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.

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.

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 physicomechanical and X-ray investigations of high entropy oxide coating obtained by the cathode sputtering of multicomponent alloy CrFeCoNiMn in plasma of compressed vacuum-arc gaseous discharge have been conducted. The hardness of high entropy oxide coating is shown to reach the level of 27 GPa at the elasticity modulus of 270 GPa, which decreases to 17 GPa after annealing at temperature 1100°C during 300 min in the open air. The friction coefficient of coating at small sliding velocities amounts to 0.045–0.132 depending on the coating hardness.

The paper presents the results of investigation of the regularities of the structure and texture formation during rolling of single crystals of Zr-25%Nb alloy differing in their initial orientations relative to the external principal directions in the rolled plate: normal (ND) and rolling directions (RD). The features of rolled single crystals with initial orientations of planes {001}, {011} or {111} parallel to the rolling plane and different crystallographic directions along RD are considered. A comparison of the peculiarities of plastic deformation in a polycrystalline alloy of the same composition is made. For the samples studied, a decrease in the lattice parameter of the beta-phase has been recorded, the minimum of the parameter being observed for different degrees of deformation, varying from 20 to 50%. Observed decrease in the unit cell parameter can be connected with the precipitation of the alpha(alpha')-Zr phase from the deformed nonequilibrium beta-phase of the Zr-25%Nb alloy, i.e. change in the composition of the solid solution. Distributions of the increase in the dimensions of the deformed single crystal along RD and the transverse direction (TD) with its deformation up to 30% in thickness, which indicate the anisotropy of the plasticity of single crystals during their rolling, are constructed on stereographic projection. It is shown, that the deformation of single crystals occurs practically without increasing of their dimensions in the <110> direction with a total thickness deformation of up to 30%. Direction <110> is characterized by maximum hardening (microhardness) with indentation along it, which causes low plasticity of deformed and annealed foils from Zr-25%Nb alloy at the stretching along and across RD, that is connected with the features of their crystallographic texture.

In spite of great efforts undertaken to produce and examine the properties of new high-entropy alloys (bulk or film alloys), the available information is still insufficient for creating scientific ideas that would connect the properties and process parameters of these alloys. We studied the dependence of the composition and structure of Co–Cr–Cu–Fe–Ni films deposited by magnetron sputtering on the physical parameter such as energy flux delivered to the growing film surface. This parameter is directly related to process parameters such as magnetron discharge current (Id) and substrate bias voltage (Ub). The films have a nanocrystalline microstructure and crystallize as a two-phase fcc and bcc solid solution with the following lattice parameters: a = 0.363 nm for the fcc phase and a = 0.294 nm for the bcc phase. Ion bombardment of the growing film induced by bias voltage Ub varying from 0 to –300 V in the substrate influences the film structure and composition. Thus, the films deposited at ~300 eV are noticeably depleted of copper, while the composition of the films deposited without ion bombardment is the same as that of the target. Greater energy flux delivered to the growth surface (higher Id and/or Ub in the substrate) increases the growth surface temperature, leading to grain coarsening and film texturing. The bcc phase also substantially decreases in volume, vanishing in the films deposited at Ub = –300 V. The films formed by the bombardment of ions with ≈100 eV energy showed the maximum (~19 GPa) microhardness.

An analysis of simple structures of the solid-solution non-ordered high-entropy alloys (HEAs) with a bcc crystal lattice has allowed us to determine the effect of various parameters on their physicomechanical properties. It was found that, as the hardness increases, the size mismatch results in a decrease in the modulus of elasticity; however, the normalized hardness characteristic increases. It has been found that, when the enthalpy of mixing of the bcc high-entropy alloys shifts to negative values, its effect on the hardness and modulus of elasticity is nonmonotonic. A formula for calculating the modulus of elasticity of high-entropy alloys with a bcc structure has been suggested that is based on the alloy composition and role of the most refractory metallic component.

Mechanical properties of the Ti30Zr25Hf15Nb20Ta10 high entropy bcc alloy have been studied in wide range of low temperatures (4.2–350K). Values of microhardness and Young modulus at 300K, temperature dependencies of the yield strength, deforming stress and strain rate sensitivity have been registered and analyzed in framework of thermally activated deformation models. Empirical estimates have been made of the microscopical parameters of plasticity, such as Peierls stress, activation energy for dislocations, as well as level of internal stresses.

The tribotechnical properties of high-entropy alloys in pair with 65G steel in air under dry sliding friction conditions are investigated in comparison with wear-resistant steel and powder materials. The sliding friction rate was 6, 8, and 12 m/sec and the pressure was 0.5 and 1.0 MPa. It is determined that the wear intensity of high-entropy alloys at the sliding friction rate 5–10 m/sec under 0.5 and 1.0 MPa loads ranges from 6.1 · 10 –10 g/km to 1.6 · 10 –9 g/km for the samples and from 5.5 · 10 –8 g/km to 1.1 · 10 –8 g/km for the counterface. It is established that, when friction, the shear deformations promote the formation of thermally stable nanostructures with grains 30–70 nm in size in the surface layer of the secondary structures. It is shown that the formation of nanostructures is accompanied with 20–30% increase in hardness for both high-entropy alloys and counterface material. It is established that, when friction, high temperatures at the contact points promote the formation of ordered β-phase with BCC lattice on the friction surface of the Fe 25 Cr 20 Ni 20 Mn 15 Co 10 Al 10 high-entropy alloy.

The wear behavior of a FeCoNiCrMn (counterbody)–Ti 30 Zr 25 Hf 15 Nb 20 Ta 10 (finger) friction pair in the temperature range of 77–873 K has been determined. It has been found out that the finger wear significantly decreases with an temperature increase compared with the counterbody due to the spur increase in the hardness of the friction surface structures of up to 18.0 GPa due to the formation of a high-temperature oxide. It has been revealed that the depth of secondary structures increases with temperature, while at 523 K and higher, it reaches 40 μm.

An analysis of more than 200 high-entropy alloys (HEA) allowed us to find interrelations between the electron concentration, phase composition, lattice parameter, and properties of solid solutions with bcc and fcc crystal lattices. Main conditions for the appearance of high-entropy chemical compounds, such as Laves, σ, and μ phases were determined. The necessary condition for the formation of 100% high-entropy σ phase is the formation of σ phase in two-component alloys for different combinations of elements, which are components of the HEA, and the electron concentration should be 6.7–7.3 electrons per atom. To form a 100% high-entropy Laves phase, the following conditions should be fulfilled: the total negative enthalpy of mixing of alloy is about –7 kJ/mol and less; the difference between the atom sizes in a pair is more than 12%; the enthalpy of the mixing of two present elements is less than –30 kJ/mol; and the average electron concentration is 6–7 electrons per atom. It was shown that the ratios of lattice parameters of solid-solution HEA, which were experimentally determined, to the lattice parameter of the most refractory metal in the HEA determine the value of the modulus of elasticity.

ГСП, Киев-142, Украина В работе выполнено исследование процессов, происходящих при окислении многокомпонентного высокоэнтропийного эквиатомного сплава (ВЭС) FeCoNiMnCr, кристаллизующегося в ГЦК-решётке.Сплав был приготовлен методом вакуумно-дуговой плавки и исследовался методом in situ в высокотемпературной приставке УВД-2000 при температурах 293-1273 К в дифрактометре ДРОН-УМ1 на воздухе.При выборе металлов для ВЭСа учитывались следующие факторы: атомные радиусы металлов (должны быть близкими по отношению друг к другу), соизмеримая электроотрицательность, подобные электронные концентрации элементов, энтальпия и энтропия смешения сплава.Установлено, что сплав в исходном состоянии представляет собой твёрдый раствор на основе кубической структуры с ГЦК-решёткой (а  0,3609 нм) и коэффициентом термического расширения (13,9  0,2)10 6 К 1 в интервале температур 293-773 К. При температурах 873 К и выше были обнаружены оксиды MnO и Fe 2 MnO 4 .Показано, что по сравнению с исходным состоянием образца период ГЦК-решётки твёрдого раствора, отожжённого при 1273 К, уменьшился (а  0,3596 нм), что связано с протеканием процессов перераспределения атомов в кристаллической решётке, а также снижением внутренних напряжений.Измерение микротвёрдости высокоэнтропийного сплава FeCoNiMnCr после окисления выполнялось путём автоматического микроиндентирования на приборе «Микрон-гамма» пирамидой Берковича и дало значение 2,1  0,2 ГПа, а для модуля Юнга -130  5 ГПа.Металлофиз.новейшие технол./ Metallofiz.Noveishie Tekhnol.2014, т. 36, № 6, сс.829-840 Оттиски доступны непосредственно от издателя Фотокопирование разрешено только в соответствии с лицензией 2014 ИМФ (Институт металлофизики им.Г. В. Курдюмова НАН Украины) Напечатано в Украине.

To understand the unique mechanical properties of high-entropy alloys, it is important to know the nature and strength of interatomic interactions between similar and dissimilar atoms. In this regard, the objective of this study is to use the phenomenon of secondary ion emission for Cr 14.3 Mn 14.3 Fe 14.3 Ni 28.6 Co 14.3 Cu 14.3 alloy with fcc structure. The yield of secondary ions for all alloy components and corresponding pure metals is quantitatively compared for the first time and an equation is proposed to calculate the atomic bond energy based on the existing models of secondary ion emission mechanism. Compared to pure metals, the bond energy increases in the alloy for Cr and Fe atoms. The greatest decrease in the bond energy is observed for Mn atoms. Reduction in the bond energy for Co and Ni is insignificant. It is suggested that the atomic interaction energy is influenced by changes in the local electron density in fusion as compared with pure metals.

The phase composition, microstructure, and mechanical properties of the single-phase CrMnFeCoNi high-entropy alloy with fcc lattice produced by argon-arc vacuum melting are studied. The alloy solid-solution hardening mechanism is analyzed. The abnormally high athermic solid-solution hardening of the alloy is due to variation in the Burgers vector along the dislocation line and a vector component perpendicular to the slip plane. The activation energy of dislocation movement and activation volume are calculated. The activation energy of dislocation movement is close to the activation energy of pure metals with fcc lattices, and the activation volume is significantly lower compared to that of pure metals because picosized distortions grow in the crystal lattice of the multicomponent alloy. The ratio of hardness and yield stress for this alloy is examined.

The mechanisms of strengthening of V-Cr-Cu-Ni-Co-Fe-Al high entropy alloy, (W, Ti)N, and TiN-Cu nanocomposite films deposited by DC magnetron sputtering (MS) and combined “vacuum arc evaporation - MS” have been investigated. Combined effect of compositional and structural changes occurring under the ion bombardment results in high (~ 14 GPa) hardness of HEA films. The microstructure of (W, Ti)N films depends on film-forming species arriving at the condensation surface (WN and TiN molecules, W, Ti, and N atoms). When the concentration of molecules is higher than that of atomic nitrogen, dispersed two-phase W2N+β-W material with maximal hardness (~ 55 GPa) forms. When the concentration of N atoms exceeds that of molecules, W2N single-phase film with coarse grains and lower hardness (~ 35 GPa) grows. The hardness of films deposited by simultaneous vacuum arc evaporation of titanium and MS of copper in Ar-N 2 ambient depends on copper content in the film. With increasing the copper content from 0 to ~ 1.5 at % the hardness increases and reaches maximum (~ 42 GPa). Further increase in Cu content decreases the hardness. We discuss the results based on the idea that mechanical properties of a film are defined by the composition of film-forming species and the energy of particles bombarding the growth surface.

High-entropy TiZrVNbTa, AlCrFeCoNiCuV, and TiZrHfNbTaCr alloy coatings with a thickness of 2.5–6 μm and with various phase compositions were deposited by dc magnetron sputtering. The chemical and phase composition of the TiZrVNbTa and TiZrHfNbTaCr coatings do not change substantially during deposition. Only when the substrate bias is higher than –180 V, the deposited AlCrFeCoNiCuV alloy coatings are depleted of Al and Cu. All the coatings are nanostructured, and their microhardness varies between 10 and 19 GPa, and reduced elastic modulus changes between 106 and 192 GPa depending on the phase composition.

A series of high-entropy equiatomic alloys have been analyzed to determine the main factors that influence the formation of various solid solutions and chemical compounds. The key factor leading to the formation of phases in high-entropy equiatomic alloys is mean electron density (e/a). The necessary condition for the high-entropy σ-phase to emerge is the presence of elements forming it in two-component alloys in various ratios, the electron density of the alloy is to be between 6.7 and 7.3 e/a. The Laves phase shows up in the high-entropy equiatomic alloys at a mean electron density of 6–7 e/a in the presence of atoms differing by more than 12% in size and having mixing enthalpy lower than −30 kJ/mol. It is revealed that the lattice parameter in bcc high-entropy equiatomic alloys influences their elastic modulus and hardness.

Alloys of the AlCrFeCoNiCu (x) system (x = 0, 0.5, 1.0, 2.0, 3.0) were smelted by argon-arc smelting in pure argon. The phase composition and structure of fabricated alloys are investigated and their mechanical properties are determined. The results showed that an increase in the amount of copper in alloys leads to a change in the phase composition from single phase (bcc) to three phase (bcc + fcc(1) + fcc(2)), which is accompanied by the structural change from coarse-grain polygonal structure to complex dendritic structure (primary dendrites (DR) + secondary dendrites (SDR) + interdendrite phase (ID)). The region of electron concentrations of alloys, in which bcc and fcc phases are present simultaneously, is determined. The limiting electron concentration of stability of the bcc lattice is found experimentally. Microhardness is measured and Young moduli of alloys over the entire range of varying the copper concentration are determined.