Review of alloys developed using the entropy approach

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 2 2021 using thermodynamic calculations, studies were conducted on the choice of HEAs rational compositions [128, 129]. There is no doubt that in the coming years this approach will be one of the most promising when justifying HEAs for various purposes. Purpose of high-entropy alloys The properties, characteristic of various types of HEAs, give grounds to consider these materials prom- ising for use in the rocket and space industry, aircraft, mechanical engineering, and nuclear power [9, 14, 36, 78, 104]. Attempts are being made to develop HEAs characterized by a high level of heat resistance [26]. According to the results of the work [130], some HEAs can perform the function of radiation-resistant coatings applied to the shells of fuel elements. One of the applications of amorphous HEAs is associated with the formation of high-temperature diffusion barriers between copper and silicon [131]. The possibili- ties of using high-entropy oxide systems in electronics, magneto-optics, microwave devices, and acousto- electronics are discussed [44]. Some of the developed HEAs are characterized by high corrosion resistance and can be used as functional coatings. One of the directions of HEAs development is associated with the development of alloys that can be op- erated under high loads in a high-temperature state [2, 26]. We are talking primarily about materials for the modern aviation industry. In the temperature range of 800-1600 °C, the yield strength of the high-entropy VNbMoWTa alloy is higher than that of the Haynes 230 and Inconel 718 superalloys [19]. The possibility of using HEAs as high-temperature materials was discussed in the works [19, 23, 26, 130, 132-135]. One of the main disadvantages of HEAs based on refractory metals is the high density, which limits its practical use as heat-resistant materials. At the same time, VIAM specialists believe that there are grounds for increas- ing the ductility of heat-resistant materials by expanding the range of elements and forming strengthening phases in the materials. Among the positive qualities, characteristic for the equiatomic alloy CoCrFeMnNi, its high level of fracture toughness, which is 200 MPa × m 1/2 , deserves attention [136]. The increase in the strength properties and ductility of the specified material when cooled to cryogenic temperature [58, 136] makes it attractive for the manufacture of equipment for responsible purposes intended for operation in the Far North. In the works of D.A. Vinnik et al. [44, 137, 138] multicomponent oxide phases with high values of the configurational entropy of mixing are analyzed. The related hexaferrites with the magnetoplumbite structure are considered as materials for the manufacture of permanent magnets, as well as devices for stor- ing and rewriting high-density information. The main factors explaining the possibility of widespread use of hexaferrites in magneto-optics, microwave devices, acoustoelectronics are high values of its hardness, Curie temperature, coercive force, and indices of chemical inertness [44]. It was shown in [139, 140] that hexaferrites containing more than one element replacing iron can differ in the ferromagnetic resonance frequency and transmission capacity. Thus, by varying the composition of the material, one can smoothly change the level of the properties noted above. Russian-language publications in the field of HEAs There are relatively few studies in the field of high-entropy alloys published in Russian. The most detailed review of the work in the field of HEAs, published in the Russian Federation, was carried out by Rogachev and presented in 2020 in the journal “Physics of Metals and Metallology” [17]. It reflects the most important primary sources related to the development of multicomponent equiatomic alloys, as well as analyzes the research carried out in 2017-2020. One of the tasks set by the author was to identify the degree of correlation between the trend chasing of the HEAs concept and the prospects of these alloys as objects corresponding to the “new paradigm of materials science”. The works of Bashev and Kushnerev [22, 78], Firstov, Karpov, Gorban, Krapivka, etc. [23, 24, 27, 103, 115], Nadutov, Makarenko, Volosevich [51], Pushin, Ivchenko, Kourov et al. [31, 36, 141], Chikov, Vyukhin et al. [142-145], Salishchev, Shaisultanov, Kuznetsov et al. [60, 122 ], Kochetov, Rogachev et al.