New observations in micro-pop-in issues in nanoindentation of coarse grain alumina

The present experiments were focused on nanoindentation behaviour and the attendant “micro-pop-in” in a dense (∼95% of theoretical) coarse-grain (∼20μm) alumina ceramic as a function of loading rate variations at three constant peak loads in the range of 105–106μN. Based on the experimental results here we report for the first time, to the best of our knowledge, an increase in intrinsic nano scale contact resistance as well as the nanohardness with the loading rate. These observations were explained in terms of the correlation between the nanoscale plasticity and shear stress active just underneath the nanoindenter.