L. S. Vasil’ev

On the analysis of the mechanisms of the strain-induced dissolution of phases in metals

The relationship between the processes of the nanostructure evolution and the strain-induced dissolution of phases upon severe plastic deformation is studied. The known mechanisms of these phenomena are analyzed, and new ones are proposed. The extended metastable and equilibrium phase diagram used for the analysis of the deformed nanostructured solid solution allows for the relationships of the equilibrium states of the system of bulk phases with the equilibrium and metastable states of the systems of planar, linear, and point defects.

On possible mechanisms of nanostructure evolution upon severe plastic deformation of metals and alloys

Nondislocation mechanisms of deformation-induced fragmentation of nanostructures in metals upon plastic deformation are discussed. Conditions under which the refinement of nanograins can effectively occur via deformation twinning and/or deformation-induced phase transformations of a martensitic type are considered. It is shown that for each metal system and each deformation method, there exists a limiting nanostructure with a minimum possible average size of nanocrystallites.

Structural transformations, distribution of nonequilibrium vacancies, and anomalous diffusion in plastically deformed metals and alloys upon mechanical alloying

Processes of structural transformations leading to the generation of fluxes of nonequilibrium point defects and anomalously high rates of diffusion of substitutional impurities in nanostructured metallic systems upon mechanical alloying have been investigated. The basic contribution to the anomalous acceleration of diffusional mass transfer was shown to come from the nonequilibrium vacancies generated by processes of the deformation-induced migration of intercrystallite boundaries. The influence of interstitial atoms on the diffusion and processes of recrystallization was found to be negligible. The specific features of the formation of strongly supersaturated substitutional solid solutions upon severe plastic deformation of metals and alloys have been examined.

To the theory of the anomalously high diffusion rate in metals under shock action: I. Basic equations of diffusion mass transfer upon plastic deformation of materials

Specific features of the diffusion mass transfer in metals under impact mechanical action are considered. Diffusion fluxes that arise during intense plastic deformation of materials are determined. It is shown that under some conditions the diffusion of impurities from the external surface into the bulk of metal can proceed in the regime of a wave process, in which the mass transfer occurs in the form of a convective motion of atoms through the crystal lattice of the solid. The velocity of propagation of diffusion waves is determined.

To the theory of the anomalously high diffusion rate in metals under shock action: II. Effect of shear stresses and structural and phase state of the diffusion zone on the rate of mass transfer

Phenomena of diffusion mass transfer in metals under shock mechanical actions have been investigated. The effect of shear stresses on the diffusion processes is considered. It is noted that the impact loads acting on alloys that possess polymorphic modifications lead to the development of structural phase transformations, which take place by the martensitic mechanism, and to the generation of numerous vacancies. In combination with the high temperatures and significant shear stresses in the diffusion zone, these phenomena substantially accelerate the processes of diffusional mass transfer. The basic result of an impact action is the changeover of the medium into a strongly nonequilibrium state which is characterized by anomalously high velocities of the displacement of diffusion fronts, which was observed experimentally.

Topological dislocation-type defects and mechanisms of plasticity and failure of nanostructured and amorphous materials

Possible mechanisms of plastic deformation and failure of nanostructured and cluster amorphous materials have been considered. It is shown that the most probable carriers of plastic deformation in these materials are macrodislocations—linear topological defects of the regular nanocrystallite packing in the nanostructure or cluster packing in amorphous materials. Continuum models are proposed to describe the processes of plastic deformation and failure of nanostructured and cluster amorphous materials.

Reactions of cyanofurazans with β-dicarbonyl compounds

In the presence of nickel acetylacetonate, β-dicarbonyl compounds readily add at the nitrile group of 4-R-3-cyanofurazans to form enaminofurazans. The adducts obtained from 4-amino-3-cyanofurazan underwent intramolecular cyclization on heating with AcOH in EtOH to give furazano[3,4-b]pyridine derivatives in high yields.

Trifluoromethyl-substituted 1,6-naphthyridines and pyrido[4,3-d]pyrimidines

A convenient method for the synthesis of 1-alkyl-5-trifluoromethyl-1,6-naphthyridin-4(1H)-ones was elaborated based on the reaction of 4-alkylamino-3-trifluoroacetimidoyl-3-penten-2-one diphenylboron chelates with dimethylformamide dimethyl acetal. 3-Acetyl-4-amino-2-trifluoromethylpyridine was used to obtain 5-trifluoromethyl-1,6-naphthyridin-4(1H)-one and its 2-methoxycarbonyl derivative, as well as 4-methyl-5-trifluoromethylpyrido-[4,3-d]pyrimidine.

Kinetics of dissolution of phases upon deformation of nanostructured metals and alloys

The kinetic features of dissolution of foreign inclusions in the bulk of nanostructured metals upon plastic deformation have been discussed. It has been shown that the rate of dissolution of inclusions substantially depends on the character of structural transformations in the subsystem of intercrystallite boundaries of nanomaterials. Equations that determine the kinetics of dissolution of chemical compounds of metals depending on the rate of structural transformations in intercrystallite boundaries upon deformation have been obtained. The behavior of the kinetic curves of dissolution has been described qualitatively. Numerical estimates of the time of dissolution of inclusions Fe3C and Fe2B in steels are given which are in satisfactory agreement with experimental data on the mechanical alloying of iron with nonmetals in ball planetary mills.

Four-coordinate six-membered ketiminate and diketiminate boron complexes. Synthesis, structure, reactivity, and application in the design of nitrogen heterocycles

The data on ketiminate and diketiminate boron complexes are first reviewed. The present review is focused on the synthesis and chemical transformations of these chelates. The special attention is paid to the application of these boron chelates in the synthesis of nitrogen heterocycles including CF3-substituted derivatives.