Vol 125, No 8 (2024)

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.

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.

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.

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.

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 (σ_u) greater than 700 MPa and a relative elongation (δ) greater than 40%, respectively.

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.

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.

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.