Some critical experiments on the strain-rate sensitivity of nanocrystalline nickel

Systematic experiments have been performed to investigate the rate sensitivity of deformation in fully dense nanocrystalline Ni using two different experimental techniques: depth-sensing indentation and tensile testing. Results from both types of tests reveal that the strain-rate sensitivity is a strong function of grain size. Specifically microcrystalline and ultra-fine crystalline pure Ni, with grain size range of 1 µm and 100–1000 nm, respectively, exhibit essentially rateindependent plastic flow over the range 3 × 10 4 to 3 × 10 1 s 1 , whereas nanocrystalline pure Ni with a grain size of approximately 40 nm, exhibits marked rate sensitivity over the same range. A simple computational model, predicated on the premise that a rate-sensitive grain-boundary affected zone exists, is shown to explain the observed effect of grain size on the rate-dependent plastic response.  2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.