The introduction of high-entropy alloys, notable for their increased hardness and thermal stability, gave impetus to the study of their properties in coatings. High-entropy metal coatings are characterized by high hardness, ranging from 7 to 19 GPa. The general laws governing the influence of various parameters on the mechanical properties of high-entropy metal coatings were analyzed. Single-layer metal, nitride, oxide, and carbide coatings and multilayer nitride coatings from high-entropy alloys produced by different deposition techniques were examined. The phase composition, structure, hardness, elastic modulus, and friction coefficient of the coatings were determined. The mechanical properties of high-entropy coatings, along with those of cast alloys, depend on the lattice parameter. With increase in the lattice parameter in bcc metal coatings, the elastic modulus and hardness decrease. The increased hardness of vacuum high-entropy coatings contributes to decrease in their friction coefficient compared to the cast state. The influence of pressure in the sputtering chamber and the voltage applied to the substrate on properties of the nitride coatings was established. The capabilities of producing thick (up to 80 μm) coatings combining metal and nitride interlayers from high-entropy alloys and determining their properties were shown. For the high-entropy carbide in the TiZrNbVTaHf system, the influence of the lattice parameter on hardness was revealed. The lowest friction coefficient (0.05) was observed in high-entropy oxide coatings. The high-entropy coatings showed high hardness. A hardness level of 19 GPa was reached for a metal coating based on the TiZrNbTaHfCr alloy, 63 GPa for a nitride coating based on the TiZrNbVHf alloy, and 48 GPa for a carbide coating based on the TiZrNbVHfTa alloy. The analysis showed that nitride coatings were the hardest, while the lowest friction coefficient was possessed by oxide coatings.

The influence of electron concentration, mixing enthalpy, and dimensional mismatch on the lattice parameter, elastic modulus, and normalized hardness of fcc high-entropy alloys (HEA) is studied. The lattice parameter, which determines the elastic modulus of HEA, is influenced by both the electron concentration and the mixing enthalpy. A rectilinear dependence of the normalized hardness of these alloys on the dimensional discrepancy is established. Formulas for calculating the hardness and the elastic modulus for hard-soluble HEA with fcc lattice are proposed.

High-entropy alloys (HEA) based on the renewal of elements of the V–IX groups of the Periodic Table, which are capable of forming σ-phase with each other, are studied. The formation of the σ-phase in the range of electronic concentration of 6.7-8 el/at was monitored. The effect of electron concentration on the content of the σ-phase in HEA-containing elements forming the σ-phase in a two-component system is shown. The conditions for the formation of a single-phase structure of the σ-phase during crystallization of multicomponent HEA are determined. The limits of the existence of a 100

By the arc-melting method, we obtain a high-entropy boride by adding boron powder to the Ti 30 Zr 25 Hf 15 Nb 20 Ta 10 alloy. The data of X-ray phase diffraction analysis show that the Ti 30 Zr 25 Hf 15 Nb 20 Ta 10 alloy is a single-phase alloy with body-centered cubic (bcc) structure and that the main phase of the Ti 15.8 Zr 13.4 Hf 7.8 Nb 10.5 Ta 5.3 B 47.2 alloy is MeB boride with insignificant amount of bcc and hexagonal close-packed structures. The microstructure of the obtained alloys is analyzed and it is shown that the addition of boron leads to the segregation of constituent components of the alloy. The addition of boron also increases the level of hardness from 3.5 to 33.5 GPa, the modulus of elasticity from 75 to 290 GPa, and the yield strength from 1.06 to 10.28%.

This work presents a magnetron sputtering system with a cylindrical magnetron to can be used for protective coatings in the internal surface of pipes.The main advantage of the system is to operate in both constant and pulse current mode, to perform the preliminary surface cleaning and to form a single-layer or multi-layer coating in one technological cycle.The tantalum and chromium coatings obtained using the systems with the cylindrical magnetron have high physical and mechanical properties.

We study the influence of electron concentration, lattice distortion, and phase ratio on the hardness, elasticity modulus, and normalized hardness of high-entropy two-phase alloys. It is shown that the fractions of phases depend on the concentrations of electrons. A sharp increase in the FCC phase is observed for electronic concentrations higher than 8 el/at. For high-entropy two-phase alloys, we establish a linear dependence of the normalized hardness on the dimensional mismatch. The values of normalized hardness increase from 0.025 to 0.043 as the level of distortion increases from 2.3 to 4.3%.

The phase composition, type II microstresses, and coherent scattering domains (CSDs) of multicomponent (medium- and high-entropy) bcc solid solutions with an average electron concentration, Csd, ranging from 4.6 to 5.47 e/a were studied. The effect of these characteristics on the hardness and Young’s modulus was analyzed. The alloys were melted in a MIFI-9 vacuum arc furnace using components with a purity of at least 99.5 wt.%; the ingots were remelted six times. The hardness and Young’s modulus of the alloys were determined from nanoindentation curves plotted with a Micron Gamma unit under a load from 0.98 to 2.94 N using a Berkovich diamond pyramid under automated loading and unloading. A relatively small change in the quantitative chemical composition of the samples led to a noticeable change in the lattice parameter, type II microstresses, CSDs, microhardness, and Young’s modulus. The greatest possible type II microstresses and minimum CSD sizes were observed for the alloys characterized by high average mismatch between the atomic sizes of their constituent elements. Increase in the electron concentration in the alloys led to higher hardness and Young’s modulus and lower lattice parameter. Increase in the type II microstresses was also accompanied by higher hardness and Young’s modulus. The microhardness H of alloys significantly exceeded that calculated with the mixture rule, Hmix, and was determined by solid-solution hardening (∆H = H – Hmix ranging between 2.9 and 6.4 GPa). Type II microstresses precisely calculated from the X-ray line width can be used for measuring the distortion of the solidsolution lattice and assessing solid-solution hardening. The relationship between the magnitude of solid-solution hardening, Young’s modulus, and lattice microdistortions (type II microstresses) was proposed.

We determined the effect of temperature on the hardness of thick (up to 100 µm) multilayer metal–metal nitride coatings. The nature of the change in hardness from temperature is individual for each of the tested multilayer coatings. The hardness of composite multilayer coatings largely depends on the ratio of components in the coating. For a multilayer metal–metal nitride composite coating based on molybdenum, the most refractory metal, with a component ratio of ~60 : 40, the hardness reaches 22 GPa at room temperature and a load of 1 kg, and at 900°C, it reaches 5.0 GPa.

We present the results of investigation of the structure and properties of four titanium alloys of the Ti–Nb–Mo system after their subsolidus annealing and annealing with quenching from 870°С. The obtained results indicate that heat treatment strongly affects the phase composition, microstructure, microhardness, Young’s modulus, and elastic properties of investigated specimens. The annealed alloys are two-phase α′ + β alloys and their Young’s modulus is close to Young’s modulus of pure titanium (87–100 GРа). Quenching leads to the formation of the α′′ -phase and the amount of β -phase becomes insignificant. As a result, the microhardness somewhat decreases and Young’s modulus becomes ∼ 1.5 times lower.

The physicomechanical and tribotechnical characteristics of metal–metal nitride composite multilayer coatings in air are determined by friction with 65G steel, a diamond indenter, and an abrasive belt. Friction is carried out in the speed range from 16 mm/s to 12 m/s with a load of up to 100 N. The smallest wear is recorded for the Mo/MoN composite coating, which is characterized by hardness values of about 25 GPa and a friction coefficient of 0.065. It is shown that small wear values with respect to the abrasive belt are characteristic for metal–metal nitride composite multilayer coatings.

The mechanical properties of a high-entropy CrMnFeCoNi2Cu alloy with an FCC lattice have been studied in a broad temperature range (4.2–350 K). The microhardness and Young’s modulus were measured at 300 K for two structural states. The temperature dependences of the yield strength, deforming stress, and strain rate sensitivity have been obtained. It was found that a high-strength state is realized in the alloy while maintaining high plasticity, over the entire temperature range. Empirical estimates of microscopic plasticity parameters and internal and effective stresses have been obtained using the thermally activated deformation model.

The strength properties of cast solid-solution high-entropy alloys based on bcc and fcc lattices in the temperature range from -70 to 900°C have been investigated. Melting ingots weighing up to 200 g were carried out in a vacuum-arc furnace MIFI-9 by melting the mixture in an atmosphere of purified argon with a non-consumable tungsten electrode on a water-cooled copper hearth. The X-ray phase analysis and scanning electron microscopy in combination with INCA X-ray microanalyzer were used. Hardness (HIT) and reduced elastic modulus (Er) were determined using automatic microindentation on a Micron-gamma device using the Berkovich pyramid with a 2 N load in accordance with ISO14577-1:2015. High-temperature indentation of the Vickers pyramid was carried out at a 9.8 N load in vacuum. Thehigh-entropy composition of Nb1.5Cr1.25MoV0.75Ta0.5, which is a solid solution based on the bcc lattice, is characterized by high values of hardness up to 900°C. The yield stress and plasticity of solid-solution alloys are determined depending on the temperatures of the compression tests and the type of crystal lattice. For the high-entropy composition TiZrHfVNbTa based on the bcc lattice, the yield points are almost twice as high as those of the CrMnFeCoNi composition based on the fcc lattice. To create high-entropy alloys with improved characteristics of hot hardness, it is necessary to take into account such factors as the melting point, enthalpy of mixing, and dimensional mismatch in the lattice. It was found that alloys based on bcc lattice at positive values of the enthalpy of mixing are characterized by high characteristics of plasticity and deformability, as well as normalized hardness HIT/Er and compressive yield strength at room temperature. This can be attributed to the cluster structure and distortion of the crystal lattice.

The evolution of phase composition and mechanical properties and the formation of oxide layers on Fe 40–x NiCoCrAl x (x = 5 and 10 at.%) alloys in long-term oxidation at 900 and 1000°C were studied. In the initial cast state, depending on the aluminum content and valence electron concentration, the alloys contain only an fcc solid solution (VEC = 8 e/a) or a mixture of fcc and bcc phases (VEC = = 7.75 e/a). Thin continuous oxide scales containing Cr 2 O 3 and NiCr 2 O 4 spinel formed on the surface of both alloys oxidized at 900°C for 50 h. A further increase in the annealing time to 100 h leads to the formation of aluminum oxide Al 2 O 3 in the scale on the Fe 30 Ni 25 Co 15 Cr 20 Al 10 alloy, having high protective properties. An increase in the oxidation temperature to 1000°C results in partial failure of the protective layer on the alloy with 10 at.% Al. Long-term holding at 900°C (100 h) + 1000°C (50 h) does not change the phase composition of the Fe 35 Ni 25 Co 15 Cr 20 Al 5 alloy matrix, being indicative of its high thermal stability. In the two-phase Fe 30 Ni 25 Co 15 Cr 20 Al 10 alloy, the quantitative ratio of solid solutions sharply changes: the amount of the bcc phase increases from 4 to 54 wt.% and its B2-type ordering is observed. The mechanical characteristics of the starting alloys and those after long-term high-temperature annealing were determined by automated indentation. The hardness (H IT ) and elastic modulus (E) of the cast Fe 35 Ni 25 Co 15 Cr 20 Al 5 alloy are equal to 2 and 147 GPa, respectively, and decrease to 1.8 and 106 GPa after a series of long-term annealing operations. The Fe 30 Ni 25 Co 15 Cr 20 Al 10 alloy shows the opposite dependence: H IT increases from 2.5 in the initial state to 3.1 GPa after annealing and E decreases from 152 to 134 GPa. This indicates that the Fe 30 Ni 25 Co 15 Cr 20 Al 10 alloy is promising as a high-temperature oxidation-resistant and creep-resistant material.

Coatings that consisted of the high-entropy AlTiCrVNbMo alloy were obtained by ion sputtering in plasma of compressed vacuum-arc discharge. The hardness of this metal coating is at the level of 18 GPa due to the presence of nanostructures along with cluster structures. Coatings made of this alloy in a nitrogen atmosphere are solid solutions based on an FCC lattice; the hardness of these coatings is in the range of 28–44 GPa and the combined elastic modulus is in the range of 255–340 GPa for coatings obtained in different technological modes. The hardness values of the oxide coatings are in the range of 33–35 GPa and the values of the combined elastic modulus are in the range of 280–290 GPa. The friction coefficient of this alloy depends on alloy hardness and ranges from 0.24 to 0.061.

The effect of negative bias potential (U-b = -40, -110, and -200 V) during the deposition of multi-element coatings on their composition, structure and mechanical properties was studied. It was established that during the transition from a multi-element alloy to a nitride, a single-phase state possible to form on its basis (based on the fcc metal lattice, structural type NaCl). In this case, the composition (FeCoNiCuAlCrV)N of coatings with increasing U-b is depleted by the element with the lowest enthalpy of formation of nitride (Cu). In (AlCrTiNbSi)N and (AlCrTiZrNbV)N coatings, the content of low-mass elements (Si and Al) decreases with increasing U-b. In (TiZrHfVNb)N coatings of strong nitride-forming elements with increasing U-b to 200 V, the composition practically does not change. The structure of such coatings is characterized by the presence of a texture with the [111] axis. The presence of weak nitride-forming elements in (FeCoNiCuAlCrV)N coatings leads to the formation of texture [110] for large U-b = 110...200 V. In such coatings, the hardness does not exceed 35 GPa. It is shown that to achieve high hardness at high U-b it is necessary to increase the content in the high-entropy alloy of elements with high nitride-forming ability. In this case, in (TiZrHfVNb)N coatings (made of strong nitride-forming elements with a large mass) at U-b = 200 V, the hardness exceeds 45 GPa.

The microstructure, phase composition, and mechanical properties of Ti–Cr–Al–Si–O alloys in ascast state and after annealing at 800°C have been studied. The as-cast alloys with 50 and 60 at.% Ti have two phases: a 1/1 α(TiCrSi) cubic approximant of the quasicrystalline phase and an intermetallic Cr2Ti(C14) Laves phase in different ratios. The as-cast alloy with a high titanium amount (72 at.%) contains three phases: a 1/1α(TiCrSi) approximant and two α-Ti and β-Ti solid solutions. The effect of annealing on the phase composition of the alloys has been studied. After annealing, the alloys with the lowest (50 at.%) and highest (72 at.%) Ti contents change their phase composition with the formation of Ti5Si3 silicide, while the alloy with 60 at.% Ti exhibits high thermal stability—its phase composition remains unchanged. The changes in hardness of the starting and annealed alloys have been examined by automatic indentation. The highest hardness, 11.7 GPa, is shown by the as-cast Ti 72 Cr 20 Al 2 Si 2 (SiO 2 ) 4 alloy. The hardness of the annealed Ti 50 Cr 30 Al 13 Si 2 (SiO 2 ) 5 alloy increases to 14.8 GPa.

Mechanical experiments and X-ray diffraction studies of high-entropy vacuum coatings produced by vacuum arc evaporation and sputtering in a compressed discharge from the equiatomic CrFeCoNiMn alloy have been performed. It is shown that both techniques lead to the formation of a high-entropy σ phase along with the fcc solid solution. The phase composition of the coatings has been determined. The effect of deposition conditions on the lattice parameter, hardness, reduced elastic modulus, and friction coefficient has been established. The dependence of hardness and elastic modulus of the coatings with 100% fcc phase on the lattice parameter is shown. The friction coefficient and linear wear rate of the coatings in pair with diamond at a load of 2.2 N and a rotational speed of 16 mm/sec have been determined.

The structural and chemical microinhomogeneity of the high-entropy TiVZrNbHfTa coating is studied. Electron microprobe analysis shows that the content of elements varies within 10 at.% at a distance of several nanometers. The density of (s + d) electrons remains constant. High-resolution electron microscopy used to examine the fine structure found clusters with the size close to the ‘periodicity’ of the chemical inhomogeneity.

The mechanical characteristics of high-entropy alloys and their constituent metals were examined by dry friction against diamond at low sliding velocities in air. The friction tests were performed at a velocity of 16 mm/sec and a diamond load of 2.2 N. With increasing friction coefficient, the wear rate of the metals and alloys tends to become higher. The linear wear ranges from 1.06 · 10–7 for chromium to 12.76 · 10–7 for aluminum. In addition, the linear wear of multicomponent alloys is lower than that of their constituent metals and ranges from 0.35 · 10–7 to 4.38 · 10–7. The linear wear of high-entropy alloys is a half to a quarter of the linear wear of individual metals because they differ in hardness, the friction coefficients being equal.