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Friction and wear regularities of the bronze-steel joint have been studied during continuous sliding and friction with recurrent start and stop periods. The test results for friction without cooling and constant temperature of the lubricating material have been compared. Under the conditions of the forced cooling of the oil, transfer from continuous to periodic sliding is accompanied by a growing coefficient of friction and the wear rate of the bronze counterbody. Under conditions without cooling and in certain loading modes, the reverse scenario is probable.

A physical model of the lubricity of cholesteric liquid-crystal nanomaterials has been proposed in accordance with which the transition from single-crystal layers of a cholesteric liquid-crystal nanomaterial to polymolecular structurally sensitive liquid-crystal films, which occurs with varying temperature and is governed by the effect of molecules of cholesteric liquid-crystal compounds contained in the lubricant, as well as the reverse transition, lead to a reversible change in the shear resistance. This change results from the formation of continuous planar-oriented and helically twisted boundary layers in the zone of dynamic contact, which consist of molecules of the cholesteric liquid-crystal nanomaterials. The pitch distance of the helix and, therefore, the thickness of cholesteric liquid-crystal films of these nanomaterials exhibit a structurally sensitive response to changes in the temperature in the friction zone, which varies the dissipation of the energy during friction.

The growth concentration of cholesteric liquid crystals (CLCs) in lubricating materials was found to reduce the time needed to achieve the optimal tribological characteristics. It was also noted that, in the presence of small amounts of CLC in the lubricating material, the initial microrelief of the friction surfaces transformed into the flat-topped one during friction. A mechanism of CLC lubricity is proposed based on established regularities, according to which the gradual wear dosed by the friction-induced adsorption of CLC molecules in the lubricating material leads to the appearance of a flat-topped submicrotopography on the friction surfaces. This provides the conditions for the continuous formation of a lubricating film made from CLC molecules that screens the conjugated friction surfaces.

The kinetics of sample wear on a four-ball friction-testing machine using various lubricants is analyzed. It is shown that the growth of the contact-patch area on the balls obeys the kinetic second-order equation, which, within the limits, corresponds to catastrophic wear. The linear wear rates and the strain level of the ball material in different lubricating media are estimated.

The authors studied the friction and wear properties of PAOM�4 synthetic oil under the friction of steel samples, the working surfaces of which are coated by a thin layer of hard carbon coatings of different composition and structure. It was found that some of them result in improved antiwear and antifriction behavior of the test oil. The polyalphaolefin oil shows the highest lubricity when steel rubs against carbon dia� mondlike coatings, namely, monocrystalline tungst enalloyed coatings and amorphous coatings with increased sp 3 phase.

The paper presents an analysis of the state of the art in research into the effect of the composition of lubricants and additives of various origin on the friction of solids. It is shown that the combined application of additives with various structure, including those containing nanomaterials, is most effective from the viewpoint of lubricity. The objective is to attain an ordered state of lubricating films with a low shear strength in the friction zone.

It is shown that the coefficient of friction of polycrystalline graphite materials is governed by the crystallite size and adsorption heat of the molecules making up the lubricating layer. In the absence of a lubricating layer in the actual contact zones (in vacuum, dried gases, and in air at temperatures above 200°C), graphite loses its lubricity. To maintain low friction within 800°C, ultraphosphates are introduced into graphite pores; in heating, they release vapors of phosphoric anhydride to form a lubricating film. At 300°C, chalcogens MoS2, WS2, and MoSe2 release S and Se vapors that are adsorbed in contact and create a lubricating film. The capacity to release vapors is governed by the presence of solid solutions of chalcogens in addition to stoichiometric compounds.

The effect of wear debris on the antifriction and antiwear properties of industrial oils I-20A and I-40A in boundary sliding of steel against steel is studied. Variations in the tribological characteristics, including the friction coefficient, linear and energy wear rates, carrying capacity, and others, are studied during running-in and friction of run-in contacts. Among the specified concentrations of wear debris, the concentration of 0.8–1.0 mg/ml is found to be inadmissible and requires oil replacement. The temperature dependences of the friction coefficient for run-in contacts are obtained. It is shown that in all cases the properties of oil I-40A surpass those of oil I-20A.

The lubricity of medical and tribological preparations based on blood serum and intended for injection into joints is studied. It is found that the lubricity of the blood serum of osteoarthritis patients improves after the use of Doxycycline, a semisynthetic antibiotic from the tetracycline group. The induction method is used to measure the magnetic susceptibility of preparations based on blood serum and synovia sampled from joints with various pathologies. It is shown that all of the preparations are diamagnetics. The atomic-force microscopy method is used to find variations in the structure of patients’ blood serum resulting from the biochemical bonding of Doxycycline with blood proteins. Increase in the imaginary part of the magnetic susceptibility, which characterizes the absorption of the magnetic energy by the sample, is caused by growth of the magnetic moment in the fluid; the moment is directed oppositely to the electromagnetic field of the joint. It initiates the transformation of the lubricating film structure, reduces friction in the joint, and acts as a biophysical ground for methods of transfusion chondroprotection that favor the improvement of the tribological state of joints.

It is established experimentally using a pendulum tribometer that medical preparations based on hyaluronates and chondroitin sulfate exert unequal effects on the lubricity of blood serum during friction of cartilage against cartilage. The best tribological characteristics for the combinations with blood serum are demonstrated by drugs based on chondroitin sulfate, which display characteristics close to natural synovial fluid during frictional interaction of cartilage.

Analysis of the development of ideas concerning the bioelectrical fields of living organisms shows that approaches to the modeling of the electromagnetic field of synovial joints in experiments in vitro have not yet been developed. The current work considers the biophysical and biochemical processes of the formation and circulation of synovia in joints, which are controlled by their natural electromagnetic field. The basic conditions are determined of the adequacy of the effect on friction and lubrication of a natural biofield in a synovial joint and of an external electromagnetic field in a friction pair that imitates a joint. Examples of the modeling of the electromagnetic field of the joint in experiments in vitro are given, demonstrating the pronounced effect of the external field on the lubricity of synovia.

In previous works we have shown that to improve oil lubricity one should increase the orientability of the working surfaces of solid bodies. This can be achieved by applying special carbon orientant coatings to ensure the formation of highly oriented boundary layers whose molecules acquire some orientation under the effect of the solid-phase force field. The level of the orientation effect and coating characteristics are dependent on its synthesis parameters, which makes it possible to regulate them during coating application. It is shown that with increasing structural ordering of the boundary layers, the friction coefficient decreases, thus widening the limits of resistance to temperature. In contrast, tribological tests of traditional carbon coatings of the amorphous structure are devoid of the above-described effect. The estimate of the total activation energy of failure of the boundary layers for steel samples with a polycrystalline coating-orientant has proved this value to be much higher than for the same steel with a coating without the orientant coating properties.

Results of study of the friction and wear characteristics of carbon frictional composite materials used in aircraft brakes are reported. The effect of the reinforcement type and the heat treatment conditions of the materials on their friction coefficient, wear rate, and the stability indicator of the friction coefficient are studied. Also, the effect of water and detergents on the friction and wear of carbon frictional composite materials is discussed, and it is demonstrated that higher density is an effective way of elimination of the negative effect of detergents and considerable reduction of the water effect.

The processes running in the friction contact zone of lead-containing fluoroplastic composites and steel counterbody are studied. The results of X-ray phase examination of the transfer films on the steel counterbody are presented for the case of friction of lead-fluoride-containing fluroplastic composites. In friction of the given composites, the secondary structure, namely lead fluoride, is shown to arise in the contact zone. It is found that the fluorite crystalline structure β-PbF2 possesses lubricity and increases the wear resistance of PTFE-based composites.

The paper discusses a methodology for correcting the tribological state of synovial osteoarthritic joints by means of blood dialysis. The concept of medicinal and immunological modification of lubricating fluids based on blood serum is substantiated. The concept is based on the fundamental capacity of living tissues, as frictional materials, to regenerate defects on the friction surfaces of cartilage during metabolism.

The effect of aerosil on the formation of structure and surface layers of ultrahigh-molecular-weight polyethylene (UHMWPE) and its low-filled composites is studied during friction. Surface modification of aerosil by vinyl triethoxysilane is found to result in elevated crystallinity degree and hardness of the filled polymeric system, and hardening of the composite surface layer under friction. This can be, evidently, attributed to friction-induced grafting of binder macromolecules to the organophilicized aerosil surface. Strengthening of the matrix bonding with the filler is accompanied by worsening of lubricity, growth of wear resistance, and increasing contribution of the adhesive mechanism instead of the abrasive one to the wear of low-filled UHMWPE composites.

A computer model of the adsorption process of lube oil molecules on friction surfaces reveals that carbon monocrystalline coatings with a strongly orientating effect promote the level of molecular orientation in boundary layers contrary to the amorphous ones because there is no essential orientating effect on these layers. The results of lab tribological tests of carbon coatings deposited on steel surfaces in some model oils corroborate that the coatings with a higher level of orientation ability yield better lube properties.

The structure of a three-ball friction machine developed for testing lubricants is described and its advantages over the four-ball one in tests with sliding friction are shown. Using the developed machine and the testing procedure, a lubricant grease Litol-24 was subjected to testing with additions of solid lubricants (graphite powder and MoS2) and organic dopes containing P, Cl, S, and O. According to results of investigation of their lubricity in conditions of boundary friction with abrasives, the optimal formulations of lubricants have been determined.

The apparent activation energy of seizure in boundary lubrication was calculated using the temperature-kinetic approach to the description of boundary lubrication. The tests were carried out with the ball-on-disc machine. The ball was made of chromium ball-bearing steel and the disc was made of stainless steel. Discs made of stainless steel coated with aluminum nitride and high-ordered polycrystalline carbon were also used. The pair was lubricated with model lubricants. It was shown that the apparent activation energy of seizure in friction against steel coated with carbon is by almost an order of magnitude higher than in friction against uncoated steel.