Role of twin thickness gradient and grain size gradient in work hardening of gradient nanotwinned metals

Abstract Gradient nanotwinned (GNT) structures exhibit superior strength and work hardening compared to homogeneous nanotwinned (HNT) structures. However, the relative effectiveness of twin thickness gradient (TTG) versus grain size gradient (GSG) on enhancing material properties remains unclear. In this study, the tensile behavior of various homogeneous, TTG, GSG, and dual gradient (DG) nanotwinned (NT) specimens was investigated using molecular dynamics simulations (MDs). The mechanisms of plastic deformation and the additional dislocation densities in different gradient structures were compared. The results indicate that both TTG and GSG structures facilitate dislocation slip within grains by stabilizing grain boundaries (GBs), dispersing shear bands, and promoting grain rotation. For the components in the DG structure, the extra dislocation density generated by the DG structure is approximately the average of the densities produced by the TTG and GSG structures individually. For the gradient structure as a whole, an appropriately designed DG can yield a higher extra dislocation density than a single gradient. This study contributes to the further enhancement of work hardening in NT metals through microstructural design.