In-situ transmission electron microscopy observation of the evolution of dislocation loops and gas bubbles in tungsten during H₂⁺ and He⁺ dual-beam irradiation

Abstract

Dislocation loop and gas bubble evolution in tungsten were in-situ investigated under 30 keV H₂⁺ and He⁺ dual-beam irradiation at 973 K and 1173 K. The average size and number density of dislocation loops and gas bubbles were obtained as a function of irradiation dose. The quantitative calculation and analysis of the migration distance of 1/2 $\langle{111}\rangle$ loops at low irradiation dose indicated that the main mechanism of the formation of $\langle{100}\rangle$ loops should be attributed to the high-density helium cluster inducement mechanism, instead of the 1/2 $\langle{111}\rangle$ loop reaction mechanism. H₂⁺ and He⁺ dual-beam irradiation induced the formation of $\langle{100}\rangle$ loops and 1/2 $\langle{111}\rangle$ loops, while increasing the irradiation temperature would increase $\langle{100}\rangle$ loop percentage. The percentage of $\langle{100}\rangle$ loops was approximately 18.6% at 973 K and increased to 22.9% at 1173 K. The loop reaction between two 1/2 $\langle{111}\rangle$ loops to form a large-sized 1/2 $\langle{111}\rangle$ loop was in-situ observed, which induced not only the decrease of the number of 1/2 $\langle{111}\rangle$ loops but also the significant increase of their sizes. The $\langle{100}\rangle$ loops impeded the movement of dislocation line and tended to escape from it instead of being absorbed. With the increase of irradiation dose, the yield strength increment ($\Delta {\sigma }_{\mathrm{l}\mathrm{o}\mathrm{o}\mathrm{p}}$) caused by the change of loop size and density increased first and then decreased slightly, while the yield strength increment ($\Delta {\sigma }_{\mathrm{b}\mathrm{u}\mathrm{b}\mathrm{b}\mathrm{l}\mathrm{e}}$) caused by the change of bubble size and density always increased. Meanwhile, within the current irradiation dose range, $\Delta {\sigma }_{\mathrm{l}\mathrm{o}\mathrm{o}\mathrm{p}}$ was much larger than $\Delta {\sigma }_{\mathrm{b}\mathrm{u}\mathrm{b}\mathrm{b}\mathrm{l}\mathrm{e}}$.