Vol 120, No 3 (2019)

Research has been carried out on the dynamics of magnetization of a deformed ferromagnet in an external ac magnetic field. A microscopic model of a deformed magnetically soft ferromagnet has been suggested, based on the example of an α-iron crystal, which takes into account the Zeeman energy, the energy of interaction with the crystal field, and the magnetic dipole interaction of domains. The parameters of model Hamiltonians agreed with the experimental data on the magnetostriction of iron. Minimization of the functional of the density of the crystal energy by varying the magnetization of the sample made it possible to obtain an expression for the equilibrium magnetization of the ferromagnet in the approximation quadratic in terms of deformation. The numerical solution to the dynamic Bloch equation yielded a solution with the characteristic form of a hysteresis loop, the basic parameters of which depend on the amount of relative deformation of the sample. These numerical results were compared with the experimental data.

Nanopowders Ni@C synthesized by gas condensation have a core-shell structure. The size of the core is 2–10 nm and the thickness of the shell is 1–3 nm. The changes in the magnetic properties and the structure of these particles upon annealing in the 100–1100°C temperature range are investigated in this work. Analysis of changes in the magnetic properties, the structure, and the chemical stability shows that the core of the particles in the initial state after synthesis is a supersaturated solid solution of carbon in nickel, which decomposes into nickel and carbon upon high-temperature annealing. Rather slow cooling of nickel particles causes the carbon shell to form. The shell ensures their chemical stability.

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The response of uniform and binary plane lattices of magnetic nanoparticles with uniaxial anisotropy to a short Gaussian pulse of magnetic field is studied in this work. It is shown that the dipole–dipole interaction and the presence of two types of nanoparticles modulate and decrease the response amplitude. The complicated periodic dependence of the amplitude and duration of the system response on the duration and peak value of the applied pulse has been discovered. The possibility of controlling the magnetization reversal of both the entire lattice and its parts by choosing the lattice composition and parameters of the bias field and pulse is demonstrated.

Core–shell CoFe@C and NiFe@C nanocomposites were prepared by gas-condensation synthesis. CoFe@C and NiFe@C particles had bcc and fcc cores, respectively. The treatment of these nanocomposites with hydrochloric acid revealed that they are more chemically stable than Fe@C composites. The maximum specific magnetization of CoFe@C and NiFe@C nanocomposites at room temperature in the field with a strength of 27 kOe was 125 and 58 G cm³/g, respectively. The processes of longitudinal and transverse relaxation of nuclear proton spins of aqueous suspensions of nanocomposites in various magnetic fields (0.5, 1, and 2 kOe) were studied. NiFe@C and CoFe@C nanocomposites have high transverse relaxivity values and can be used as magnetic markers for detection of low concentrations of bioobjects by NMR relaxometry.

In this study, tri-layered Ti/Al composites were synthesized using hot press/roll bonding, and then the annealing treatment was executed in the temperature range of 550–650°C for 2, 4, and 6 h. Interfacial layers were characterized using scanning electron microscopes (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD). The results of microstructural characterization for all annealing temperatures and times indicated that the Al₃Ti compound is the only intermetallic compound observed in the diffusion layers. The Al₃Ti growth obeyed linear kinetics and was characterized by an activation energy of 128.7 kJ mol^–1. The results indicated that the dominant diffusing component was aluminum and the growth of the Al₃Ti layer occurred mainly at Ti/Al₃Ti interfaces.

Optical metallography, transmission electron microscopy, and EBSD analysis have been used to study the structural and phase transformations at various rates of shock-wave loading in the 0.4N–20Сr–6Ni–11Mn–2Mo–V–Nb (Kh20N6G11М2AFB) austenitic stainless steel. The shock deformation of the investigated steel at a rate of 471 m/s resulted in an increase in the density of dislocations to 8 × 10¹⁰ cm^–2 and in the formation of ε martensite with a hcp lattice. An increase in the loading rate from 471 to 904 m/s at the initial room temperature led to a heating of austenitic steel samples without the formation of recrystallized grains but caused a reverse ε → γ transformation with inheritance of dislocations.

This work investigates the effect of the rate, temperature, and magnitude of the strain induced preliminarily to heating for developing shape memory effect on the phase composition, martensite transformation, phase transition temperature, lattice parameters, substructure parameters, and thermomechanic characteristics of the shape memory (SM) 45Ti–45Ni–10Nb (at %) alloy in the press-formed state. The relation between structural and thermomechanical parameters of the alloy is identified. The conditions of prestraining the SM alloy for achieving the best thermomechanic characteristics are determined. The results of this study have been used to develop a fire-protection device for nuclear power facilities.

The following materials-science aspects of the frictional treatment (FT) of martensitic and austenitic steels with sliding indenters were considered in this study: mechanisms of nanostructuring of iron alloys upon FT under sliding-friction conditions; strengthening, resistance to thermal softening, wear resistance, and mechanical characteristics of steels subjected to frictional and combined thermomechanical treatments; application perspectives of the nanostructuring FT in innovative technologies.