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 mum and 100-1000 nm, respectively, exhibit essentially rate-independent plastic flow over the range 3 x 10(-4) to 3 x 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. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.