V. F. Gorban

Effect of Electron Density on Phase Composition of High-Entropy Equiatomic Alloys

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.

Ultimate Strengthening, Theoretical and Limit Tool Hardness

The influence of passing from a microcrystalline to a nanocrystalline structure on the mechanical properties of chromium deposited by magnetron sputtering is studied. The possibility of additional strengthening nanomaterials due to enrichment of grain boundaries by “useful” additives elements is established. A wide spectrum of materials in different structural states was investigated by the method of micromechanical tests. The notions of the “theoretical” hardness (largest hardness for the material) and “limit tool” hardness, connected with tool limitations in indentation, are introduced.

Properties of coatings of the Al–Cr–Fe–Co–Ni–Cu–V high entropy alloy produced by the magnetron sputtering

It has been found that coatings from an Al–Fe–Co–Ni–Cu–Cr–V high entropy equiatomic alloy produced by the magnetron sputtering have nanocrystalline microstructures, are textured, and present a solid two-phase solution, which crystallizes in the bcc (a = 2.91 Å) and fcc (a = 3.65 Å) phases. The ion bombardment of a growing coating caused by the bias voltage (0–(–200) V), which has been applied to the substrate, decreases the growth rate of a condensate and affects its composition and structure. It has been shown that the composition of coatings deposited without an ion bombardment coincides with the target composition, whereas an increase of the ion bombardment intensity leads to the depletion of the coating composition in Al, Cu, and Ni and increase the microhardness. The anisotropy of the coating produced has been revealed.

Superhard Vacuum Coatings Based on High-Entropy Alloys

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.

Features of phase and structure formation in high-entropy alloys of the AlCrFeCoNiCux system (x = 0, 0.5, 1.0, 2.0, 3.0)

Alloys of the AlCrFeCoNiCux 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 + fcc1 + fcc2), 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.

Influence of plastic deformation on the phase composition, texture, and mechanical properties of the CrMnFeCoNi2Cu high-entropy alloy

The deformation of the CrMnFeCoNi2Cu multicomponent high-entropy alloy has been studied. X-ray diffractometry, scanning electron microscopy, and microindentation have been used to analyze the distribution of elements, microstructure, phase transformations, and mechanical properties of the CrMnFeCoNi2Cu alloy. It has been shown that this alloy has a high potential of hardening in the course of the cold plastic deformation.

Effect of dry friction parameters on the tribosynthesis of secondary structures on composite antifriction iron-based material

The paper examines the tribological characteristics of a Fe–W–CaF2 composite antifriction material (CAM) in combination with 65G steel during dry friction in air at a high sliding velocity (15 m/sec) and insignificant (0.64–1.28 MPa) pressures. It is established that with twofold increase in pressure (from 0.64 to 1.28 MPa), CAM friction coefficient decreases from 0.25 to 0.20 (by 20%) and wear increases from 0.0158 to 0.03085 mg/km (by 49%) but remains insignificant. The factors acting in the friction process lead to the formation of secondary lubricating films. They prevent mechanical contact between the rubbing surfaces and provide necessary antifriction and operating properties. It is shown that the secondary lubricating films as thin layers with inclusions of solid lubricants differ from the starting material in chemical and phase composition, structural state, and better mechanical characteristics.

Gradient Structure Formation by Severe Plastic Deformation

Severe plastic deformation (SPD) techniques are the best for producing of massive nanostructured materials. The methods of equal channel angular pressure (ECAP) and twist extrusion (TE) are realized by simple shear uniform deformation without change of cross-section sizes of sample. In the case of roll forming (RF) the shear strain is localized in the near-surface layer of metal. Intensity of shear strain in the near-surface layer depends on variation of parameters of deformation and conditions of friction in a contact. Steel 65G (0.65C, 0.3Si, 0.6Mn, 0.3Cr, and 0.3Ni) was deformed by roll forming. Transmission electron microscopy (TEM) of “cross-section” samples was used for studying of gradient structure of deformed material. TEM investigation shown that cell substructure in a near-surface layer have been formed. The depth of deformed layer is approximately 40 micrometers. Average cell size in cross-section direction is about 100 - 200 nm. Thin nanostructure layer with cell size about 20-30 nm was detected. In our opinion such substructure formed due to effect of “good” impurities.

Mechanical Properties and Formation of Phases in High-Entropy CrFeNiCuCoAl x Alloys

The effect of aluminum on the phase composition, microstructure, and mechanical properties of CrFeNiCuCoAlx multicomponent high-entropy alloys is examined. According to X-ray diffraction data, the phase composition of the alloys significantly varies depending on aluminum content: with higher aluminum content, the two-phase structure (mixture of FCC1 + FCC2 solid solutions) changes to a single-phase one (BCC solid solution). Scanning electron microscopy is employed to examine the alloy microstructure and determine the chemical composition of dendritic and interdendritic regions. The primary and secondary dendrites include all elements of the alloy. The interdendritic region has high content of copper as it possesses high pairwise positive enthalpy of mixing with most elements of the alloy. The microhardness increases from 3.1 to 8.4 GPa with greater aluminum content of the CrFeNiCuCoAlx system.

Effect of temperature on wear behavior of high-entropy alloys

The wear behavior of a FeCoNiCrMn (counterbody)–Ti30Zr25Hf15Nb20Ta10 (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.