Comparative studies of mechanical properties of stishovite and sapphire single crystals by nanoindentation
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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.
Key wordsnanoindentation nanohardness elasto-plastic transition sapphire stishovite
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