Journal of Friction and Wear最新文献

Samples of fasteners were studied: bolts, nuts, and washers with a zinc coating applied in various ways, namely galvanic, thermal diffusion, gas thermal, hot galvanization in molten zinc and in melt galfan (Zn + 5% Al), as well as with zinc lamellar coating. Data on roughness, microhardness, and friction coefficient of zinc coatings were obtained. It has been established that the thermal diffusion coating has the greatest hardness, and the coating obtained by hot-dip galvanizing in molten zinc has the least hardness. Maximum roughness R_a is observed in gas-thermal and thermal-diffusion coatings. The lowest roughness is found in coatings obtained by hot-dip galvanizing and galvanic deposition. The friction coefficients of coatings were studied in finger-disk geometry for all types of coatings. It has been established that zinc-lamella and thermal diffusion coatings have the highest coefficient of friction, and the lowest, gas-thermal coating and those obtained by hot-dip galvanizing. The nominal tightening torques for M3, M10, and M16 bolts are calculated. It has been established that the tightening torque of coatings applied by hot-dip galvanizing in molten zinc and gas-thermal spraying complies with the standards of RD 37.001.131–89. For other coatings, the friction coefficient requires adjustment through the use of lubricants or the application of additional coatings. The results can be used when choosing a zinc coating for fasteners.

Nanoindentation at temperatures of 23 and 150°C is used to study the coating of molybdenum disulfide doped with silver and calcium fluoride. The Nanoscan-4D scanning nanohardness tester was used for the experiments. A method is presented for determining the elastic properties of a coating from elastic indentation curves, taking into account the real shape of the indenter head, which is determined by optical profilometry. The elasticity modulus of the coating is determined based on the exact solution of the contact problem for a two-layered elastic foundation, taking into account the calculated compliance of the measurement system. Newton’s method is used for the inverse problem solution. The input parameters of the problem, in addition to the geometry of the indenter head and the load, are the elastic properties of the head and substrate materials. The elastic type of indentation was provided at maximal load of 10 mN for both temperatures. The loading–unloading curves at room temperature and at 150°C turned out to be close (within the experimental error), which proves the stability of the elastic properties in the considered temperature range. The calculated elastic modulus of the coating was 326 GPa. Using the same device, equipped with a lateral force sensor, the sliding friction coefficient of the coating was determined under different loads (5, 10, and 20 mN). Such a study can be considered as a physical model of the contact of the coating with a single asperity. The experiments were carried out on straight tracks 1 mm long at a speed of 11 µm/s. It is shown that the coatings are antifrictional (with friction coefficients in the range 0.033—0.078). The coefficient of friction increases with increasing load, which may be due to the dissipation of energy for plastic deformation of the coating material at relatively high loads. The conclusion about the presence of plastic deformation is based on the results of optical profilometry, which showed plastically deformed and pushed material along the edges of the friction track under relatively high loads. At low loads, this phenomenon is not observed. This coating can be used in sliding friction units that require one or two applications with a low friction coefficient.

The study of the structural-phase state and tribotechnical properties of antifriction gas-thermal coatings made of aluminum alloy AlSi12, welding bronze CuSi3Mn1, as well as composite material CuSi3Mn1 + AlSi12 and a coating of bronze CuSn10P1 obtained by centrifugal induction surfacing was carried out. It is shown that composite gas-thermal coatings from CuSi3Mn1 + AlSi12 after spraying include Cu, Al, Cu₉Al₄, CuAl₂, Cu₃Al, Si, and Al₂O₃ phases. The matrix phase of the bronze interlayers is doped with aluminum, while the Al interlayers are doped with copper. It has been established that annealing of coatings CuSi3Mn1 + AlSi12 at temperatures of 175 and 225°С for 2 h leads to the release of an additional amount of intermetallic compounds in them and an increase in their microhardness. It is shown that composite gas-thermal coatings have ≈1.2–1.7 times higher wear resistance in the environment of I-20A and Litol-24 lubricants compared to coatings of CuSn10P1 bronze. Annealing of composite coatings from CuSi3Mn1 + AlSi12 leads to an increase in their wear resistance in the environment of I-20A liquid lubricant up to 30% and Litol-24 up to 20% compared to the initial state. The coefficients of friction of all antifriction coatings based on copper in the environment of the I-20A lubricant did not exceed 0.08, and in the environment of the Litol-24 lubricant, 0.10.

The article presents the results of experimental studies on the effect of circulation pump operating modes on the wear of a double reciprocating slit throttling hydrostatic bearing operating in a lead coolant environment. The experiments were conducted on a high-temperature circulation test bench at a lead coolant temperature of 420–450°C. Results were obtained for operation modes with a high number of start-stop cycles (approximately 100 cycles per 100 h of operation), sustained operation with a low number of start–stop cycles and nominal speeds of 1000–1100 rpm (not exceeding 8 cycles per 100 h of operation), with 25 start–stop cycles per 100 h, and at low pump speeds below nominal values of 600–700 rpm with a maximum of 8 start–stop cycles per 100 h of operation. Data on the wear of the bearing bush and shaft are presented in the article. Processing and analysis of the research results led to the conclusion that this type of bearing can be used in low-pressure axial pump systems only under conditions where the pump creates a head exceeding 1.1 m of liquid lead.

The properties of a semi-liquid lubricant (Lb) with additives were tested using a KT-2 oil testing machine; its stability and influence on the ‘wheel flange—rail’ friction pair was assessed. The analysis is based on laboratory wear tests of locomotive wheel flanges. Investigation of lubricants with additives showed their low colloidal stability, the highest oil release being observed with the addition of sulfo compounds and phospho additives. The thermal stability of lubricants with additives shows that at approximately 220°C the lubricants melt completely and turn into a liquid state. After conducting tribological tests on a KT-2 oil testing machine of a lubricant with a hydroquinone additive, white crystals formed on the surface of the facility. The dependence of the friction coefficient on the test temperature of the studied lubricant with additives was obtained. X-ray fluorescence analysis of the locomotive wheel flange surface showed a change in the concentration of chromium and manganese in the surface layer of the sample before and after bench tests, which may indicate the formation of a stable transfer layer providing good tribological properties. Empirical coefficients were obtained to determine the wear rate of the locomotive wheel flange for the studied additives.

The tribomechanical properties of UPA-6130UV antifrictional polyamide composite filled with short carbon fibers have been studied in relation to metal-polymer bearings, gears, etc. The “pin-on-disc” setup was used to determine the macroscopic characteristics, and contact indentation and scratch testing, were employed to find submicroscopic parameters of the surface layer of this material before and after friction. It has been found that the tribological properties of studied carbon-filled polyamide are superior to those of glass-filled polyamide. With increase in the specific load, the mass wear of the UPA-6130UV composite increases less (from 0.0012 g at 10 MPa to 0.004 g at 40 MPa) and is significantly smaller than that of the PА6-L-SV30-1 glass-filled composite, the wear of which is 0.003 g at 10 MPa and 0.042 g at 40 MPa, respectively.

In this paper, we study the effect of corrosion inhibitors in compositions of friction composites on corrosion processes and noise generation in friction units. Model composites containing complex corrosion inhibitors as target additives were prepared. Tribological tests of the friction composite were performed using the “plane-to-plane” scheme. Transfer films on the surface of a steel counterbody are shown to be formed predominantly by laminar wear particles of the composite with sizes up to 50 μm. X-ray photoelectron spectroscopy data confirmed the presence in the transfer films of all elements related to the main components of the friction material, including corrosion inhibitors. Climatic tests were carried out. In a friction pair with a composite containing no corrosion inhibitor, continuous corrosion of the metal counterbody is shown to be predominant while pitting actively develops over time. The degree of corrosion damage to the surface reaches 90–95% of the nominal contact area. The introduction of a complex corrosion inhibitor into the composition of friction composites in an amount of 1.5–3.0 wt % was established to reduce the degree of corrosion damage to the nominal friction area of the metal counterbody by 20–35%. Outside the nominal friction area, the effect of reducing the degree of corrosion damage to the surface area of the metal counterbody by 50–60% was found. Triboacoustic tests were carried out on metal counterbodies subject to corrosion during climatic tests. Levels of sound pressure produced by the friction pair in the frequency range of 50 Hz–20 kHz are determined. The use of corrosion inhibitors was found to lead to a decrease in noise levels while the most significant decrease of 7–30 dB occurs in the high-frequency region of 6–20 kHz.

The results of a study on the influence of the modes of obtaining sintered BrO12 bronze on its structure, phase composition and tribological properties during friction with a lubricant are presented. It is shown that the phase composition of BrO12 bronze sintered for 5 min consists of a solid solution of tin in copper and inclusions of intermetallic phases δ-Cu41Sn11 and Cu81nSn22. An increase in the exposure time during sintering leads to an increase in the homogeneity of the solid solution of tin in copper, a decrease in the crystal lattice parameter of copper from 3.69 to 3.68 Å, an increase in the grain size from 2–5 µm at 5 min of sintering to 15–46 µm at 120 min, a decrease in the content of the intermetallic phase δ-Cu41Sn11, and the disappearance of the Cu81nSn22 phase at 60 min of sintering and the virtual absence of intermetallic compounds after sintering for 120 min. Tribological tests have shown that the friction coefficient of bronze sintered for 5 min at a pressure of 4 MPa varies from 0.08 to 0.03, and at 20 MPa, from 0.105 to 0.04, the average wear value at a pressure of 4 MPa and 20 MPa was 2.0 µm. The coefficient of friction at the above pressures of bronze sintered for 60 min was 0.11–0.036 and 0.095–0.023; 0.045 and 0.12–0.5, respectively, wear was 6.3 µm.

Carbon–carbon composite materials (CCCMs) are used in brake systems and in movable sealing joints, since they can have both frictional and antifriction properties, depending on their structure. In recent studies, data were obtained on the thermal properties of various CCCMs and the coefficient of friction in a pair with various counterbodies as a function of temperature. In this case, the nature of the dependences of the friction coefficient and the coefficient of linear thermal expansion on temperature is similar and has close critical points. The paper investigates the contact interaction of a heated heat-insulated annular punch with a half-space, the thermal expansion coefficient of which depends on temperature. Analytical expressions are obtained for calculation of the contact pressure and the penetration of the punch for various temperature distributions over the contact area. To take into account the uneven heating of the contacting surfaces, the temperature distribution under the annular punch was calculated during its frictional interaction with the elastic half-space. The case of temperature distribution during heating from spinning friction, which is typical for tribological tests and operation of interfaces made of CCCMs, is considered. It is established that in the considered case the temperature increases from the inner radius of the annular punch to the outer one. The joint effect of the ring width and temperature distribution on the value of contact pressures is studied. Calculations show that taking into account frictional heating is more important for narrow punches, while the minimum pressure in the contact area can significantly decrease at a fixed value of the external load.

The main regularities of friction and wear of surface layers of composite materials for antifriction and friction purposes have been established. It has been shown that mineral fillers modified with an organic lubricant (travertine, bentonite, tuff, marble, basalt) have a significant effect on the structure and properties of heterochain polymers based on a copolymer of formaldehyde, polyamides, and polyphenylene oxide. The developed composites are characterized by high wear-resistance (1.43–1.9 times), improved strength properties (1.5–2.0 times), and decreased friction coefficient (1.17–1.4 times) compared to the initial polymer materials that extend the opportunities of their application in modern friction units. The main mechanism of fatigue-delamination high-temperature wear of brake friction composite materials with mineral additives is revealed and based on it a physical model of the surface layer destruction is developed. It was established that the performance of these materials under conditions of high-temperature wear is determined by the stress-strain state of thin surface layers, in which tensile and compressive stresses exceeding the ultimate strength at shear act. At the stage of designing brake devices an analytical method to predict the wear resistance of friction linings was developed.