Vol 38, No 4 (2017)

The friction of an ultrathin coating (~5 nm) formed as a result of the modifier segregation towards the surface of modified epoxy polymer in the form of multiple short chains of Si, F modifier has been investigated in a range of loads from 0.1000 to 0.0005 N. During the investigation of the reverse friction of ceramic (Al₂O₃) ball on the coating, the sharp decrease in coefficient of friction at a load of less than 0.002 N has been shown, which is probably caused by the change in the mechanism of friction during the transition of friction to the zone of a self-lubricating coating. Under these conditions, the difference between the static coefficient of friction (stop effect) and dynamic coefficient of friction increases.

The influence of the strengthening phases on the tribological characteristics (wear intensity, specific work of wear, coefficient of friction) and the wear mechanisms in two-body abrasion tests with abrasives of different hardnesses (corundum Al₂O₃, ~2000 HV and silicon carbide SiC, ~3000 HV) has been investigated for PG-SR2 (Cr₂₃C₆, 1000–1150 HV), PG-10N-01 (Cr₇C₃, 1650–1800 HV; CrB, 1950–2400 HV), and 75% PG-SR2 + 25% TiC (TiC, 2500–2900 HV; (Cr,Ni)₂₃(C,B)₆ and (Ti,Cr)(C,B), ~2000 HV) coatings. The dominant role of the strengthening phases (compared with the role of the metal matrix) in the abrasive wear resistance of laser-clad NiCrBSi coatings has been estimated. Different wear mechanisms have been identified and, accordingly, different levels of coatings wear resistance have been achieved depending on the ratio between the hardness of the strengthening phases (carbides, borides, carboborides) and abrasive particles.

This paper outlines the results of an experimental study of the influence of high hydrostatic pressure on the abrasive wear of hard-alloy materials based on tungsten carbide (~90% WC ± 10% Co), as well as alloys based on iron with high contents of chromium. A specially developed setup has been described in the paper that makes it possible to test materials under the hydrostatic pressure of up to 250 MPa at different friction speeds. An investigation of the surfaces of samples using the Scanning Electron Microscopy method has revealed that the main damage of alloy surface occurs due to the delamination and spalling of hard particles. It has been revealed that the hydrostatic pressure significantly influences the wear rate of the investigated materials. When the pressure increases to 200 MPa, the wear of materials with high contents of chromium increases seven times, while for the material based on tungsten carbide, it increases twice.

One method for the early examination of the aviation reduction gear’s state is to predict the rates of process of surface fatigue wear according to the type of fatigue wear particles, which appear in friction units. We perform this investigation based on example of the main reduction gear of the helicopter and reduction gears of the KSA type of MIG-29K/KUB aircraft during their bench testing.

The paper treats the results of investigating asphaltenes, which present natural nanometer formations obtained by oil genesis. The use of asphaltenes as a filler for lubricating oils has been substantiated. Tribological properties of asphaltene fillers, the morphology of surface films and their chemical composition have been discussed and an attempt has been made to explain the mechanism of the friction surface cladding by the asphaltene structures. It has been proved that asphaltenes display satisfactory tribological and technical properties for their application in low-speed heavy-loaded friction joints.

The relative fluctuation of sliding friction force in a stationary friction regime has been estimated by the statistic theory of the fluctuation of adaptive physical variables. General mathematical equations and corresponding estimations of relative fluctuations have been given for various friction regimes, such as the regime of mixed and boundary friction, including friction with cladding metal nanoparticles in lubricant and friction with selective transfer. It has been found that relative fluctuations of friction forces are fairly high compared with the fluctuation of physical variables related to the volume of thermodynamic systems. Relative fluctuations for a mixed friction regime are particularly high and can reach 1–10% of the average friction force.

This article discusses the regularities of modifying the contact approach upon the reindentation of a spherical indenter into the surface of an item. An equation has been proposed for determining an elastic approach upon repeated loading.