Formation of carbide phases upon the mechanosynthesis of the (Fe<Subscript>0.93</Subscript>Cr<Subscript>0.07</Subscript>)<Subscript>75</Subscript>C<Subscript>25</Subscript> alloy compared with other carbide-forming processes

Methods of X-ray diffraction, differential thermal analysis, and measurements of the dynamic magnetic susceptibility have been used to investigate the sequence of phase transformations upon the mechanical alloying of a mixture of powders of the initial components of the composition (Fe_0.93Cr_.07)₇₅C₂₅. It has been shown that, at later stages of mechanical alloying, the phase composition is determined by the conditions of the dynamic equilibrium between the crystalline and amorphous phases. A change in the conditions of mechanical alloying leads to a shift in this equilibrium and to a change in the phase composition of the alloy. A comparison of carbide formation in the Fe–C system upon the mechanosynthesis, tempering of martensite, the saturation of iron with carbon from the gaseous medium, the quenching of the melt, and the sputtering deposition of films has been performed. Some general regularities have been established, from which it follows that an important role in phase formation upon the mechanosynthesis, just as in other abovementioned processes, is played by the thermally activated phenomena.     

Development of methods of investigation of the interfacial layer in “iron-protective nanoscale polymer film” systems

The application of double-layer substrate from ⁵⁶Fe nonresonance isotope and ⁵⁷Fe ultrafine layer allows one to use Mössbauer spectroscopy to investigate the interfacial area in the “iron-nanoscale polymer film” system. The anodic dissolution of iron substrate is used to investigate the interfacial layer by X-ray photoelectron spectroscopy.     

Effect of compaction method on the structure and properties of bulk Cu + Cr<Subscript>3</Subscript>C<Subscript>2</Subscript> composites

Cu + Cr₃C₂ composites have been produced using the mechanical alloying of the elemental components, followed by severe plastic deformation by torsion, magnetic-pulse pressing, and electric-pulse plasma sintering. The composites are studied using X-ray diffraction and light and electron microscopy, as well as measurements of the hardness, density, and electric conductivity. Magnetic-pulse pressing at a temperature of 500°C makes it possible to produce volume nanocomposites with a homogeneous distribution of dispersed carbides over the copper matrix, which has a density of 96%, a Vickers microhardness of 4.6 GPa, a Rockwell hardness of 69 HRA, and an electric conductivity of 19% IACS units. Using electric-pulse plasma sintering at a temperature of 700°C, composites with the nanostructured copper matrix, which contains carbide inclusions and consists of domains surrounded by a layer of nearly pure copper, have been produced. These composites have a density of 88%, a Vickers microhardness of 4.0 GPa, a Rockwell hardness of 58 HRA, and electric conductivity of 26% IACS units.     

Software-defined radio technology in the problem concerning with the successive sounding of HF ionospheric communication channels

The problem concerning new software-defined radio technology is investigated as applied to the successive sounding of HF ionospheric communication radio channels. The algorithm for quadrature processing of chirp signals subjected to elementwise compression in the frequency domain is developed. It is established that a channel scattering function and a delay power profile are related to a compressed-signal spectrum and their basic parameters. Data on the key characteristic of HF communications modems are presented. The efficiencies of different modems are estimated using the experimental data on channel parameters. It is demonstrated that the aforementioned technology can be used to estimate not only HF communication channel parameters from the pass band of a radio line but also select the optimal one and, furthermore, makes it possible to combine communications and radio sounding systems in the single device.     

Mechanical Alloying of Immiscible Elements in the Fe–Mg System

Mechanical alloying of immiscible elements in the Fe–Mg system (32 at % Mg) is achieved by grinding in a planetary ball mill. The process is studied by x-ray diffraction, Mössbauer spectroscopy, and magnetic measurements. The results attest to the formation of supersaturated solid solutions of Mg in -Fe. The highest Mg content of the solid solutions is 5–7 at %. Mössbauer results are used to evaluate the changes in the hyperfine magnetic field at Fe nuclei associated with the presence of one Mg atom among the nearest neighbors and next nearest neighbors of Fe in the solid solutions: H ₁ = –1760 kA/m and H ₂ = –800 kA/m, respectively. Increasing the Mg content of the starting mixture reduces Mg solubility in Fe. Thermodynamic analysis indicates that the driving force for the formation of solid solutions may be associated with the excess energy of coherent interfaces in the Fe–Mg nanocomposite resulting from mechanical alloying. The elastic strain arising from the lattice mismatch between Fe and Mg facilitates incorporation of Mg into -Fe. Above a certain Mg content, no coherent interfaces are formed, and the thermodynamic driving force for Mg dissolution disappears. As a result, the system becomes immiscible.     

Iron-cementite nanocomposites obtained by mechanical alloying and subsequent magnetic pulsed pressing

X-ray diffraction, atomic-force microscopy, and density, microhardness, and coercive force measurements were used to study bulk iron-cementite nanocomposites obtained by different regimes of magnetic pulsed pressing of mechanically alloyed samples with a total carbon content ranging from 5 to 25 at. %.     

The possibility of testing the structural state of highly-deformed high-carbon steels by the magnetic method

The influence of cold plastic deformation on phase transformations and on the magnetic properties of powder specimens of the Fe-5-at. % C alloy modeling U12 high-carbon steel has been investigated in the context of nondestructive testing. It has been shown that under high plastic deformation dissolution of cementite Fe3C occurs by the scheme -Fe + Fe₃C -Fe + (Fe₃C)_d + -Fe + Am(Fe-C). An increase in the rate of plastic deformation of powders decreases the coercive force from 50 to 13 A/cm due to the low coercivity of the #x03B1;-Fe and Am(Fe-C) phases. The structural state of high-carbon steels following a strong cold plastic deformation can be determined by measuring two magnetic parameters: the coercive force, and the temperature dependence of differential magnetic permeability.Translated from Defektoskopiya, Vol. 40, No. 7, 2004, pp. 42–52.Original Russian Text Copyright © 2004 by A.I. Ulyanov, Arsenteva, Zagainov, A.L. Ulyanov, Elsukov, Dorofeev.     

Effect of Structure and Phase Composition on Coercive Force and Saturation Magnetization of Mechanically Alloyed Fe100 – xCx (x = 25, 32) Powders

Mechanical fracture of iron and graphite powders leads to formation of the amorphous Fe–C phase and subsequent precipitation of the Fe₃C carbide in the Fe(75)C(25) system and Fe₃CFe₇C₃ carbide in the Fe(68)C(32) system, which are in strongly strained states. After annealing, carbides with undistorted structures are formed, and their content is higher. On the initial stage of this mechanical alloying, the magnetic characteristics of these structures are determined by their defectiveness, and on the subsequent stages of fracturing and annealing by the types, quantities, and structural conditions of the resulting carbide phases.     

A thermodynamic analysis of the environmental indicators of natural gas combustion processes

Environmental indicators of the natural gas combustion process are studied using the model of extreme intermediate states developed at the Melent’ev Institute of Power Engineering Systems. Technological factors responsible for generation of polycyclic aromatic hydrocarbons and hydrogen cyanide are revealed. Measures for reducing the amounts of polycyclic aromatic hydrocarbons, hydrogen cyanide, nitrogen oxide, and other pollutants emitted from boilers are developed.     

Structural and phase transformations during heat treatment of the Fe(71.4)Si(14.3)C(14.3) amorphous alloy prepared by mechanical alloying

Differential scanning calorimetry, X-ray diffraction, Mössbauer spectroscopy of ⁵⁷Fe nuclei, magnetic measurements, and different heat treatments have been used to study the sequence and mechanisms of solid-state reactions in the Fe-Si-C amorphous alloy in the course of the structure transition to equilibrium. Three stages of structural and phase transformations have been found; these are the structural relaxation, formation of an Fe₅SiC silicocarbide, and its decomposition. It has been shown that the second and third stages occur during isochronous annealing within sufficiently narrow temperature ranges of 380–405 and 530–555°C, respectively. The kinetics of the decomposition of the metastable Fe₅SiC silicocarbide and the formation of the ordered Fe-Si alloy during isothermal annealing has been studied.