Abstract: Metallic materials, although composed of metallic bonds, exhibit a wide range of mechanical properties: some are ductile and deformable, while others undergo a pronounced ductile-to-brittle transition (DBT), displaying ceramic-like brittle behavior once below a critical temperature. For decades, the dominant mechanism driving the ductile-to-brittle transition of metals-whether dislocation nucleation or disloca-tion slip-has been a topic of ongoing debate. A new concept of dislocation source efficiency, however, suggests that both processes are complementary and essential for overall ductile deformation. The rel-ative mobility of screw versus edge dislocations dictates the efficiency of dislocation sources, which in turn governs dislocation multiplication and ultimately the material's ability to plastic deformation. Fur-thermore, we developed a new model that incorporates factors affecting dislocation activities, such as the initial dislocation density and the number of dislocation sources, offering promising toughening strategies for both metallic structural alloys and ceramics.

Key words: Ductile, Brittle, Dislocation, Mobility, Plasticity