Intersectant coherent twin boundaries governed strong strain hardening behavior in nanocrystalline Cu

Introducing parallel coherent twin boundaries (p-CTBs) is a high effective approach to material strengthening. However, it has been widely verified that the strengthening effect of p-CTBs reaches saturation at a critical twin lamellar thickness. In this work, we demonstrate by experiments and molecular dynamic simulations that the novel intersectant coherent twin boundaries (i-CTBs) involving Lomer-Cottrell (L-C) dislocation locks trigger off a strong strain hardening on nanostructured metal, which exceeds the strength induced by p-CTBs strengthening. A transition from strain burst to dislocation multiplication occurs as the p-CTBs turn into i-CTBs in nanoscaled single crystals. The i-CTBs with different orientations can significantly promote the formation of L-C dislocation locks inside a nanocrystal, reflecting an intrinsic correlation between the i-CTBs and the L-C dislocation locks. The unique strain hardening primarily originates from the synergistic strengthening effect of the i-CTBs blocking and the L-C locks pinning on the glissile dislocation slip. These findings provide the impetus for a new strategy to design high strength and high plasticity crystalline materials.