N. I. Danilenko

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.

Sintering of Zirconium Diboride and Phase Transformations in the Presence of Cr3C2

The kinetics of sintering and phase interactions in the diffusion contact zones of Cr3C2 and ZrB2 are investigated. It is found that using Cr3C2 as a sintering activator for ZrB2 sintering reduces the hot pressing temperature from 2200°C to 1500–1750°C, depending on the Cr3C2 content. The phase formation accompanied with the formation of new high-temperature refractory compounds, such as zirconium carboborides, chromium borides and carboborides, and zirconium-chromium carboborides, rapidly develops at the Cr3C2 and ZrB2 interface within the diffusion zone. An intense diffusion of chromium and carbon into zirconium diboride accompanied with the formation of nonporous states in zirconium diboride (to a depth of 50–100 μm at 1360°C) near diffusion contact zone is observed. It is established that the contact interaction during sintering in the diffusion zone results in the formation of the vanishing eutectic liquid phase, which is consumed to forming new high-refractory compounds (phases based on zirconium carbide and chromium borides).

Structural Changes in Iron upon Large Plastic Deformations and Their Influence on the Complex of Its Mechanical Properties

The influence of the degree of preliminary strain, obtained by equal-channel angular pressing, on the character of work hardening of highly deformed armco-iron is investigated. The effect of the deformation on the evolution of dislocation and cellular structures is analyzed. The structural sensitivity of the mechanical properties is studied.

Structural Features and Solid-Solution Hardening of High-Entropy CrMnFeCoNi Alloy

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.

High-Entropy Coatings—Structure and Properties

Metal and nitride coatings of high-entropy alloys (HEA) having different phase compositions produced by different methods were investigated. It is shown that for the high-entropy coatings is characteristic the presence of the nanostructured state, which in parallel with the cluster structure provides hardness for metal coatings ~ 10–19 GPa; for nitride coatings are characteristic 50–60 GPa and the modulus of inelastic buckling more than 300 MPa. The relation of the lattice parameters, which are defined experimentally, to the parameter of the lattice of the most refractory metal in the HEA reflects the level of the elastic modulus relative to the theoretically possible both in the cast HEA and in metal coatings on their base.

COPPER HARDENING WITH FINE IRON PARTICLES

The production of sintered bulk Cu–(5–25% Fe) pseudoalloys retaining the α-iron phase is studied. The pseudoalloys with a relative density of 97.5–98.1% are prepared by sintering a powder mixture of the metals reduced from their nanosized oxides. The microstructure of the composites represents a copper matrix with α-iron phase inclusions of about 20–200 nm in size, formed by 6.5–16 nm nanocrystallites. When iron content is 5 and 10%, the composites show matrix microstructure in relation to copper, providing 47–52% electrical conductivity and promoting higher hardness (to 1380 MPa) through precipitation hardening of the copper matrix by iron nanoparticles. The composites acquire matrix-statistical microstructure with increasing iron content.

Structure and Mechanical Properties of Quasicrystalline and Approximant Phases Obtained from Titanium-Based Quinary Alloy

The paper presents the investigation of influence of cooling rate and conditions of melt crystallization on the change in phase composition and physical and mechanical properties of alloy Ti60Cr30Al3Si2(SiO2)5. The influence of thermal treatment on the stability and properties of quasicrystalline and approximant phases is studied. Using the method of high-temperature indentation it is found that the diffusive mechanism of plastic strain of the alloy is strongly observed at 800°C (0.68Tm).

Influence of deformation on the structure and the mechanical properties of a high-entropy Fe25Cr20Ni20Co10Mn15Al10 alloy

The phase composition, the hardness, and the elasticity modulus of a high-entropy Fe25Cr20Ni20Co10Mn15Al10 alloy have been studied in the as-cast state, after rolling deformation, and after subsequent high-temperature annealing. The alloy consists of the following two phases: solid substitutional solutions with bcc and fcc crystal lattices; in the as-cast state and after annealing the bcc solid solution is ordered according to B2 type (CsCl). The mixture rule is applied for the calculation of the electron density, the atomic radius, and the melting point at grain boundaries and in the grain volume of the alloy after deformation and annealing. The obtained data demonstrate that the alloy is thermally stable.

‘Fluoroplastic–Multi-Walled Carbon Nanotube’ Composites: Structural, Mechanical, and Tribotechnical Characteristics

The paper studies the production of ‘fluoroplastic–carbon nanotube’ composites, analyzes their structure, and determines their mechanical and tribotechnical characteristics. The properties of the composites depending on the reinforcement content are examined. It is established that addition of only 3% carbon nanotubes significantly increases the hardness and Young’s modulus while the wear becomes two orders of magnitude lower under friction without lubrication. The structure of ‘fluoroplastic–carbon nanotube’ composites is analyzed in detail. A mechanism whereby carbon nanotubes influence the mechanical characteristics and wear resistance is proposed.