


Vol 125, No 8 (2024)
ЭЛЕКТРИЧЕСКИЕ И МАГНИТНЫЕ СВОЙСТВА
Magnetization distribution in single-crystal of iron-silicon alloys
Abstract
The magnetization distribution in a single-crystalline silicon iron following quenching at the paramagnetic state and after annealing in the ferromagnetic state has been determined by Mössbauer spectroscopy. The specimens containing 5, 6, and 8 at % of silicon had cubic ({100}<001>) and Goss ({011}<100>) orientations of crystallographic axes. An original method of calculating the relative fractions of magnetization oriented along the magnetic easy axes, including in the plane of a single-crystal specimen or at an angle to this plane, was proposed. The parameters obtained as a result of discrete approximation of the Mössbauer spectra were used. It is shown that following quenching at the paramagnetic state the magnetization is oriented approximately equidistantly along the three <100> axes, while after ferromagnetic annealing it redistributes along the <100> directions lying in the specimen plane.



Simulation of the five-component Potts model on triangular lattice by the Monte Carlo method in pure and diluted modes
Abstract
The Monte Carlo method is used to simulate the five-component Potts model on a triangular lattice in pure and diluted modes. Systems with linear dimensions L × L = N and L = 20÷120 in units of interatomic length are considered at spin concentration p = 1.00 and 0.90. The obtained numerical data show that a phase transition of the first kind is observed in the five-component Potts model on a triangular lattice according to the theory. Introduction of an insignificant nonmagnetic order into the considered model leads to the phase transition of the second kind. The fourth-order method of Binder cumulants and the histogram analysis are used to refine the value of localization of the temperature Tl of phase transition of the first kind in the undiluted mode.



Structure and magnetotransport properties of multilayer Co77Fe17Ni6/Cu96In4 and Co77Fe17Ni6/Cu nanostructures with the giant magnetoresistance effect
Abstract
Structural and magnetoresistive properties of multilayer Co77Fe17Ni6/Cu and Co77Fe17Ni6/Cu96In4 nanostructures with a number of magnetic layers and nonmagnetic interlayers of 1 to 11 are studied. The sharp axial ⟨111⟩ texture and more perfect interfaces are shown to form in the nanostructures with Cu96In4 interlayers, and a relatively small magnetoresistance hysteresis is observed. Atomic force microscopy is used to estimate the surface roughness and crystallite size of the samples under study. As the number of layers in the Cu96In4-based samples increases, the crystallite size is found to slightly change from layer to layer in a range of 18–22 nm, whereas, for the Cu-based sample, the crystallite size substantially increases. For superlattices with Cu interlayers, the 10-fold decrease in the magnetoresistance is observed as the thickness of Co77Fe17Ni6 layers slightly, namely, from 1.5 to 2 nm increases.



СТРУКТУРА, ФАЗОВЫЕ ПРЕВРАЩЕНИЯ И ДИФФУЗИЯ
Crystallographic theory and mechanism of the polymorphic β→α transition in a zirconium single crystal
Abstract
A crystallographic theory of the polymorphic bcc → hcp transition in a zirconium single crystal has been formulated. According to the theory, a mechanism of the transition includes the main parameters of the martensitic transformation, namely, the lattice strain and the strain in an invariant lattice. The package of parallel plates that are formed during the transformation is considered as a single martensite crystal. It has been established that the deformation of martensite during this transition (with an invariant lattice) is aimed at restoring the shape of the initial section of the bcc phase (prototype), rather than at obtaining an invariant plane. The calculation shows that shape restoration in the basal plane of the hcp phase is mainly caused by the action of two systems of prismatic sliding. The sliding is concentrated in narrow layers of localized shear, which leads to the formation of a lamellar structure of the package. The shape restoration along the c axisoccurs due to the pyramidal sliding.



Martensite phases in Cu–Zn metastable alloys with the shape memory effect
Abstract
The martensitic transformations in Cu–38Zn and Cu–39.5Zn (wt %) alloys with shape memory effect have been studied using a combination of transmission and scanning electron microscopy, optical metallography, and X-ray diffraction analysis. The cooling of the specimen to low temperatures in the transmission electron microscope column has revealed the features of martensite morphology and fine structure, as well as electron microdiffraction in the alloys. The structural types of martensite phases β2′(3R) and γ2′(2H) have been identified in Cu–38Zn alloys, as well as β2″(9R) and γ2′(2H) – in Cu–39.5Zn alloys. The proposed crystallographic models of martensitic rearrangement in alloys are based on an analysis of X-ray and electron diffraction, including diffuse electron scattering, as well as based on the packing defects of the internal substructure of martensite.



Effect of deformation on the diffusion properties of β-Zr at high temperatures
Abstract
The method of classical molecular dynamics with application of moment tensor potential of interatomic interaction were used to study diffusion properties of pure bcc β-Zr in the temperature range 1800–2100 K. The used potential was pre-trained on the data of ab initio calculations and verified by comparing the calculation results with the available experimental and theoretical data. The constructed potential reproduces the temperature phase transition from hcp α-Zr to bcc β-Zr, the experimental values of the thermal expansion coefficient and the diffusion coefficient, as well as the ab initio calculated equations of state of both phases at low temperatures. The dependence of the self-diffusion coefficient in zirconium is obtained in dependence on the strain in the range from –3 to 3%. It is shown that melting of the distorted structure can occur at a temperature below the melting temperature of the undeformed crystal.



The effect of a Sc : Zr ratio on the corrosion resistance of cast Al–Mg alloys
Abstract
The results of the studies of the corrosion resistance of Al–Mg alloys with different contents of magnesium and different ratios of scandium and zirconium (Sc : Zr) have been presented. The alloys have been obtained using induction casting. The effect of the annealing temperature on the microhardness and specific electrical resistivity of cast Al–Mg–Sc–Zr alloys has been studied. Electrochemical corrosion tests were performed in an environment simulating intergranular corrosion in aluminum alloys. It has been shown that an increase in the content of magnesium results in an increase in the corrosion current, and a decrease in the content of scandium (under the condition of Sc + Zr = const) results in a decrease in the rate of intergranular corrosion. It has been established that the dependence of the corrosion current density on the annealing temperature of Al–Mg–Sc–Zr alloys with an increased Sc : Zr ratio exhibits a non-monotonic pattern with a maximum.



Structure features and mechanical properties of metastable Cu–39.5 wt % Zn (α+β) alloy with shape memory effect subjected to thermomechanical treatment
Abstract
A comprehensive study of structural-phase transformations and physical and mechanical properties of metastable Cu–39.5 wt % Zn α + β alloy with shape memory effect subjected to thermomechanical treatments including cold rolling and annealing has been carried out. The features of the fine structure formed at the intermediate and bainitic phase transformations have been studied using optical and electron microscopy as well as X-ray phase analysis. The temperature intervals of bainitic 3R/9R and other phase transformations were established by differential scanning calorimetry during heating up to 500°C. In the case of the hardened alloy, the temperature of the bainitic transformation was close to 170°C. In mechanical tests conducted using uniaxial tension, it has been demonstrated that cold deformation and post-deformation heat treatment under different modes can be employed to obtain the alloy in high-strength or ductile states. These states are characterized by an ultimate strength (σu) greater than 700 MPa and a relative elongation (δ) greater than 40%, respectively.



Effect of Cа addition on the phase composition and properties of low-alloyed Al–Mn–Fe alloys
Abstract
The phase composition of Al–Ca–Mn–Fe-based aluminum alloys with an unchanged Ca content of 2 wt % and variable Mn (0.5 and 1wt %) and Fe (0.1 and 0.3 wt %) contents is analyzed using calculations and experimental methods. Scanning electron microscopy and electrical resistivity and hardness measurements are used to estimate changes in the phase compositions of experimental alloys with the cast and deformed microstructure (ε = 80%) after annealing in a temperature range of 300–600°C.



Structural defects of superconducting core of the single fiber MgB2/Nb,Cu composite
Abstract
The microstructure of the MgB2 core of the single fiber composite consisting of MgB2, the Nb barrier, and the Cu shell (MgB2/Nb,Cu), which is synthesized by the powder-in-tube method with an ex situ option and by subsequent annealing, has been studied. It is shown that a dislocation microstructure that exhibits high thermal stability is formed in the MgB2 core during cold deformation, in addition to powder compaction. A high dislocation density is observed inside MgB2 grains. Dislocations form walls with small misorientation angles between subgrains. Annealing at a temperature of 900°C for 1 h leads to a higher density of MgB2 ceramics, and the intergranular contact area increases. Moreover, MgO inclusions with a size of 10 nm or less are formed. Thus, various kinds of structural defects are formed, which can be considered as probable pinning centers for the magnetic flux.



Crystallographic features of shear transformation in martensitic and martensitic–ferritic stainless steels
Abstract
The microstructure of stainless steels belonging to the martensitic and martensitic–ferritic classes was examined by orientation microscopy (EBSD) following quenching. The steels comprised 15 wt % Cr, Ni, and Nb, and were distinguished by the addition of Cu or Mo as alloying elements. Using the deviation spectra of interfacial α/γ-boundaries from orientation relationships (OR), as well as the initial austenitic grain recovery procedure according to OR, it was found that the martensitic transformation occurring in both steels is realized according to the closest to Kurdyumov–Sachs OR, or OR. It is demonstrated that the δ-ferrite grains present in the martensitic−ferritic grade steel before and following quenching are in the same OR with austenite. This appears to be a consequence of the nucleation of martensitic crystals at the δ-ferrite/austenite phase interface. It is demonstrated also that the application of orientation microscopy enables the estimation of the grain austenitic structure of stainless steels at elevated temperatures with an acceptable degree of precision. This is achieved by analyzing the structure resulting from shear transformation.



Phase transformations upon crystallization of an Al87Ni6Nd7 amorphous alloy
Abstract
The crystallization process of an Al87Ni6Nd7 amorphous alloy has been studied. It has been established that the crystallization of an amorphous alloy occurs in three stages, and the temperatures and activation energies of each crystallization stage have been determined. At the first crystallization stage, Al nanocrystals are formed; at the second stage, in addition to Al nanocrystals, the crystals of an Al11Nd3 phase are precipitated from the remaining amorphous phase. At the third crystallization stage, a previously unknown crystalline phase is formed. The structure of the new phase has been determined.



Orientation dependence of cyclic stability of superelasticity of Ti50.2Ni49.8 alloy single crystals under compression
Abstract
The effect of marforming (low-temperature compression deformation of В19′-martensite at 203 K and subsequent annealing at 713 K for 0.5 h) on superelasticity (SE), temperature range of SE, and cyclic stability of superelastic behavior 323 K are studied on [001]В2 and [12]В2 single crystals of the Ti50.2Ni49.8 (at %) alloy under compression. It is shown that marforming leads to an increase in the offset yield strength σ0.1 of the high-temperature В2-phase and to the development of SE, which was not observed in quenched crystals. The orientation dependence of the SE temperature range and the cyclic stability of superelastic behavior, which is determined by the orientation dependence of the σ0.1 stresses of the В2-phase, is established. The maximum SE temperature range is 87 K, and the cyclic stability of superelastic behavior at a temperature of 323 K is sound in the [001]В2 orientation with a high σ0.1 stress level of the В2-phase.



ПРОЧНОСТЬ И ПЛАСТИЧНОСТЬ
Crack resistance of maraging steel at cyclic loading
Abstract
The effect of the structure on the strength and crack resistance of maraging steel is studied at cyclic loading. The impact of dispersity of intermetallide precipitates formed during tempering on the cyclic crack resistance is considered. The paper discusses the variation in the characteristics of cyclic crack resistance of the studied steel depending on the elements of its microstructure and on the modes of quenching and ubsequent tempering. It is shown that in a maraging steel with a coarse-grained structure, there is a high level of near-threshold cyclic crack resistance, probably related with the ratio of the number of loading cycles and the size of the cyclic plastic deformation zone.



Structural studies and convergence scenario for a shell made of Mg–Zn–Zr magnesium alloy
Abstract
The paper considers the deformation behavior of a cylindrical shell made of industrial wrought magnesium alloy MA-14 (Mg 93 wt %–Zn 5–6 wt %–Zr 0.3–0.9 wt %) loaded by a method of sliding detonation of a laid-on explosive uniformly placed on the outer surface of the shell. The convergence scenario of the magnesium alloy shell is analyzed on the basis of the X-ray data. The methods of optical and scanning electron microscopy are used to investigate the evolution of the structure at high-rate deformation. The hardness is measured along a radius and over the length of the shell.


