Volume 119, Nº 12 (2018)

Based on analyzing experimental data and existing theoretical approaches, this study has formulated concepts of regular change in scenarios of phase transformations developing under severe plastic deformation. Depending on the temperature and deformation conditions, the dissipation of delivered energy can be realized by various routes (dislocation glide and climb, dynamic recrystallization, amorphization, and redistribution of alloy components), giving rise to a diversity of observed phase and structural states. A diagram of nonequilibrium states of alloy as a function of conditions of severe plastic deformation has been proposed. The applicability of the presented concepts has been demonstrated for a wide range of alloys and compounds.

Metastable equilibrium of the α- and α'-phases comprising solid solutions of carbon in iron with cubic and tetragonal lattices, respectively, has been analyzed using the Zener–Khachaturyan theory of tetragonality of martensite of Fe–C alloys. The condition of the absence of carbide precipitates was imposed, as in the case of very low tempering or the formation of non-carbide bainite. A phase equilibrium diagram has been plotted in the region of low temperatures between 300–600 K. The violation of the linear dependence of the degree of tetragonality c/a on the carbon concentration in the concentration range 0.17–0.61 wt % C, established by Academician G.V. Kurdyumov for higher carbon concentrations, is explained.

This paper presents the results of an investigation of the influence of the polymeric coating used in the course of the production of magnetic shields and conditions necessary for its formation on the distribution of magnetization and magnetic properties of amorphous soft magnetic ribbons made from AMAG-172 alloy (Co‒Ni–Fe–Cr–Mn–Si–B). Study was performed on samples with a nearly zero saturation magnetostriction. The coating was applied onto the ribbon in the 90–130°C temperature range after heat treatments in air, which formed a state with a positive saturation magnetostriction. This study has shown that the formation of a polymeric coating at temperatures of 110–130°C leads to a reduction in the volume of domains with the orthogonal magnetization because of the change in the sign of the saturation magnetostriction. The maximum magnetic permeability in the ribbon with a coating is decreased upon its formation in the entire temperature range; however, a certain increase is observed over time.

The study of the magnetooptical properties of magnetics in polarized and natural light is important because of a number of urgent problems in the fields of physics and technology. This paper considers the traditional magnetooptical Kerr and Faraday effects, which are intensively used in practice, alongside the high-magnitude effects of the magnetotransmission and magnetoreflection of nonpolarized light in magnetic semiconductors, such as ferro- and ferrimagnetic spinels, which either possess or not possess high magnetostriction values. Some physical problems requiring further study are formulated.

The spin polarization of charge carriers moving in a ferromagnet through a 180° Bloch domain wall is calculated. It is demonstrated that a magnetization component parallel to the electric current and proportional to its strength emerges after the passage through a wall.

Thermo-Calc calculations and experimental methods (optical and electron scanning microscopy, and electron microprobe analysis) were used to study the phase composition of alloys of the Al–Ca–Si–Sc–Zr system with the same scandium and zirconium contents (0.1 and 0.25 wt %, respectively) and the same total silicon and calcium content (6 wt %). It was shown that the hardening due to the precipitation of nanoparticles of the phase Al₃(Zr, Sc)–L1₂ reaches a maximum after annealing at 300–450°C in alloys within the phase region (Al) + Al₄Ca + Al₂Si₂Ca, where (Al) stands for a solid solution based on aluminum. In alloys within this region, almost all of the zirconium and scandium are contained in (Al), and the silicon content of the alloys is minimum. However, Zr and Sc additions have almost no effect on hardening in alloys within the (Al) + (Si) + Al₂Si₂Ca phase region. The aluminum–calcium eutectic has an essentially finer structure than that of aluminum–silicon.

The influence of heat treatment in the 100–900°С temperature range on the phase composition, structure, and micromechanical characteristics of the surface layer of the 12Kh18N10T steel subjected to nanostructuring frictional treatment (FT) with a sliding indenter has been studied. This study considered opportunities for strengthening metastable austenitic steel using combined thermomechanical treatments. Annealing at 400–450°C allows for the retention of nanocrystalline martensitic–austenitic structures formed in the surface layer of the steel and a significant increase in the micromechanical characteristics owing to the strengthening of the strain-induced martensite. The annealing of the steel at 650°C leads to the formation in the surface layer of an austenitic predominantly submicrocrystalline and nanocrystalline structure with a hardness of 630 HV 0.025, which is almost 3 times higher than the hardness of steel in the initial quenched state. The transmission electron-microscopic studies of the surface layer of the austenitic steel deformed by FT made it possible to reveal the retention of highly dispersed austenitic regions in addition to the recrystallized regions upon heating to 800°C, as well as the absence of abnormal growth of recrystallized austenite grains upon heating to 900°C.

The structure and the mechanical and electrical properties of new ternary composites based on Al‒Mg deformable alloy obtained by fluid extrusion are studied. The evolution of structural and phase transformations in dissimilar fibers (Cu, Mg, and Al–Mg alloy) during thermomechanical treatment are studied using the methods of metallography, scanning electron microscopy, and hardness measurements. It is established that the strengthening of the ternary composite results from solid state reactions at the boundaries of the fiber, which lead to the formation of intermetallide phases (AlCu, Al₂Cu, Mg₂Cu, and MgCu₂) and nonequilibrium supersaturated solid solutions of copper in aluminum and magnesium.

This paper presents the results of a study of the formation of the structure and properties of the 40Au–25.4Pd–34.6Cu alloy (wt %) in the course of its atomic ordering. A number of literature sources have been analyzed, and possible reasons for the deviation between experimental data of different authors are discussed here. Earlier field ionic microscopy (FIM) results have been confirmed: ordered В2-phase nuclei in a matrix with an L1₀-superstructure were observed in this alloy after prolonged annealings. It has been shown that the kinetic of atomic ordering is abruptly accelerated in a field of external tensile stresses. The results of this work demonstrate the possibility to control the structure in the course of “disorder ↔ order” transitions and can be used for the creation of new approaches to the treatment of orderable alloys.

Samples of 0.6 mm thickness made from a VTI-4 alloy (Ti–21Al–23Nb–0.7Zr–1.4V–0.4Mo–0.31Si, at %) are treated by heating in the 850–950°C range, then continuously cooled in a gaseous atmosphere at rates close to 2.5 K/s and cold-rolled to a reduction degree of 60%. This study has established the cause of deterioration in the technological plasticity of samples heat-treated at 950°С upon cold rolling. Cracking during rolling is caused by the presence of fine O-phase precipitates formed during cooling in the structure. The heat treatment regime of the VTI-4 alloy, which provides sufficient technological plasticity for cold rolling to reduction degrees of at least 60%, together with vacuum annealing in the temperature range 850–900°С and cooling by purging with an inert gas at cooling rates higher than 2.5 K/s should be used.