Evolution of precipitate and its effect on dislocation loops during in-situ He+ irradiation and annealing

The microstructural evolution of irradiation-induced point defects around the precipitates during in-situ 30 keV He ⁺ irradiation was systematically investigated in Mo 3Nb alloy using transmission electron microscopy (TEM) at various temperatures: room temperature (RT), 573 K, and 1073 K. The average size and volume number density of dislocation loops were obtain under the influence of irradiation temperature, fluence and different types (sizes and shapes) of precipitates. The irradiated defects showed distinct characteristics that correlated with the precipitate types. Dislocation loops of larger size and lower density were observed around the larger precipitates, which were also influenced by the precipitate morphology. Temperature had a great effect on defect migration, resulting in a decrease in loop density and an increase in loop size. Furthermore, the hardening effect attributed to irradiation-induced loops decreased with the increase of temperature and precipitate size. The dissolution of precipitates became increasingly pronounced with the increase of temperature, and irradiation could accelerate the process. At 573 K, the dissolution was only found in the large non-spherical precipitate, while at 1073 K, all the precipitates underwent dissolution. The annealing experiment conducted at 1073 K showed that the dissolution of large-sized precipitates would lead to the dispersion of small-sized precipitates, which was beneficial to increase the interfaces and potentially improve the radiation tolerance and mechanical properties of the alloy.