USING A DOUBLE CONVOLUTION OF LORENTZ AND GAUSS FUNCTIONS FOR PROCESSING THE MÖSSBAUER SPECTRA OF THE SUPERSATURATED DISORDERED SOLID SOLUTIONS

An algorithm for mathematical processing of the Mössbauer spectra of supersaturated disordered solid solutions by the Tikhonov regularization method using a double convolution of the Lorentz function and two Gaussians is proposed. By the examples of spectra of supersaturated disordered solid solutions Fe100–xGex (x = 10—25 at.%) and Fe75Si15Al10, it is shown that the algorithm allows more correct processing, which provides a reliable distribution function of the hyperfine magnetic field. It is shown that to take into account the statistical ensemble of nonequivalent local atomic configurations of Fe atoms in disordered supersaturated solid solutions, it is necessary to use not only the convolution of two Gaussian functions, but also the projection scaling factor of the hyperfine magnetic field onto the velocity scale.

Physical Regularities for Cellular Precipitation of Co-, Cu-, and Pb-Based Supersaturated Solid Solutions

The decomposition of supersaturated solid solutions through the cellular mechanism is considered in terms of the physical regularities of this phenomenon. The general characteristics of this process are described. The mechanisms of nucleation and subsequent cell growth, as well as kinetic parameters of processes, are partially described. The influences of some external factors on the cellular precipitation process and its stages are characterized. Particularly, the effects of annealing temperature and a third element on the cellular precipitation process are studied.

Annealing effect on temperature stability and mechanical stress at the “CdxPb1−xS film – substrate” interface

The article establishes the upper temperature steadiness limit of СdxPb1-xS supersaturated solid solutions obtained by chemical bath deposition. СdxPb1-xS (x = 0.06; 0.122; 0.176) and (x = 0.02–0.05) films remained stable under the heating up to 405–410 and 450 K, respectively. SEM studies have shown that heating of СdxPb1-xS films (x = 0.02–0.05) to 620 K leads to the structure destruction. Internal mechanical compressive stresses at the "СdxPb1-xS film-substrate" interface was calculated in the range of 300–900 K for the first time ever, the highest values reached 2000–2750 kN/m2 for a number of the films compositions. In contrast to solid solutions, the expansion stresses up to 100 kN/m2 were derived for the CdS layer at 900 K. The obtained temperature steadiness boundaries and the mechanical stresses of СdxPb1-xS films must be taken into account in the development of photonic devices based on such materials.

Influence of decomposition of oversatured liquid solutions on the structure and microhardness of quickly curing alloys of the Pb–Sn system

The results of studies of the structure and microhardness of foil alloys of the lead–tin system obtained by high-speed cooling from the liquid phase are presented. The foil sample had the following dimensions: length – up to 10 cm, width – up to 1 cm, and thickness – 30–80 microns. Melt cooling rate was not less than 105 K/s. A rapidly cooled foil is chara cterized by a dispersed structure. The size of the discharge of tin and lead does not exceed 5 μm. The specific surface of the interfacial boundaries achieve 1.7 μm–1. Due to supercooling, a microcrystalline structure forms in the foil. The average lengths of chords of random secants on lead and tin grain sections in the Pb–73 at.% Sn alloy foil are 0.8 and 1.8 μm respectively. The texture of (111) lead and (100) tin is formed in the foil of alloys of the lead – tin system under certain conditions. The formation of the structure of lead alloys containing from 20 to 95 at.% tin is due to the occurrence of spinodal decomposition of a supersaturated liquid solution, and, in other alloys, due to decay by the mechanism of formation and growth of nuclei of crystalline phases. The stratification of the liquid solution leads to the formation of areas enriched in lead and tin, which contribute to the formation of crystallization centers that are equally distributed in the volume of the foil. The microhardness of the foil alloys, whose compositions are close to eutectic, is less than the microhardness of massive alloys of the same composition, which is associated with the softening effect of grain boundaries and interphase boundaries. Exposure of these alloys at room temperature causes an increase in microhardness due to a decrease in slippage at the boundaries. The decomposition of supersaturated solid solutions of Pb–5 at.% Sn and Sn–1 at.% Pb alloys leads to a decrease in microhardness due to the weakening of the effect of the solid solution hardening mechanism. The results of the study can be used to create fusible solders, bearing alloys, alloys for cable sheaths with improved physicochemical properties.

Diffusionless (chemically partitionless) crystallization and subsequent decomposition of supersaturated solid solutions in Sn–Bi eutectic alloy

Results of a study on microstructural evolution of eutectic Sn-57 wt.% Bi processed with cooling rates of 10 −2 , 1 K s −1 and approximately 10 5 K s −1 are presented. In order to distinguish different mechanisms of microstructure formation, a comparison with microstructures of different hypoeutectic alloys with compositions down to below the maximum solubility of Bi in Sn–Bi is undertaken. It is found that at the cooling rates of 10 −2 and 1 K s −1 , coupled eutectic growth occurs, leading to lamellar structures with different length scales. At the rapid quenching rates of approximately 10 5 K s −1 , structure formation in the eutectic alloy is qualitatively different. Partitionless solidification resulting in a supersaturated solid solution with the initial composition is observed in both eutectic and hypoeutectic alloys. It is shown that the observed microstructure of the rapidly solidified alloys forms by the decomposition of the supersaturated solid solution. This article is part of the theme issue ‘Heterogeneous materials: metastable and non-ergodic internal structures’.

Magnetic Binary Supersaturated Solid Solutions Processed by Severe Plastic Deformation

Samples consisting of one ferromagnetic and one diamagnetic component which are immiscible at the thermodynamic equilibrium (Co-Cu, Fe-Cu, Fe-Ag) are processed by high-pressure torsion at various compositions. The received microstructures are investigated by electron microscopy and synchrotron X-ray diffraction, showing a microstructural saturation. Results gained from microstructural investigations are correlated to magnetometry data. The Co-Cu samples show mainly ferromagnetic behavior and a decrease in coercivity with increasing Co-content. The saturation microstructure of Fe-Cu samples is found to be dual phase. Results of magnetic measurements also revealed the occurrence of two different magnetic phases in this system. For Fe-Ag, the microstructural and magnetic results indicate that no intermixing between the elemental phases takes place.

Interaction of metals and alloys with gas media under spark discharges

The paper studies the penetration of nitrogen, oxygen, hydrogen, carbon, argon and krypton into copper, nickel, molybdenum, titanium, aluminum, iron and different steels under the action of spark discharges in various media based on radioactive indicators using step-by-step radiometric analysis, macro-, micro-, electron-microscopy and activation autoradiography, Mössbauer and Auger spectroscopy, secondary ion-ionic emission, X-ray diffraction and X-ray microanalysis. The study describes distribution features of penetrating atoms and their concentration profiles. Phase composition of near-surface layers is also determined. It is shown that supersaturated solid solutions of iron in copper and copper in iron are formed during simultaneous iron and oxygen penetration in copper and spinel (Fe6Cu3O4)4. Diffusion of iron and carbon results in supersaturated solid solutions of iron and carbon in copper, copper and carbon in iron, graphite and cementite. Inert gases and nitrogen form solid solutions with copper. Phase composition of near-surface layers in Fe is determined. Iron dioxide FeO, a carbon solid solution in iron with fcc lattice γ-Fe, tetragonal martensite and cementite, two iron (III) hydroxide FeOOH modifications, a supersaturated solid solution of nitrogen and nitride Fe4N, solid solutions of inert gases in iron are formed in the diffusion zone. Simultaneous interaction of molybdenum with iron (the anode material) and various gases results in the formation of substitutional solid solutions of iron in molybdenum and molybdenum in iron, a small amount of interstitial solid solutions of nitrogen and carbon in molybdenum and nitrogen in iron, interstitial phases: molybdenum nitrides and carbides and traces of nitrides of iron (Fe4N, Fe2N) and Fe1,9Mo (λ) phases in the form of needles. Treatment of nickel with a nickel anode in the nitrogen medium promotes formation of a solid solution of nitrogen and nitride Ni3N in the matrix with preserved hexagonal symmetry and lattice parameters that are characteristic of this phase under equilibrium conditions. Atoms of oxygen, nitrogen, carbon and argon are present in the interstitial solid solutions in treatment of nickel in ambient air; however, oxides are not found even on the surface (in the layer ~200 nm). Interaction of titanium with atmospheric gases leads to formation of a solid solution of nitrogen, oxygen, carbon, hydrogen and argon in titanium and titanium nitride Ti2N (ε). Simultaneous saturation of the titanium surface with nickel and nitrogen in the interaction zone causes formation of phases in the following order: nickel nitride; a solid solution of nitrogen and titanium in nickel and a solid solution of both alloying elements in titanium.