Abstract

Molecular dynamics simulations were conducted to investigate the brittle-to-ductile transition in aluminum bicrystals containing edge cracks and grain boundaries (GBs) with varying tilt misorientation angles. This work presents the first atomistic-level study that systematically correlates GB tilt misorientation with a fracture mode transition, integrating mechanical indicators such as fracture toughness, crack-tip opening displacement (CTOD), and local stress triaxiality. The results reveal a sharp increase in fracture toughness for misorientation angles in the range of 20°–25°, associated with a transition from cleavage-dominated fracture to ductile tearing. Bicrystals with GB angles above this threshold exhibit toughness values up to four times higher than those with low-angle boundaries, accompanied by enhanced plastic activity and void formation. In contrast, GBs below 20°show limited plasticity, no tearing, and fracture behavior similar to that of monocrystalline aluminum. This transition correlates strongly with a reduction in crack-tip stress triaxiality, with a critical threshold near 1.5 marking the onset of ductile fracture mechanisms. These findings provide a mechanistic link between GB misorientation, local stress state, and fracture response, offering a physically grounded descriptor for predicting fracture mode transitions and guiding grain boundary engineering in nanostructured aluminum. © 2025 Elsevier Ltd