Review of alloys developed using the entropy approach

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 2 2021 substitution solid solutions, is a factor that favorably affects the combination of strength properties and its tendency to deformation [26, 7, 108-110]. The combination of strength and ductility indicators allows us to assess the prospects of the developed materials as structural materials in the first approximation. The analysis of the HEAs properties in various conditions of external influence is described in many works [8, 9, 11, 13, 15, 35, 111]. The largest amount of information is related to systems based on 3d- transition metals. The level of strength properties of some of it can be defined as high [17]. According to the data presented in [112], the value of this indicator for the alloy Co30Cr10Fe50V10 reaches 2000 MPa. At the same time, the level of deformation e corresponding to the destruction of the material reaches 71 %. Castings of the high-entropy CoCrFeNiMn alloy having the structure of FCC solid solution are highly plastic ( d = 68 %) and at the same time have a low level of strength properties ( s 0.2 = 140 MPa, s в = 443 MPa) [82]. The author made similar conclusions about the four-component CoCrFeNi alloy. In contrast to manganese, which addition does not significantly affect the strength properties and ductility of the four- component system, the role of vanadium, which leads to the formation of a brittle s -phase, in reducing the ductility of CoCrFeNiV and CoCrFeNiMnV alloys is very noticeable. Vanadium-alloyed alloys exhibit noticeable ductility only when subjected to compressive stresses. A low level of ductility (0.2 %) is also characteristic of CoCrFeNiAlCu alloys with a multiphase structure at room temperature. The thermal stability of the HEAs assumes the preservation of the structure of a disordered solid so- lution when the material is heated and kept in a high-temperature state. The result of the ordering of the solid solution during the annealing process, which consists in the diffusion redistribution of atoms with its fixation in certain thermodynamically favorable positions of the unit cell, can be the formation of a super - structure [17]. Attempts to study the rearrangement of the structure of a solid solution during its heating and control by X-ray diffraction methods were discussed. The solution of this problem, which is important from an applied and fundamental point of view, is methodically problematic. High-entropy alloys are considered as promising heat-resistant materials [26, 113, 114]. In [24], we studied the thermal stability of superhard nitride coatings based on a five-component high-entropy al - loy containing Ti, V, Zr, Nb, and Hf. The objects of the study were thin coatings obtained by vacuum-arc evaporation of a pre-prepared multicomponent cathode. The substrates were plates made of chromium- nickel austenitic steel. Nitride coatings (TiVZrNbHf)N obtained in the presence of nitrogen (0.27–0.66 Pa) when a constant negative potential is applied to the steel plate are characterized by high hardness values (50–60 GPa). This level of material properties is explained by the formation of a polycrystalline structure with a grain size of ~ 30-50 nm and significant distortions of the crystal lattice. The studies carried out in this work indicate a high thermal stability of single-phase nitride coatings. Its structure is preserved during annealing up to 1100 °C [24]. Conclusions about a sufficiently high thermal stability in the temperature range from 20 °C to 1000 °C were made by S.A. Firstov and co-authors on the basis of experimental studies of nine high-entropy alloys [115]. In [82], the possibility of creating new composite materials by diffusion welding of plates made of FeCoNiMnCr and FeCoNi2MnCrCu HEAs and an aluminum alloy of the Al-Si system was studied. It is established that the diffusion processes that occurred during the heating of layered packages led to the formation of heterogeneous materials with the formation of transition zones, dendritic structures, and intermetallic phases. The ultimate strength of the composite obtained by pressure diffusion welding is stable at ~ 615 MPa in the temperature range of 20–850 °C. At the same time, the ultimate strength of the HEAs plates at 750 °C outside the composite did not exceed 375 MPa. The five-component amorphous alloy TiZrHfCuNi, obtained by pouring the melt into a cooled copper mold, acquiring a high level of ultimate strength (1,930MPa), has a ductility close to zero at room temperature [116]. A thin film made of the six-component alloy AlCrMoTaTiZr, characterized by high values of the elastic modulus (11.2 GPa) and hardness (193 GPa), was obtained by magnetron sputtering [117]. In the work of M.V. Karpets and co-authors [102], the results of evaluating the behavior of a high- entropy alloy VCrMnFeCoNix (where x = 1.0; 1.5; 2.0) under friction against non-rigid abrasive particles are presented. After argon-arc melting, a solid solution with a FCC-type lattice and a s -phase similar to the tetragonal s -phase of the binary Fe-Cr alloy were fixed in the alloy structure. As the nickel content