Physics of Metals and Metallography (v.106, #2)

A new method of the correction of the expression for the magnetostatic energy in the theory of stripe domain structure of an “open” type of thin ferromagnetic films is suggested.
Keywords: 75.70.Kw

Reflection and refraction of acoustic waves at the boundary between the ferromagnetic Heusler alloy and liquid by M. M. Karpuk; D. A. Kostyuk; Yu. A. Kuzavko; V. G. Shavrov (115-126).
Reflection and refraction of quasi-longitudinal and quasi-transverse acoustic waves at a flat interface between a liquid and a ferromagnetic crystal of the Heusler alloy Ni2 + x + y Mn1 − x Ga1 − y (in the region of its premartensitic and martensitic phase transitions) is considered. The directions of propagation and polarization and the amplitude of reflected quasi-longitudinal and quasi-transverse and of transmitted longitudinal waves in the (110) plane of the crystal are determined. In a wide region of phase transformations of this alloy, the possibility is shown of using temperature to efficiently control the angles of reflection and refraction of wave modes and the coefficients of their conversion due to a colossal acoustic anisotropy of the crystal. Beginning from a certain critical angle of the quasi-transverse wave, the quasi-longitudinal wave arising upon reflection acquires the nature of the accompanying surface vibration and at a large proximity to phase transition can be emitted into the bulk of the crystal. On the basis of the available experimental data for Ni2MnGa crystals, numerical estimations of the above acoustic effects have been carried out.
Keywords: 43.35.+d; 72.55.+s

A microscopic justification has been given for the experimentally observed shift and splitting of maxima of light scattering in silver nanoclusters upon changes in their size. It has been shown that the resonances of metallic nanoclusters can be strongly shifted with allowance for the self-effect in an optical-radiation field. A formula has been derived for the effective polarizability of valence electrons in a spherical metallic nanocluster when the self-effect of electrons in the field of an external optical radiation and the interaction of nanoclusters are taken into account. Using this formula, the optical properties of different optical systems composed of nanoparticles can be described, in particular, conditions were obtained under which the real index of refraction of these systems can take negative values. It has been shown that the shift of resonances in metallic nanoclusters makes it possible to reach an ideal antireflection coating of the surfaces of optical media coated by a layer of nanoparticles.
Keywords: 78.20.Bh; 78.67.Bf

On the magnon spectrum in La0.83Ca0.17MnO3 by B. V. Karpenko; L. D. Fal’kovskaya; A. V. Kuznetsov (136-140).
Theoretical expressions are obtained for the spin-wave spectrum in a ferromagnetic cubic crystal with variable-valence ions. Interactions up to the fourth coordination shell (i.e., with 32 neighbors) are taken into account. Both a Heisenberg-type superexchange and a non-Heisenberg double exchange are assumed to occur in the system. The anisotropy energy has a single-ion character. Eighteen interaction parameters are taken into account. The formulas derived for the spin-wave energy are valid for the first full Brillouin zone. For three principal crystallographic directions, the calculated dispersion curves are compared with the experimental curves obtained for La0.83Ca0.17MnO3 using inelastic neutron scattering. As a result, the numerical values of the total exchange parameters for each of the four coordination shells can be found.
Keywords: 76.50.+g; 75.30.Et

Static properties (structure and energy) of vortexlike domain walls in three-layered magnetically triaxial films with the surface of the (110) type have been investigated by the numerical minimization of the complete functional which contains the contributions of exchange, magnetically anisotropic, and magnetostatic energies. Films have been investigated whose layers had different saturation inductions. It is shown that the structure of domain walls and their stability depend substantially on the structure of the layered film. The wall energy in such films changes nonmonotonically depending to the relative thickness of the middle layer.
Keywords: 75.60.Ch; 75.70.Kw

Magnetic structure and phase composition of microinhomogeneous PdMn x Fe1 − x alloys by V. V. Serikov; N. M. Kleinerman; N. V. Volkova; N. I. Kourov (148-156).
Mössbauer analysis of ternary PdMn x Fe1 − x alloys in the range of concentrational transition from a ferromagnetic PdFe (F 1) (T C = 725 K) to an antiferromagnetic PdMn (A) (T N = 815 K) phase has been carried out at temperatures T ∼ 80 and 295 K. An estimation of the relative volumes of the ferromagnetic and antiferromagnetic ordered phases in the molecular-field approximation was performed via calculation of the magnetic susceptibility of the alloy with x = 0.5; an analysis of the microstructure of the alloy with x = 0.45 was performed using the Bitter-figures technique. For the alloys with extreme concentrations, Mössbauer spectra have been obtained in two different forms, i.e., a doublet with H hf < 50 kOe for the antiferromagnetic alloys with x > 0.8 and a sextet with H hf ∼ 350 kOe for the ferromagnetic alloys with x < 0.2. In the intermediate concentration range, a wide spectrum of hyperfine fields 0 < H hf < 350 kOe has been observed, which is due to a microinhomogeneous multiphase state.
Keywords: 76.80.+y; 75.30.Kz

Problem of the origin of the enhanced paramagnetism of icosahedral phases below room temperature is studied experimentally. Temperature dependences of the magnetic susceptibility (χ(T)), Hall constant (R H(T)), and conductivity (χ(T)) of the i phase of a nominal composition of Al63Cu25Fe12 are studied at temperatures of 4.2–400 K in magnetic fields of to 5 T. Temperature-dependent components of these quantities, namely, σ t , χ t , and R t were separated. The temperature-dependent component of the magnetic susceptibility χ t is approximately proportional to T 2. The number of thermally-induced charge carries n t and the ratio χ t /n t are approximately proportional to T 3 and T −1, respectively. Thus, we found two distinctive criteria indicating that temperature-induced changes in the conduction-electron paramagnetism play a substantial role in the magnetic properties of icosahedral phases at low temperatures. Earlier, these changes were considered to be substantial only at temperatures above the Debye temperature.
Keywords: 75.50.K; 61.44.Br

Study of the structural and dimensional features of the magnetization reversal in transparent weak ferromagnets by A. P. Kuz’menko; E. A. Zhukov; V. I. Zhukova; Tsz. Li; A. V. Kaminskii (164-172).
The work id devoted to experimental investigation of the interrelation of magnetic growth inhomogeneities and dimensions of thin platelet samples with magnetoelastic interaction and nonlinearity of the dynamics of domain walls in fields that are substantially lower than the spin-flop field in weak ferromagnets (orthoferrites). It is shown that the excitation of elastic vibrations by a moving domain wall bears a resonance nature.
Keywords: 75.60.-d; 76.70.Hb

Structure of three Zlatoust bulats (Damascus-steel blades) by V. M. Schastlivtsev; V. Yu. Gerasimov; D. P. Rodionov (179-185).
Chemical composition, structure, and hardness of samples of three Zlatoust bulats (Damascus steels), namely, an Anosov bulat blade (1841), Obukhov bulat blade (1859), and a Shvetsov forged bulat-steel blank (crucible steel) have been investigated. The Anosov bulat possesses all signs of the classical Damascus steel; this is a hypereutectoid carbon steel with a structure formed from chains of carbides against the background of fine pearlite (troostite). A banded pattern is revealed on the surface of the blade. The Obukhov blade cannot be referred to classical Damascus steel. The pattern on the surface of the blade is absent, despite the fact that the initial steel is hypereutectoid. The structure of the blade does not correspond to the structure of classical Damascus steel; this is bainite with numerous cementite particles. The Shvetsov sample cannot be regarded as Damascus steel since it is made from a hypereutectoid steel alloyed by managanese and tungsten. The pattern on the surface of the metal is a consequence of the dendritic structure of the ingot which is developed during forging. The structure of this pattern differs from classical damascene pattern, since the latter is formed due to a specific arrangement of a variety of carbide particles against the pearlitic or some other background obtained during heat treatment.
Keywords: 81.30.-t; 61.66.-f

Structural aspect of delamination crack formation during the HTMT of steels with a ferritic structure by D. A. Mirzaev; I. L. Yakovleva; N. A. Tereshchenko; I. V. Gervas’eva; D. V. Shaburov; A. V. Panov (186-194).
The fine structure, texture, and fracture of the ferritic 08Kh18T1 steel subjected to repeated hot rolling at temperatures of 800–1100°C and reductions of 35, 50, and 65% have been studied. When significant strains are reached, a layered subgrain structure forms in the steel, and {100} and {111} planes are predominantly located in the rolling plane. The mechanisms of delamination crack formation during rolling under HTMT conditions are considered. The development of a crack in a material with a layered structure is analyzed theoretically.
Keywords: 62.20.Mk; 81.40.Np

The methods of decreasing temper brittleness of quenched steels are considered, which were proposed by Academican Sadovskii with his colleagues and were based on the study of the nature and specific features of temper embrittlement. Various methods of decreasing steel sensitivity to the development of brittleness are discussed, which are based on the use of new steelmaking technologies and specific features of realization of heat and thermomechanical treatments. The effect of steel quenching from the intercritical range on the development of temper brittleness has been studied in detail.
Keywords: 62.20.Mk; 81.40.Np

It has been established that the processes of high-temperature deformation of polycrystalline aluminum can be monotonic or jumplike. A monotonic time dependence of the root-mean-square voltage of acoustic emission observed in such a process corresponds to the monotonic character of deformation accumulation, whereas macroscopic deformation jumps are accompanied by single high-amplitude pulses of acoustic emission correlating with the strain rate in the jumplike portion. The technique has been developed, and activation parameters (activation energy and activation volume) of the high-temperature deformation process have been determined. The character of the dependence of the activation parameters on the mechanical stress and temperature indicates a good correlation of elementary deformation acts in the course of high-temperature deformation.
Keywords: 43.40.Le; 81.40.Lm

Mechanical behavior of ultrafine-grained titanium rods obtained using severe plastic deformation by I. P. Semenova; A. I. Korshunov; G. Kh. Salimgareeva; V. V. Latysh; E. B. Yakushina; R. Z. Valiev (211-218).
We present the results of the investigation of the mechanical behavior of ultrafine-grained (UFG) titanium rods—semifinished products obtained by equal-channel angular (ECA) pressing in combination with subsequent thermomechanical treatment. This material shows ultimately high values of strength (1240 MPa) and plasticity (relative elongation 12.5%) at room temperature. At the same time, at elevated temperatures the UFG titanium exhibits signs of superplastic behavior with large relative elongations and an enhanced strain-rate sensitivity to the flow stress. The greatest elongation at fracture equal to approximately 300% was reached at 500°C and a strain rate of 10−4 s−1. The microstructure and microhardness of the samples after superplastic deformation have been investigated. It has been established that superplastic treatment can favor “structural improvement” of the UFG titanium and further enhancement in its strength.
Keywords: 62.25.+g; 81.40.Lm