Reversal of stress gradient in gradient nanograined copper during the uniaxial tensile deformation

Abstract

Gradient nanograined metals, as advanced metallic materials, have been widely studied for their better mechanical properties. Due to the spatial gradient distribution of grain size, gradient nanograined metals exhibit the spatially gradient distribution of stress, which alleviates the stress concentration and reduces the chances of occurrence of strain localization, thus enhancing the ductility of metallic materials. The stress distribution in gradient nanograined metals has been widely reported, however, most of the existing studies focused on only within the elastic range of materials. In this work, we report that the stress distribution gradient undergoes a reversal during the transition from elasticity to plasticity stage, which originates from the unique structure of gradient nanograins. A series of molecular dynamics simulations were carried out to study the mechanism of the stress reversal in the gradient nanograins. The results show that the tensile stress increases with the increase of the average grain size in the elastic stage while in the plastic stage the distribution gradient is reversed. This reversal in stress distribution can be attributed to the change in the deformation mechanisms during the transition from elasticity to plasticity and the difference in deformation capacities of regions with different average grain sizes. Our work provides a unique insight into the deformation behavior of gradient nanograined metals. © 2025 Elsevier B.V.