Holubenko O. Features of determination of physical and mechanical properties of solids under local loading in micro- and nanovolumes

The physical ideas about the indentation size effect of crystalline materials at nanoindentation have been developed. A phenomenological approach to the largeindentation size effect, which allows to ignore the specific dislocation mechanisms of deformation during indentation, has been proposed. The nature of the indentation size effect in relation to the ratio of elastic  e and plastic  p deformation of the material under the indenter is discussed. It is established that the dimensional effect is determined by the difficulty of plastic deformation and the growth of elastic deformation, which leads to an increase of hardness in accordance with Hooke's law. To standardize the hardness results of different materials, a number of formulas have been developed and a method of calculating the hardness from one load to another or from one imprint depth to some fixed depth hf has been proposed. This allows a more accurate comparison the results of nanohardness measurements obtained by different researchers. It is shown that the plasticity characteristic calculated at instrumental indentation A=Ap/At (where Ap and At is the work of plastic and total deformation, respectively), almost coincides with H=εp/εt (where εp and εt are plastic and total deformation during indentation, respectively) if H  0,5, i.e. for all metals and most refractory compounds and ceramics. For the first time, the deformation curves (  t) for brittle materials – monocrystalline Si and ceramics based on TiB2 and SiC in a wide range of temperatures (20 – 900 °С) and deformations (εt = 2 – 30 %) has been created. According to the obtained curves for Si and TiB2 ceramics the parameters of deformation hardening in the temperature range of 400 – 900 °С has been determined. Using the developed methods of indentation, the mechanical characteristics of nanostructured materials has been studied and determined. Changing the temperature dependence of the plasticity characteristic δH makes it possible to determine the temperature range of superplasticity in the materials in which this phenomenon is inherent. Key words: scale dependence of hardness, nanohardness, mechanical properties, plasticity, temperature.