Physics of Metals and Metallography (v.114, #3)

First-principles calculations of the total energy of interstitial and substitutional solid solutions in intermetallic compound Ni3Al were performed based on methods using Vienna ab-initio simulation package (VASP). The results of the calculations for interstitial solutions of carbon in Ni3Al confirmed the priority role of chemical interactions over deformational ones for the nearest neighbors. We attempted to use first-principles methods of calculation of the deformation interaction and continuum approaching in the theory of solutions to calculate coefficients of the concentration changes of the lattice spacing. Comparison of the calculation results with experimental data of substitutional impurities in Ni3Al has shown that the proposed method can aid in the study of the distribution of impurity atoms on the sublattices of the ordered phases, intermetallic compounds. We have proposed a method of calculating the partial molar volume of impurity in interstitial solid solutions.
Keywords: interstitial and substitutional solid solutions; effective interactions

Competition of K and F sinks during void formation by A. M. Gusak; N. V. Storozhuk (197-206).
The kinetics of void evolution in a binary alloy with two competing types of vacancy sinks is considered. In the course of interdiffusion, the competition of F and K sinks manifests itself in the competition of Frenkel voiding and Kirkendall shift of a lattice. The equations for the void-growth rate are obtained, depending on the dislocation-sink strengths. The maximal void sizes which can be reached during individual growth stage are found for two cases: (1) for a homogenous quenched alloy and (2) for a diffusion zone during interdiffusion process.
Keywords: interdiffusion; evolution of voids; Frenkel effect; Kirkendall effect

The dependences of the parameters of the formation of vacancies and self-diffusion have been calculated as functions of the degree of compression of iron crystals along isotherms of 300 and 3000 K. It has been shown that, in the range of 1 > V/V 0 > (V/V 0)min, the suppression of the activation processes occurs upon isothermal compression and, upon isochoric heating, they are strengthened. Here, V/V 0 is the ratio of the molar volume of the crystal at a pressure P and temperature T to that at P = 0 and T = 0. However, at V/V 0 = (V/V 0)min = 0.0548, the probability of the formation of vacancies and the self-diffusion coefficient become minimum and, in the course of the further isothermal compression, the strengthening of activation processes occurs, and the activation parameters cease to depend on temperature. It is indicated that this is due to the quantum subbarrier tunneling of atoms over the volume of the crystal. It has been shown that, at V/V 0 < (V/V 0)fr, the surface energy is negative, which should stimulate the process of the fragmentation of the crystal and that (V/V 0)fr > (V/V 0)min. The isothermal dependence of pressure in bcc iron has been estimated upon its compression to V/V 0 = 0.001. Based on the calculated isotherms, the magnitudes of pressure at characteristic points of pressure dependences of the parameters of self-diffusion and surface energy have been estimated.
Keywords: self-diffusion; vacancies; pressure; Debye temperature; Grüneisen parameter; surface energy

Ferro-paramagnetic transition in a Fe-Ni-Si-B alloy in amorphous and crystalline states by B. A. Kornienkov; M. A. Libman; B. V. Molotilov; E. I. Estrin (217-220).
The effect of annealing of an initially amorphous Fe-Ni-Si-B alloy (2HCP) on its Curie temperature for the amorphous and crystalline states has been studied. Annealing at temperatures that correspond to the region of existence of the amorphous phase was found to lead to an increase in the Curie temperature as the annealing temperature increases up to the temperature of the onset of crystallization. The dependence of variations in the Curie temperature on the annealing temperature is described by an exponential function that indicates the development of temperature-activated processes directly in the amorphous phase. In the case of annealing at temperatures above the crystallization temperature, the Curie temperature of the crystalline phase increases with increasing annealing temperature.
Keywords: amorphous phase; crystalline phase; Curie temperature; dilatometry; magnetometry; crystallization

The effects of the electrolytic hydrogenation and oxidation and of the interaction of the surface ribbon with water and vapor on the frequency dependence of magnetic losses per magnetization-reversal cycle are studied based on the example of soft magnetic Fe81B13Si4C2 amorphous alloy, which exhibits a positive saturation magnetostriction. It was shown that, after the hydrogenation and oxidation of soft magnetic amorphous alloys, their frequency dependences of magnetic losses per magnetization-reversal cycle, which are reduced to unit induction, exhibit groups of hydrogen- and oxygen-related peaks in the frequency ranges of 35–55 and 55–80 Hz, which can be explained by the formation of O-A and H-A atomic pairs (where A are atoms of alloy components) and their reorientation in a magnetic field in the course of magnetization reversal at certain frequencies. The formation of analogous groups of peaks for samples of soft magnetic Fe-based amorphous alloys was observed after the interaction of the ribbon surface with water and vapor and after heat treatment in air. This fact confirms the possibility of the hydrogenation and oxidation of the alloys during the aforementioned processes.
Keywords: amorphous alloys; magnetic losses; heat treatment; electrolytic hydrogenation and oxidation

Calculations have been carried out to determine the composition and mass of two equilibrium phases in binary systems under the effect of temperature. We have considered 99 Pb + (1–99)% Sn alloys, which consist of lead- and tin-based solid solutions, in the temperature range of 183–50°C, as well as 99 Co + (1–99)% Cu alloys, which consist of liquid and solid phases, in the temperature range of 1495–1112°C. It has been shown that, depending on the alloy composition, the mechanism of changes in the composition and mass of the phases can involve the passage of both components either from one solid phase into another (Pb-Sn alloys) or from the liquid phase into a solid one (Co-Cu alloys). The concentration of one of the components, which is conventionally called the first component, in the passing substance diminishes to zero. Then, the other (second) component continues to move in the previous direction, the first component moves in the opposite direction, and the second component replaces the first one in the same amount; i.e., the opposing movement of the components from one phase to the other occurs.
Keywords: mechanism of changes in the composition of phases; two-phase equilibrium; crystallization; retrograde solidus

Dislocation structure of cementite in granular pearlite after cold plastic deformation by L. E. Kar’kina; T. A. Zubkova; I. L. Yakovleva (234-241).
Cementite microstructure of the U8 steel with a granular pearlite structure has been investigated by the method of electron microscopy. It has been established that, at the early stages of deformation, carbide particles are deformed through the movement of stacking faults, which are characterized by an α[010] partial shift in the (001) planes of cementite. The Burgers vector, the slip plane [010](001) of the split dislocations forming pileups, and deformation bands have been determined using gb analysis. The stacking fault energy has been estimated in a (001) cementite plane: γsf ∼ 12.8 mJ/m2. With increasing degree of deformation, an additional slip has been shown to occur in cementite by the system [100](011).
Keywords: granular pearlite; cold plastic deformation; electron microscopic analysis; stacking faults; dislocations

Predicting type of morphology of primary phase in aluminum alloy castings produced in a thin-walled metal mold by A. G. Borisov; N. I. Tarasevich; I. V. Korniets; A. I. Semenchenko (242-245).
The direct thermal method, mathematical simulation, and computer experiments have been used to study the relationship between the initial conditions of casting an aluminum alloy and the type of the morphology of its structure. A graph of morphologies has been obtained that makes it possible to predict the resulting structure of the casting.
Keywords: direct thermal method; morphology; mathematical simulation; casting; cooling rate

Effect of Mn and Cr additions on kinetics of recrystallization and parameters of grain-boundary relaxation of Al-4.9Mg alloy by A. V. Mikhailovskaya; I. S. Golovin; A. A. Zaitseva; V. K. Portnoi; P. Dröttboom; J. Cifre (246-255).
Methods of microstructural analysis, measurements of hardness, and temperature and time dependences of internal friction (TDIF and TDIF(iso), respectively) have been used to study recrystallization in cold-rolled alloys and grain-boundary relaxation in annealed alloys. A complex analysis of the effect of additions of transition metals (Mn, Cr) on the magnitude of the activation energy of the background of the internal friction in deformed and annealed states and on the activation parameters of grain-boundary relaxation has been performed. Methods of amplitude dependences of internal friction (ADIF) have been used to determine the critical amplitude that corresponds to the beginning of microplastic deformation in the alloys at different temperatures.
Keywords: internal friction; grain-boundary relaxation; recrystallization; aluminum alloys

In high-carbon vanadium steel, the temperature range (600°C and higher) and time (∼0.1 s) of the formation of vanadium carbide particles 5–10 nm in size at the interphase boundary upon pearlitic transformation have been established. Their distribution in ferrite has been subjected to crystallographic analysis with allowance for the habit of cementite plates. Based on the results of this analysis, a model has been suggested for the volume distribution of vanadium carbide nanoparticles in ferrite interlayers between cementite plates of the pearlitic colony in the form of successive (periodic) corrugated spherical surfaces with a period of ∼20 nm. This particle distribution is determined by the shape of the moving pearlite-austenite interphase boundary and by the direction of growth of the pearlitic colony.
Keywords: pearlite; vanadium carbide; interphase boundary

The growth of a bainite plate is considered to be a relay-type process, in which fast (with τg ∼ 10–10 s) acts of the formation of sublaths (with a width 3d ∼ 1 μm, where d is the thickness of the sublath) occur in an ultrasonic regime and the successive acts are separated by pauses of length τp ∼ 10−2 s. The value τp corresponds to the time of diffusion on a scale d with allowance for the pipe diffusion. The effective growth rate of the plate of bainite ferrite v eff is estimated by the relationship 3dp.
Keywords: bainitic transformation; dynamic theory; carbon diffusion; incubation periods; bainite growth rate

Development of mathematical models of superplasticity properties as a function of parameters of aluminum alloys of Al-Mg-Si system by A. Yu. Churyumov; A. V. Mikhailovskaya; A. D. Kotov; A. I. Bazlov; V. K. Portnoi (272-278).
The article discusses the superplasticity properties and structure parameters of cold-worked alloys of a quasi-binary section of the Al-Mg-Si system with a volume fraction of eutectic particles of 0.08–0.18. Mathematical models of yield stress and effective elongation as a function of the structure and engineering parameters have been developed for alloys of this system. An analysis of the developed models shows that, in the temperature range of 520–560°C, superplastic deformation is controlled by the rate of diffusion of aluminum atoms in the grain bulk.
Keywords: aluminum alloys; mathematical simulation; superplasticity; eutectic particles; yield stress