Journal of Friction and Wear最新文献

The mechanism of the lubricating effect of two model lubricants based on medical vaseline with 0.5 wt % additives of carbon nanostructures (CNSs), namely graphene oxide (GO) and shungite nanocarbon (Sh), under hard friction conditions (2070 SMT-1 friction machine, “disc–roller” friction pair made of hardened ShKh15 steel, load 2000 N) has been established. The friction surfaces were examined by confocal laser microscopy and scanning electron microscopy. The elemental composition of the friction surfaces was determined with the help of energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The contribution of the chemical component (formation of iron oxides) to the anti-wear process was analyzed. It was found that despite the difference in the spatial structure of the used CNSs, the processes occurring in the friction zone are chemically similar. It has been demonstrated that with the use of both model lubricants, protective oxide films consisting of iron oxides (FeO, Fe₂O₃, Fe₃O₄) are formed in the contact zone. The chemical composition of the oxide film and the quantitative ratio of the formed iron oxides are not significantly affected by the type of CNS additives used. The results, together with the studies we performed earlier, demonstrate that the mechanical component, associated with the spatial organization of CNS additive, makes the decisive contribution to the anti-wear process under severe friction conditions.

An analysis of the wearless effect for carbon steels subjected to surface alloying with metallic bismuth using the technology of short-pulse laser melting is performed. The tribological studies have been conducted in conjunction with industrial metal alloys such as gray cast iron, nickel-aluminum bronze, and aluminum alloy. Under boundary lubrication conditions, the bismuth-alloyed steel surface tested in contact with the analyzed alloys has shown ultralow value of the friction coefficient in the range from 0.04 to 0.08. It is established that a high level of fatigue strength of the aluminum alloy and the absence of adhesion with respect to a bismuth-alloyed steel surface provide conditions leading to the manifestation of the wearless effect (zero wear) at friction velocities amounting up to 9 m/s and at normal loads amounting up to 250 N. The metallographic analysis and 3D profilometry of friction surfaces have revealed that the process of self-organization of the contact zone is athermal in nature (without frictional heating) and is determined by a plastic flow of the contacting surfaces with no mutual destruction thereof.

This paper considers the mechanisms of contact interaction of diamond-bearing composite materials (diamond cutting wheel segments) when cutting steel and concrete using scanning electron microscopy. It is established that an increase in the cutting ability of a diamond cutting wheel with an increase in the concentration of diamond grits in the diamond-bearing composite material of the segments is associated not only with an increase in the number of diamond grits on the segment surface, but also with a change in the mechanism of contact interaction of the diamond-bearing composition with the workpiece. It is established that an increase in grit size, even with a small change in concentration (from 17.5 to 25 rel. %) in the segment, changes the cutting ability of the tool. Diamond grits reduce the contribution of frictional interaction of the bond with the workpiece, and their higher concentration in the segment leads to a decrease in impact loads on the grit. When cutting a steel pipe, an increase in the concentration of diamond grits reduces the frictional component of the contact interaction of the diamond-bearing composite material with steel, reducing the thermal effect of frictional interaction, and an increase in their size helps to increase the strength of their fixation by the bond, leveling the influence of the thermal effect of frictional interaction of the bond with steel and the increase in its temperature in the frictional contact zone.

For a high-strength coating–base layered material with different values of the thickness of the strengthened layer, finite element modeling of the stress-strain state formed during friction was carried out. It is shown that with a decrease in the thickness of the coating, a significant increase in the level of shear stresses acting in the base during friction is recorded. The patterns of wear under dry friction conditions of AISI 304 and AISI 420 high-chromium steels modified with nitrogen ions, differing in the hardness of the base and the thickness of the nitrided layer, have been studied. It is concluded that the abnormally high wear rate of a thin nitrided layer in AISI 304 steel is associated with the accumulation of shear strains in the plastic austenitic base during friction, as well as with a high gradient of hardness values along the depth of the hardened layer in the steel and a γ → α phase transformation in the base during frictional interaction. The influence of base hardness on the wear resistance of AISI 420 nitrided steel was studied. It has been established that an increase in the hardness of the AISI 420 steel base leads to a decrease in the wear rate of thin nitrided layers at the later stages of tribological tests, which is associated with a slowdown in the accumulation of shear strains in the solid steel base during friction.

The paper considers the results of studies on the wear resistance of machine parts made of structural steels during the formation of micropores in their surface layer by the dealloying method based on electrolytic plasma treatment. The technological conditions for the formation of a microporous surface layer by electrolytic plasma treatment with subsequent modification by ion implantation and ion nitriding are presented. It is shown that the creation of a microporous layer contributes to an increase in the tribotechnical characteristics of surfaces under lubrication conditions. It is shown that the use of the electrolyte-plasma surface treatment method allows high-performance formation of a microporous surface layer that does not require further mechanical processing, and in one technological cycle is able to polish it. It is shown that the use of preliminary preparation of the surface layer for nitriding using high-energy processing methods can significantly increase the wear resistance of the microporous layer. The results of comparative tests of microporous surfaces with various processing options are presented. It is shown that the use of microporous surfaces in conditions of friction with lubrication makes it possible to increase the wear resistance of 40X and 40KHN steels by about 1.5–2 times, and their nitriding provides an increase in wear resistance compared with simple traditional nitriding by about three times, and compared with microporous surfaces without nitriding by more than nine times.

The research includes the development and analysis of a mathematical model of a truly viscous lubricant in a modified sliding bearing design with a composite fluoroplastic coating on the surface of the shaft and a groove, which helps to improve the distribution of lubricant and increase the durability of the system. Based on the equation of motion, the liquid lubricant under study, the continuity equation, and the equation of state, new mathematical models have been obtained that additionally take into account a parameter such as compressibility. The novelty of the work lies in the development of a methodology for engineering calculations of the design of a radial sliding bearing with a polymer coating, taking into account the presence of a groove, as well as the dependence of viscosity on pressure and compressibility of the lubricant, allowing one to determine the value of the main tribotechnical parameters. The results of the study provided a reduction in errors in bearing capacity by 11–13%, and in coefficient of friction by 9–12% of the modified bearing in comparison with traditional designs. As a result, it was possible to achieve an increase in the service life of radial bearings, which is of great importance for their industrial application.

By means of wire additive electron beam manufacturing aluminum bronze/stainless steel BrAMts9-2/12Kh18N9T alloys with the following concentration ratios of 90 : 10, 75 : 25, 50 : 50, and 25 : 75 were obtained. The microstructure, mechanical and tribological properties of the materials were investigated. Ceramic Si3N4 balls were used as counterbodies, which slid without lubrication on disks of the materials. The maximum and minimum levels of tensile strength were 813 and 635 MPa, achieved for samples of BrAMts9-2/12Kh18N9T in the ratio of 50 : 50 and 75 : 25, respectively. It is shown that with an increase in the steel content from 10 to 75%, there is an increase in the average friction coefficient and wear intensity. There is a change in the wear mechanism from excessive plastic deformation to abrasive wear. This transition is accompanied by a decrease in the fluctuations of the friction coefficient values. Despite the presence of subsurface defects in alloys with a large amount of steel, their average friction coefficient values are in the range of smaller values (0.38–0.42) compared to materials known from the literature, the friction coefficient of which is in the range of 0.46–0.52 under comparable tribological test conditions. Thus, the materials are obtained in the work have high properties that allow these materials to be used in the manufacture of highly loaded parts and units of shipping equipment subject to wear under aggressive environments.

The probability of formation of new phases on triboconjugated metal surfaces of the contact zone at physicochemical interactions of lubricating and cooling technological products (LCTPs) or their components with juvenile metal surfaces of iron and titanium when cutting tools are used has been substantiated. Studies of changes in the appearance of surfaces of 45 steel and VT1-0 titanium alloy, formed during cutting with the use of air and its separate components (oxygen and nitrogen), including those activated by corona discharge, as LCTPs, at the pressure of external media of 10^–1 mm Hg have been carried out. The best surface quality of 45 steel was recorded at activation of SDS by negative potential on the corona electrode. For VT1‑0 titanium alloy the best surface quality was recorded during activation of LCTPs by positive potential on the corona electrode. It has been established that titanium, having a higher chemical affinity to oxygen, has a higher chemical affinity to free-radical fragments of oxygen-containing organic LCTPs. It has been suggested that LCTPs containing organic compounds can be used in the treatment of both iron and titanium, as well as their alloys.

In order to optimally select antifriction polymer materials (PMs) for metal-polymer plain bearings, the method of system triboanalysis is considered, including model tribotesting of PMs and calculation of generalized wear resistance characteristics depending on specific friction forces. The method is used to assess the wear resistance of several existing PMs (polyamide, polytetrafluoroethylene, polyacetal, polyethylene terephthalate, and polyetheretherketone) and composites based on them. Experimental studies are performed using an end-friction tribometer. The obtained wear resistance characteristics are the basic parameters of a well-known mathematical model describing the kinetics of material wear during sliding friction and an analytical method for calculating metal-polymer plain bearings. The research results are presented in the form of diagrams covering a wide range of specific friction forces, which allows for a visual comparison of antifriction PMs by wear resistance. The friction patterns of PMs in a pair with 45 steel are established, the qualitative and quantitative influence of the filler type on the wear resistance of the specified polymer materials is analyzed. In each group of PMs under consideration, a material with maximum wear resistance in comparison with the base (unfilled) polymer is found.

This article presents the results of tests of the BrA5 bronze–45 steel reverse sliding friction pair in dispersion-lubricating media characterized by different degrees of surface activity with respect to bronze. Changes in the microstructural characteristics during metal tribodeformation are analyzed from the standpoint of the Rehbinder effect, which determines the possibility of selective transfer (wear-free mode) in tribological conjunction. It is shown that during friction of bronze in lubricating-dispersion media characterized by relatively low surface activity, the effect of the medium on the surface structure of the tribomaterial is based on the implementation of the surface-hardening effect, the total density of dislocations in the deformed near-surface layer increases. The wear intensity in this case is I_h ≈ 1.5 × 10^–7 to 4.0 × 10^–8. When bronze is subjected to friction in moderately surface-active media, both surface-plasticizing and surface-hardening effects are realized, with the latter predominating. In this case, the wear intensity decreases slightly, taking values in the range of I_h ≈ 1.2 × 10^–7 to 1.5 × 10^–8. During tribotesting of bronze in media with increased surface activity, the wear intensity of bronze remains at a fairly low level: I_h ≈ 2.2 × 10^–8 to 3.0 × 10^–8. However, in this case, two crystallographically isostructural solid solutions are formed in the near-surface layer of the tribomaterial, one of which is enriched with copper. Based on the concepts of physicochemical mechanics of contact interaction, the systemic and structural foundations of the materials science approach are presented, which underlie the analysis of the tribological efficiency of liquids used as dispersion media for plastic lubricants.