Effect of grain size on the interface deformation mechanism and mechanical properties of polycrystalline Cu/Al2Cu/al layered composite materials: A molecular dynamics simulation

Molecular dynamics simulations were first employed to investigate effect of grain Size(D = 6-15 nm) on the interface deformation mechanism and mechanical properties of polycrystalline Cu/Al2Cu/Al layered Composite Materials. The results showed that tensile strength decreased significantly with increasing grain size, while Young's modulus exhibited an increasing trend. The average flow stress peaked at a critical grain size of D = 12 nm, corresponding to a transition in the dominant deformation mechanism from grain boundary migration to dislocation slip. By adjusting grain size, a balance between strength and ductility was achieved, resulting in excellent overall mechanical performance. Size-dependent responses primarily originated from grain-regulated interface shear strain and dislocation density redistribution. Grain size had minimal influence on the fracture mechanism. Cracks consistently initiated at the Al2Cu grain boundary and propagated laterally, displaying characteristics of brittle fracture. A decrease in grain size led to reduced failure strain, and higher stress was required to initiate crack propagation. Crack propagation behavior exhibited a strong dependence on grain size. At the critical size of D = 12 nm, crack tip blunting effectively suppressed microvoid formation and crack advancement. Dislocation density and mobility were identified as key factors underlying the pronounced size effect in polycrystalline Cu/Al2Cu/Al interfaces. These findings clarify the competing mechanisms underlying the strength-ductility trade-off influenced by grain size and provide theoretical and practical insights for microstructural design and optimization of intermetallic compound interface materials.