Vol 119, No 2 (2018)

The frequency dependence of the total and eddy-current magnetic losses P_tot and P_edd for rotary magnetization reversal has been studied on an Fe–3%Si single crystal with a thickness of d = 0.10 mm within a range of frequencies f = 20–200 Hz and induction amplitudes B_m = 0.25–1.90 T. Some new specific features in the behavior of magnetic losses have been revealed. In particular, the induction that corresponds to the maximal magnetic losses in the curve P_tot = P(B_m) has been established to monotonically decrease with increasing frequency of magnetic field rotation. The specific features of the frequency variation of magnetic losses were discussed based on the observed dynamics for the domain structure of the specimen.

The temperature dependences of the electrical resistivity and magnetization of the Ni₅₀Mn₃₆Sb_14–xZ_x (Z = Al, Ge; x = 0; 2) alloys have been used to determine the characteristic phase transition temperatures. The isothermal entropy change ΔS was determined using Maxwell’s equation and the field dependences of magnetization. The partial substitution of Ge for Sb has been shown to result in a slight increase in ΔS and a shift in the ΔS maximum to the low-temperature range. The substitution of Al for Sb leads to a decrease in the effect and shift in the ΔS maximum to the high-temperature range. It has been found that the maximum magnetocaloric effect has been observed for the Ni₅₀Mn₃₆Sb₁₂Ge₂ composition and is equal to ΔS = 1.3 J/(kg K) in a field change of 10 kOe.

Differential scanning calorimetry has been used to study the effect of the temperature and holding time upon isothermal annealing on the calorimetric effects of the martensitic transformations (MTs) of an aging Ti–50.7 at % Ni alloy produced by hot helical rolling at a temperature of 850–900°С with subsequent cooling in air. The sequence of the phase transitions upon reverse MT has been determined using X-ray diffractometry. The regularities of the evolution of the characteristic temperatures of martensitic transformations after annealing at temperatures of 400, 430, and 450°С for 1–10 h have been analyzed. The results of electron-microscopic studies of the structure of the alloy in the initial state and after annealing have been presented; the features of the morphology of the Ti₃Ni₄ phase precipitated upon aging have been analyzed. Based on the results of calorimetric and structural studies, the temperature of the highest intensity of the aging processes has been determined.

X-ray diffraction analysis has been used to study the structure of the α-Zr matrix phase and the precipitation of β-Nb particles upon the annealing of a Zr–2.5% Nb deformed alloy. It has been found that the process of the precipitation of the strengthening β-Nb particles in the alloy is accompanied by the appearance of fields of elastic interphase deformations in the matrix α phase of the alloy due to the difference in the specific atomic volumes of the crystal structures of the matrix and precipitated phases. It has been shown experimentally that, as a result of the presence of interphase deformations in the alloy, the bcc crystal structure of the precipitating β-Nb particles undergoes monoclinic distortions.

Solid solutions in the form of alloy coatings have been obtained for the first time in the Cd concentration range of 64.5% using ion-plasma sputtering and the codeposition of Nb and Cd ultrafine particles. This supports thermal fluctuation melting and the coalescence of fine particles. A coating of niobium and cadmium layers less than 2 nm thick at 68 at % Cd results in the formation of a new phase identified as NbCd2. The tetragonal fcc phase with lattice parameters a = 0.84357 nm and c = 0.54514 nm forms directly during film coating. XRD data for the identification of the intermetallic compound have been determined. The thermal stability of the NbCd2 intermetallic compound is limited by 200°C. The properties of the synthesized NbCd2 phase are typical of semiconductors.

The effect of high-temperature thermomechanical treatment (HTMT) on the brittleness connected with deformation-induced aging and on the reversible temper brittleness of a low-carbon tube steel with a ferrite–bainite structure has been studied. When conducting an HTMT of a low-alloy steel, changes should be taken into account in the amount of ferrite in its structure and relationships between the volume fractions of the lath and the acicular bainite. It has been established that steel subjected to HTMT undergoes transcrystalline embrittlement upon deformation aging. At the same time, HTMT, which suppresses intercrystalline fracture, leads to a weakening of the development of reversible temper brittleness.

Methods of Mössbauer spectroscopy and electron microscopy have been used to study the effect of the severe plastic deformation by high pressure torsion in Bridgman anvils on the dissolution and precipitation of chromium nitrides in the austenitic and ferritic structure of an Fe_71.2Cr_22.7Mn_1.3N_4.8 high-nitrogen steel. It has been found that an alternative process of dynamic aging with the formation of secondary nitrides affects the kinetics of the dissolution of chromium nitrides. The dynamic aging of ferrite is activated with an increase in the deformation temperature from 80 to 573 K.