Nanoindentation-induced elastic-plastic transition and size effect in a-Al2O3(0001)
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The mechanical properties of a-Al2O3(0001) have been investigated by 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.