Ultratough nanocrystalline copper with a narrow grain size distribution

We report a unique way of using mechanical milling/in situ consolidation at both liquid-nitrogen and room temperature to produce artifact-free nanocrystalline $\mathrm{Cu}\left(23\mathrm{nm}\right)$ with a narrow grain size distribution. This nanocrystalline Cu exhibits an extraordinarily high yield strength $\left(770\mathrm{MPa}\right)$ , as predicted from a Hall–Petch extrapolation, along with good ductility (comparable with $\sim 30\%$ uniform tensile elongation). Possible factors leading to this excellent optimization of strength and ductility are discussed.