Effect of defects on fracture and mechanical properties in Cu/Zr nanolayers

In this work, the effects of strain rate, characteristics of defect on the tensile deformation and fracture behaviour of Cu/Zr nanolayers were systematically investigated. Increasing the strain rate enhances the Young's modulus, tensile strength, effective fracture toughness and critical energy release rate by suppressing strain localization and delaying crack propagation. Crack geometry also governs fracture resistance, with circular cracks exhibiting the most uniform stress redistribution and the highest resistance to crack propagation, whereas other cracks promote localized deformation and preferential shear-band development. Atomistic analyses reveal that deformation is dominated by Shockley partial dislocations, FCC-to-HCP transformation in the Cu layers, amorphization of the Zr layers, and heterogeneous deformation across the Cu/Zr interfaces. The formation of an intermixed Cu-Zr transition region further facilitates stress transfer and contributes to interface strengthening.

The Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) was used to perform simulation. Atomic interactions in the Cu/Zr multilayer system were described using the embedded atom method (EAM) potential. Prior to tensile loading, the models were energy minimized and equilibrated under periodic boundary conditions. Uniaxial tensile deformation was applied at strain rates ranging from 10⁸ to 10¹⁰ s^-1. Structural evolution and deformation mechanisms were characterized using stress-strain analysis, Common Neighbour Analysis (CNA), the Dislocation Extraction Algorithm (DXA), atomic shear strain, von Mises stress, and dislocation density in the Open Visualization Tool (OVITO). The effective fracture toughness K_Ic and critical energy release rate G_c were evaluated based on linear elastic fracture mechanics using the maximum tensile stress and the characteristic crack dimension.