Physics of Metals and Metallography (v.115, #12)
Orientational transitions in four-row magnetic-dipole lattices by A. M. Shutyi (1179-1185).
Square lattices with four rows of dipoles have been considered. It has been shown that, if there are several stable equilibrium configurations, an external field excites transitions that change the direction of the dipole moments of one of the lattice rows. Orientational transitions in the structure that consists of intersecting perpendicular lattices have been studied. It has been found that the front of the orientational transition that results in a configuration with rows having alternating directions passes through the region of the intersection of the lattices into the other part of the lattice. The front of the other orientational transitions stops in the region of the intersection. The effect of an external field on certain dipoles located in the region of the intersection makes it possible to control the movement of the orientational-transition front; i.e., the front can be forced to pass through the region of the intersection in the initial direction; its direction can be changed, the configuration of the orientational transition can be changed or the front can be stopped in the region of the intersection.
Keywords: lattice of magnetic dipoles; orientational transition; intersection of dipole lattices; controlling orientational-transition front
Investigation of the effects of aging and temperature dependence of the transverse rigidity of a system in the two-dimensional XY model by V. V. Prudnikov; P. V. Prudnikov; S. V. Alekseev; I. S. Popov (1186-1193).
The phenomenon of aging in the low-temperature nonequilibrium critical behavior of the two-dimensional XY model has been investigated by the Monte Carlo methods from different initial states. The temperature dependence of the transverse rigidity in the low-temperature critical behavior of the two-dimensional XY model has been investigated by the Monte Carlo methods.
Keywords: critical dynamics of a two-dimensional XY model; effects of aging; Monte Carlo methods
Specific features of magnetic and electrical hyperfine interactions in titanates according to ab initio calculations by P. A. Agzamova; Yu. V. Leskova; V. P. Petrov; V. A. Chernyshev; D. O. Zakir’yanov; A. E. Nikiforov (1194-1199).
Ab initio calculations of the parameters of magnetic and electrical hyperfine interactions at the nuclei of magnetic ions 47,49Ti and nonmagnetic ions 139La and 89Y have been performed in the model of a periodic crystal and in the cluster model for lanthanum and yttrium titanates. A comparison has been performed with experimental data and with the results of calculations in the model of crystalline field and with data from calculations in the LDA and LDA + U approximations.
Keywords: orbital physics; titanates; NMR; hyperfine interactions
Kinetic properties of ternary alloys Ni3Mn x Al1 − x by N. V. Volkova; N. I. Kourov; V. V. Marchenkov (1200-1207).
Kinetic properties of Ni3Mn x Al1 − x alloys have been studied at temperatures of 4.2 to 800 K in magnetic fields up to 12 MA/m. Separate contributions to the electrical resistance have been determined: the residual resistance, phonon component, and magnetic component. The behavior of the kinetic properties typical of the ferromagnets is observed, including the positive temperature coefficient of resistance and features in the form of a bend in the curves of the temperature dependence of resistance at the Curie temperature. It is shown that the parameters of the investigated kinetic properties change substantially upon the isomorphic concentration transition L12 → L12 from the ordinary superstructure of Ni3Mn type to the Ni3Al intermetallic compound. It has been revealed that the concentration dependence of the resistance can be described in terms of the percolation theory in the model of effective medium.
Keywords: electrical resistance; thermal emf
Magnetic phase transitions in the Ce(Fe1 − x Si x )2 compounds by A. V. Vershinin; V. V. Serikov; N. M. Kleinerman; N. V. Mushnikov; E. G. Gerasimov; V. S. Gaviko; A. V. Proshkin (1208-1215).
The structure of the Ce(Fe1 − x Si x )2 compounds (with x ≤ 0.075) has been studied and, magnetic susceptibility, heat capacity, and Mössbauer effect have been measured. The compounds with x ≥ 0.05 are antiferromagnetic at low temperatures; as the temperature increases, the compounds become, at first, ferromagnetic and next paramagnetic. The temperatures of magnetic phase transitions have been determined using data on the magnetic susceptibility, and the magnetic phase diagram of the system has been constructed. The heat capacity has been measured and the data were used to calculate the entropy change upon magnetic phase transitions; it is 7.9 and 6.0 J/kg K for CeFe2 and Ce(Fe0.93Si0.07)2, respectively. An analysis of Mössbauer spectra for the alloys in the paramagnetic state allowed us to find that silicon atoms statistically substitute for iron atoms in the crystal lattice intermetallic.
Keywords: rare-earth intermetallic; magnetic phase transition; structural transition; Mössbauer effect; crystal structure; entropy change
On the migration of oxygen in the superconducting YBa2Cu3O7 − x upon heating by I. A. Evstyukhina; N. V. Boiko; V. S. Kruglov; V. Yu. Miloserdin; A. Yu. Mishchenko; S. G. Rudakov; V. T. Samosadnyi; S. V. Shavkin; A. S. Sharapov; A. K. Shikov (1216-1220).
Processes connected with the diffusion of oxygen in targets for the laser ablation of a superconductive ceramics of composition YBa2Cu3O7 − x have been investigated by the methods of thermal analysis. A two-step mechanism of oxygen diffusion upon isothermal annealings in air has been revealed, which is explained by the incorporation of atmospheric oxygen into different positions, namely, into the interstices and directly into the sites of the crystal lattice.
Keywords: high-temperature superconductivity; superconducting phase YBa2Cu3O7 − x ; oxygen stoichiometry; kinetics of oxygen diffusion; thermogravimetric analysis; differential scanning calorimetry
Structural and phase transformations in aluminum-copper alloys under the effect of electroplastic deformation by I. G. Shirinkina; I. G. Brodova; V. V. Astaf’ev; T. I. Yablonskikh; V. V. Stolyarov; A. A. Potapova; A. V. Frolova; V. V. Mukhgalin; A. L. Bel’tyukov (1221-1230).
The deformational structure and the phase composition of binary and commercial aluminumcopper alloys produced using electroplastic deformation by rolling (EPDR) have been studied. It has been shown that structural transformation in the materials and changes in their hardness in the course of EPDR are governed by the initial state, which determines the distribution and the thermomechanical stability of a dislocation ensemble. It has been found that EPDR causes the dynamic deformation-induced aging of the aluminum-based supersaturated solid solution, which is accompanied by the precipitation of the strengthening θ phase in the Al-Cu alloy and the S phase in the D16 alloy.
Keywords: aluminum alloy; electroplastic deformation by rolling; cold deformation; current density
Choice of copper-based alloys for ribbon substrates with a sharp cube texture by Yu. V. Khlebnikova; D. P. Rodionov; I. V. Gervas’eva; T. R. Suaridze; Yu. N. Akshentsev; V. A. Kazantsev (1231-1240).
It has been shown that, in some copper-based alloys subjected to cold deformation by rolling to 98.6–99% followed by recrystallization annealing, a sharp cube texture can be produced. Optimum conditions of annealing have been determined, which make it possible to produce a sharp biaxial texture in Cu-Ni, Cu-Fe, and Cu-Cr alloys with the fraction of cube grains of more than 95%; this opens a possibility of using thin ribbons made of these alloys as substrates for multilayer film compositions, in particular when developing second-generation high-temperature superconductors.
Keywords: copper-based alloys; cold deformation by rolling; annealing; recrystallization; perfect cube texture; electron diffraction
Structure and ductility of the heat-affected zone of welded joints of a high-strength steel by T. I. Tabatchikova; A. D. Nosov; S. N. Goncharov; N. Z. Gudnev; S. Yu. Delgado Reina; I. L. Yakovleva (1241-1248).
Methods of optical microscopy and scanning and transmission electron microscopy have been used to study the structure of welded joints of a high-strength structural steel with different types of the weld metal. The impact toughness of the heat-affected zone (HAZ) has been determined at temperatures of +20 and −40°C. Based on the fractograph investigations of the character of the fracture of the welded joints after tests for impact bending, the regions that are the most dangerous for crack initiation have been determined. Structural factors that affect the brittleness of the near-weld zone of welded joints with the austenite metal of the weld are indicated, including the existence of an austenite-bainite structure and coarse carbides, as well as the specific distribution of hydrogen.
Keywords: heat-affected zone; welded joint; cold cracks; impact toughness
Peculiarities of the volume ratio of α and β phases in the superplastic eutectic Bi-43 wt % Sn Alloy by V. F. Korshak; P. V. Mateychenko; Yu. A. Shapovalov (1249-1258).
This work deals with the study of the volume ratio of α(Sn) and β(Bi) phases in the as-cast eutectic Bi-43 wt % Sn alloy, as well as in this alloy after casting, followed by compression in a hydraulic press to a degree of deformation of ∼70%, and in this alloy aged for various time intervals. This alloy demonstrates superplastic behavior even at room temperature. The experiments were carried out using scanning electron microscopy and electron-microprobe analysis using a JSM-6390LV scanning electron microscope equipped with an INCA-350 attachment for EDS analysis. Based on the obtained cooling curves, it has been found that, under the selected experimental conditions, the crystallization of the alloy is nonequilibrium. The original phase state of the alloy is characterized by an excessive relative amount of the α(Sn) phase compared to the equilibrium amount even for the eutectic temperature, which is indicative of the quenching of the liquid melt. The phase state of the alloy formed in the course of crystallization is metastable. This is confirmed by the volume ratio of the phases in the specimens subjected to fairly long aging. The data on the earlier discovered effect of the enrichment of open outer surfaces of the specimens in tin in the course of aging are presented. As a cause of the metastability of the phase state of the alloy, internal compression stresses are considered, which arise in the course of crystallization due to an increase in the specific volume of the bismuth phase in going from the liquid to the solid state. The results presented are first reported and are significant for gaining insight into the physical nature of the effect of superplasticity.
Keywords: superplasticity; eutectic alloy; phase state; volume ratio of phases; concentration of components; metastability; internal stresses
Effect of alloying with titanium on the microstructure of an oxide dispersion strengthened 13.5% Cr steel by S. V. Rogozhkin; A. A. Bogachev; D. I. Kirillov; A. A. Nikitin; N. N. Orlov; A. A. Aleev; A. G. Zaluzhnyi; M. A. Kozodaev (1259-1266).
Microstructure and phase composition of a high-chromium oxide dispersion strengthened (ODS) steel Fe-13.5% Cr-2% W-0.3% Y2O3 without a titanium additive, as well as alloyed with 0.2, 0.3, and 0.4 wt %Ti, has been studied using transmission electron microscopy. A comparison of the nanoscale state of the steels under investigation with that of an ODS Eurofer steel alloyed with 0.2 wt % V has been carried out. In all of the states found, a high number density of nanosized oxide inclusions has been observed. Upon an increase of the titanium concentration in the steel Fe-13.5% Cr-2% W-0.3% Y2O3 to 0.3 wt %, the average size of the particles decreases, while their number density grows. In this steel, single nanosized (0.1–0.7 μm) grains or their agglomerates have been found, as well as coarse (6–8 μm) grains.
Keywords: transmission electron microscopy; oxide dispersion strengthened steels; alloying additives; structural materials for nuclear engineering