Vol 37, No 3 (2016)

There is a solution to the contact problem for sliding on the elastoplastic half space of an individual asperity. It has been shown that the solution adequately reflects the mechanics of individual asperity sliding on the surface of an elastoplastic solid that begins with their interactions under elastic contact conditions and ending the interaction with perfect plastic contact.

A plane elastohydrodynamic problem for a radial sliding bearing with a thin liner under reciprocating motion under a constant load is considered. It has been shown that at the moment of time when the velocity becomes equal to zero the thickness of the lubricating film exceeds zero and that it continues to decrease during a period of time after changing the direction of rotation of the shaft. Film thickness and pressure distributions at various moments in time, as well as time dependences of the eccentricity and the minimum film thickness along the spatial coordinate, are presented for various values of the dimensionless parameter, which depends on the period of reciprocating motion. It has been shown that the smallest value of film thickness over the entire period of reciprocating motion increases with shortening period of reciprocating motion.

It has been shown that the term that describes viscous friction in the standard Prandtl–Tomlinson model and is traditionally introduced artificially can be obtained naturally when the electrification of contact surfaces of dielectrics and conductors is taken into account. The obtained system of nonlinear equations of the Prandtl–Tomlinson model in which electrification is considered has a complex phase space with modes like dynamic chaos, attractors, etc. It has been found that the consideration of electrification leads to the vanishing of the cardinal difference between the traditional modes of movement in the Prandtl–Tomlinson model, namely, the stick–slip mode and the superlubricity mode. Analytical solutions have been obtained for elastically stable movement. It has been shown that the electrophysical characteristics of a friction pair can serve as control parameters for choosing the mode of friction.

The kinetics of damage accumulation in specimens of rail steels with the pearlitic structure manufactured by various companies has been studied in contact fatigue tests. The parameters of damage to the steels, such as the number, dimensions, and area of defects, the angular coefficients of cumulative size statistical distributions of the defects, as well as the velocity of propagation and the attenuation coefficient of ultrasonic waves, have been assessed. New criteria have been proposed to characterize the evolution of damage under contact fatigue. A linear interrelation between the number of surface defects and the number of subsurface defects in the zone of contact has been established, which can serve as a basis for continuously monitoring the condition rail steels and for assessing their current and remaining service lives.

Electrical and tribological properties of a copper-based composite material reinforced by superelastic hard carbon particles are studied. Composite material specimens have been produced using the hightemperature pressing of mixtures of copper and fullerene powders. Electrical and tribological reciprocal tests carried out using the plane-on-plane arrangement have shown that the coefficient of friction of the composite material–Ni pair is lower than that of the reference L63 brass–Ni pair at similar values of contact electrical resistance. The abrasive wear resistance of the composite material is 40 times higher than that of brass. The developed copper-based composite materials reinforced by superelastic carbon particles hold promise for use in sliding electrical contacts.

The tribotechnical characteristics of nitride coatings in a pair with a diamond on air have been determined. The friction has been applied in the range of velocities of 6–16 mm/s and loads on diamond in the range of 1.5–5.5 N. A decrease in the friction for all nitride coatings under study with a decrease in the slip velocity has been determined. The intensity of periodic wear of nitride coatings decreases with growth in the load and varies from 1.6 × 10^–6 to 5.3 × 10^–6. High-entropy nitride coating possesses higher tribotechnical characteristics relative to mononitride coatings.

A comparative study of the antifriction characteristics of specimens of the VT6 titanium-based alloy subjected to nitriding without preliminary treatment and after hydrogen heat treatment has been carried out. Hydrogen heat treatment that precedes nitriding reduces the coefficient of friction of the nitrided specimens of the VT6 alloy in pair with the 12Kh18N10T stainless steel by 4–9% under dry friction and increases it by ~47% in a working fluid, which is a 0.9% NaCl solution. Hydrogen heat treatment combined with ionplasma nitriding reduces the coefficient of friction in working fluid by ~41%.

The effect of deposition conditions on the tribological behavior of titanium nitride thin films produced by reactive magnetron sputtering has been studied. Dependences of the hardness, the width of the friction track, the friction coefficient, and the volume wear of the TiN films on the N₂ reactive gas flow rate have been obtained. Conditions of deposition under which the coatings with the best tribological characteristics are formed have been determined.

Comparative tribotests of bicomponent Al–Pb and Al–Sn coatings produced using the codeposition of the metals from the vapor phase on glass substrates having room temperature and cooled to–100°С have been carried out. It has been found that changes in the mechanisms of the friction of the cryogenic coatings are related to conditions of their condensation. If the dimensions of the structure units of the coatings are similar, the tribological characteristics of these coatings are inversely proportional to the strength and the adhesion of their components. The most fusible metals are recommended for use as the solid-lubricating component of the coatings, since they have lower strength and surface energy.