Comparative studies of mechanical properties of stishovite and sapphire single crystals by nanoindentation

Abstract

Comparative nanoindentation tests of stishovite and sapphire single crystals have been performed. It has been found that nanohardness of the (0001) plane of sapphire at a depth of 200 nm is 29.1 ± 0.1 GPa, while the nanohardness of the (110) plane of stishovite is 38.1 ± 0.6 GPa, the tests conditions being the same. The specifics of elastoplastic transition in sapphire and stishovite single crystals and alumina-based polycrystalline ceramic when plastic deformation is localized in a submicron region have been studied. Anomalous elastoplastic transition in stishovite has been revealed. A possibility that anomalous mechanical behavior of stishovite at the nanoscale may be due to a strong softening of the lattice as a precursor of the formation of a post-stishovite phase of silica with the CaCl2 structure in an indent has been discussed.