Ultra-large room-temperature compressive plasticity of a nanocrystalline metal

We report ultra-large room-temperature plasticity of nanocrystalline Ni subjected to uniaxial compression. Up to 200% true plastic strain is achieved with a steady flow stress of ∼2 GPa at strain rates ranging from 10 ^-3 to 10^-1 s^-1. The low temperature, high strain rate, and high flow stress demonstrate that the observed ultra-large plasticity in nanocrystalline Ni is intrinsically dissimilar to that in traditional superplastic materials deformed at high temperatures. Microstructural observations reveal significant nanograin growth accompanied with the ultra-large plastic deformation, indicating the ultra-large plasticity in nanocrystalline Ni at room temperature is mainly performed by a grain-boundary-mediated process that is driven by high stresses rather than by thermal diffusion.