Browsing by Author "Chornoivanenko, Kateryna O."

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    In situ Composites: A Review
    (G. V. Kurdyumov Institute for Metal Physics of the N.A.S. of Ukraine (IMP NASU), Kyiv, 2021) Movchan, O.  V.; Chornoivanenko, Kateryna O.
    ENG: The review of the works on the fabrication-technology studies, patterns of structure formation, and properties of in situ composites is presented. The main advantage of in situ (natural) composites is the thermodynamic stability of their composition and the coherence (conjugation) of the lattices of the contacting phases. All these ones provide the composite with a high level of the physical and mechanical properties. As shown, composite materials of this type are formed in the process of directed phase transformations, such as eutectic crystallization, eutectoid decomposition, etc., caused by a temperature gradient, as well as a result of diffusional changes in composition. The conditions for the growth of in situ composites are formulated. The mechanisms of growth of composite structures of the eutectic type are considered. The factors influencing on the morphology of structures of the eutectic type are indicated. The considered technological methods make it possible to obtain materials with predetermined properties, in which the size, volumetric composition, and spatial arrangement of phases are characteristic of in situ composites. The paper provides a large number of examples of in situ composites: from low-melting Bi-based alloys to refractory eutectics based on Mo and W (Bi–MnBi, Cd–Zn, Al–Al3Ni, Al–Al4La, Al–Al10CaFe2, Al–Al9FeNi, Al–Al3Zr, Al–Al3Sc, Au–Co, Si–TaSi2, Cr–HfC, Cr–ZrC, Cr–NbC, Cr–NbC, Cr–TaC, Nb–Nb5Si3, Mo–ZrC, Mo–HfC, W–TiC, W–ZrC, W–HfC, etc.). Processes and aspects of structure formation are considered. The influence of additional doping on the structure and properties of composite materials of the eutectic type of binary systems, as well as the features of the structure formation of ternary colonies in the composite are considered.
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    Methods of Improving the Structure and Properties of High-Speed Steels
    (G. V. Kurdyumov Institute for Metal Physics of the N.A.S. of Ukraine (IMP NASU), Kyiv, 2023) Movchan, O.  V.; Chornoivanenko, Kateryna O.
    ENG: We review the works on the technologies of high-speed steels (HSSs) production. Different methods for improving the structure homogeneity of HSSs are considered. State-of-the-art techniques for controlling the structure of steels, the advantages and disadvantages of technologies are formulated. Modification methods for improving the structure of HSSs using various alkali metals, alkaline earth metals, rare-earth metals, misch metals are studied. An increase in cooling rate and the implementation of a spheroidizing treatment process to refine carbide dimensions in HSSs are considered. The sub-zero treatment for improving the fatigue characteristics, impact strength, hardness and wear resistance of HSSs are studied. Powder metallurgy is able to promote the refined and more uniform microstructures. This is their main advantage leading to improved properties and higher isotropy of HSSs. The regularities of phase and structural transformations by diffusion composition changing in the pressed powder mixture of alloys (in which the concentration of the alloying elements is similar to standard HSSs, but with different carbon content) are considered. As shown, using metal injection moulding and coating technologies are efficient ways to improve hardness and wear resistance of HSSs. The possibility of applying chemical-heat treatment to improve the structure of HSSs is shown. Diffusion changes in composition due to chemical-heat treatment allow obtaining in situ composite with a high level of physical and mechanical properties. The influence of additional doping on the structure and properties of composite materials of the eutectic type of binary systems, as well as the features of the structure formation of ternary colonies in the composite are considered.
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    Properties of Railway Wheels Made of Metal with Increased Copper Content
    (Printing House “Technologija”, Kaunas, Lithuania, 2024) Proidak, Yurii S.; Chornoivanenko, Kateryna O.; Pikil, O.
    ENG: The content of non-ferrous metals and, in particular, copper is limited by numerous standards regulating the chemical composition of steels. Thus, for instance, according to the Ukrainian standard for wheel steel, the residual content of nickel, chromium, and copper should not exceed 0.25% each. According to the international UIC standard, this content should not exceed 0.30% each. The residual copper content according to the Japanese standard is allowed to be not more than 0.35%. Many steelmakers are concerned about the presence of copper due to its red shortness. However, the beneficial effect of Cu on hardenability and transformation kinetics is well-known, enabling the formation of a structure with a high density of dislocations at cooling rates feasible in industrial conditions, thus imparting high initial strength to the matrix. Experimental smelting was conducted in the open-hearth furnaces to obtain 0.15-0.60% of copper in the metal. It was found out that the resistance of slag truck wheels made of metal with increased copper content against the formation of ridge notches, which are the main reason for repairs of these wheels during operation, is significantly higher than that of serial ones.
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    Steady State α→γ-Recrystallization of Ferritic Iron Alloys with a Cellular Structure of the Interfacial Surface during Carburization
    (G. V. Kurdyumov Institute for Metal Physics of the National Academy of Sciences of Ukraine, Kyiv, 2025) Chornoivanenko, Kateryna O.; Movchan, O.  V.
    ENG: The mathematical model of single-phase cellular growth of the γ-phase layer during isothermal α→γ-recrystallization of a carburized ferritic iron alloy is constructed based on the performed analysis. Diffusion transfer of carbon through the γ-phase to the interphase surface is the main factor that determines the kinetics of α→γ-recrystallization during carburization. The expression for the distribution of carbon within the γ-phase in front of the flat phase interface (PI) during a steady-state process is obtained. The near-boundary concentration differences between the curved and flat PI are determined. The near-boundary mole fractions of the components inside the α- and γ-phases are calculated. Diffusion processes within the α-phase before PI are described. The expression relating diffusion processes within the α-phase in front of PI with the velocity of front advancement is obtained. Longitudinal sections of cells corresponding to limiting cases of surface-tension coefficient σ and microstructures during α→γ-recrystallization are presented. As shown, the PI cells have a pronounced crystalline facet during solid-phase recrystallization. In this case, the morphology of the cells depends on the crystallographic direction of growth of the γ-phase.