Characterization of pop-in phenomena and indentation modulus in a polycrystalline ZrB2 ceramic

Low-load nanoindentation tests were carried out on a polycrystalline ZrB2-based ceramic. Pop-in phenomena were observed when indentation marks were placed in the interior of the ZrB2 grains. Both pop-in loads and pop-in extents were statistically distributed with a mutual strong correlation. The critical shear stresses at pop-in were in good agreement with the theoretical shear strength of ZrB2. The experimental pop-in extents were also compared to a simplified model developed for homogeneous dislocation nucleation. The influence of the grain orientation on the indentation modulus was derived from the model of Delafargue and Ulm (2004) and compared to the experimental results. Some results were definitely influenced by the polycrystalline structure of the investigated ceramic.