Friction Pair Materials Research Articles

Friction and wear behaviors of polycrystalline diamond self-mated pairs in air and water lubrication conditions

Polycrystalline diamond (PCD) is one of the hardest man-made materials with excellent wear resistance, also a preferred friction pair material for sliding bearings on geological drilling and deep-sea energy development equipment which has demanding requirements for extreme load carrying and abrasive wear resistance. However, the friction and wear characteristics of PCD self-mated conformal contact sliding bearings are still not fully understood. PCD self-mated pairs may exhibit some special tribological characteristics, such as abnormal friction vibrations, even if the roughness of the friction surfaces is at the nanometer level, resulting in PCD damage and reliability problem of bearings. In order to reveal the cause of friction vibration and the wear mechanism of PCD self-mated pairs, the friction and wear behaviors of PCD self-mated pairs in air and water lubrication conditions were hereby studied using a ring-on-ring test apparatus. The friction torque at different rotational speeds and loads was measured, the wear surface features of the PCDs were examined, and the composition of the solid film formed during the test at the friction interface was identified. The results show that PCD self-matching pair tends to generate severe friction vibration due to the adhesion of diamond grains rather than the increase of friction interface roughness under the dry friction condition. Water matters considerably in reducing the adhesion. The wear forms of PCDs are adhesive and abrasive wear in dry friction, and abrasive wear in water. PCD with large diamond grains is provided with a better wear resistance.

The influence of important factors on the distribution of heat flows in elements of drum brakes of vehicles

The movement of motor vehicles at high speeds is impossible without a braking system capable of ensuring high braking efficiency. It has been established that the most unstable link of the braking system is the brake mechanism, since from the energy point of view, braking with friction brakes is the process of converting part of the mechanical energy of the motor vehicle into heat. Braking is a long process during which many counterbody parameters change, in particular, thermophysical parameters due to temperature changes, friction coefficient, etc. If, under these circumstances, the surface and volume temperatures exceed the permissible values, then the frictional properties of the friction pairs and the conditions of the interaction of the parts change, which leads to a change in the characteristics of the brake mechanisms and the brake system as a whole. The standards of most countries and international prescriptions regulate braking performance meters not only for one-time emergency braking with cold brakes but also for emergency braking performed after the conversion of a given amount of energy into heat during a given time. It was found that the preservation of the necessary braking efficiency after the conversion of a given amount of energy into heat will be ensured only if the braking system has sufficient energy capacity. The object of the research is the distribution of heat flows in the elements of the brake mechanism, which determine the critical temperature of the friction surfaces. It was established that F. Charron's formula cannot correctly estimate such a distribution due to taking into account only the thermophysical properties of materials of friction pairs. It is shown that the influence of the design parameters of the brake and its modes of operation on the distribution of heat flows in the drum brake of a motor vehicle can also be estimated on grid thermal models with the involvement of the "Fourier-2xyz" software complex.

Polymer composites based on aromatic polyamide and fillers of spherical and layered structure for friction units of high-performance equipment

Without the employment of new equipment, with units functioning at high levels of weights, sliding speeds and temperatures, the current growth of the sector is all but impossible. High levels of labour intensity have a detrimental impact on the dependability and durability of the product. Moving joints, which comprise friction units, frequently fail at the same time. It is vital to increase their dependability and durability. This can be accomplished by substituting more recent materials with higher-quality qualities for the friction pair materials. To create such materials, the researchers created an aromatic polyamide polymer that was filled with silicon- (silica gel, bentonite) and carbon-containing (technical carbon, graphite) components. It was determined that depending on their nature, structure and content in the polymer matrix, the addition of these fillers enables the reduction of the coefficient of friction and wear of the produced polymer composites by 1.5–2.5 and 20–40 times, respectively, during frictional interaction with steel. It was found that 10–15% by weight of the examined fillers in aromatic polyamide is the ideal concentration. It has been proven that polymer composites filled with layered materials (bentonite, graphite) perform better in terms of tribological qualities when in contact with steel than those filled with spherical elements (technical carbon, silica gel). The improvement of the tribological properties of the developed polymer composites in comparison to the original polymer was determined based on the microphotographs of steel surfaces and the study of their morphological (roughness) and physical (microhardness) properties. It was determined that the change in the friction nature was due to the creation of an antifriction coating on the metal friction surface from the products of tribochemical reactions occurring during friction.

STUDY OF WEAR OF THE BUILDING-UP ZONE OF MARTENSITE-AUSTENITIC AND SECONDARY HARDENING STEELS OF THE Cr-Mn-Ti SYSTEM

The work deals with wear of the building-up zone of martensite-austenitic and secondary hardening steels of the Cr-Mn-Ti system (partially alloyed with Mo, B, and V). Additional alloying of the studied steels with titanium in the amount of 2…5% supported avoiding cleavages along the building-up zone. It was determined that there is a 7…15 µm wide parent metal zone next to the weld line. The influence of temperature on the weld toughness of the building-up zone was assessed according to the criterion of Malkin and Tetelman. The microhardness of the surface layers of built-up layers and the range of its dispersion are close to the results of laboratory tests, where ТСт ~ 823 K. This approves the formation of structure of metal of contact volumes with the collective effect of heating, plastic deformation and diffusion. It was experimentally approved that the change of microhardness in the sub-surface layers at the wear stage is justified simultaneously with the processes of mutual diffusion of friction pair materials, selective oxidation and thermodiffusion redistribution of the hardening phase under the influence of temperatures and deformations. The diffusion coefficient in the deformed sub-surface layer, which is up to some dozen micrometers thick, is one of the values providing the kinetics of growing of nuclear cracks and development of destruction cracks. The received results provide an opportunity to use martensite-austenitic and secondary hardening steels of the Cr-Mn-Ti system with built-up surface for the hot forming tools.

Robust and universal macroscale superlubricity with natural phytic acid solutions

Using superlubricants to reduce friction and wear can dramatically reduce energy consumption and economic losses in industrial production. In this paper, we report a natural and environmentally friendly lubricant based on phytic acid solution (PA-0) that can achieve robust macroscale liquid superlubrication between PDMS and glass interfaces, and the superlubrication state can be maintained for at least 13 h. Significantly, its superlubrication can also be extended to other friction pair materials, reflecting its robustness and universality as a superlubricant. The calculation of the lubricating film thickness reveals that the superlubrication realized by the PA-0 solution belongs to the mixed lubrication state that comprises boundary lubrication and hydrodynamic lubrication. These findings may advance the practical application of liquid superlubrication.

Research of sliding friction pairs of powder coatings with metal counterbodies in conditions of low temperatures

A stand for low-temperature wear testing of tribological couplings with powder coatings is developed. The tribological properties of materials of friction pairs of mechanisms operated at low temperatures are analyzed, and the process of their wearing away is studied. Dependences of the temperature change of the friction unit during the cold start of the mechanism are determined. The patterns of wear of the coating and the counterbody are studied. Keywords: tribological coupling, sliding friction, wear-resistant powder coating, counterbody, testing, wearing away, low temperature, wear. g.g.vinokurov@iptpn.ysn.ru

Friction-induced reconstruction of sliding interface and low friction mechanism of WC/a-C films

Tungsten carbide reinforced amorphous carbon (WC/a-C) films exhibit significantly lower coefficient of friction (COF) than typical a-C films in the atmospheric environment; thus, they are promising candidates for use as solid lubricants. However, the low friction mechanism of WC/a-C films remains poorly understood. Here, we revealed that the friction-induced formation of WO3-rich transfer film changed the real sliding interface between the initial friction pair materials into an interface between a WO3-rich transfer film and carbon-rich worn film surface (WO3/C interface). First-principles calculations indicated that the WO3/C interface showed weaker interactions than the C/C interface of the a-C film under the same conditions, particularly when the dangling carbon bonds at the sliding interface were not completely passivated. This resulted in a reduced COF of the WO3/C interface. Thus, friction-induced reconstruction of the sliding interface to an intrinsically weak-interacting interface is proposed as a new path to further improve the tribological performance of a-C-based films.

Temperature during Repetitive Short-Term Operation of a Brake with Functionally Graded Friction Element.

The object of study is the temperature of a braking system, operating in repetitive short-term (RST) mode. One element of the considered friction pair is made of a functionally gradient material (FGM), and the other of a homogeneous material. To determine the temperature on the friction surfaces of both elements, the previously obtained, exact solution of the boundary value problem of heat conduction was adopted, with account of the heat generation due to the friction. A calculation scheme was proposed that takes into consideration thermal sensitivity of materials and variations of the friction coefficient under the influence of temperature. Calculations were performed for two-component FGM (ZrO2-Ti-6Al-4V) in combination with gray cast iron (ChNMKh). It was found that for selected friction pair materials, consideration of their thermal sensitivity reduces the time of braking and the value of temperature achieved on the friction surfaces. At the same time, the whole process was characterized by a good stability of braking with a slight decrease in efficiency in each subsequent cycle.

Static and dynamic coefficient of friction in friction pairs of disc-pad brakes

Problem This scientific article is devoted to the value of static and dynamic coefficients of friction of disc-pad brakes. The issue of disc-pad brake wear is very acute because the safety of using the machine itself depends on its reliable operation. Therefore, the relevance of the chosen topic cannot be doubted. Goal. The aim is to establish patters of influence of the main operational parameters of friction pairs of a model disc-pad brake on the potential and kinematic coefficient of friction. Methodology. The methods of analytical mechanics and the theory of elasticity were used in the article. Results. Theoretical and experimental studies of the static (former rest) and dynamic coefficients of friction in the frictional interaction of materials FK-24A - steel 35KhNL were carried out on a model disk-shoe brake in a long-term braking mode. At the same time, it was established in the range of real impulse loads implemented during braking in the contact area of the friction lining with the brake disc, the stress-strain state of the contact according to the criterion of micro deformation in the contact corresponds to the elastic-plastic property. The elastic and plastic properties of materials appear when, in each individual case, the total stresses exceed the yield strength or reach its limit. With an increase in the impulse force of the normal pressing of the pad lining to the treadmill of the disc friction, the static coefficient of friction tends to increase, and with an increase in the static coefficient of mutual overlap kvz.s, it tends to decrease with the elastic-plastic property of materials. When choosing materials for friction pairs, the dynamic coefficient of friction must include the value of the static coefficient of friction and be at least 20% greater than the calculated value of the dynamic coefficient of friction. Practical value An increase in the static and dynamic friction coefficient in the friction pairs of a disk-pad brake leads to an increase in the plastic deformation of their microprotrusions. The data obtained can be used in the design of disc-shoe brakes

Experimental study on the tribological properties of high water-based piston friction pairs with different ceramic materials

The effects of load and reciprocating frequency on reciprocating sliding of ZrO2/steel, Si3N4/steel, and SiC/steel under high water-based emulsion lubrication were studied by the ball-block sliding tester, including a series of tribological behavior and wear mechanisms. Through the analysis of the above characteristics, determine the influence of load and frequency on the friction and wear properties of the ceramic/steel friction pair. The results show that with the increase of load, the friction coefficient of the three ceramic friction pairs decreases, and the wear rate increases continuously. With the increase of frequency, the friction coefficients of ZrO2/steel and Si3N4/steel steadily decrease, the friction coefficient of SiC/steel increases slightly, and the wear rates of the three friction pairs decrease continuously. The comprehensive comparison shows that the ZrO2/steel friction pair shows the best tribological performance under different working conditions, which is more suitable for the friction pair material of high water-based hydraulic components, and the Si3N4/steel friction pair shows better wear resistance when the load is above 50 N.

Tribological Properties of Two Typical Materials of Hydraulic Motor’s Rotor at Different Ambient Temperatures

Cold starting is the biggest challenge for mechanical equipment in polar environments. Selecting suitable friction pair materials and exploring the wear mechanism are keys to improving the reliability in a low-temperature environment. This study analyzed the tribological properties of the two typical materials of hydraulic motor’s rotor at different ambient temperatures, especially at low temperature. Finally, it explored the wear process and mechanism of two sets of friction pairs. The results showed that the low temperature environment not only affects the viscosity of the hydraulic medium in the hydraulic system and changes the lubrication state between the friction pairs, but also enhances the cold brittleness of metal materials and affects the wear characteristics between the friction pairs. There is a maximum difference of around −20 °C. The wear volume of material QT500-7 sharply increases and reaches a maximum of 0.107 mm3 when the normal force is 20 N, which is 3.65 times as much as the wear volume of the LC2-1. When the normal force is 30 N, the wear volume of materials QT500-7 and LC2-1 are 0.125 and 0.036 mm3, respectively. The wear volume of the former is 3.4 times that of the latter. In addition, it indicates that the impact energy of the material affects its tribological properties since the impact energy of the material QT500-7 decreases sharply, including two consecutive subintervals of sharp decreases from 97.3 J to 42.2 J and then to 18.0 J at the temperature of −10 to −30 °C. The material LC2-1 with stable wear performance is more applicable for being processed and manufactured into parts for low-temperature environmental conditions, as there is no serious fluctuation in the temperature range from −40 °C to room temperature. The research findings are expected to provide a theoretical support for hydraulic motors design, material selection and the maintenance of polar deck machinery. They are of great significance for improving the operational reliability of hydraulic motors for polar ships.

Методика оценки концентрации мелкодисперсных частиц PM10 при работе центробежных фрикционных роликов

One of the solutions to increase the storage capacity and speed of handling palletized goods in warehouses is the use of gravity pallet racking. As elements of the safe operation of such conveyors, centrifugal friction rollers are widely used, which ensure the speed of the pallet within the limits that do not exceed the permissible values. During the operation of centrifugal friction rollers, wear products — brake dust, which have an adverse effect on the human body, may enter the atmosphere. Therefore, an urgent task is to study the operation of friction-type brake rollers from the point of view of the environmental assessment of the released brake dust. The paper assesses the concentration of fine particles with dimensions from 10 micrometers to 2.5 micrometers during the operation of centrifugal friction rollers in gravity pallet racks, and proposes a method for estimating their concentration in the warehouse working area. The coefficient of environmental friendliness of the design of the brake roller of the friction type has been introduced, which is one of the factors determining the maximum number of braking, and takes values from 0 to 1.0 for various designs of the friction roller — closed type, ventilated and open type. The results of an experimental study of materials for friction pairs of brake rollers show that the maximum amount of braking is provided at a pressure on the friction lining of 0.1 MPa, which corresponds to a pallet weight of 1000 kg. An example of using the methodology for estimating the concentration of particles in the working area for a warehouse consisting of one block of gravity racks for pallets 1200x800x1500 mm (length x width x height), weighing 1000 kg, with a total number of 546 pallet places is considered. Analysis of the results showed that the maximum number of pallet braking at which the maximum permissible concentration of particles with a dimension of 10 micrometers to 2.5 micrometers is reached and the maximum turnover of the warehouse can serve as a comprehensive assessment of its environmental friendliness.

Study on temperature field and surface damage characteristics of railway brake disc/pad at low temperatures

PurposeThe purpose of this paper is to study the wear of railway brake disc/pad in low-temperature environment and to explore the damage form of brake disc/pad materials and the law of temperature rise in braking process and its influence on friction pair material damage.Design/methodology/approachThe influence of ambient temperature on tribological properties of brake materials was studied by using low-temperature environment simulation device and MM-1000 high-speed brake testing machine. The law of temperature rise in the braking process was simulated by temperature field module of COMSOL.FindingsThe damage of disc sample increases with the decrease of ambient temperature, and the main damage form is furrow. With the decrease of ambient temperature, pitting corrosion, wear, spalling and cracks appear successively. The maximum temperature of brake disc decreases linearly with the decrease of ambient temperature. However, when the ambient temperature is 0 in the experiment, the surface temperature of the disc will increase abnormally because of the increase of abrasive particles caused by the toughening and brittleness transformation of the material.Originality/valueIn this paper, through the study of train braking in low-temperature environment, the damage mechanism and law of train braking pair in low-temperature environment are found, which provide some basis for the development of high-speed railway in low-temperature environment.

Investigation of tribological properties of environmentally friendly ionic liquids as a potential lubricity improving additives for water-based lubricants

PurposeThis paper aims to investigate the tribological properties of two protic ionic liquids used as lubricity-improving additives in the water. Their concentration was optimized for different metal friction pairs including bearing steel, stainless steel and aluminum alloy.Design/methodology/approachIn this study tribological properties were investigated by using a ball-on-plate reciprocating tribometer. Three different friction pairs were selected: bearing steel-bearing steel; bearing steel-stainless steel; bearing steel-aluminum alloy. To optimize the concentration of investigated protic ionic liquids four concentrations were selected. Wettability was investigated using the droplet method. The corrosiveness of additive-loaded water was investigated using the iron chip method.FindingsThe results show that by using protic ionic liquids the lubricity of water could be greatly improved. However, the friction pair material and additive concentration play a significant role. The positive tribological effect was attributed to the polarity of the additive molecule which tends to form an adsorption layer. The polarity of molecules also leads to better surface wettability. It was also found that both investigated protic ionic liquids can improve the anticorrosion properties of water.Originality/valueTo the best of the authors’ knowledge, this is the first study to present a complex investigation of tribological properties of two protic ionic liquids as additives in the water. In this case, three different metal friction pairs and four additive concentrations were investigated. The results could be interesting to those who are working in the field of water-based lubricants and luck for multipurpose lubricity-improving additives.

Friction Behavior of a Textured Surface against Several Materials under Dry and Lubricated Conditions.

This paper reports research on the frictional behavior of a textured surface against several materials under dry and lubricated conditions, and this is aimed to provide design guidelines on the surface texturing for wide-ranging industrial applications. Experiments were performed on a tribo-tester with the facility of simulating A ball-on-plate model in reciprocating motion under dry, oil-lubricated, and water-lubricated conditions. To study the frictional behavior of textured SiC against various materials, three types of ball-bearing –elements, 52100 steel, silicon nitride (Si3N4), and polytetrafluoroethylene (PTFE), were used. Friction and wear performance of an un-textured surface and two types of widely used micro-scale texture surfaces, grooves and circular dimples, were examined and compared. The results demonstrated that the effect of surface textures on friction and wear performance is influenced by texture parameters and the materials of friction pairs. The circular-dimple texture and the groove texture, with certain texture parameters, played a positive role in improving friction and wear performance under specific operating conditions used in this research for SiC–steel and SiC–Si3N4 friction pairs; however, there was no friction and wear improvement for the textured SiC–PTFE friction pair. The results of this study offer an understanding and a knowledge base to enhance the performance of bearing elements in complex interacting systems.

TO ESTIMATE AND PREDICT TRIBOTECHNICAL PARAMETERS OF FRICTION PAIRS FROM SINTERED POWDER FRICTION MATERIAL WITH DIFFERENT STEEL COUNTERFACES FOR DISK FRICTION DEVICE

Approximating dependencies of tribotechnical parameters of friction pairs sintered powder friction material and different steel counterfaces of disk friction device on sliding speeds, obtained by results of tests on friction machine and intended for selection of materials of friction pairs, are given.

Experimental study on the influence of friction pair material hardness on the tribological behaviors of water lubricated thrust bearings

Purpose This paper aims to confirm that increasing the hardness of thrust collars can improve the load carrying capacity (LCC) and wear resistance of water lubricated thrust bearings (WTBs) made of polymers paired with non-polymeric thrust collars, and to design a WTB with high LCC and durability for a shaftless pump-jet propulsor of an autonomous underwater vehicle. Six kinds of WTBs were manufactured by matching aluminum bronze, stainless steel and silicon nitride with two different polymer bearing materials. Their tribological behaviors were tested and compared. Design/methodology/approach The tribological behaviors of the WTBs made with different materials were investigated experimentally on a specially designed test rig. Findings Aluminum bronze is not suitable for crafting thrust collars of heavy load WTBs due to severe abrasive wear. Two body abrasive wear first occurred between the thrust collar and the polymer bearing. Next, aluminum bronze wear particles were produced. The particles acted between the two materials and formed three body abrasive wear. Stainless steel/polymer bearings showed better wear resistance while Si3N4/polymer bearings were the best. Improving the hardness of thrust collars is significant to the LCC and service life of WTBs. Originality/value The wear mechanism of WTBs under heavy load conditions was revealed. Improving the hardness of the thrust collar was confirmed to be a preferable method to improve the wear resistance and LCC of WTBs. The results of this study may provide an important reference for the selection of water lubricated materials and the design of heavy load WTBs.

Analysis and Experimental Study on Friction and Wear Characteristics of Super High-Speed Mechanical Seal

Mechanical seal is the core component of the servo system. It’s sealing, reliability and wear resistance depend not only on the structural design of the seal, but also on the matching of friction pair materials on the end face of the seal. On the basis of the feasibility study of ion implantation on the surface of the seal ring, a comprehensive test scheme is proposed to verify the friction and wear characteristics of the seal pair. By selecting typical graphite and rotating metal ring pairs to test and test under dry grinding conditions, changing the linear velocity and the end face specific pressure, the friction and wear characteristics of paired friction pairs are compared and analyzed by using friction and wear testing machine, the influence of load and rotational speed on the pair friction coefficient of sealing pair is systematically studied, and the sealing tribological characteristics are revealed. This paper introduces mechanical-seal work reliability of temperature stress and system test performace based seal pair, the application of these plans will provide a reasonable and efficient technical way for the verification of life and reliability test of ultra-high speed mechanical seal.

Developing a system and criteria for directed choice of technology to provide required quality of surfaces of flexible coupling parts for rotor machines

The paper discusses the process of normal friction and wear as a result of fretting corrosion, as well as measures to reduce its level. There are considered the issues of reliability and accuracy of the connection of “shaft - sleeve with key” type, which is of particular danger. The disadvantages of the considered connections are shown, namely the relative complexity of the disassembly-assembly processes; high level of stress concentration; the tendency to corrosion at contact. There has been proposed a physically based mathematical model of the wear process for the strengthened surfaces of the flexible coupling parts on the friction conditions. By using the friction work value, the model allows determining the wear expressed through the change in the surface roughness. A method has been developed for determining the constant of the wear equation for various materials of friction pairs. Using the energy and economic criteria, the technique of the integral description of the method for achieving the required quality of the surface layers of the elastic coupling parts is given. A mathematical model has been developed to reliably allow predicting the wear amount for the surfaces of the elastic coupling parts whose surface layers are formed in various ways. It is proposed a system for the directed choice of the technologies to produce the surface layers of the flexible coupling parts taking into account all the stages of their life cycles. In doing so, both economic and environmental requirements are also taken into consideration. The use of the system for the direct choice of the technology to ensure the required quality of the flexible coupling parts at the repair stage allows more economically solving the problem of restoring their performance. As practice shows, at this stage, the application of the results of the scientific research gives a significant economic effect.

Estimation of energy levels of contacts and tribological properties of materials of friction pairs

Estimation of energy levels of contacts and tribological properties of materials of friction pairs