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.