Journal of Friction and Wear最新文献

Research is carried out on the wear resistance and friction coefficients of a friction composition made from PC30, Al₂O₃, SiO₂, TiO₂, and Cr₂O powders and an additive containing carbon fiber in combination with GE-1 graphite, using the SFP-012A phenolic powder binder material. The study of tribotechnical properties is carried out on an IM-58 inertial stand. Using a stereoscopic microscope and a scanning electron microscope with a micro-X-ray spectral attachment, the morphology of the friction surfaces of experimental samples is analyzed, and information about the elements forming the friction surface is obtained. It is established that promising additives for the friction composition are 5–6% coarse Al₂O₃ and SiO₂ powders. They promote an increase in friction of the friction material to the recommended minimum value of 0.3. Promising additives also include carbon fiber in an amount of 25–50%, which makes it possible to maintain the wear rate of the composition at a level not exceeding 30 µm/km. By increasing the carbon fiber content to 50%, a minimum value of the friction coefficient was obtained at the initial moment of contact of the tribocoupling surfaces. In this case, the experimental curve of changes in the friction coefficient is characterized by a smooth transition to the slipping region.

During operation of springs, especially cyclic buffer and high-speed springs, there are inevitable relative movements of their surfaces, friction, and coil contacts. Due to friction, a lot of energy is converted into thermal energy, this is а cause of spring wear on the contact points of the coils and of overheating of the machines and mechanisms. The known methods of increasing spring resourcefulness do not consider the issue of friction and wear of springs surfaces contact. Тhe new technologies for increasing the wear resistance of compression springs using contact predeformation are presented in the article. In this case, an additional axial load exceeding the load on the spring in the product by more than 5% and determined theoretically at the stage of development of the technological process is applied to the compressed spring coils into contact. The exposure time under axial load is 1–1.5 s. Serial springs were manufactured and two batches of experimental springs were produced using new technologies. The dispersion of the force parameters of the springs of experimental batch No. 1 as compared with serial springs was reduced by 14.3%, and as compared with experimental batch No. 2 by 42.9%. After cyclic tests the decrease of workload for serial springs averaged 1.17%; for springs of experimental batch No. 1, 0.23%; for springs of experimental batch No. 2, 0.45%. Contact clamping not only promotes the formation of useful residual stresses, but also increases the bearing capacity of the springs. The strip of hardened material is formed, which increases the wear resistance of the contacting surfaces of the coils and reduces friction due to parallel layering. On the contact places of the spring coils, the specific pressure decreases and the deformation wear resistance of the springs increases. Therefore, contact clamping should also be considered as a finishing operation to reduce friction on the places of contact of the spring’s coils and increasing their wear resistance.

The method is aimed at comparing the lubricating capacity of different emulsions. The purpose of the work is to evaluate the possibility of using a universal friction machine, type MMW-1A, to determine the value of the friction coefficient in the cold rolling of very thin strips of carbon steel. The article analyzes the research related to the methods of measuring the friction coefficient in lengthwise rolling. The methodology of experiment determination of friction coefficient value between the material of RCM-1250 reversing mill rolls (steel of working rolls—analog of 60S2HFA steel) and the sample of annealed strip, 0.224-mm thick, made of TS-435 steel grade (analog of 08ps steel, GOST 1050) has been developed. The selected friction conditions are semi-fluid friction. The experiment applied the emulsion, based on the lubricating-cooling liquid, such as Quaker 2185, and used an RCM-125 reversing mill. Two types of ring-shaped samples made of roll material were used in the experiment with wall thicknesses of S = 4 mm and S = 2 mm. The results of the experiments showed that the use of the ring-shaped sample with S = 4 mm is more reasonable from the point of view of stability of the created friction conditions. The recommended average value of friction coefficient between the above materials of rolls and strip was determined: f_cf = 0.038. In the course of the experiment the values of the friction coefficient fluctuated within the boundaries, from the minimum of f_min = 0.012, to the maximum of f_max = 0.048. In general, these experimental results are correlated with reference data on the value of the friction coefficient for this type of rolling and the results of other experiments described in the literature, conducted under similar friction conditions. Proceeding from this, it is possible to draw a conclusion that estimation of the lubricating capacity of various lubricating-cooling liquids, application of universal friction machines of the design described in the article is expedient.

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.