Deformation behavior and mechanical properties of polycrystalline and single crystal alumina during nanoindentation

The nanoscale pop-in phenomena in polycrystalline α-Al2O3 and single crystal α-Al2O3(0 0 0 1) were comparatively investigated by nanoindentation with Berkovich indenters. It was found that different radii and loading rates have significant effects on the pop-ins formation, stress distributions and dislocation nucleations. Using the Hertzian contact theory and energetic model approach, the pop-in observations and resolved shear stress analysis are consistent with the explanation that the first pop-in corresponds to the nucleation of homogeneous dislocations when the theoretical shear strength is exceeded.

► The nanoscale pop-in phenomena of alumina crystals were discussed.
► Hardness exhibits strong ISE at small indentation depth range of ∼100 nm.
► The maximum resolved shear stress occurs at a different position for each crystal.
► The dislocation loop radii were estimated successfully for pop-in events.
► The indenter tip radii play an important role during nanoindentation tests.