Some critical experiments on the strain rate sensitivity of nanocrystalline materials
R. Schwaiger, B. Moser, M. Dao,
N. Chollacoop, S. Suresh
Acta Materialia, Band 51, Seite 5159 (2003)
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 ?m 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.