Journal of Friction and Wear最新文献

The structure, phase composition, hardness, and tribological properties of composite gas-thermal 50% Cu–50% (Al–Si) coatings under various friction conditions were studied. It has been shown that during the process of high-speed metallization, active interaction of molten aluminum and copper particles occurs, leading to the formation of solid solutions and intermetallic compounds in sprayed coatings. In particular, in 50% Cu–50% (Al–Si) coatings, in addition to the matrix phases of Cu and Al, intermetallic compounds Cu₉Al₄, CuAl₂, and Cu₃Al are recorded. The hardness and microhardness of the composite are 180 HV 1 and 180–190 HV 0.025, respectively. It has been established that a composite coating of 50% Cu–50% (Al–Si) has higher wear resistance under various friction conditions than the widely used coating of CuSn11P-C antifriction bronze, obtained by centrifugal induction surfacing. In particular, in the environment of I-20A lubricant, the wear resistance of the composite coating exceeds the wear resistance of bronze by ≈1.2 times, in the environment of Litol-24 plastic lubricant, by ≈1.4 times, and with dry friction up to ≈2.8 times. It has been shown that during boundary friction, dislocations accumulate in aluminum particles of the composite, while in copper particles at elevated test pressures, a predominant formation of a subgrain structure occurs. Based on the studies conducted, it was concluded that the increased wear resistance of the composite is due to the presence of solid intermetallic compounds in it, solid solution strengthening, the presence of silicon in aluminum interlayers, as well as dislocation strengthening of aluminum interlayers and the formation of a subgrain structure in copper interlayers.

The work examines the conditions of tribological tests of steel samples with nitride ion-plasma coatings. A calculation and analytical model is proposed for quantitative assessment of contact and wear parameters during sliding friction tests: the size of the contact area, the depth of contact approach, the depth of the plastic zone, stresses in the coating, fatigue limit, and the critical thickness of the coating, which excludes its deflection. It has been shown that coatings with a thickness above critical realize their potential for physical, mechanical, and tribological properties regardless of the substrate. If the coating thickness is insufficient, the result of tribological tests is determined by the behavior of the “coating–substrate” system, a high-hard nitride coating on a ductile steel substrate experiences deflection and premature brittle failure. To assess the wear of coatings in this case, it is recommended to use fatigue failure models with construction of the Wöhler fatigue curve and determination of the fatigue limit based on the Murakami–Endo theory. The implementation of the recommended approach was carried out for the studied nitride coatings using a database of our own experimental data.

The effect of treatment with a pulsed magnetic field on the triboacoustic characteristics of polymer friction composites containing up to 20 wt % dispersed copper. It has been shown that among various physical and mechanical properties, a statistically significant response to magnetic field treatment of a mixture of composite components is demonstrated by dynamic mechanical characteristics. It was found that magnetic treatment of initial mixtures of composites in both unipolar and bipolar modes with a field strength of 20 kA/m leads to a decrease in the difference between the coefficients of static and dynamic friction by 3.0—3.4 times without a statistically significant change in the wear rate and loss of braking efficiency. A reduction in sound pressure levels during friction by 23–24 dB in the frequency range above 2 kHz has been experimentally confirmed.

This work examines combined antifriction coatings obtained by electric spark processing of a metal substrate with an electrode made of the X20N80 alloy, followed by filling discontinuities, depressions, and pores with copper powder. Copper powder was applied using supersonic gas-dynamic spraying. The combined coatings under study had a thickness of 60–350 μm. The work also obtained the dependences of the friction coefficients for coatings with different surface areas of the electric spark and copper components. The magnitude of the friction coefficient depends on the applied load. It was found that the minimum friction coefficient for coatings was in the range of 0.077–0.142. The pressure values for the appearance of plastic contact for various types of experimental coatings are in the range of 178–241.5 MPa. Coatings with a higher percentage of copper on the surface, other things being equal, have a lower temperature in the friction zone. Reducing the area of the electric spark component from 78 to 4% makes it possible to reduce the temperature in the friction zone by 2.5 times. At a relative sliding speed of 55 m/min, a self-lubricating effect is observed. The quasi-liquid form of copper is fragmentarily transferred into the roughness cavities of the electric spark component. As a result of the research, combined antifriction coatings with a surface area of the electric spark component of less than 50% are recommended for use in friction units with contact pressure up to 240 MPa; in pairs with contact pressure below 170 MPa, coatings with an area of the electric spark component of 4–30%, having low coefficient of friction.

One option for solving the scientific and applied problem of increasing the efficiency of finishing quartz crystal elements (QCEs) through controlling the structural, mechanical, and rheological characteristics of abrasive suspensions is presented. The finishing technology for manufacturing QCEs is flat finishing on machines using an abrasive suspension of fine Al₂O₃ particles. The dispersion medium in the abrasive suspension during finishing of QCEs ensures uniform distribution of abrasive grains over the lap, minimizes the sticking of separating quartz particles, and facilitates its dispersion. Control of the structural and mechanical characteristics of the abrasive suspension is achieved by introducing into the dispersion medium (water) stabilizers such as protective colloids, which prevent the approach of abrasive particles and the destruction of quartz. The problem of QCE finishing has been solved by the authors for the first time ever.

The results of a study of the influence of the introduction of powders of intermetallic compounds of various compositions obtained by self-propagating high-temperature synthesis (SHS) with preliminary mechanical activation on the structure, mechanical, and tribological properties of sintered bronze are presented. It was found that the introduction of 0.2–0.5 wt % of nickel and titanium aluminides, both single-phase and two-phase, leads to an increase in the density and strength of sintered bronze; maximum strength is achieved with the introduction of 0.2 wt % aluminides. The dependence of the hardness of powder bronze on the amount and composition of the intermetallic compound differs from the dependence of strength; with the introduction of single-phase intermetallic compounds, the hardness increases with increasing additive content, and with two-phase intermetallic compounds it decreases. It has been shown that the introduction of aluminides ensures a refinement of the structure of the bronze during sintering, and at an additive content of 1 wt %, an increase in the amount of eutectoid (α + δ). The introduction of aluminides also has a positive effect on the tribological properties of sintered bronze. With the introduction of 0.5 wt % two-phase nickel aluminide and 0.2 wt % single-phase titanium aluminide, the seizure pressure and wear resistance increase by 2.8 times and 3.5 times, respectively. Adding 0.5 wt % of single-phase nickel, titanium, and iron aluminides allows reducing the friction coefficient to 0.009–0.011, and two-phase iron aluminide to 0.005. The introduction of iron aluminides most effectively increases the tribological properties of sintered bronze, so the seizure pressure increases to 10 MPa and wear resistance by almost 10 times. Aluminides help reduce the relief of the friction surface during adhesive wear of sintered bronze and the formation of microlacunae, which are additional reservoirs for lubrication. The smoothest friction surface and a higher content of microlacunae are observed in samples made of powder bronze with the addition of single-phase iron aluminide.

This work investigated the hydrocarbon degradation and depletion of the anti-wear additive zinc dialkyldithiophosphate (ZDDP) in several used marine motor oils using high-resolution nuclear magnetic resonance (NMR). The article presents research results showing that during engine operation several characteristics of motor oil change: degree of aromaticity, ratio of methyl/methylene groups, and composition of phosphorus-containing additives. The possibility of determining oil using the NMR spectrum lines of antiwear additives has been demonstrated. For anti-wear additives containing phosphorus, such as ZDDP and molybdenum dialkyldithiophosphate (MoDDP), ³¹P NMR has been found to provide both depletion rates and insight into the wear mechanism of the additives. The high efficiency of using the high-field NMR spectroscopy method for studying fresh and used marine motor oils has been demonstrated. ¹H, ¹³C, and ³¹P NMR studies show the presence of changes in motor oil caused by the accumulation of products of its decomposition, degradation, and decomposition of additives during engine operation. The ability of the NMR radiospectroscopy method to monitor additive depletion is analyzed, which is apparently one of the most difficult problems in used oil analysis. A characteristic feature of the NMR spectra of all used oils is line broadening caused by the presence of metal wear particles. It is characteristic that the broadening of the ¹³C NMR lines for waste oils is significantly less than the broadening in the NMR spectra of protons. In the ¹³C NMR spectrum of used oil, an increase in the intensity of the line from aromatic hydrocarbons is observed, i.e., as the degree of oil degradation increases, the content of aromatic compounds increases. The results of the study of fresh and used motor oils obtained in this work are new. They can be used to create a system for monitoring the quality of motor oils and for diagnosing engine malfunctions using used oil.

The phasing of the friction process provides for the formation of the intersurface phase of the rubbing surfaces of the friction pair, the “third body”. In essence, the third body is a hinge of internal friction of a developed stage of joint plastic deformation of surfaces. Being a consequence of the self-organization of surface adaptation processes in the presence of environmental chemistry, the third body can have a wide range of tribological properties. These properties, in turn, are a consequence of the formation of a wide range of optimal (compatible) structures of the third body, which determines the controllability of friction. The relationship of structure and properties as the basic principle of tribomaterial science provokes the question of what are the limits of this relationship? For example, what are the minimum properties of friction and how are they reflected in the essence of the structural structure and behavior of the friction contact? The equation of a quasi-ideal solid third body under friction is obtained, which proves the existence of an elementary structural element of a solid body under friction (deformation), a mechanical (nano) quantum. A mechanical quantum, as an ideal (theoretical) crystal of atomically rough and spherical shape, is an oscillator of dynamic dissipative friction structures. The potential energy accumulated initially during the evolution of contact is further dissipated in the area of compatibility into these formed mechanical quanta of the third body (elementary tribosystem) in the form of surface energy, creating prerequisites for their elastic reversals with an abnormally low coefficient of friction between them. The efficiency of the third body is proportional to the spectrum of elastic reversals of structural shapes.

Tribotechnical testing results for antifriction solid lubricant coatings in a metal–polymer friction pair are presented. The testing has been carried out according to an ASTMG99 standard with the use of a friction machine operating according to a sphere–disk pattern at sliding velocity V = 0.8 m/s, load F = 23 N, and rotation frequency n = 310 min^–1. While testing, the value of sliding friction force was permanently registered, and the value of the friction coefficient was automatically calculated. Testing was carried out until preset friction path L = 2880 m accumulated. After testing a level of linear wear was measured for the spherical counterbody. Antifriction solid lubricant coatings based on molybdenum disulfide and polytetrafluoroethylene deposited onto steel samples were tested. Polyoxymethylene spheres 10 mm in diameter were used as a counterbody. The testing was performed with the use of different greases based on mineral and synthetic oils with a complex of antifriction additives. It is revealed that the use of antifriction solid lubricant coatings together with greases makes it possible to provide a 5.9 to 10.1-fold decrease in the linear wear of counterbodies, as well as a 1.5 to 2.3-fold decrease in the friction coefficient depending on the grade of the coating under application. By selecting an optimum combination of antifriction solid lubricant coatings and plastic grease one can achieve a decrease in the linear wear of the counterbodies amounting up to 14.2 times, and an approximately 4.4-fold decrease in the friction coefficient.

The article presents the results of an experimental determination of the friction coefficient of various materials (95Kh18 steel and BrAZh9-4 bronze, F-4 fluoroplastic, PA-6 polyamide, and MPG-7 graphite) in a friction pair with single-crystalline aluminum oxide under low speeds and various loading conditions. Determining the friction coefficient of aluminum oxide at low sliding velocity allows recording and evaluating the static friction for various counterbody materials, identifying the mechanisms of interaction between rubbing bodies and their influence on friction processes. Studies of the tribological characteristics of single-crystal aluminum oxide show that it has no antifriction properties, and, when using it in a friction unit, we need to take into account the pairing material, the load on the friction contact, and the sliding velocity. Aluminum oxide has a high affinity for metals, which causes strong adhesive interaction up to wear with cohesive destruction of metals. Polymer materials such as fluoroplastic and polyamide weakly adhesively interact with aluminum oxide, which ensures stable sliding within lubrication with low friction coefficients over a wide range of loads and velocity. Dry friction of the self-lubricating graphite material is determined by the tribological properties of the graphite. At low loads and sliding velocity, the adsorption component of friction is revealed. When forces are sufficient to destroy bonds in crystalline layers of graphite, the friction process is limited by the effect of self-lubricating of graphite.