Journal of Friction and Wear最新文献

Tribotechnical testing results are presented for novel carbon–carbon composites (CCCs) based on a pitch matrix and a pyrocarbon matrix material, developed by foreign companies for aircraft multidisk brakes. The carbon composites under consideration differ in the internal structure affected both by the technology of carbon fiber production and by the level of thermal treatment, as well as by many other factors. The length of the fibers used for the reinforcement of the composite matrix is varied, too. The tribotechnical properties have been determined using a laboratory tribometer according to a ring-to-ring contact scheme for normal loads ranging from 0.5 to 1.1 MPa and sliding velocities ranging from 1 to 4 m/s. The experimental investigation has been carried out with the use of a two-factor experimental design method. In order to eliminate the intense oxidation of the samples caused by the frictional heating thereof, the testing has been performed in an inert gas environment. The friction film has been studied by means of Raman spectroscopy using a green laser with a wavelength of 532 nm for excitation. The tribotechnical properties of the developed materials have been determined to demonstrate that the temperature on the friction surface exerts a significant effect on the friction coefficient and the wear rate of the material. It has been found that a frictional film is formed on a friction surface, resulting from the formation of the third body, whose film, in turn affects the tribotechnical properties of the friction pair. Depending on the structure of the composite and the maximum temperature on the friction surface, the friction film can consist both mainly of a matrix, and mainly of carbon fibers.

The investigated materials were prepared via sintering a mixture of Al, Sn, and Fe elemental powders under vacuum conditions for 1 h at a temperature of 710°C and subsequent compaction in a closed pressing mold at a pressure of about 300 MPa and a temperature of 250°C. The structure of the obtained Al–Fe–Sn composites is represented by an aluminum matrix with the inclusions of FeAl₃ particle agglomerates bound between each other by tin interlayers. Then, the materials were tested for wear resistance under the conditions of dry friction against a rotating disk made of strengthened 40Kh grade steel. The testing was carried out according to a pin-on-disk scheme using a Tribotechnic tribotester (France), the applied pressure varying from 1 to 5 MPa, the sliding velocity of the disk was 0.6 m/s. It was found that adding iron to the Al–Sn alloy provides a significant decrease in the wear rate of the steel disk, but less significantly affects the wear resistance of the samples based on the aluminum matrix. The Al–9Fe–13Sn composite containing about 31 vol % of FeAl₃ and 20 vol % of Sn exhibits the highest wear resistance. Increasing or decreasing tin concentration compared to the mentioned value leads to a decrease in the wear resistance of the investigated materials. A similar effect is caused by an increase or decrease in the iron concentration. It has been found that in the course of dry friction, a thin highly deformed layer that actually consists of oxides including iron oxides transferred from the disk is formed on the surface of Al–Fe–Sn samples. The matrix grains and tin interlayers located under the upper oxide layer are flattened and stretched in the sliding direction. A part of wear particles formed on the sample surface stick onto the steel disk surface in the form of hard adhering particles that cause an intense deformation of the sample surface. The wear mechanism of aluminum matrix composites with a high concentration of iron and tin phases is under discussion.

This article describes the analysis of influence of biocarbon (BC) produced by pyrolysis from a pine nutshell on tribological properties of friction material. The research object has been presented by copper-based friction material doped with 12% tin with 10–40 vol % of carbon additive in the form of BC. The average particle size of BC is 10 μm. The tribological properties has been analyzed using an IM-58 friction machine. The tribological tests demonstrate that with an increase in the BC content the dynamic friction coefficient increases from 0.041 to 0.066. With the aim of comparison, addition of GE-1 grade powdered graphite results in an increase in the friction coefficient from 0.038 to 0.069. Simultaneously with the increase in friction coefficient the wear of friction material also increases not exceeding its ultimate value. Thus, at 10 vol % of BC addition the wear is 4.0 μm/km, at 40 vol %, 12.1 μm/km. Analysis of surface morphology of bronze demonstrates that the BC particles are worn uniformly with bronze layer, retaining the initial porous structure. The products of BC destruction with sizes of 50–500 nm have been introduced into the surface layer of bronze. The results demonstrate opportunities of biocarbon additive in friction material, which can be used as a substitution of conventionally used graphite. It should be mentioned that the promising opportunities of BC addition to powdered antifriction material are determined by initial raw material for its production.

The study is devoted to the optimization of tribotechnical properties of fibrous carding tape for the production of artificial fur. The influence of the amount of IS-2 emulsifier applied to the fibers of the carding tape on the quality indicators of artificial fur, such as the surface density of the pile cover, the mass of loosely fixed fibers, the specific surface electrical resistance, resistance to pile dumping and the strength of the tape, has been studied. The mechanisms of the influence of the oiler on the dynamic coefficient of friction and the coefficient of tangential resistance of the fibrous carding tape were established and the consumption of the emulsifier applied to the fibers was optimized to achieve maximum quality indicators of artificial fur (2–3 g of emulsifier per 1 kg of fiber). The results of the conducted studies have shown that the oiling of fibers in the production of artificial fur with fat-free emulsifier IS-2 at an optimal concentration of 2–3 g of emulsifier per 1 kg of fiber, depending on the type of fur, leads to an increase in the mass of the pile cover from 5.4 to 19% (fur density increases), to a significant decrease from 77.8 to 81.3% of the mass of loosely fixed fibers in the pile, reducing the specific surface electrical resistance from 22.6 to 45.4%. It has been established that the resistance of the pile to dumping does not depend on the concentration of the emulsifier on the fiber surface. Also, at an optimal concentration the greatest strength and the minimum coefficient of variation are achieved, i.e., the best uniformity of strength along the tape.

Atomic structures arising during the vacuum deposition of TiAlN nanocoatings on the iron surface are studied using quantum chemistry methods. The effects that appear during the deposition of the first atomic layers of such coatings are considered. Calculations of the bond strength of such coatings with the surface are carried out. Within the framework of the model used in this study, it is shown that the most durable is the coating, the lower layer of which consists of Ti atoms, located directly on the iron surface. The upper layers consist of a mixture of Ti, Al, and N atoms. The bond strength of such a coating with iron can increase by 13% compared to its bottom value. When modeling the interaction of the coating with the substrate, it is has been established that the strength of the bond between the components is almost independent of the substrate thickness, if the substrate consists of three or more iron atomic layers. This fact testifies to the short-range nature of the interatomic forces at the coating–substrate interface, which greatly simplifies the theoretical analysis of the strength properties of such systems. The paper shows that when calculating the atomic configurations appearing on the iron surface during vacuum deposition, it is necessary to look for configurations with a minimum energy. It is these configurations that are most likely to form on the substrate surface. Traditional methods of studying atomic structures based on the principle of the minimum system enthalpy are not applicable in this case. The results of this study are compared with known experimental data related to similar objects.

The features of the structure formation of a biodegradable grease with a mixed dispersion medium (a mixture of rapeseed and mineral group III according to American Petroleum Institute (API) standard oils) and a heterogeneous lithium–calcium soapy dispersed phase are considered. An original process technology is used for the manufacturing of the grease, which makes it possible to minimize the negative effect of water and high temperature on the vegetable component of the dispersion medium during the thermodeformation action on the reaction mass. The formed structure of the dispersed phase of this grease is a combination of both relatively thin fusiform fibers of lithium 12-hydroxystearate with a length of 10–25 μm and a diameter of 2–5 μm and larger lamellar strips with a length of 20–40 μm and a thickness of 5–10 μm formed by the salts of calcium 12-hydroxystearate. This provides the optimum combination of the rheological and tribological properties of the grease, in particular, the increase in the water resistance and shear resistance in comparison with simple lithium greases and increase in the dropping point in comparison with simple calcium greases. The biodegradability of the lamellar lithium–calcium grease is 89%. The formulation and production process of an OIMOL CL BIO biodegradable lamellar lithium–calcium grease for general technical purposes are developed, and its industrial production is organized.