In-situ TEM investigation of dislocation loop reaction and irradiation hardening in H2+-He+ dual-beam irradiated Mo

Abstract Through in-situ TEM observation during 30 keV H2+-He+ dual-beam irradiation at 723 K, the reaction and transformation of dislocation loops in pure Mo were investigated, especially for loops. Irradiation could directly cause the formation of 1/2 loops and loops, but 1/2 loops were dominant. In-situ observation confirmed the formation mechanism of loops, including direct irradiation induced mechanism, 1/2 loop direct conversion mechanism, and reaction mechanism of two 1/2 loops. Meanwhile, the reaction of two 1/2 loops to produce loop should not require the strict size similarity condition. The reaction between 1/2 loops could also produce 1/2 loop, which was essentially a process in which one loop absorbed another one. The yield strength increment caused by irradiation-induced loops was analyzed, and its saturation value reached 0.48 GPa at 0.06 dpa. Compared with single He+ irradiation, the number density and average diameter of loops increased significantly and more serious damage was caused under the synergistic effect of hydrogen and helium. The mechanism based on in-situ experimental observation was discussed in depth.