Physics of Metals and Metallography (v.111, #6)

Effect of an external magnetic field H on the superconductivity of bilayer (FS) and trilayer (FSF) heterostructures consisting of layers of ferromagnetic (F) and superconducting (S) metals has been studied. The case has been considered where the scattering in both metals is sufficiently strong (the so-called “dirty limit”), which makes it possible to use the Usadel equations to describe the proximity effect. For the Gor’kov function, a boundary problem is formulated that is free of restrictions on the magnitudes of the transparency of the FS (SF) interface and takes into account both the wave and diffusional types of motion of quasi-particles. Special attention is given to the case of a trilayer system, for which a detailed analysis of two states with parallel (P) and antiparallel (AP) directions of the magnetizations in the F layers has been performed. Based on the results obtained, the possibility of a technical application of the FSF system is considered.
Keywords: superconductivity; proximity effect; magnetism; magnetic field; critical temperature; critical field; layered structures

Multiple signals of nuclear spin echoes in ferromagnets excited by radio-frequency pulses of arbitrary duration by M. D. Zviadadze; R. L. Lepsveridze; G. I. Mamniashvili; A. M. Akhalkatsi (547-553).
Calculations have been performed of multiple signals of nuclear spin echoes excited in ferromagnets by two radio-frequency pulses whose duration can exceed the time of free-induction decay. The values obtained for the number of echo signals and for the moments of their appearance proved to be in good agreement with the results of experiments performed using lithium ferrite.
Keywords: spin echo; enhancement effect; inhomogeneous broadening; lithium ferrite

Statistics of magnetization jumps in nanowires by A. A. Ivanov; V. A. Orlov (554-560).
The model of a polycrystalline nanowire has been used to theoretically solve the problem of searching for the distribution function of the following characteristics of the magnetization process: the field of the start of a domain wall; and the magnitudes of Barkhausen macro- and microjumps. The results have been tested using computer simulation.
Keywords: nanowire; Barkhausen jumps; pinning

Effect of pulsed laser heating on the magnetic properties of amorphous alloy 30KSR by V. V. Girzhon; A. V. Smolyakov; N. I. Zakharenko; N. G. Babich; M. P. Semen’ko (561-565).
It has been established using magnetometric methods that irreversible magnetic anisotropy appears in the amorphous ribbon of a 30KSR alloy after pulsed laser heating in an external magnetic field. Effects of laser heatings on the physical properties of the alloy, in particular, on the Curie temperature and the temperature of crystallization have been studied. It has been shown that the direction of the arising magnetic anisotropy does not coincide with the field direction during laser heating. A mechanism of the appearance of the uniaxial magnetic anisotropy of amorphous ribbons during pulsed laser heatings in a magnetic field by regimes which do not lead to crystallization has been suggested.
Keywords: amorphous alloys; magnetic anisotropy; laser heating

Combined thermomagnetic and ion-beam treatments of anisotropic electrical materials by Yu. N. Dragoshanskii; V. V. Gubernatorov; V. I. Pudov; T. S. Sycheva (566-572).
Problems of a substantial increase in the functional characteristics of soft magnetic Fe-3% Si- and Fe-70% Ni-based alloys have been studied. Variants of efficient combined thermomagnetic and ion-beam treatments have been developed. They ensure the optimization of the magnetic domain structure and a substantial decrease (to 15–20%) in magnetic losses for anisotropic transformer steels, a decrease (to 60%) in the coercive force of permalloys, and an increase in the linear saturation magnetostriction of the Fe-7% Al-1% Si and Fe-6% Al-2% Co alloys to a value of (40–60) × 10−6 corresponding to those of high-cobalt alloys.
Keywords: soft magnetic alloys and materials; domain structure; magnetic losses; linear magnetostriction; thermomagnetic treatment; ion-beam treatment

It has been established experimentally that the magnetic state of austenite of a preliminarily completely austenitized chromium-nickel steel at the initial stage of the deformation-induced martensitic transformation can be represented in the form of two fields. The first field (below the true deformation martensitic point ε s ) is characterized by increasing paramagnetic state of austenite to a constant maximum value; the second field (after ε s ), by the formation and accumulation of strain-induced martensite in it.
Keywords: magnetic susceptibility; austenite; strain-induced martensite; true deformation martensitic point

Structure of Al-Ti-C master alloys by E. A. Popova; I. G. Brodova; T. I. Yablonskikh; I. G. Shirinkina; N. M. Barbin; L. E. Bodrova; A. V. Dolmatov; E. A. Pastukhov; N. A. Vatolin; V. V. Chebykin; Ya. B. Chernov (579-586).
A binary Al-Ti master alloy of hyperperitectic composition, whose structural characteristics ensure high modifying efficiency, has been prepared by the aluminothermy method. The treatment of the alloy by low-frequency vibrations (LFVs) and its interaction with the carbon emitter of LFVs in the process of crystallization lead to the formation of a ternary Al-Ti-C alloy containing titanium aluminide Al3Ti and titanium carbide TiC. The presence of these phases creates favorable conditions for the formation of solidification nuclei in the aluminum melt when using a ternary master alloy as a modifier. A comparison of the efficiency of the structure refinement when using experimental master alloys and the standard Al-Ti master alloy poured into a metallic chill mold has been performed.
Keywords: aluminum alloys; master alloy; modification

In the regions of the deformed cube-on-edge single crystal of the Fe-3% Si-0.5% Cu alloy with an enhanced density of deformation twins, the nucleation of new grains during primary recrystallization (PR) occurs via several mechanisms. The majority of nuclei of PR are formed on twins as on substrates. The newly formed grains of PR are characterized by the presence of a cube-on-edge texture and are in special misorientations of the Σ3 type with respect to the twin orientation and of the Σ9 (Σ27) type with respect to the octahedral matrix. The mechanism of the formation of nucleation centers for PR on the twins as on substrates can be a splitting of the nonequilibrium special boundary Σ3. A significant role of special misorientations in the formation of the Goss texture upon PR has been shown experimentally.
Keywords: commercial alloy Fe-3% Si; (110)[001] single crystal; cold deformation; twinning; special misorientations; primary recrystallization

It has been shown that upon pearlitic transformation of a high-carbon vanadium steel, vanadium carbides 5–10 nm in size precipitate in the ferrite interspaces of the pearlite in the form of periodic rows (with a period of ∼20 nm). A correspondence between the distribution of vanadium carbides and the shape of the γ/α interphase boundary in the pearlite has been found. It has been supposed that in commercial steels the pearlitic transformation is accompanied by the formation of segregates of different atoms at the discretely moving γ/α interphase boundary.
Keywords: pearlite; vanadium carbides; interphase boundary

Methods of thermionic emission and measurements of the brightness and true temperatures have been used to study the effect of intense diffusion of potassium atoms in iridium on the variation of the electrical, optical, and emission properties of iridium. It has been shown that after the intense diffusion of potassium atoms through the interphase boundary between the surface and the bulk of the Ir(111) face the work function of iridium decreases from 5. 8 to 5. 3 eV, whereas the integral emissivity, spectral emissivity, and electrical resistance increase by ∼10, ∼30, and ∼20%, respectively.
Keywords: work function; diffusion; surface ionization

Effect of recrystallization annealing on the formation of a perfect cube texture in FCC nickel alloys by D. P. Rodionov; I. V. Gervas’eva; Yu. V. Khlebnikova; V. A. Kazantsev; N. I. Vinogradova; V. A. Sazonova (601-611).
Based on the data of X-ray diffraction, dilatometry, transmission electron microscopy, and electron backscatter diffraction, the optimum regimes of heat treatment of cold-rolled (to 98.5–99%) tapes made of binary Ni-W, Ni-Cr, Ni-Fe and ternary tungsten-containing Ni-Pd-W and Ni-Cr-W alloys that are widely utilized in the world practice for the fabrication of high-temperature superconducting cables of the second generation, which make it possible to obtain a perfect cube texture. In all five alloys, the spreed of the texture upon slow heating and two-step annealing decreases by 0.2°–1.5° around the RD and by 0.1°–0.6° around the RD in comparison with the single-stage high-temperature annealing.
Keywords: nickel alloys; severe deformation; recrystallization annealing; electron microscopy; perfect texture

Study of the structure and mechanical properties of submicrocrystalline and nanocrystalline copper produced by high-rate pressing by I. V. Khomshaya; E. V. Shorokhov; V. I. Zel’dovich; A. E. Kheifets; N. Yu. Frolova; P. A. Nasonov; A. A. Ushakov; I. N. Zhgilev (612-622).
Evolution of the structure of pure copper (99.8 %) in the course of severe plastic deformation performed by the new method of dynamic channel-angular pressing (DCAP) and the mechanical properties of the arising mixed SMC+NC structures have been studied. The rate of deformation of the material during DCAP is ∼105 s−1, the duration of the process of deformation is 500 μs, the pressure does not exceed 2 GPa. It has been established that in the course of twofold-fourfold pressing the grains and subgrains of copper become refined by three orders of magnitude. It has been found that a decrease in the inner radius of the profile of the zone of intersection of the channels in the die (R) from 7 mm to 0 leads to the formation in the bulk samples of an SMC+NC structure consisting of grains and subgrains with a size from 50 to 350 nm. It is shown that the high-rate deformation with the use of the DCAP method increases the copper hardness by a factor of 2–2.2; the strength grows by a factor of 1.4; and the plasticity remains high. The estimation of the variation of the value of shear along the cross section of the samples upon DCAP showed that in the scheme with R = 7 mm the relative shear is γ ≤ 1.65; in the scheme with R = 0, γ = 1.8-2.0. In the case of a scheme with R = 0, the DCAP leads to a considerable (in comparison with the initial state) increase in the strength without loss of plasticity even upon single-pass pressing.
Keywords: bulk nanomaterials; dynamic pressing; high-rate deformation; interconnection of structure and mechanical properties

Mechanism of the plastic deformation of the AZ31 alloy upon low-cycle reverse bending by A. A. Bryukhanov; M. Rodman; A. F. Tarasov; P. P. Stoyanov; M. Shaper; D. Bormann (623-629).
The development of texture upon deformation by reverse bending of sheets of the AZ31 alloy has been studied. The deformation was represented as the alternation of tension and compression of the layers remote from the middle of the sheet. The mechanisms of plastic deformation that are responsible for the formation of texture at different stages of deformation are proposed on the basis of the data of X-ray diffraction analysis of the texture and substructure and metallographic data.
Keywords: magnesium; deformation bending; twinning; texture; pole figure; detwinning; substructure@

Evolution of the structure of V95 aluminum alloy upon high-pressure torsion by I. G. Brodova; I. G. Shirinkina; A. N. Petrova; O. V. Antonova; V. P. Pilyugin (630-638).
The effect of the degree of deformation upon torsion under quasi-hydrostatic pressure on the structural and phase transformations in the V95 alloy has been studied by the methods of electron microscopy and X-ray diffraction. It has been found that, upon severe plastic deformation, a nanocrystalline structure with a hardness of 2.5 GPa is formed. The nanostructure with a minimum average grain size of 55–80 nm is being formed at e = 5.5–6.4. It has been shown that during dynamical strain aging at e ≥ 4.8, a hardening metastable phase MgZn2 precipitates from the supersaturated α solid solution, and the quantity of this phase increases with increasing degree of deformation.
Keywords: severe plastic deformation; nanocrystalline structure; electron microscopy; aluminum alloys