Nanoindentation-induced elastic–plastic transition and size effect in α-Al₂O₃(0001)

Abstract

The mechanical properties of α-Al₂O₃(0001) have been investigated using the technique of nanoindentation with a Berkovich indenter. Coupled with the Hertzian contact theory, a theoretical shear strength of 28 ± 2 GPa was determined from the onset of pop-in events on load–displacement curves during loading, and the intrinsic hardness 30 ± 3 GPa was obtained by analysis of the so-called indentation size effect, based on the concept of geometrically necessary dislocations. The predicted values of the shear strength, hardness and elastic modulus are in good agreement with available experimental data. The importance of experimentally calibrating the area function over the contact depth range prior to nanoindentation tests is emphasized.

Acknowledgements

This work has been supported by the Australian Research Council (ARC) and the Research Grant of the City University of Hong Kong under project No. 7001783. Y.-W. Mai is Australian Federation Fellow tenable at the University of Sydney.