Origin and fate of loop punching in Mo-5Re alloy

Loop punching is the basic physical process of lattice expansion due to the introduction of insoluble gas atoms into the crystalline metals leading to the emission of interstitial atoms and even the formation of prismatic dislocations loops, which therefore dominate the degradation of the material. Despite more than half a century of research, experimentally capturing its fundamental process is still lacking, resulting in known mechanisms being speculated and inferred. Here, we reported for the first time the clearest and most direct experimental details of loop punching and proposed a new mechanism. According to the in-situ experiment, the origin and fate of loop punching were detailed into four stages: incubation, loop punching, synergetic growth, and interaction. At temperatures above ∼ 0.4 T_m, the nucleation and growth of dislocation loops became completely induced by bubble growth, which provided direct evidence of loop punching. The critical bubble size window for experimentally detectable loop punching was defined and evaluated, showing that it became wider and increased in average value with increasing temperature, which made that the critical energetics required for loop punching were further quantified. Furthermore, the subsequent fate of punched-out loops involved not only their mutual coalescence to form super-large 〈111〉 loops but also interactions with adjacent bubbles, during which the bubbles acted as pinning sites decorating the loop edges and mediating their growth. These results provide a comprehensive new understanding of the loop punching mechanism and promisingly contribute to the development of related theories.