Physics of Metals and Metallography (v.113, #2)

A new interatomic potential for uranium is proposed. The potential is constructed in terms of the embedded-atom method (EAM). As the reference data used for the optimization of potential functions, the values of forces, energies, and stresses obtained from ab initio computations have been employed. The potential has been applied for studies of properties of crystalline phases of uranium. It has been established that the lattice parameters of the α and Γ phases, the elastic moduli, the isochore, the room temperature isotherm, and the energies of vacancy formation are in good agreement with the available experimental data and calculated results in the framework of the density-functional theory. The potential suggested facilitates simulation of the first-order phase transitions between Γ uranium and liquid and between Γ and α uranium. The melting points of uranium at pressures of up to 80 GPa, and the temperature of the phase transition between the Γ phase and α phases, at ∼3 GPa have been determined. For the first time, atomistic simulation of the phase transition between α and Γ phases of uranium has been performed.
Keywords: uranium; molecular dynamics; interatomic potential; phase transitions

The possibility has been investigated of the appearance of superconducting states with a mixed symmetry of order parameters in the model of two-dimensional Fermi liquid with a cylindrical Fermi surface. It has been shown that the superconducting states to be mixed, if having different symmetry corresponding to any two different harmonics of the gap function, should be shifted in phase with respect to one another by an angle of ±π/2. It has been established that at the zero temperature the region of the existence of the phase with a mixed symmetry of the superconducting order parameters is restricted to a narrow window of the ratios of the amplitudes of interaction from different pairing channels that are concentrated near the critical value of the ratio of these amplitudes corresponding to the point of intersection of the lines of the temperatures of superconducting transitions into the “pure” states of different symmetry to be mixed.
Keywords: superconductivity; two-dimensional Fermi liquid; harmonics of the gap function; mixed symmetry of the superconducting-order parameters; free energy; difference of phases of superconducting states

Influence of magnetostatic fields of a ferromagnetic substrate on the electrodeposition of nickel dendrites by S. V. Gorobets; O. Yu. Gorobets; O. K. Dvoinenko; G. L. Lebeda (129-134).
The influence of the magnetic state of a ferromagnetic wire substrate on the morphology of deposited nickel obtained by electrolysis has been studied. It has been demonstrated using statistical analysis that in the course of nickel electrodeposition without external magnetic field the dimensional characteristics of the arising dendritic structures are affected significantly by the residual magnetization of the substrate. When in the course of Ni electrodeposition even a weak dc magnetic field is applied perpendicularly to the wire axis, nearly identical structures are formed; that is, the system “forgets” its previous magnetic state. The magnetic properties of the substrate were visualized using powder patterns.
Keywords: ferromagnetic materials; magnetic field; domains; Bitter powder patterns; electrodeposition; nickel dendrites

Optical and magnetooptical properties of Heusler alloys XMnSb (X = Co, Pt) by I. D. Lobov; A. A. Makhnev; M. M. Kirillova (135-145).
The ellipsometry method (with photon energies ħω= 0.1–5.0 eV) has been used to study the optical properties of the CoMnSb phase with a structure of the L21 type. Infrared-absorption features indicating the existence of a pseudogap in the density of states at the Fermi level N(E F) have been revealed. The transverse Kerr effect in CoMnSb and PtMnSb has been measured at photon energies ħω = 0.4–4.5 eV. It has been shown that the observed peaks of magnetooptical activity in CoMnSb are due to the off-diagonal component ɛ ij of the tensor of the complex dielectric constant $$hat varepsilon$$ . Spectral dependences of the magnetooptical effect δ q quadratic in magnetization M have been studied for the first time for PtMnSb for the s and p polarizations of the light wave. In the region where a giant Kerr effect (ħω ∼ 1.7 eV) is observed in PtMnSb, a sharp increase in the δ q effect has been revealed caused by the change in the diagonal component ɛ ii of the tensor] of the dielectric constant in an external magnetic field. Based on the δ q spectra for the p polarization of the light wave, additions have been calculated to the real and imaginary parts of the diagonal component of the $$hat varepsilon$$ tensor in the magnetic field (Re(Δɛ ij ) p and (Δɛ) ij ) p , respectively). The spectrum of Im(Δε ij ) p has been analyzed in terms of the existing concepts on the electron structure of PtMnSb.
Keywords: Heusler alloys; optical properties; magnetooptical properties

Optical properties of Fe2NiAl and Fe2MnAl Heusler alloys by E. I. Shreder; A. D. Svyazhin; K. A. Fomina (146-152).
Results of the investigation of the optical properties and of the calculations of the electronic structure of Fe2NiAl and Fe2MnAl alloys are presented. The main attention is paid to the ellipsometric study of the spectral dependence of the real (ɛ1) and imaginary (ɛ2) parts of the dielectric constant in the range of wavelengths λ = 0.3–13 μm. An anomalous behavior of the optical conductivity σ(ω) at IR frequencies has been revealed in Fe2MnAl, which differs substantially from that in Fe2NiAl. The results obtained are discussed based on the calculations of the electronic structure of the alloys.
Keywords: Heusler alloys; optical properties; electronic structure

Effect of temperature on the regularities and scale of form changes of a palladium plate has been studied in a cantilever mode of fixation of a specimen, during its one-sided saturation with hydrogen. The form change of the plate is confirmed to be developed in two stages. During the first short-time stage, the maximum form change (bending) of the plate is reached. The temperature dependence of the maximum bend of the plate is described by an extremal function. During the second stage, which is of substantially longer duration, a plate straightening takes place. At low temperatures, the residual steady-state bend of the plate is 20–30% of the maximum form change. As the temperature increases, the bend reversibility increases and at 320–350°C the phenomenon becomes completely reversible. The mechanism of form change is discussed, and its phenomenological analysis is given.
Keywords: hydrogen; palladium plate; gradient alloy; concentration stresses; form change

Features of the formation of the submicrocrystalline structural state upon plastic deformation of a V-4Ti-4Cr alloy in Bridgman anvils by I. A. Ditenberg; A. N. Tyumentsev; A. V. Korznikov; V. M. Chernov; M. M. Potapenko (160-169).
Results are presented of electron-microscopic investigations of the main features of the microstructure of an V-4Ti-4Cr alloy after severe plastic deformation by high-pressure torsion in Bridgman anvils. Parameters of the defect structure in the bulk and at the boundaries of grains have been studied using the method of dark-field analysis of discrete and continuous misorientations. Fields of local internal stresses and gradients of these stresses on the submicron level have been analyzed. Mechanisms of the formation of the submicrocrystalline structural state have been discussed.
Keywords: submicrocrystalline structure; severe plastic deformation; high-pressure torsion; transmission electron microscopy; gradient of local internal stresses

Phase and structural transformations in the aluminum amts alloy upon severe plastic deformation using various techniques by I. G. Shirinkina; A. N. Petrova; I. G. Brodova; V. P. Pilyugin; O. A. Antonova (170-175).
The paper presents experimental data on the structure formation in the commercial aluminum alloy of grade AMts subjected to severe plastic deformation using dynamic channel-angular pressing and torsion under high quasi-hydrodynamic pressure in Bridgman anvils. The dependences of the structural characteristics and hardness on the degree, rate, and scheme of deformation have been analyzed.
Keywords: severe plastic deformation; ultramicrocrystalline structure; electron microscopy; aluminum alloys

Inhomogeneities of the interface produced by explosive welding by B. A. Greenberg; M. A. Ivanov; V. V. Rybin; A. V. Inozemtsev; O. V. Antonova; O. A. Elkina; A. M. Patselov; S. V. Kuz’min; V. I. Lysak; V. E. Kozhevnikov (176-189).
Results of studying structure of the transition zone for a number of joints produced by explosive welding are presented. The joints of dissimilar metals (titanium-orthorhombic titanium aluminide, coppertantalum, and others) have been investigated. The welded pairs of metals differ from each other in mutual solubility; moreover, some pairs (copper-tantalum) virtually lack it. The interface was found to be uneven; it contains inhomogeneities, irrespective of whether it is flat or wavy. It is shown that the formation of interfacial protrusions determines the adhesion of materials. A granulating fragmentation has been found near the protrusions. The role of various processes in explosive welding has been discussed. The formation of protrusions does not depend on whether the metals of a pair have mutual solubility or not. However, this factor affects the structure of zones of local melting. The metals that have mutual solubility form true solutions; in the absence of solubility, these zones represent colloidal solutions. It is shown that sometimes the local melting zones do not present a real danger for the strength of the joint. A hypothesis is proposed that the formation of a wavy surface is possible through the self-organization of the previously formed protrusions.
Keywords: explosive welding; joint formation; transition zone; fragmentation; local melting; nanoparticles

Structural and phase states of the eutectic alloy Sn-38 wt % Pb, which exhibits superplastic properties at room temperature, have been studied using samples that were cast, forged in a hydraulic press to ∼73%, aged in the as-cast state, as well as preliminarily forged samples and samples deformed in the regime of superplasticity. It has been shown that the phase state of the alloy in as-cast condition does not correspond to the equilibrium tin-lead phase diagram. The superplastic flow of the alloy occurs against the background of processes of decomposition of the supersaturated solid solution. In the preliminarily forged samples, the aging is accompanied by an increase in the concentration of lead in the surface layers. This is related, in particular, to the existence of tensile stresses in the tin-based phase and to their relaxation in the process of aging. In the structure of cast and preliminarily forged samples, an amorphous-crystalline component has been revealed, which most likely is located at grain boundaries. The experimental results agree well with the previously obtained results that are indicative of the nonequilibrium character of the initial structural phase state of the Sn-38 wt % Pb alloy and of the occurrence of structural-phase transformations under conditions of superplastic deformation, and substantially supplement them.
Keywords: superplasticity; eutectic alloy; structural-phase state; nonequilibrium; internal stresses

Effect of irradiation by heavy ions on the nanostructure of perspective materials for nuclear power plants by S. V. Rogozhkin; A. A. Aleev; A. G. Zaluzhnyi; R. P. Kuibida; T. V. Kulevoi; A. A. Nikitin; N. N. Orlov; B. B. Chalykh; V. B. Shishmarev (200-211).
An imitation experimental technique on the irradiation with heavy ions of structural materials of nuclear power plants using tomographic atom probe analysis has been elaborated. The scheme of irradiation of specimens for atom probe analysis has been realized on a MEVVA ion source of an TIPr accelerator (ITEP) with ion energy 75 keV per charge. Test experiments with irradiation and analysis of samples of the EK-181 steel by aluminum ions to a fluence of ∼2 × 1015 ion/cm2 have been performed. Experiments on the Fe-ion irradiation of the samples of ODS EUROFER perspective steel for fission and fusion reactors to different damaging doses have been carried out. The analysis of distribution of different chemical elements in the volumes tested has revealed that under ion irradiation a change in the composition of nanosized clusters, which are present in the initial material takes place. Comparison of the data obtained with the results of reactor irradiation of the ODS EUROFER steel has been carried out. These data testify a correspondence between nanoscale changes in the steels oxide dispersion strengthened in imitation experiments and under the conditions of reactor irradiation.
Keywords: nanostructure; heavy-ion irradiation; radiation damage; nuclear materials