Physics of Metals and Metallography (v.119, #3)

Transitions between Segments of C- and S-Shaped Domain Walls in Magnetically Uniaxial and Triaxial Films by M. N. Dubovik; E. Z. Baykenov; V. V. Zverev; B. N. Filippov (203-211).
A three-dimensional micromagnetic computer simulation of transition structures that separate regions of C- and S-shaped vortex asymmetric domain walls in films with easy magnetization axes parallel to the surface has been performed. Films with uniaxial and triaxial magnetic anisotropy (with the surface parallel to crystallographic plane (100)) have been examined. New types of transition structures (including those containing Bloch points) have been obtained.
Keywords: magnetic films; micromagnetism; domain walls; Bloch lines; Bloch points

A short review of the results of a computer simulation of ferromagnets of limited sizes (nanoplatelets, thin films, and rods of rectangular section) using the method of minimizing the functional of the free energy of a magnetic system has been carried out. The implicit dependence of the functional on the magnetization distribution has been taken into account via the potential of the intrinsic field, which made it possible to exclude the points of the labile equilibrium upon minimizing the functional. The efficiency and adequacy of this method for studying micromagnetic properties of nanoobjects have been established. The specific features of the formation of domain structures of nanoobjects, as well as new possibilities of employing them in the magnetic recording of information have been shown.
Keywords: analysis; magnetic properties; computer simulation

The Effect of Synthesis Conditions on the Phase Composition and Structure of EuBa2Cu3O6 + δ Samples by L. A. Klinkova; V. I. Nikolaichik; N. V. Barkovskii; V. K. Fedotov; A. F. Shevchun (216-228).
The composition and the structure of ceramic EuBa2Cu3O6 + δ (Eu-123) oxide samples annealed in steps with varying processing conditions (in air or oxygen and argon atmosphere at a temperature of 940–960°С for 1–70 h with or without homogenization) were studied by the X-ray phase and chemical analysis, electron diffraction pattern analysis, elemental analysis, and high-resolution transmission electron microscopy. Regardless of the processing conditions, Eu-123 nanostructured oxide with a tetragonal or orthorhombic structure and domains 1–20 nm in size was obtained as a result of annealing. Nanostructuring of the samples, which was revealed by high-resolution electron microscopy, is attributed to their chemical nature: the presence of identical structural elements in members of the homologous Eu n Ba m Cu m + n O y series of oxides allows them to intergrow coherently and create an illusion of a single crystal. Just like any other member of the Eu n Ba m Cu m + n O y series, oxide Eu-123 is disproportionate depending on the annealing conditions to form other members of this series located on either side of the dominant oxide. Temperature T c of the superconducting transition of each member of the series depends on the average oxidation state of copper $$overline {Cu} $$ C u ¯ . At $$overline {Cu} $$ C u ¯ < 2, all members of the series have a tetragonal structure and do not exhibit superconducting properties. At $$overline {Cu} $$ C u ¯ = 2.28, five members of the Eu n Ba m Cu m + n O y series with matrices (Ba : Cu) 5 : 8, 3 : 5, 2 : 3, 5 : 7, and 3 : 4 exhibit superconducting properties with T c = 82–90 K.
Keywords: EuBa2Cu3O6 + δ oxide; Eu n Ba m Cu m + n O y homologous series; nanostructuring; high-temperature superconductivity

Diffuse Scattering from Single Crystal Cobalt by A. E. Shestakov; F. A. Kassan-Ogly; Yu. E. Turkhan (229-240).
The history of the research of anomalous diffuse scattering by perfect single crystals has been briefly described. Some traditional techniques for recording the diffuse scattering have been considered. The mono-Laue experiment has been considered in detail. A series of mono-Laue measurements on single-crystal cobalt (hcp structure) has been carried out at room temperature. The results are in a good agreement with theoretical calculations. The principal possibility of these measurements under laboratory conditions has been shown. The possible use of diffuse scattering measurements in the study of structural phase transitions in metals has been substantiated.
Keywords: diffuse scattering; structural phase transitions; mono-Laue experiment

Results of an analysis of the mechanical properties and macro- and microstructures and the fractographic analysis of the fractures of samples of the Al–6 wt % Ni and Al–7.6 wt % Ca aluminum–matrix composite alloys of eutectic type after thermomechanical treatment, including radial–shear rolling (RSR),—have been presented. The hot deformation of preliminarily annealed ingots of studied alloys with a circular section 60 mm in diameter using RSR method at 400–450°C with total reduction μ = 9.0 can lead to the formation of the gradient microstructure with external more deformed layer characterized by high microhardness and thickness of about 1.5–2.5 mm. The microhardness decreases smoothly from the periphery to the center of samples. Uniaxial tensile tests revealed that the strength of alloys after RSR increases by 2.0–2.5 times compared to the as-cast or the annealed state, the plasticity is the same as in the annealed state or increases by several times as in the case of the Al–7.6 wt % Ca alloy. The latter fact is clearly illustrated by the results of the analysis of the fractures of samples, for which the transition from the brittle or mixed type of the fracture before deformation treatment to the pronounced ductile dimpled type after RSR has been observed.
Keywords: aluminum alloys; radial–shear rolling; composites; eutectic; microstructure; mechanical properties

Interaction between Carbon Atoms and Carbon Activity in fcc Iron: Thermodynamic Theories and Computer Simulation by Ya. M. Ridnyi; A. A. Mirzoev; V. M. Schastlivtsev; D. A. Mirzaev (251-257).
The literature data on the interactions between carbon atoms and the methods of calculating its activity in the γ-iron lattice have been analyzed. Both statistical thermodynamic results and the data obtained by methods of computer simulation have been considered. To compare the available results, the simulation of the carbon activity in austenite using the Monte Carlo method has been carried out. It has been shown that the experimental curve of the concentration dependence of the carbon activity can be reproduced using a large number of strongly differing energies of interactions between carbon atoms in the first two coordination shells. Thus, the problem of determining the parameters of the С–С interaction in fcc iron according to the data on the activity is mathematically ill posed and first-principles calculations are necessary. It has been shown that, at carbon concentrations of up to 7 at %, the approximate statistical theories lead to accurate results. An analysis of the results of an ab initio simulation showed that the inclusion of the interaction between carbon atoms in the third and fourth coordination shells hardly affect the carbon activity.
Keywords: first-principles simulation; fcc iron; carbon impurities; Monte Carlo method; WIEN2k

Formation of Phases upon the Mechanosynthesis and Subsequent Annealing of Samples of Cementite Composition Alloyed with Chromium and Nickel by A. A. Chulkina; A. I. Ul’yanov; V. A. Volkov; A. L. Ul’yanov; A. V. Zagainov; I. A. Elkin (258-266).
Using X-ray, Mössbauer, and magnetic measurements, the formation of phases has been investigated upon mechanosynthesis in a ball planetary mill and upon the subsequent annealing of samples of the cementite composition (Fe0.95–у Сr0.05Ni y )75C25, where у = 0–0.20, which contains two alloying elements (chromium and nickel). It has been shown that, in the mechanosynthesis process, cementite alloyed with chromium and a small amount of nickel and an amorphous phase alloyed with chromium and nickel have been formed. Upon heating above 300°С, the amorphous phase is crystallized into nickel-enriched cementite. In the process of annealing at higher temperatures, the most nickel-rich cementite decomposes with the formation of austenite. As a consequence, after annealing at medium temperatures, the composition of the alloys contains cementite alloyed mainly with chromium and some amount of alloyed austenite, which can be found in ferromagnetic or paramagnetic states depending on the Ni content. Annealing at 800°С bring about the complete or partial decomposition of cementite contained in the alloys. The intensity of the decomposition has been determined by the nickel content in the samples.
Keywords: mechanosynthesis; cementite; alloying with chromium and nickel; annealing; phase and structural changes; X-ray; Mössbauer; thermomagnetic studies

Influence of High-Temperature Annealing of the Textured Metal Ni–W Substrate on the Structural Properties of Seed Layer in HTS 2G tapes by M. Y. Chernykh; T. S. Krylova; I. V. Kulikov; I. A. Chernykh; M. L. Zanaveskin (267-271).
The surface reconstruction of the textured metal tapes at the temperatures typical for the formation of the seed buffer Y2O3 layer of HTS 2G tapes have been revealed and studied for the first time. The influence of a terrace structure of the substrate surface on the characteristics of the texture of the seed Y2O3 layer has been shown. This effect is critically important to the deposition of buffer layers on the moving tape and allows to expand the temperature range of growth, in which the full inheritance of substrate texture by the seed Y2O3 layer is occurred.
Keywords: textured metal substrate; HTS 2G tapes; epitaxial growth; vicinal surfaces; thermo-stimulated diffusion; pulsed laser deposition

Structure of Quenched Ti–Ru Alloys by A. V. Dobromyslov; N. I. Taluts (272-281).
Quenched titanium–ruthenium alloys containing 0.25–4 at % ruthenium have been studied using X-ray diffraction analysis, optical metallography, transmission electron microscopy, and microhardness measurements. It has been found that, during the quenching of the alloys containing 0.25, 0.5, and 1 at % ruthenium, a polymorphic β → α transformation occurs with the formation of a two-phase (α + β) structure. In Ti–1.5 at % Ru and Ti–2 at % Ru alloys, a martensitic β → α″ transformation occurs. The quenched Ti–3 at % Ru alloy has a β + ω structure. The complete stabilization of the β phase takes place in the alloy with 4 at % ruthenium. In the electron-diffraction patterns of alloy containing 4 at % ruthenium, diffuse scattering that indicates the formation of ω-phase-related displacements in the locations of atoms has been observed.
Keywords: Ti–Ru alloys; structure; α″ phase; ω phase

Features of the Decomposition of Delta Ferrite in Nitrogen-Containing Austenitic Steels by V. V. Sagaradze; O. V. Fomina; T. V. Vikhareva; N. V. Kataeva; I. G. Kabanova; V. A. Zavalishin (282-288).
Features of the decomposition of the ferromagnetic δ ferrite with the formation of nonferromagnetic constituents (γ and σ phases) at temperatures of 900–1200°C in a nitrogen-containing austenitic steel have been determined. The transformation of δ ferrite at high temperatures (1100–1200°C) occurs with the formation of Widmanstäatten austenitic crystals in the ferritic matrix. At lower temperatures (900–1000°C), the transformation of δ ferrite develops by discontinuous decomposition with the formation of colonies of alternating plates of paramagnetic γ and σ phases. In the course of formation of the nonferromagnetic state as a result of the decomposition of δ ferrite at 900–1000°C (for 1 h), a subgrain structure with an increased density of dislocations, which is typical of thermomechanical treatment, is retained in the steel previously strengthened by high-temperature deformation.
Keywords: nitrogen-containing austenitic steel; delta ferrite; sigma phase; electron microscopy; magnetometry

Study of the Properties of a High-Temperature 50Ti–40Pd–10Ni Shape Memory Alloy by N. N. Popov; V. F. Lar’kin; D. V. Presnyakov; E. N. Grishin; T. I. Sysoeva; T. A. Morozova; G. A. Potemkin; A. A. Kostyleva (289-300).
Combined studies of the properties of the 50Ti–40Pd–10Ni alloy with a high-temperature shape memory effect have been carried out. The elemental and phase compositions and its mechanical and thermomechanical characteristics have been determined. Samples cut from the strip with a thickness of 2.04 mm have been studied. The phase transformations are in the range of M f = 371.3°С to A f = 436.9°С. These are acceptable values. The maximum values of the shape memory effect εSME and of the degree of shape recovery ηSME are 3.9 and 49%, respectively. These values are insufficient to create workable safety devices. These characteristics can be improved via optimal changes in the elemental composition of the shape memory alloy and by an adequate choice of the regimes of heat treatment and of the regimes of providing strain in the investigated objects. The results of these studies are necessary in order to develop different devices used in nuclear power plants.
Keywords: 50Ti–40Pd–10Ni alloy; high-temperature shape memory effect; heat treatment; elemental analysis; microstructure; X-ray diffraction analysis; differential thermal analysis; mechanical characteristics; thermomechanical characteristics

Influence of Heat Treatments on the Fracture Toughness of 2017A Aluminium Alloy by L. Hemmouche; A. Meghalet; A. Henni Chebra (301-308).
The present study was carried out on 2017A aluminium alloy, in order to determine the influence of heat treatments on the fracture toughness determined by three point bending tests and empirical formula correlations used Charpy impact energy. The three point bending test has shown that the minimum values of fracture toughness and maximum load were found in the annealed state. Moreover, the hardening heat treatment increases them considerably, especially in the artificially aged condition of the alloy where it provided the maximum values. Schindler’s empirical formula gave the best estimation of fracture toughness in all metallurgical states of 2017A aluminium alloy.
Keywords: heat treatments; fracture toughness; Charpy impact energy; 2017A aluminium alloy; three point bending tests