Effects of grain growth on interface diffusion in nanostructured Cu

► Apparent microstructure evolution occurs in the nanostructured Cu during the annealing at 423 K. ► The microstructure evolution significantly affects the penetration rate of tracer atoms. ► Interfacial diffusivities are determined by considering and neglecting the effect of grain growth. ► The diffusivity value determined by neglecting the effect of grain growth is ∼10 times lower.