Estimating the stress exponent of nanocrystalline nickel: Sharp vs. spherical indentation

To overcome the newly found difficulties in estimating the creep exponent through the popular constant-load, sharp-indentation creep method, we propose here a modified way that involves using a spherical tip. Both sharp and spherical indentation creep experiments were performed on nanocrystalline nickel (∼30 nm), which is known to show creep-like behavior at room temperature. The results suggest that nanocrystalline nickel exhibits a strong strain-rate-dependent deformation mechanism, and that spherical indentation creep may produce more reliable data than sharp indentation creep.