, and reprecipitation mechanisms.