Nanoindentation hardness of submicrometer alumina ceramics

Nanoindentations at loads of 20–200 mN were performed on submicrometer sintered alumina ceramics of different residual porosity. The indentation size effect of the hardness can be obtained without variation of the maximum load directly from loading curves, if the Youngʹs modulus of the material is known and if the shape of the penetration curve is analyzed carefully. Similar influences of testing load (indentation size effect), grain size and porosity are observed as known from conventional measurements. At small testing loads of 25–50 mN, the Vickers hardness of dense sub-μm corundum ceramics rises to 25–30 GPa depending on the microstructure.