In-situ TEM observation and MD simulation of the reaction and transformation of <100> loops in tungsten during H2 + & He+ dual-beam irradiation

Low mobility loops significantly affect the mechanical properties of body-centered cubic materials and their generation and evolution have been a hot research topic recently. However, there is still a lack of direct observation on the reaction of the formed loops during subsequent irradiation, which hinders a better understanding of the degradation of mechanical properties induced by irradiation. Here, we reported for the first time that the reaction between loops produced 1/2 loop through in-situ TEM observation during 30 keV H₂⁺ & He⁺ dual-beam irradiation in tungsten. Molecular dynamics simulation showed that this reaction required appropriate relative position of the initial loops and high temperature that could induce loop split into 1/2 segments and then transformed into 1/2 loop. Meanwhile, the evolution of loops was in-situ observed. The average size and areal number density of loops were quantified as a function of irradiation fluence.