Optimal strength-ductility trade-off in gradient nano-grained Cu: a crystal plasticity finite element study

Gradient nano-grained (GNG) metals usually exhibit a strength–ductility trade-off compared with their homogeneous counterparts, but the understanding on the gradient distribution in grain size corresponding to the optimal strength–ductility trade-off is still limited. Here, the tensile processes of GNG Cu with different grain-size gradient distributions are simulated by the crystal plasticity finite element method (CPFEM). The influence of grain-size gradient rate on the mechanical behaviors of strength and plasticity, and the distribution of strain and stress are analytical analyzed, and the relations between the structural gradient and the deformation gradient are investigated. It is found that the GNG Cu has optimal strength-ductility trade-off and the largest extra strengthening effect, when the gradient distribution in grain size meets a linear relationship. It is also found that the optimal strength-ductility trade-off comes from the largest deformation gradient and favorite multiaxial stress. These simulation results obtained by CPFEM are in accordance with the experiment observations and that obtained by MD simulations on atomic scales.