Journal of Friction and Wear最新文献

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.

To study the wear and friction force of a solid surface during friction with the ground, a carousel-type laboratory stand was created. The main task was to measure friction forces under various parameters of model soil and speeds of relative movement close to real ones during field agricultural work. Traditional electronic dynamometers are designed for static or slowly varying loads. Laboratory stands with such sensors have a linear design, a limited friction path (up to 2 m), and very low relative movement speeds (up to 0.15 m/s). The short friction path complicates the running-in process at the beginning of the experiment. Integral friction forces depend on speed. The adhesion component depends entirely on the presence of soil water at the interface and, thus, on the time required for water to move to the friction surface. With a carousel design of the stand, the friction path is infinite, and the speed can be increased by an order of magnitude (up to 1.5 m/s). Since studies usually compare the influence of different materials or soil compositions on the results of experiments, the systematic error due to the difference in the friction path from a straight line is insignificant. To measure rapidly changing loads, a force measuring station was developed based on a flat spring and a small displacement mechatronic sensor. The advantage of mechatronic linear displacement sensors is high sensitivity, ease of switching on, and high reliability. Disadvantages include dependence on temperature conditions and consequently the need for calibration in each experiment.

Friction is often accompanied by local fracture at the boundary of the contacting bodies. The gap between the bodies usually contains moving particles of different origin (“third body”), a change in the effective friction conditions may be associated with some changes in the structure of the third body. This paper presents a new series of experiments in which the process of rearrangement of intermediate layer particles interacting with various elastic materials (glass-rubber and steel) is modeled at different scale levels. A technique for visualizing the effect of mutual influence that occurs when two balls are pressed into a layer of rubber is proposed. It is the mutual influence that causes the effect of convergence or separation of the balls or particles during reciprocating frictional loading. The velocity of these processes depends on humidity and, in case of contact with the rubber layer, on the thickness of the layer. At high humidity, the configuration of the particles changes faster, and the friction force decreases. Replacing sand with an abrasive leads to an increase in the coefficient of friction and wear with a change in the microrelief of the surface. The minimum roughness is obtained for a humidity of 30%.

The work sets the task of determining the conditions for tribological testing of coatings in which the coating realizes its potential of physical, mechanical, and tribological properties regardless of the substrate. A standard method of tribological testing was used on a friction machine according to the pin–disk scheme with a circular motion of a spherical indenter pin. Experimental data are presented on the study of the structure and properties of vacuum ion-plasma nitride coatings of TiN, TiAlN, and CrAlSiN. The coatings had a thickness of 0.8–4.0 μm and were applied to plate steel samples intended for testing in a friction machine. The wear process of coatings is considered from the perspective of contact fracture mechanics and fatigue theories. A calculation and analytical model is proposed for quantitative assessment of contact and wear parameters during 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 critical thickness of the coating, which excludes its deflection. To assess the wear of coatings in this case, it is recommended to use fatigue failure models with the construction of a Woehler fatigue curve and determination of the fatigue limit based on the Murokami–Endo theory. The implementation of the recommended approach was carried out for the nitride coatings using a database of the authors’ experimental data.

The influence of the abrasive particle size and modifiers (low molecular weight liquid rubbers (LMWRs), sulfidosilane) on the rate of wear on abrasive paper of rubbers based on natural rubber (NR), carbon black (CB), and polyoxadiazole (POD) fiber is studied as a function of structure and mechanical properties of rubbers. Model rubber blends were prepared in a closed-type mixer, the abrasive wear tests were conducted on a drum-type machine, the structure and the mechanical properties of rubbers were characterized by DMA, static tensile tests, hardness measurements, and tear resistance. The wear surfaces were analyzed by SEM. Tests have shown that the addition of fiber does not affect the rate of abrasive wear of the original NR/CB rubber regardless of the grain size of the abrasive. Addition of modifiers that increase tensile modulus M10, hardness H_Sh, tear resistance T_R, tensile strength A, and degree of crosslinking γ reduces the wear rate under friction on coarse abrasive, which is characteristic of abrasive wear with a predominance of micro-cutting. The greatest influence, judging by the value of the correlation coefficient, is exerted by the value of M10, dependent on the bond strength between the matrix and the fiber, which allows predicting the wear rate of rubbers based on the results of mechanical tests. When worn on a fine abrasive paper, the increase in M10, H_Sh, T_R, and γ on the contrary, raises the wear rate of rubber, and the tensile toughness has practically no effect on it. This is attributed to the predominance of the fatigue wear mechanism, in which the wear rate increases with contact stresses, in proportion to the strength properties, with tear resistance exerting the greater effect on the wear rate.

The results of a study of the tribological properties and microstructure of rapidly solidified Al–12.2 wt % Si–0.2 wt % Fe (AK12vp) and Al–12.5 wt % Si–0.8 wt % Mg–0.4 wt % Mn–0.7 wt % Fe–0.9 wt % Ni—1.7 wt %, Cu (Al–Si–M) alloys are presented. The effect of multicomponent alloying on the microstructure of near-eutectic silumin was studied using scanning electron microscopy and X-ray spectrometry. Multicomponent alloying of the Al–Si eutectic alloy with magnesium, manganese, iron, nickel, and copper leads to a reduction in the size of the primary α-Al dendrites to 3–4 μm. Tribological tests carried out under conditions of dry friction with reciprocating motion of the indenter showed that alloying by metals of rapidly solidified eutectic silumin leads to a reduction in the coefficient of friction by 25%. An analysis of the surface state of the track showed that, as a result of deformation heating, the oxidation of the α-Al phase occurs, the destruction of the oxide film, which represents the third body, and its removal beyond the track. The fragmentation of silicon plates in the track area into nano-sized particles was also obtained. The impact of the indenter also leads to a uniform distribution of equiaxed particles of intermetallic compounds while maintaining their phase composition.

The contact problem of free rolling on a rigid foundation of a cylindrical body consisting of a non-deformable central part and an elastic rim is considered. A technique for an analytical solution is developed on the basis of a second-order asymptotic approximation. The contact interaction of the composite body with a non-deformable foundation under the action of a vertical force is investigated as a calculation example assuming a small rolling resistance moment. The calculated distributions of normal and tangential contact stresses, the distribution of the stress tensor intensity in the rim near the contact area, and the “force–displacement” dependence are obtained. These data are compared with the estimates obtained by the authors on the basis of finite element modeling and the results of using an alternative version of the asymptotic approximation. A conclusion is made about the advantages of the developed technique in comparison with the known asymptotic approach in terms of the accuracy of calculating the contact parameters and the simplicity of the applied mathematical apparatus. It is shown that the maximum of the stress tensor intensity is localized on the line of action of the vertical force (axis of symmetry) for a deformable rim material with Poisson’s ratio ν less than 0.4 and on the inner surface of the rim near the boundary of the adhesion and slip zones for ν > 0.4. The data derived are used to analyze the loading of roller interfaces of mining equipment.

One of the options for solving the scientific and applied problem of the predicted formation of ion-plasma coating tribological characteristics is presented. The problem is solved by creating and analyzing a carbon coating database. The object of research in this work is ion-plasma diamond-like coatings (DLCs) deposited on a steel substrate. It is shown that the use of nitrogen instead of hydrogen to stabilize carbon coatings not only ensures stable thicknesses of DLCs at the level of 1.0–1.5 μm, but also serves as an important and convenient technological parameter for regulating the tribological coating characteristics during deposition. Based on the predicted and experimental values of friction coefficient μ and data on sample path length L, the intervals of optimal values of technological parameters %N and λ are determined. The studied ion-plasma DLCs, obtained according to the established optimal application modes, can be recommended for application under friction conditions equivalent to the tribological tests carried out at friction load F ≈ 10 N.