Vol 2016, No 5 (2016)

A method is developed to fabricate briquettes with nanostructured materials aimed at modification of cast iron resulting in the improvement of the physicochemical properties of cast iron and its castings. This improvement is achieved by grain refinement, stable modification, the elimination of pyroelectric effect upon modification, and a decrease in the sensitivity to chilling upon melt solidification.

It is shown that, in the course of developing the technology of pure vanadium pentoxide preparation from manganic vanadium-containing metallurgical slags, their oxidative roasting and cinder formation without alkaline additives are accompanied by the decomposition of spinelides with the formation of manganese meta- and pyrovanadates. Concentrated aqueous solutions of soda ash with an Na₂CO₃ concentration of 120–150 g/dm³ are accepted as a selective leaching reagent for vanadium from a cinder. Manganese metaand pyrovanadates are synthesized, and the procedure of their preparation is presented. The solubility of vanadium from manganese vanadates in aqueous solutions of soda ash at \(C_{Na_2 CO_3 } = 150 g/dm^3 \) is studied at 20–95°C for pyrovanadate and at 85–95°C for metavanadate. It is shown that vanadium should be leached from converter manganic slags roasted without alkaline metal additives at a leaching solution temperature higher than 95°C. There is a possibility to increase the vanadium content in a leaching solution to 60–80 g/dm³. The results obtained are used in the development of the technology of vanadium leaching.

Thermal analysis is used to study the saturation of the copper melt by oxygen from an oxygen-containing gas phase and the possibility of deoxidation of this melt by nanosized diamond–graphite, which enters in the reaction mixture used to synthesize chromium carbide in the production of copper-matrix composites, are studied. The oxygen and chromium carbide contents are found to affect the mechanical properties of copper and copper-matrix composites. Diamond–graphite is shown to have a high refining ability, which can substantially increase the plasticity of copper and copper-matrix composites. A low chromium carbide content is found to play a modifying role in grain refinement, and a high chromium carbide content is shown to cause the formation of a precipitation-hardened structure and an increase in the physicomechanical properties of copper-matrix composites.

An NT50 alloy of the composition Nb–(48.5 ± 1.5)% Ti is studied after severe plastic deformation and subsequent 100-h annealing. During heating at a rate of 2 K/min, the NT50 alloy subjected to this thermomechanical treatment demonstrates two internal friction peaks at 493 K and 573 K. As the heating rate increases by a factor of three, both peaks shift to higher temperatures and the peak height at 573 K increases. A diffusion mechanism of the temperature-dependent internal friction in the strongly deformed NT50 alloy is proposed. Using this mechanism, the effect of the heating rate on the internal friction in this alloy is explained as the volume titanium diffusion due to the diffusion growth of α-Ti precipitates in subgrains in the alloy. In this case, the first peak is related to the bulk diffusion that accompanies grain-boundary diffusion in subgrains, and the second peak, to usual bulk diffusion in subgrains.

The contributions at a temperature of 500 and 600 K of the chemical, elastic, vibrational, magnetic, electronic, and configurational energies to the Gibbs energy of mixing of bcc alloys without regard for the contribution of a short-range order are calculated as functions of composition and temperature using physical–empirical models. The temperature dependences of the heat capacity of an alloy in both one- and twophase states are calculated. The heat capacity jumps calculated for alloys of various compositions can be used to estimate the equilibrium solubility boundaries of Fe–Cr alloys, which can hardly be found from experimental data because of the slow diffusion processes that occur when an equilibrium state is reached. The calculated solubility boundary of bcc solid solutions and the spinodal and the heat capacity of Fe–Cr alloys are compared with the experimental data and the calculation results obtained in other works. The agreement and discrepancy between these data are discussed.

Steel samples of important railway parts are analyzed. The surface roughness and the microstructure of the steel are shown to affect the shape and the half-width of diffraction lines when the surface stresses are determined by an X-ray diffraction (XRD) method. It is found that preliminary preparation of the sample surface is necessary to perform XRD measurements. It is shown that the XRD method can be used to determine the surface stresses for all characteristic types of steels of railway parts.

The contact interaction of a heterogeneous powder medium with the surface of a steel or hard-alloy tool is subjected to mathematical simulation. Under known compacting conditions, the developed mathematical model can be used to find the character of particle motion in the medium to be compacted and the density distribution over the volume of the semiproduct or the end product.

The elastoplastic deformation of a billet by bending is considered. The deformation forces are determined and formulas are derived to estimate the accuracy of the curvature of the billet. A bending technology is developed to increase the accuracy of a billet and to decrease the metal losses. The results obtained were used at Tver’ Glass Company to produce curved billets.