Brittle nanomaterials: Hardness and superplasticity

The data on the hardness and superplasticity of nanomaterials based on brittle high-melting point compounds such as carbides, nitrides, borides, intermetallics, and oxides are analyzed. The nonmonotonic change in the hardness with a change in the nanolayer thickness in multilayer films and the grain size in bulk nanomaterials is discussed. The fracture of these materials has intercrystalline character. However, residual plastic deformation is observed in some cases, for example, in for nanocolumnar TiN coatings and SiC single-crystal nanowire. The nanostructured approach was very successful in the development of nanocomposites with high-strain-rate superplasticity (∼10⁻² s⁻¹, T = 1400°C). The poorly investigated problems are pointed.