Enhanced nanotwinning by special grain growth in nanocrystalline materials

Experiments have revealed that stress-driven grain growth can strongly affect the movement and distribution of the dislocations in nanocrystalline materials. Meanwhile, nanotwinning often originates from the generation and glide of partial dislocations, which is also influenced by grain growth. However, the underlying effect of the grain growth on the nucleation of nanoscale twins remains unclear. In this work, a theoretical model is established to investigate the effect of cooperative grain growth by nanograin rotation and grain boundary migration on the nucleation of nanoscale twins in deformed nanocrystalline solids. The results indicate that, in most cases, the cooperative mechanism controls the nucleation of nanoscale twins. In particular, the cooperative mechanism significantly enhances the nanotwin nucleation outside the deformed grain, while inhibits that inside the deformed grain. The capacity of nanotwin nucleation can be significantly enhanced via decreasing the level of rotation or increasing the migration distance, and it can be maximized by tailoring the coupling factor of the migration process. Moreover, the nanotwin nucleation and its length can be simultaneously optimized via tailoring the cooperative grain growth. As a result, the cooperative grain growth can serve as an effective approach to enhance nanotwinning and thereby improve the plasticity of nanocrystalline materials.