Institute of Technology of Metals

The use of large-mode-area tapered holey fibers with collapsed air holes for refractive index sensing is demonstrated. The collapsing of the holes is achieved by tapering the fibers with a "slow-and-hot" method. This non adiabatic process makes the core mode to couple to multiple modes of the solid taper waist. Owing to the beating between the modes the transmission spectra of the tapered holey fibers exhibit several interference peaks. They shift remarkable to longer wavelengths as the external index increases. The multiple peaks, combined with a fitting algorithm, may allow high-accuracy refractometric measurements which can be used for diverse applications.

It has been shown that atomic and atomic cluster theories cannot be the basis for theories of crystallization and modification of metals and alloys. Based on thermodynamic calculations, a nanostructural theory of metal melts has been developed. In this theory, the main structural elements are not atoms, but nanocrystals. They are thermodynamically stable in the metal melt, so they determine its structure and properties. Crystallization centers consist of nanocrystals. The intensity of aggregation of nanocrystals is determined by the concentration of demodifying surface-active elements. The action of modifiers is explained by the process of linking these elements. Nanostructural theory of metal melts explains the mechanism of action of modifying non-metallic inclusions and intermetallics, the effect of re-modification, high crystallization rate with high cooling intensity of the metal melt. Nanostructural theory of metal melts is the basis for theories of crystallization and modification of metals and alloys.

Crystallization of casting alloys has been shown to be a nanostructured process. Microcrystals of phases in the temperature range of liquidus and solidus, during eutectic and peritectic reactions, are formed from nanocrystals of components A and B of alloys, their free atoms and atomic complexes. Microcrystals of primary austenite and austenite-graphite eutectics during crystallization of cast iron, microcrystals of austenite and δ-ferrite during crystallization of steel are formed as a result of nanostructural reactions from elementary nanocrystals of iron and graphite, free atoms of iron and graphite, iron-carbon complexes. Primary and eutectic microcrystals of silumin are formed from elementary nanocrystals of aluminum and silicon, free atoms of aluminum and silicon, aluminum-silicon complexes.

Based on thermodynamic calculations, it is shown that metal crystallization is an equilibrium nanostructural process. At the beginning, trigonal or tetragonal structure-forming nanocrystals are formed from elementary nanocrystals. Then crystallization centers are formed from them. Further, tetragonal or hexagonal dendrites are formed from them and tetragonal or trigonal structure-forming nanocrystals. Their forms depend on the degree of branching of dendrites. The most branched of them (compact dendrites) are tetragonal or hexagonal crystals.

In this work, the effect of rapid quenching from the partially liquid and solid condition is studied on the as-cast microstructure, tensile properties and fracture features of a secondary hypereutectic Al-18%Si-2%Cu alloy. For comparison purposes, the same ingots of 50 mm in diameter and 300 mm in height were also fabricated using conventional chill casting. The microstructure of the samples was subjected to detailed characterisation using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses. The tensile properties and fracture were also evaluated. A significant grain refinement of the eutectic constituents (α (Al) + Si), as well as primary silicon and intermetallics accompanying coarse plate and Chinese script with a well-dispersed morphology transition for the intermetallics, was observed in the alloy subjected to the rapid quenching. The connection between primary and eutectic silicon was shown metallographically, confirming the fact that primary silicon served as a nuclei site for eutectic silicon. The microstructure refinement, together with a favourable morphology transition, resulted in greatly enhanced tensile properties and the more ductile fracture behaviour of the studied alloy.

We obtain sufficient coefficient conditions for the unique solvability of a multipoint boundary value problem for the Lyapunov matrix differential equation in the case of strong degeneration of the boundary conditions. We suggest an efficient algorithm for constructing the solution.

On the basis of thermodynamic calculations it is shown that crystallization of metals is a thermodynamic process, which takes place mainly at constant temperature. The exception is crystallization at very high cooling rates of the metal melt when the released solidification heat is not enough to stabilize the crystallization temperature of the liquid metal. In crystallization, the specific interfacial surface energy of crystals is not a constant value, but is proportional to their dimensions (bend radius). Nanocrystals of crystallizing phases exist in the metal melt steadily. Metal crystallization aggregates nanocrystals and free metal melt atoms into microcrystals. Mechanism of dendritic crystallization of metals is proposed.

Publication in the conference proceedings of EUSIPCO, Poznan, Poland, 2007

Modern conventional notions of metallic melt structure are associated with clusters that have no interfacial boundaries. The maximum time of formation and life of the cluster is 10 –7 s. Clusters are formed statistically, randomly. According to probability theory, even an elementary cubic crystal cannot be formed in a time of 10 –7 c. The probability of forming a cluster with 100 atoms is zero. It should be considered that the metallic melt is mainly composed of nanocrystals.

Based on thermodynamic calculations, it is shown that metal melting is an equilibrium process that occurs at a constant temperature. In melting, microcrystals mainly disintegrate into nanocrystals. Metal melt is a twophase system consisting of nanocrystals and atomic gas. Nanocrystals ranging in size from one to hundreds of nanometers exist stably in the metal melt.

A new technique for fast fusion of multiresolution satellite images with minimal colour distortion is presented in the paper. The technique allows to reconstruct multispectral images with resolution higher than resolution of the panchromatic image. Combination of image super-resolution restoration and image fusion based on global regression was applied. Super- resolution image restoration is based on simultaneous processing of several multispectral images to reconstruct a panchromatic image with higher resolution. This method is quasi-optimal on minimum squared errors of image restoration.

It has been shown that Brownian movement in water occurs as a result of elastic collisions of ice nanocrystals with Brownian particles. Water consists of 87 % of ice nanocrystals and 13 % of water molecules. At 300 K, the ice nanocrystal in water on average consists of 24 water molecules. Brownian movement is an experimental confirmation of the nanocrystalline structure of liquids. This concept of liquids is of great importance for the theory of crystallization and modification of alloys. In metallic liquids, Brownian motion refers to microscopic non-metallic particles and intermetallides that have densities comparable to melt densities. In liquid aluminum alloys, Brownian particles are microscopic alumina particles that remain in the castings when they solidify.

Based on the calculations of the model of the elementary crystal cell γ‑iron, it is shown that carbon ions cannot be present in its open pores. Carbon in Fe‑C alloys dissolves and distributes mainly as elementary graphite nanocrystals. In steel austenite, carbon is found in elementary graphite nanocrystals and in iron‑carbon complexes. In cast iron austenite, carbon is found in elementary graphite nanocrystals.

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The classical theory of crystallization of metal melts has been investigated. It is shown that it does not correspond to the second law of thermodynamics. Based on thermodynamic analysis, it was found that the classical theory of crystallization of metal melts is very problematic. To solve theoretical problems, it must be considered that the crystallization of metal melts is mainly an equilibrium process in which nanocrystals play a major role.

It is shown that the main technological problems of modifying of structure of silumin castings are: absence of the universal modifiers, limitation of their action in time; saturation of a melt by hydrogen and oxide of silicon. Admixture modifiers do not solve these problems. These problems could be solved by method of hereditary modifying. For this purpose it is necessary to use the silumin castings with a high-dispersible microstructure received by casting in a crystallizer with a high speed of cooling.

The dark matter hypothesis was created to explain the reason for the preservation of stellar clusters from dispersion. The weak point of this hypothesis is the great age of space, which is 13.8 billion years. Based on experimental data, it is shown that the age of space does not exceed 10 thousand years. In this case, the hypothesis of dark matter is not needed, since stellar clusters cannot scatter in such short cosmic time. The dark energy hypothesis was created to explain the reason for the accelerated expansion of space. The basis for this phenomenon is a large amount of spectral redshift of distant luminous space objects. It is shown that this value is mainly determined by the significant absorption of light energy of distant space objects by a huge amount of intergalactic gas, and not by the movement of these objects. In this case, the hypothesis of dark energy is not needed, and space should not rapidly expand and scatter in space.

The established regularities of the formation of powders based on iron and nickel, obtained by the method of mechanical alloying and intended for the deposition of thermal spraying coatings, as well as the manufacture of products by layer‑by‑layer synthesis. The structure, phase composition and properties of materials are investigated. Powders consist of particles with a size of 20–70 microns, differ in the submicrocrystalline type structures, and nonequilibrium phase composition. Thermal spray coatings made of them have a set of properties that significantly exceed the properties of coatings made of commercially available materials. The diameter of the grains of the material obtained by the SLМ method from the synthesized powder is 1.5–2.0 times smaller than that produced from the powder of 316L steel, and the heat resistance is higher.

A mathematical model of energy transfer in metals (alloys) during their melting and crystallization has been developed with the aid of the energy conservation equation under the appropriate boundary conditions. Using a number of substitutions, exact integral solutions of a nonlinear differential heat transfer equation have been obtained for both the liquid and solid phases. The notion of the thermal diffusion ratio concerning the change in the solid state fraction with time related to the reference temperature (the effective average value between the solidus and liquidus temperatures) has been introduced. The exact solutions for the liquid and solid phases are expressed in terms of integrals based on the effective values of the heat capacities of the phases.

Based on thermodynamic calculations, it is shown that in the temperature range of 298–1273 K, heating and cooling of aluminum are thermodynamically equilibrium processes. When aluminum is heated, the molar volume energy of Gibbs decreases and the molar boundary energy of nanocrystals increases. When aluminum is cooled, the molar volume energy of Gibbs increases and the molar boundary energy of nanocrystals decreases. Liquid aluminum is a nanostructured system. Dendritic microcrystals are formed from nanocrystals. They play a large role in the processes of changing the structure of aluminum during its heating and cooling.