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.