Vol 38, No 2 (2016)

External and internal morphologies of natural impact apographitic diamonds (paramorphoses) have been studied. The (0001) surface morphology of the paramorphoses reflects their phase composition and the structural relationship of its constituting phases. Growth and etch figures together with the elements of crystal symmetry of lonsdaleite and diamond are developed on these surfaces. The crystal size of lonsdaleite is up to 100 nm, and that of diamond is up to 300 nm. Two types of structural relations between graphite, lonsdaleite, and diamond in the paramorphoses are observed: the first type (black, black-gray, colorless and yellowish paramorphoses): the (0001) graphite face is parallel to the (100) lonsdaleite face and parallel to (111) diamond; the second type (milky-white paramorphoses): the (0001) graphite is parallel to the (100) lonsdaleite and parallel to the (112) diamond. The first type of the paramorphoses contains lonsdaleite, diamond, graphite or diamond, lonsdaleite, the second type of the paramorphoses contains predominantly diamond. The direct phase transition of graphite → lonsdaleite and/or graphite →diamond occurred in the paramorphoses of the first type. A successive phase transition graphite → lonsdaleite → diamond was observed in the paramorphoses of the second type. The structure of the paramorphoses of this type shows characteristic features of recrystallization.

The computational schemes and algorithms for numerical simulation (by the finite element method) of the mechanical state of the two-stage multi-anvil high-pressure apparatus have been developed. The stress–strain and limit states of components of the first and second stages of the apparatus at generation of the pressure 18 GPa in the container have been defined. The effect of geometrical parameters and physico-mechanical properties of a deformed gasket and second stage anvils on the limit state of the latter as well as the pressures achievable in HPA has been studied. The anvils produced of tungsten-cobalt hard alloys of different grades and polycrystalline boron nitride have been considered.

A complex study has been performed of the effect of the technological parameters, which are responsible for the energy states of deposited particles, on the elemental, phase and structure compositions, hardness, and tribological characteristics of formed vacuum–arc multilayer Mo₂N/CrN systems with a nanometric thickness. The formation of two phase and structure types has been defined in combined nitride layers: γ-Mo₂N/CrN with the isostructural cubic crystalline lattices and γ-Mo₂N/CrN with non-isostructural cubic and hexagonal lattices.

Based on investigations of the mechanism of precision surface formation in workpieces of anisotropic monocrystalline materials for optoelectronics, a generalized model of material removal in polishing with suspensions of polishing powders has been constructed. The removal rate in polishing sapphire planes of different crystallographic orientations has been found to grow in the series m < c < a < r with increasing volume, surface area, and most probable size of debris particles as well as with energy of dispersion of material from the face being polished.

The possibility of using variously dispersed powders of compacts based on synthetic and natural diamond with carbon binder in grinding wheels for machining hard alloys is studied. The partial (50%) or complete replacement of synthetic diamonds with the compact powders containing diamond grains coated with a superhard shell of Yakut diamond micron powders—the waste of gem-cutting operations—in a carbon binder is shown to provide a significant (more than three-fold) improvement of wear resistance of diamond grinding wheels.

The isobaric sections of the phase diagram of the silicon–carbon system at 8 GPa has been calculated using the phenomenological thermodynamics models with parameters of the interaction that have been defined based on the experimental data on the phase equilibria at high pressures and temperatures.