Vol 38, No 6 (2016)

Type Ib diamond single crystals of size to 5–6 mm and to 2.4 carats in weight have been grown at high pressures and temperatures. The defect-and-impurity state and dislocation structures of these crystals have been studied using the IR and optical microscopies as well as the method of the selective etching. To produce type Ib crystals of cubic habit has been made possible by the minimization of the growing temperature. Defect regions in the form of a cone with the basis 0.2–1.8 mm in diameter and 0.5–2.5 mm in height are contained by these crystals. The study of the cone-shaped defect regions using the selective etching showed that at the exposure on the faces the etching pits are of the tetragonal shape and the dislocation density in them exceeds the density of dislocations in crystals that were grown under the usual conditions by 70 to 100 times. The observed defect regions are formed in the course of the diamond crystals growth as the temperature decreases by ~ 30–35°C at the crystallization front because of the increasing heat sink in the direction of a seed crystal.

Structure and properties of (TiHfZrVNbTa)N nanostructured multicomponent coatings implanted with a very high (10¹⁸ cm^–2) dose of N⁺ions have been studied. As a result of the implantation a multilayer structure has been formed in the surface layer of the coating. The structure is composed of amorphous, nanocrystalline (disperse) and nanostructured (with the initial sizes) nanolayers. In the depth of the coating two phases (with the fcc and hcp structures) having a small volume content are formed. The nitrogen concentration near the surface attains 90 at % and then decreases with the depth. In the initial state after the deposition the coating nanohardness values are from 27 to 34 GPa depending on the conditions of the deposition. As a result of the implantation the hardness is decreased approximately by the depth of the projective ions range, i.e., to 12 GPa and then increases with the depth to 23 GPa. The investigations were conducted using the Rutherford backscattering, scanning electron microscopy with the microanalysis, high resolution electron microscopy (with local microanalysis), X-ray diffraction, nanoindentation, and wear tests.

The heat capacity, C_p, of boron-doped single-crystal diamonds grown by the temperature gradient method was studied. The boron contents were < 10¹⁶, ~ 10¹⁸, and ~ 10²⁰ cm^–3. The heat capacity data for all tested crystals match well (within the measurement accuracy 1%) in the temperature range of 150–400 K and obey the Debye law. At low temperatures the heat capacity follows linear law possibly due to metallic inclusions in diamond bulk. Using this data the amount of metal can be calculated for each sample.

To enhance grinding performance the authors consider the application of some indirect measures to stimulate oxidation processes as well as the use of oxides and oxidation-prone materials in the wheel working layer, because the direct introduction of oxygen to the machining zone, which is an important factor to change tribotechnical characteristics of the contact surfaces, presents certain difficulties.

The phase diagram of the Al–B–C system has been calculated at pressure 7.7 GPa using models of the phenomenological thermodynamics with the interaction parameters derived from the experimental data on the phase equilibria at high pressures and temperatures.