Atomic force microscopy in different operation modes (topography, derivative topography, and phase contrast) was used to obtain 3D images of Vickers indents on the surface of diamond and cBN single crystals with high spatial resolution. Confocal Raman spectroscopy and Kelvin probe force microscopy were used to study the structure of the material in the indents. It was found that Vickers indents in diamond has no sharp and clear borders. However, the phase contrast operation mode of the AFM reveals a new viscoelastic phase in the indent in diamond. Raman spectroscopy and Kelvin probe force microscopy revealed that the new phase in the indent is disordered graphite, which was formed due to the pressure-induced phase transformation in the diamond during the hardness test. The projected contact area of the graphite layer in the indent allows us to measure the Vickers hardness of type-Ib synthetic diamond. In contrast to diamond, very high plasticity was observed for 0.5 N load indents on the (001) cBN single crystal face. Radial and ring cracks were absent, the shape of the indents was close to a square, and there were linear details in the indent, which looked like slip lines. The Vickers hardness of the (111) synthetic diamond and (111) and (001) cBN single crystals were determined using the AFM images and with account for the elastic deformation of the diamond Vickers indenter during the tests.

High-purity polycrystalline cBN (pcBN) has been obtained from bulk pyrolytic graphite-like BN at a pressure of about 8 GPa and temperatures of 2500 and 2800 K. The size of grains in the sample produced at 2500 K ranged from 100 to 400 nm. The formation of the fine-grained structure has given rise to an increase in both hardness and fracture toughness of pure pcBN when compared with cBN single crystals (s.c.), the elastic modulus is close in value to the elastic modulus of s.c. High mechanical characteristics of the sample produced at 2500 K are caused by a grain small size and pure dense grain boundaries of the recrystallization origin. The increase in the synthesis temperature to 2800 K results in an abrupt decrease in hardness because of the grain size growth in the course of the collective recrystallization.

The methodological aspects of studying the time-dependent mechanical properties of materials subjected to nanoindentation under pulsed loading and unloading of a Berkovich indenter are considered. It is shown that the viscosities and relaxation times of viscoelastic materials can be determined from nanoindentation experiments. The advantages of the pulsed nanoindentation technique are demonstrated with the photoplastic effect in chalcogenide glasses.

The nucleation of dislocations in single crystals of molybdenum and a Mo-1.5 at % Ir solid solution has been investigated by nanoindentation. In the curve of indentation of a Berkovich indenter into the single crystals, an abrupt transition from elastic to plastic deformation has been observed at a depth of 20–40 nm due to the nucleation of dislocations in the initially dislocation-free region under the contact. Alloying of molybdenum by iridium results in a twofold increase in shear stresses under which dislocations nucleated in the contact. Therefore, the solid solution impurity of iridium in molybdenum leads to an increase not only in the plastic strain resistance (to an increase in the hardness) but also in the elastic shear stresses under which dislocations are generated (homogeneously or heterogeneously) in the contact. The latter effect cannot be explained only by an increase in the elastic moduli because of its smallness; however, it is determined to a large extent by a higher degree of perfection of the solid solution crystal as compared to unalloyed molybdenum.

For the first time, shear-induced metallization on the (001) face of diamond single crystals of types Ib, IIa and IIb during hardness tests is studied. The