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 max. load directly from loading curves, if the Young's 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 obsd. as known from conventional measurements. At small testing loads of 25-50 mN, the Vickers hardness of dense submicron corundum ceramics increases to 25-30 GPa depending on the microstructure.