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The stability of high-entropy alloys, like equiatomic and non-equiatomic micro- and nanostructural ones, is relevant when creating stable multicomponent compositions with improved performance. The implementation of such materials is possible by mechanical alloying, magnetron sputtering, as well as by the electrochemical method using the «top-down and bottom-to-top» strategy at moderate temperatures < 200°C with controlled production of both micro-from 0,5 to 20 μm and nanoscale high-entropy alloys with particles from 2 to 10 nm. The well-studied «structure-property» relationship for classical alloys is not yet completely clear for nano-high-entropy alloys, but it is obvious that it is possible to form excellent mechanical characteristics by selecting chemical compositions and a special heat treatment regime. Regarding the chemical composition, requirements are imposed both on the main components and alloying additives. Preliminarily, not only compositions are selected, but also methods for the synthesis of high-entropy alloys, including ab initio (density functional theory), neural network prediction, and classical molecular dynamic simulation with possible conditions for the formation of model nano- high-entropy alloy samples, as well as derivative options. The resulting descriptions are compared with real methods of high-entropy alloys synthesis, for example, exposure to various synthetic media.

The principles of designing high-entropy alloys related to the selection of elements are analyzed. When selecting elements, a parametric approach is used, including chemical and topological parameters. The main chemical parameter is the enthalpy of mixing of elements, the main topological parameter is the atomic radius. It is emphasized that the use of modified atomic radii (which take into account the local electronic environment) better predicts the formation of either amorphous or crystalline high-entropy alloys. Four main effects that determine the properties of high-entropy alloys are considered: the high entropy effect, the lattice distortion effect, the delayed diffusion effect, and the «cocktail» effect. Obtaining nanosized high-entropy materials based on high-entropy alloys is a new promising direction that allows one to significantly expand their areas of application related to energy (catalysis, energy storage, etc.), nanoelectronics, etc. The article analyzes some methods for the synthesis of nanosized high-entropy alloys and materials based on them. basis, developed as catalysts. The improved performance over conventional catalysts is explained in terms of the effects and features specific to multicomponent systems.

With unique mechanical and functional properties, amorphous, nanocrystalline and matrix duplex microstructure membrane alloys based on group V elements actively contribute to the development of hydrogen energy. There are still not completely resolved problems for these new alloys - their low thermal stability, insufficient mechanical strength (plasticity, hardness), and intermetallic and hydride embrittlement. For effective use, alloys with a triple composition are being developed – which, in addition to the elements of group V, also include nickel and titanium as alloying metals. Not only amorphous and nanocrystalline alloys are obtained that are applicable in electronics and power engineering, as well as membrane alloys with a duplex matrix structure that combines amorphous, nano- and quasicrystalline dendritic-hardening phases strengthening the amorphous matrix. In specialized membrane ternary alloys, NiTi and NiTi2 compounds are formed, which stabilize and protect nano- and crystalline membranes from brittle destruction. It has been found that the intense formation of hydrides in these alternative membrane alloys is as undesirable as for palladium-based compounds. The alloys under consideration actually make it possible to obtain high-purity gaseous hydrogen using new compositions instead of expensive membranes based on Pd-Au/Ag/Cu alloys.

An analysis was carried out of influence of , Ti Mo and W on the nature of the amorphous nano- and crystalline structures on the strength and kinetic characteristics – diffusion D and permeability Φ of hydrogen in membrane alloys based on binary Nb - Ni and V - Ni . Doping with Nb - V alloys by titanium, molybdenum and tungsten leads to the gradual replacement of niobium and vanadium, and promotes the formation of several minor phases while acting as barriers for hydrogen diffusion, but contributing hydride reduction processes. A close dependence of the hydrogen kinetics was revealed not only on thermodynamic parameters – temperature and pressure, but also on the presence of free volume in the formed amorphous, nanocrystalline and crystalline alloys. So, the processes of selectivity, the dynamics of hydrogen – its flux J determined by the product of diffusion D and permeability Φ, J = D × Φ depend on the basic composition and the choice of alloying elements (Ti, Mo and W), as well as the formed structures – amorphous, nanocrystalline and duplex, represented by multiphase crystalline microstructures. It was found that a carefully selected composition determines the productivity of the selective process and promotes the release of high-purity hydrogen with its subsequent applications for green energy.