Enhanced Mechanical Properties in Bulk Nanograined Ni with High‐Density Fivefold Twins

Abstract Fivefold twins are extensively present in nanoparticles and nanowires, enhancing their performance in physical, chemical, and mechanical properties. However, a deep insight into the correlation between mechanical properties and fivefold twins in bulk nanograined materials is lacking due to synthesis difficulties. Here, a bulk fivefold‐twinned nanograined Ni is synthesized via electrodeposition. The fivefold‐twinned nanograins typically feature decahedral and icosahedral shapes similar to fivefold‐twinned particles. The material exhibits a yield strength of ≈1.7 GPa under both compression and tension. Tensile samples achieve an ultimate strength of 2.15 GPa with 15% elongation to failure. The plastic deformation is accommodated by partial dislocation sliding on twin boundaries, splitting fivefold twins, and abnormally refining grains. The size dependence of nucleation stress for partial dislocation is responsible for strengthening and strain hardening. The results showcase the potential of incorporating fivefold twins into bulk nanocrystalline materials to tailor mechanical properties and applications across diverse fields.