Physics of Metals and Metallography (v.105, #5)

On the dimensional properties of electron gas by S. Sh. Rekhviashvili (421-426).
A statistical model of noninteracting electrons is considered. It is assumed that free electrons can possess fractal properties in phase space and form electron gas with an arbitrary degree of degeneracy. Within the framework of the model suggested, expressions for the Fermi energy, concentration, heat capacity, and electrical conductivity of the electron gas have been obtained. It has been shown also that a dimensional dependence of the Lorentz number is possible. An expression for the electronic component of the surface tension has been derived.
Keywords: 71.10.Ca; 71.10.Ay

Within the framework of the method of the electron-density functional, a self-consistent calculation of the shift of two near-surface ionic planes in different metals has been carried out. The effect of the near-surface lattice relaxation on the surface energy of the metals and the electron work function for these metallic surfaces has been investigated. To describe the arising strong inhomogeneity of the electronic system in the near-surface region, gradient corrections for the kinetic and exchange-correlation energy have been taken into account. For calculating the effect of electron-ion interaction on the energy characteristics of the surface, the Ashcroft pseudopotential has been used.
Keywords: 71.15.Mb; 68.35.Md

For describing the isomorphic heterogeneous decomposition of binary supersaturated solid solutions at the stage of coalescence under conditions of dislocation-matrix diffusion with a relaxation of stresses caused by phase separation, we consider a system representing a precipitation-phase particle in a surrounding matrix + dislocations intersecting the interphase surface and supplying an alloying component to it. In the approximations based on the continuity of the distribution of misfit dislocations on the interphase surface and of the average concentration field, we obtained an expression for the total energy of the system in the form of a functional which depends on the fraction of the relaxed regions of the interphase surface, the number of supplying (feeding) dislocations, and their mutual arrangement. The need for the use of a model functional appears within the framework of the variational problem for determining the equilibrium parameters of the system.
Keywords: 64.70.Kb; 66.30.Dn

Magnetic structure and double exchange in the La1 − x Ca x MnO3 by B. V. Karpenko; L. D. Fal’kovskaya; A. V. Kuznetsov (443-452).
This paper considers from a theoretical viewpoint the problem of the appearance of different magnetic structures in the series of compounds La1 − x Ca x MnO3, 0 ≤ x ≤ 1. It is assumed that the entire series possesses the structure of the GdFeO3 type. The problem is analyzed in the nearest-neighbor approximation with allowance for direct exchange, double exchange, and anisotropy energy (ten interaction parameters on the whole). The spin operator of double exchange interaction in the crystal between the different-valence ions of manganese Mn3+ and Mn4+ is the direct generalization of two-spin operator in the well-known problem of the Anderson-Hasegawa molecule. The minimization of the energy along the direction angles of magnetic sublattices leads to a set of transcendental equations, whose solutions give eleven types of magnetic configurations: two ferromagnetic, three collinear antiferromagnetic, and six noncollinear antiferromagnetic. As the concentration of calcium ions x changes, one spin configuration changes another as the ground state. The appearance of angular configurations in the system occurs only due to the simultaneous presence of direct Heisenberg interaction and substantially non-Heisenberg double exchange.
Keywords: 75.10.Hr; 75.30.Et

Configurations of magnetic domain structure of gadolinium-cobalt amorphous films with a perpendicular anisotropy under the effect of spatially nonuniform magnetic stray fields produced by various miniature sources have been studied. The domain structure of the amorphous films has been shown to qualitatively and quantitatively reflect the symmetry and magnitude of the normal component of the nonuniform magnetic fields and, similar to iron garnets, can be used for topographying stray fields. New features of the domain structure have been found during the visualization of small-scale sources of stray fields, on the one hand, and fields characterized by a small gradient, on the other hand.
Keywords: 85.70.Kh; 75.70.Kw

Use of mechanoactivation for obtaining hydrides of titanium aluminides by N. V. Kazantseva; N. V. Mushnikov; A. G. Popov; V. A. Sazonova; P. B. Terent’ev (460-470).
The hydrogen storage capacity of titanium aluminides Ti(Al,Nb) (β0) and Ti3 (Al,Nb) (α2) subjected to mechanoactivation has been investigated. It has been found that the mechanoactivation in a hydrogen atmosphere makes it possible to obtain hydrides of titanium aluminides with a hydrogen concentration of up to 1.8 wt % at room temperature without enhanced requirements for purity and pressure of the supplied hydrogen. The release of hydrogen from such samples in a vacuum begins at a temperature of about 175°C.
Keywords: 81.20.Wk; 81.30.Hd

Fe79Zr10N11 films 0.7 μm thick deposited on glass substrates have been produced by rf reactive magnetron sputtering. The films are a soft magnetic material, which can exhibit a combination of a high saturation inductance and a low coercive force and, therefore, shows promise as magnetic recording cores for the high-density magnetic recording. The results of X-ray diffraction studies of the phase and structural states of the films and the effect of annealing on these states are considered.
Keywords: 68.55.Jk; 81.15.Cd

Strengthening of Fe-Cu alloys during isothermal aging has been considered. The size of particles that provides a maximum strength has been found. A theory of particle growth under the conditions of continuous cooling has been developed. The cooling rate that provides the maximum contribution from age hardening has been calculated.
Keywords: 64.70; Kb.81.30.Mh

A new approach to obtaining fine-grained structure in intermetallic-compound alloys such as γ-TiAl + α2-Ti3Al has been suggested. This approach is based on the use of alloys that solidify as the β phase, which contain β-stabilizing additives such as Nb and Mo and are characterized by the small size of crystallites already in the cast state; in these alloys, a simple heat treatment makes it possible to substantially decrease the fraction of the lamellar component and to increase the content of the β(B2) phase. It is shown on the example of the Ti-43Al-7(Nb,Mo)-0.2B (at %) alloy that this heat treatment ensures superplastic properties in the material in the temperature range of T = 1050–1130°C at a deformation rate $$ dot varepsilon $$ = 1.7 × 10−4 K−1. Under these temperature-strain-rate conditions, relative elongations such as δ = 160–230% and low flow stresses such as σ = 36–100 MPa characteristic of superplastic flow have been obtained. It has been shown for the first time for the intermetallic γ-TiAl + ga2-Ti3Al alloy that a sheet semifinished product cut out from an ingot subjected only to heat treatment can have plasticity acceptable for press forming.
Keywords: 81.40.Lm; 62.20.Fe

As a result of experiments which include plastic deformation and subsequent heating without stress, self-blocking of dislocations in TiAl has been revealed. The transformations of glissile dislocations into dislocation barriers has been observed both for superdislocations with Burgers vectors <101] and 1/2<112] and for single dislocations. The preliminary deformation was performed at room temperature; the heating without stress, at temperatures both below and above the peak temperature T max in the temperature dependence of the yield stress σy(T). With a proper choice of the temperature of heating and its duration, it proved to be possible to fix the initial stages of the straightening of single dislocations along a preferred direction parallel to their Burgers vector and the subsequent formation of long blocked dislocations. As a result of TEM analysis, it has been shown that the barriers were formed during heating without stress but they were not destroyed. It has been revealed that the barriers with a total Burgers vector <101] in TiAl, in contrast to Ni3Al, remain indestructible even when the experiments included a repeated deformation.
Keywords: 61.72.Ff; 81.40.Lm

Fatigue of a fine-grained high-strength Al-6Mg-Sc alloy produced by equal-channel angular pressing by E. V. Avtokratova; R. O. Kaibyshev; O. Sh. Sitdikov (500-508).
Room-temperature mechanical properties of a fine-grained high-strength Al-6Mg-Sc alloy 1570 produced by equal-channel angular pressing (ECAP) have been studied. The alloy was deformed to a true degree of deformation ɛ ∼ 8 at a temperature of 325°C. The average size and the volume fraction of new small grains after ECAP were 1.2 μm and 0.7, respectively. It is shown that the formation of a submicrocrystalline structure makes it possible to increase the yield strength and endurance limit of the alloy 1570 with respect to the microcrystalline and coarse-grained states with small loss in plasticity. The influence of the microstructure which is formed in the process of ECAP on the behavior of the material upon high-cycle fatigue is discussed.
Keywords: 62.20.Mk; 81.40.Np

Measurements of velocities of elastic waves have been performed in polycrystalline samples of an intermetallic compound Ni3Al, this intermetallic compound alloyed with niobium or cobalt, superalloys ZhS36 and VKNA-4U, and the 60N21 alloy. Elasticity moduli have been calculated, namely, Young’s modulus, shear modulus, bulk modulus, and the Poisson ratio. The results obtained are compared with those calculated from the tensor of the elasticity moduli obtained for single crystals. The calculations have been performed in the Voigt and Reuss approximations.
Keywords: 43.58.Dj; 62.20.Dc

Evolution of the dislocation structure and the formation of fatigue microcracks in pearlitic-ferritic steels by V. I. Izotov; V. A. Pozdnyakov; E. V. Luk’yanenko; M. E. Getmanova; G. A. Philippov (517-527).
Theoretical and experimental study of the evolution of the dislocation structure in pearlite during fatigue tests using contact and bending modes of loading has been performed. Special features of the dislocation structure of pearlite with a different degree of the structure fineness upon cyclic loading have been analyzed. It has been shown that a size structural effect is realized in the pearlite, which manifests itself in the dependence of the arising dislocation structure in the ferrite interlayers on their thickness. The model of the initiation of a fatigue crack in pearlite has been developed and the period of its initiation under contact cyclic loading has been calculated. Microstructural changes upon the fatigue failure of a high-carbon pearlitic-ferritic steel with different degrees of pearlite fineness have been studied electron-microscopically during contact and bending cyclic deformation.
Keywords: 62.20.Mk; 81.40.Np