Defective twin boundaries in nanotwinned metals

Coherent twin boundaries, which usually form during the growth, deformation or annealing of crystalline solids, are widely described as perfect interfaces. Experiments and simulations now show that as-grown coherent twin boundaries in nanotwinned copper consist of incoherent segments and partial dislocations, and significantly affect the material’s mechanical behaviour and deformation mechanisms. Coherent twin boundaries (CTBs) are widely described, both theoretically and experimentally, as perfect interfaces that play a significant role in a variety of materials. Although the ability of CTBs in strengthening, maintaining the ductility and minimizing the electron scattering is well documented1,2,3, most of our understanding of the origin of these properties relies on perfect-interface assumptions. Here we report experiments and simulations demonstrating that as-grown CTBs in nanotwinned copper are inherently defective with kink-like steps and curvature, and that these imperfections consist of incoherent segments and partial dislocations. We further show that these defects play a crucial role in the deformation mechanisms and mechanical behaviour of nanotwinned copper. Our findings offer a view of the structure of CTBs that is largely different from that in the literature2,4,5, and underscore the significance of imperfections in nanotwin-strengthened materials.