The thesis is devoted to the experimental study of the structural phase state, the calculation of the nucleation time temperature dependence for competing phases, and the modeling of crystallization processes in high-entropy alloys of the Co-Cr-Fe-Ni, Al-Co-Cr-Fe-Ni, Al-Co-Cr- Cu-Fe-Ni systems obtained by laser alloying. The need to use new metal materials with high physical and mechanical properties and operational characteristics, which will ensure the necessary reliability of finished products in extreme conditions, has always been relevant for the development of modern technology. The traditional approach to the creation of new metal alloys consists in choosing one material as the main one and its subsequent alloying in order to obtain the desired combination of mechanical and technological properties. As a result of the application of this principle, a large number of alloys based on one component have been created, including steel, copper, aluminum, titanium alloys, etc. The specified method of materials development is significantly limited from the point of view of the potential application of the obtained metal alloys, even in cases where a significant amount of alloying elements are added to improve the properties. High-entropy alloys have higher mixing entropy values compared to traditional alloys, which are achieved due to an increase in the number of constituent elements (from 5 or more), the concentration of which can vary from 5 to 35 at. %. Such alloys consist of solid solutions (simple crystal structure BCC, FCC) and have improved mechanical properties. Stabilization of solid solutions and prevention of the formation of intermetallic compounds during the crystallization process is ensured by the high entropy of mixing in the initial liquid state. Entropy during the formation of a solid solution increases with the growth of the number of elements according to the Boltzmann hypothesis. High-entropy alloys are characterized by low values of diffusion coefficients compared to traditional alloys, significant hardness and wear resistance, resistance to oxidation, as well as high corrosion and radiation resistance, which allows to significantly expand the scope of their application. The vast majority of known HEAs were produced by methods of vacuum-arc melting, or melting in an argon atmosphere. However, in many cases, it is expedient to create local coatings with increased mechanical properties rather than bulk wind turbines. Among the known methods of obtaining such coatings, laser alloying is one of the most promising due to the high manufacturability of the process. Alloys in which a mixture of BCC and FCC phases is formed are of particular interest when studying HEAs obtained by laser alloying, since high cooling rates can affect the quantitative ratio between phases with different crystal lattices, and the structure of alloys directly affects their properties. HEAs based on FCC solid solution are characterized by low strength and high plasticity, and HEAs with BCC structure, on the contrary, have high strength and low plasticity. Therefore, an urgent task is to create criteria and methods for predicting the crystal structure of HEAs, taking into account the cooling rates typial for laser alloying and the heterogeneous nature of the nucleation and crystallization processes in order to obtain alloys with predetermined properties. The work carried out an experimental study of the phase composition, microstructure, and mechanical properties of four-, five-, and six-component HEAs obtained by the method of laser alloying with equiatomic mixtures of transition metal powders on the surface of technically pure aluminum and iron, the calculation of the temperature dependence of the nucleation time for competing phases and modeling of the crystallization process for high-entropy alloys of the Al-Co-Cr-Fe-Ni and Al-Co-Cr-Cu-Fe-Ni systems during laser alloying. The scientific results obtained in the work and the established physical regularities are of practical interest in the creation of methodological and scientific foundations for the development of high-entropy alloys for purposeful management of their structure and properties, as well as the practical use of this class of alloys - the creation of protective coatings on products from industrial alloys in local places with high degree of adhesion. The object of the research was the formation of phases typical for HEAs in the conditions of high cooling rates of the melt, characteristic of laser alloying. The subject of the study was the establishment of physical regularities of the influence of kinetic factors and chemical composition on the processes of structure formation and mechanical properties of HEAs.
