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

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 <111> loops at low irradiation dose indicated that the main mechanism of the formation of <100> loops should be attributed to the high-density helium cluster inducement mechanism, instead of the 1/2 <111> loop reaction mechanism. H2~+ and He~+ dual-beam irradiation induced the formation of <100> loops and 1/2 <111> loops, while increasing the irradiation temperature would increase <100> loop percentage. The percentage of <100> loops was approximately 18.6% at 973 K and increased to 22.9% at 1173 K. The loop reaction between two 1/2 <111> loops to form a large-sized 1/2 <111> loop was in-situ observed, which induced not only the decrease of the number of 1/2 <111> loops but also the significant increase of their sizes. The <100> 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( Δδloop) caused by the change of loop size and density increased first and then decreased slightly, while the yield strength increment( Δδbubble) caused by the change of bubble size and density always increased. Meanwhile, within the current irradiation dose range, Δδloopwas much larger than Δδbubble.