A. V. Kotko

Mechanosynthesis of Nanodispersed Titanium Diboride

Structural and morphological changes of titanium during intensive milling of titanium and boron powder mixtures in an AIR-015M planetary-ball mill are investigated. It is shown that the structural transformations in titanium lead to the formation of cluster precipitates (like Guinier–Preston zones) of titanium and boron atoms that are regularly oriented with respect to the titanium lattice and coherently associated with it. Cluster precipitates are very effective nuclei for the further reaction and provide an explosive transition to the almost single-phase titanium diboride. It was found that, in the investigated mechanosynthesis conditions, nanostructured titanium diboride forms in the form of flat and spatial polycrystalline particles, composed of oriented nanograins no larger than 20 nm.

On the interaction of the detonation-synthesized ultradisperse diamond and turbostratic boron nitride

The results are given of the electron-microscopic studies of the initial powders of ultradisperse diamonds with the tBN coating and after sintering of these powders both in the initial state and with coating. The possibility has been found of the interaction of the initial components in the course of sintering to form diamond-like phases.

Crystallographic Features of Nanosized Titanium Carbide Produced from Titanium and Carbon in a Planetary-Ball Mill

Structural changes that occur in titanium during grinding of a powder mixture of titanium and carbon in an AIR-015M planetary-ball mill are studied. Grinding of the powder mixture results in the formation of titanium carbide single crystals with particles 7–50 nm in size over the entire reaction zone. At the initial stage of grinding, texturing of titanium occurs and the titanium lattice cell increases in volume, thus inducing internal stresses. Based on these data, it is suggested that the introduction of carbon into the strained titanium particles leads to stacking faults in the titanium hcp lattice, acting as nuclei of fcc titanium carbide in the titanium sites fragmented. Single-crystal TiC 10–20 nm nanoparticles are formed in these sites. The length of titanium–carbon contacts naturally increases with grinding time, giving rise to more nuclei of the new fcc phase. This promotes a mechanically induced self-propagating reaction. The heat generated in the reaction contributes to the sintering of titanium carbide nanoparticles. This results in the formation of particle aggregates 0.1–0.5 μm in size.

Phase Formation During Nitriding of Vanadium Disilicide

The evolution of microstructural and phase transformations during nitriding of mechanically preactivated vanadium disilicide powder is investigated by X-ray diffraction, chemical analysis, and transmission electron microscopy. It is established that, in the initial stage of nitriding (1000–1100°C), the phase formation is accompanied by the dispersion of near-surface zones of VSi2 particles and the formation of V2N and α-modification silicon nitride. With increase in the nitriding temperature, the phase formation is accompanied by the delamination of particles and the formation of mainly VN and silicon nitride of α- and α-modifications. Nitriding of a mechanically activated vanadium disilicide powder at 1400°C enables synthesizing a fine silicon nitride–vanadium nitride composite powder in a single process. The synthesized powder is formed as loose aggregates consisting of 50 nm particles.

Structural and phase mechanism and rate of interaction between TiCu, Ti3Cu4, and Ti2Cu3 intermetallics and hydrogen. II. Destructive hydrogenation of intermetallics

The structural and phase mechanism and the rate of TiCu, Ti3Cu4, and Ti2Cu3 destructive hydrogenation (DH) are studied at 773 K under a hydrogen pressure of 1.0 MPa. The mechanism of destructive hydrogenation of the intermetallics consists in the formation of a hydrogen solid solution, selective hydrogenation of titanium, and subsequent formation of intermediate intermetallics and copper. The destructive hydrogenation products are nondestructive TiH1.9–Cu matrix composites. The rate of TiCu, Ti3Cu4, and Ti2Cu3 destructive hydrogenation is limited by the rates of hydrogen dissociation on the intermetallic surface and the diffusion of titanium hydride. The products of TiCu, Ti3Cu4, and Ti2Cu3 destructive hydrogenation are recombined in vacuum and hydrogen atmosphere.

Structural and phase transformations and rate of Ti2Co and TiCo interaction with hydrogen and synthesis of nondestructive nanostructured titanium hydride composites

The paper examines the sequence of structural and phase transformations and the rate of Ti2Co and TiCo interaction with hydrogen. Destructive hydrogenation of Ti2Co is used to produce nondestructive nanostructured titanium hydride composites. Thermodynamic analysis has shown that Ti2Co and TiCo destructive hydrogenation is thermodynamically favored in the temperature range 298–973 K. In the temperature range 773–973 K, Ti2Co interacts with hydrogen by destructive hydrogenation reaction, in which hydrogen is dissolved in the intermetallic compound, titanium is selectively hydrogenated to cubic TiH1.9, and titanium-depleted TiCo and TiCo2 intermetallics are successively formed in accordance with the Ti–Co phase diagram. The rate of Ti2Co destructive hydrogenation is proportional to temperature, hydrogen pressure, and surface area of the starting samples. Compound TiCo is hydrogenated to form a solution of hydrogen in Ti1+yCo, intermetallic TiCo2, and a solution of hydrogen in β-titanium. Nondestructive composites with nanostructured components are synthesized by Ti2Co destructive hydrogenation.