Physics of Metals and Metallography (v.117, #11)

Critical behavior of Ising ferromagnetic systems with the competition between short- and long-range interactions near the point of a second-order phase transition has been investigated. The effects of long-range interaction lead to the need to calculate the influence of next-nearest spins, which lie inside the sphere of a specific radius. The study was carried out for a power law of decreaseing the exchange integral with distance for a three-dimensional Ising model with a cubic lattice. A comparison with the results of a field-theoretical approach and data of real experiments has been carried out. It has been shown that the critical temperature grows linearly with an increase in the parameters of long-range interaction. Critical exponents have been calculated at different parameters of long-range interaction. It is shown that at small dimensions of a system it is the short-range interaction that exerts the dominant effect on the critical behavior of the system. With an increase in the linear dimension of the system, long-range forces begin to dominate.
Keywords: Ising model; critical phenomena; effects of long-range interaction

The effect of heat treatment in air on the formation of magnetic properties has been studied based on the example of soft magnetic Fe77Ni1Si9B13 and Fe81B13Si4C2 amorphous ribbons characterized by positive magneto-striction. The magnetization distribution in the ribbons in the as-quenched state was shown to affect the efficiency of annealing. Under certain conditions, heat treatment, which results in the formation of mainly amorphous state of ribbon surface, is more efficient for samples characterized by high volume of orthogonally magnetized domains. This can be related to high in-plane tensile stresses, which are induced by hydrogen and oxygen atoms introduced into the ribbon surface upon its interaction with atmospheric water vapor.
Keywords: magnetic permeability; magnetization; soft magnetic amorphous alloys; heat treatment; cooling rate; isothermal annealing temperature; magnetization distribution; interaction with water vapor

Phase transformations have been studied in a variety of different steels with the use of “in situ” electrical resistance measurements. The results were evaluated by metallography of the initial and final microstructures and with consideration of data from the published literature. On this basis a good correlation has been established and it was shown that this method is suitable for such investigations. It even presents certain advantages, thus providing a more complete understanding of the physical metallurgy of steels. We out-lined the field in which the measurement of electrical resistance is particularly suitable and an example of processes that are difficult to monitor using other commonly used methods.
Keywords: electrical resistance measurements; steel; thermal cycling; phase transformations

Evolution of grain–subgrain structure and carbide subsystem upon annealing of a low-carbon low-alloy steel subjected to high-pressure torsion by G. G. Maier; E. G. Astafurova; E. V. Melnikov; A. I. Smirnov; V. A. Bataev; E. V. Naydenkin; P. D. Odessky; S. V. Dobatkin (1101-1110).
The effect of annealing on the evolution of an ultrafine-grain structure and carbides in a 06MBF steel (Fe–0.1Mo–0.6Mn–0.8Cr–0.2Ni–0.3Si–0.2Cu–0.1V–0.03Ti–0.06Nb–0.09C, wt %) has been studied. The grain–subgrain structure (d = 102 ± 55 nm) formed by high-pressure torsion and stabilized by dispersed (MC, M 3C, d = 3–4 nm) and relatively coarse carbides (M 3C, d = 15–20 nm) is stable up to a temperature of 500°C (1 h) (d = 112 ± 64 nm). Annealing at a temperature of 500°C is accompanied by the formation in regions with a subgrain structure of recrystallized grains, the size of which is close to the size of subgrains formed by high-pressure torsion. The average size and distribution of dispersed particles change weakly. The precipitation hardening and the increase in the fraction of high-angle boundaries in the structure cause an increase in the values of the microhardness to 6.4 ± 0.2 GPa after annealing at 500°C as compared to the deformed state (6.0 ± 0.1 GPa). After 1-h annealing at 600 and 700°C, the microcrystal size (d = 390 ± 270 nm and 1.7 ± 0.7 μm, respectively) increases; the coarse M 3C (≈ 50 nm) and dispersed carbides grow by 5 and 8 nm, respectively. The value of the activation energy for grain growth Q = 516 ± 31 kJ/mol upon annealing of the ultrafine-grained steel 06MBF produced by high-pressure torsion exceeds the values determined in the 06MBF steel with a submicrocrystalline structure formed by equal-channel angular pressing and in the nanocrystalline α iron.
Keywords: steel; thermal stability; annealing; ultrafine-grained structure; carbides; high-pressure torsion; recrystallization

Recrystallization of submicrocrystalline niobium upon heating above and below the temperature of thermally activated nucleation by M. V. Degtyarev; L. M. Voronova; T. I. Chashchukhina; D. V. Shinyavskii; V. I. Levit (1111-1118).
The recrystallization of a niobium submicrocrystalline structure created by high-pressure torsion at room temperature has been investigated. It has been shown that continuous recrystallization begins at just 300°С. It has been characterized by the nonuniform growth of microcrystallites, which prevents the formation of a uniform submicrograin structure. The formation of thermally activated recrystallization nuclei at 900°C increases the nonuniformity of grain size and somehow refines recrystallized grains.
Keywords: niobium; submicrocrystalline structure; recrystallization; thermally activated nucleation; grain growth

Fine-structure parameters, such as the effective coherent domain size D hkl and microstrain ε hkl , of Ρd–5.3 at % Ιn–0.5 at % Ru alloy foil, which was subjected to electrolytic hydrogenation and subsequent prolonged (for 55000 h) relaxation, have been determined using X-ray diffraction data. The hydrogenation and subsequent relaxation of the alloy have been found to result in the refinement of coherent domains CD(hkl) and increase in the microstrains ε hkl .
Keywords: X-ray diffraction analysis; physical broadening of diffraction maxima; fine-structure parameters

Effect of cyclic treatment on the formation of a fragmented structure in a sparingly alloyed martensitic steel by T. I. Tabatchikova; I. L. Yakovleva; S. Yu. Delgado Reina; A. I. Plokhikh (1123-1128).
Methods of metallography and transmission electron microscopy were used to study the structure of a high-alloy low-carbon steel of martensitic VKS-10 class subjected to cyclic treatment according to different regimes. It has been found that the warm deformation in the α state at 700°C causes the fragmentation of the structure; however, the decomposition of the α solid solution and the precipitation of coarse carbides leads to a significant decrease in the strength. It has been shown that 12 cycles of treatment, including austenitizing at 1000°C, rolling at 700°C, and subsequent γ → α transformation during rapid cooling do not lead to a noticeable fragmentation of the structure. It has been found that the deformation of the overcooled austenite by rolling carried out using 12 cycles in the range of temperatures of 700–500°C and subsequent γ → α transformation lead to the formation of a fragmented structure with a large fraction of fine grains with a size less than 0.5 μm. This treatment and the subsequent tempering at 530°C for 1 h allow us to increase the strength and hardness of the VKS-10 steel at an insignificant decrease in the plasticity.
Keywords: low-carbon high-alloy steel; structural heredity; deformation; rolling; martensite; fragmented structure

The structure and the process of texture formation in ribbons made of Cu–Ni–M (M = Fe, Cr, V) ternary alloys have been studied upon cold rolling deformation to a degree of ~99% and subsequent recrystallization annealing. The possibility of obtaining a perfect cube texture in a thin ribbon made of copper–nickel-based ternary alloys with additives of iron, chromium, and vanadium has been shown, which opens the prospects of the use of these alloys as substrates in the technology of production of tapes of high-temperature second-generation superconductors. Optimal annealing regimes have been determined, which make it possible to obtain a perfect biaxial texture close to single-crystalline one with the content of cube-oriented grains {001}〈100〉±10° more than 99% on the surface of the textured ribbon.
Keywords: ternary copper alloys; cold rolling; deformation texture; annealing; recrystallization; perfect cube texture; yield stress

Role of stresses and temperature in the Z ordering of carbon atoms in the martensite lattice by P. V. Chirkov; A. A. Mirzoev; D. A. Mirzaev (1138-1143).
A numerical solution is given to the equation of the statistical Zener theory of the predominant ordering of carbon atoms in the z sublattice of octahedral interstices of martensite in carbon steels depending on the stress and temperature. It has been found that the external compressive stress applied along the axis of martensite tetragonality decreases the order parameter and that there is a critical value of the stress above which the degree of tetragonality of the lattice falls off jumpwise to zero. Based on the numerical analysis, a discussion of the dependences of the degree of ordering of carbon atoms and the critical stress on the temperature and carbon concentration has been performed.
Keywords: statistical analysis; tetragonality of martensite; order–disorder

Structure and thermophysical properties of aluminum-matrix composites by N. B. Pugacheva; N. S. Michurov; E. I. Senaeva; T. M. Bykova (1144-1151).
The microstructure and thermophysical properties of aluminum-matrix composites have been studied, in which a granulated Al–Zn–Mg–Cu alloy has been used as the matrix, and SiC particles taken in the amounts of 10, 20, and 30 vol % have bee used as the filler. It has been shown that, with an increase in the amount of the filler, the temperatures of the solidus and liquidus of the composites and the values of the thermal expansion coefficient and density increase, whereas the heat capacity, thermal conductivity, and thermal diffusivity decrease. The heat capacity of the composite depends on the amount of the filler: upon heating from 25 to 500°С, the heat capacity of the composite with 10 vol % SiC increases by only 16%, while that of the composite with 20 vol % SiC increases by 19%; and, at 39 vol % SiC, it increases by 36%.
Keywords: aluminum-matrix composite; aluminum; silicon carbide; particles; liquidus; solidus; heat capacity; thermal conductivity; thermal diffusivity; density; microhardness

Investigation of the structure and properties of the material of various zones of the welded joint of the austenitic nitrogen-containing steel upon elastoplastic deformation by E. S. Gorkunov; E. A. Putilova; S. M. Zadvorkin; A. V. Makarov; N. L. Pecherkina; G. Yu. Kalinin; S. Yu. Mushnikova; O. V. Fomina (1152-1162).
The structural, mechanical, and magnetic properties of metal cut out from the welded joint and from the near-weld zone of the welded joint of high-strength nitrogen-containing 04Kh20N6G11M2AFB austenitic steel have been investigated. The behavior of the magnetic parameters of materials under study subjected to various schemes of loading, such as tension, torsion, internal pressure, and combination of tension and torsion have been investigated. It has been established that the metal of the welded joint and near-weld zone of the welded joint, just as the base metal, has a stable phase composition and magnetic properties under various loading conditions. It has been concluded that 04Kh20N6G11M2AFB steel can be used in the fabrication of welded parts and elements of welded constructions that require low magnetization and high stability of magnetic characteristics under the force action.
Keywords: high-nitrogen corrosion-resistant steel; welded joint; structure; stability of magnetic characteristics; normal and tangential stresses

Evolution of the structure and mechanical properties of sheets of the Al–4.7Mg–0.32Mn–0.21Sc–0.09Zr alloy due to deformation accumulated upon rolling by V. S. Zolotorevskiy; R. I. Dobrojinskaja; V. V. Cheverikin; E. A. Khamnagdaeva; A. V. Pozdniakov; V. S. Levchenko; E. S. Besogonova (1163-1169).
The mechanical properties and microstructure of sheets of an Al–4.7Mg–0.32Mn–0.21Sc–0.09Zr alloy deformed and annealed after rolling have been investigated. The total accumulated true strain was εf = 3.33–5.63, and the true strain at room temperature and at 200 °C was εс = 0.25–2.3. The strength properties of the sheets (yield stress σ0.2 = 495 MPa and ultimate tensile strength σu = 525 MPa) in the deformed state were greater than those after equal-channel angular pressing (ECAP) deformation. The mechanical properties of the deformed sheets after annealing depended on the size of subgrains inside the deformed grains bands with high-angle grain boundaries (HABs). With the increase in the annealing temperature from 150 to 300°С, the subgrain size increased from 80 to 300 nm. The relative elongation δ in the as-cast state and after annealing at 200–250°C (δ = 40–50%) was higher than that after annealing at 300–370°C (δ = 24–29%).
Keywords: aluminium alloys; microstructure; transmission electron microscopy; mechanical properties

Effect of various kinds of severe plastic deformation on the structure and electromechanical properties of precipitation-strengthened CuCrZr alloy by A. I. Belyaeva; A. A. Galuza; P. A. Khaimovich; I. V. Kolenov; A. A. Savchenko; S. I. Solodovchenko; N. A. Shul’gin (1170-1178).
The effect of various kinds of severe plastic deformation (equal-channel angular pressing and quasi-hydrostatic extrusion at 77 and 300 K) on the structural formation of precipitation-strengthened CuCrZr alloy has been studied. A combination of experimental methods has been used. Sputtering by deuterium ions was used as the tool for the layer-by-layer study of the alloy structure. The difference between the sputtering yields of the matrix (copper) and precipitates (Cr and Zr) allowed us to visualize the alloy structure to a total depth of 0.5−1 μm. The effect of severe plastic deformation on the precipitate distribution is considered. It has been shown that the main peculiarity of the microstructure is related to the high density of precipitates enriched in chromium, which completely determine the surface roughness. Their distribution is not related to the grain size. The combination of equal-channel angular pressing and quasi-hydrostatic extrusion was shown to lead to the increase in the microhardness of the CuCrZr alloy to 2300 MPa in the case of low-temperature quasi-hydrostatic extrusion (at 77 K) and to the retained high conductivity. It has been proved that the high anisotropy of precipitate shape, microhardness, and sputtering yield of the CuCrZr alloy is determined by equal-channel angular pressing.
Keywords: precipitation-strengthened alloys; CuCrZr alloy; microstructure; precipitates; quasi-hydrostatic extrusion; SEM; electron microprobe analysis