Friction Pair Research Articles

LUBRICATION BEHAVIOR OF THE POE/R452A MIXTUREAT DIFFERENT SLIDING VELOCITIES UNDER STARVED LUBRICATION CONDITIONS

There are no international standards guiding tribological testing in oil-refrigerant mixtures. The conditions fortribological tests, including sliding velocity, are chosen arbitrarily. The article presents an attempt to examinethe influence of the sliding velocity of friction pair elements on the coefficient of friction and lubricatingproperties of compressor polyester oil (POE) and its mixture with the R452A refrigerant (POE/R452A) understarved lubrication conditions. The R452A refrigerant is currently widely used in transportation refrigeration.The authors’ original test procedure with the use of a model block-on-ring type friction pair was applied toevaluate the lubricating properties of the oil-refrigerant mixture. Tests were conducted in three operationalsituations: no lubrication, starved lubrication with POE oil, and starved lubrication with the POE/R452Amixture. In each case, the tests were performed at different sliding velocities and the same sliding distance.A series of tests was also conducted where the load was increased in steps by 20 N to determine the relationshipbetween the coefficient of friction, sliding velocity, and load on the friction pair.The results support the potential use of higher sliding velocities and the reduction in test duration. For starvedlubrication with the POE oil and the POE/R452A mixture, the differences in wear at specific velocities forthe same sliding distance reached up to 30%, and the rankings of lubricating properties at different velocitiesremained unchanged.

STRUCTURE AND PROPERTIES OF THE NITRIDED LAYERWITH SULFIDES

This study contains a short overview of sulfur nitriding methods, i.e. a modified version of nitriding. Thisinformation is accompanied by the results of our own tests of nitrided and sulfur-nitrided coatings with theaddition of MoS2 in the scope of structure assessment by means of a scanning microscope – SEM/EDS andthe results of tribological tests performed under dry friction conditions on the T-05 apparatus for four variantsof thermo-chemical treatment. In tribological tests, the degree of wear was observed by measuring the weightloss of both samples and counter-samples, and the beneficial effect of sulfides on reducing wear was indicated,with the sulfur nitriding variant with MoS2 added being the most advantageous. In this case, the lowest degreeof wear was found for the friction pair with a sulfur-nitrogen coating reinforced with MoS2, which may leadto extending the operating time.

Robust Macroscale Superlubricity in Humid Air via Designing Amorphous DLC/Crystalline TMDs Friction Pair

AbstractSuperlubricity, a cutting‐edge concept, has the potential to drive the Fourth Industrial Revolution giving its near‐zero energy consumption, but the challenge is how to achieve it in humid air with chemical activity and at macroscale surfaces with unavoidable defects. Here, a novel principle involving the amorphous/crystalline  friction pair based on the cognition that tribochemical interaction sites originate from grain boundary defect locations is proposed to achieve macroscale superlubricity in humid air. The absence of grain boundaries in amorphous diamond‐like carbon (DLC) significantly reduces chemical interaction during the sliding process. This is supported by experimental observations of priority oxidation at the grain boundaries. Results indicate DLC versus MoS2 friction pair has weakened chemical interaction and less humid insensitivity compared to the MoS2 versus MoS2 pair, even increasing the contact area. Theoretical simulation suggests that DLC versus MoS2 pair eliminates the cross‐linking of friction interlayers induced by the enrichment of H2O molecules at MoS2 defects. The robust superlubricity is achieved for the typical friction pair of DLC versus MoS2 in air (RH≤25%) at macroscopic contact pressure (1.1 GPa) with friction coefficient in 10−3 magnitude and extra‐long anti‐wear life (more than 2 × 105 cycles), which is of significance for the industrialization of superlubricity.

The Induced Orientation of Hydroxypropyl Methylcellulose Coating for Ultralow Wear

This study investigated the frictional properties of HPMC under different load and concentration conditions through friction experiments and surface characterization. The study aimed to explore and reveal the influence of load and concentration on the frictional properties of HPMC, as well as its anti−wear mechanism. The results of the study indicated that under the same solution concentration, the effect of load on the friction coefficient of HPMC was not significant. Specifically, for samples with low concentration (C−0.2), the wear ratio of HPMC under a 4 N load (1.01 × 10−11 mm3·N−1·m−1) was significantly lower than the wear ratio under a 2 N load (1.71 × 10−10 mm3·N−1·m−1). The orientation−driven formation of graphite−like carbon nanosheets, initiated by the decomposition of HPMC short chains, created a tribofilm−containing organic−chain mixed nanosheet on the sliding contact surface, which prevented direct contact between the upper and lower friction pairs. This achieved the anti−wear mechanism of two−body wear (tribo−film of an mDLC−coated ball and tribo−film of a GLC−coated Si wafer), ultimately leading to a state of ultra−low wear at the interface. The excellent anti−wear performance of HPMC suggests its potential as a candidate for the next generation of environmentally friendly bio−based solid lubricants.

Lubrication Mechanism of TC4 Titanium Alloy Against Silicon Nitride by ILs ([Li (Synthetic Esters)] NTF2)

ABSTRACTThe ILs ([Li (synthetic esters)] NTF2) were prepared by the in situ synthesis method. The tribological behaviour of the ILs to friction pairs of Ti‐6Al‐4V titanium alloy against silicon nitride was studied by SRV‐V under different concentrations and friction frequencies; the wear scar was studied by SEM, XPS and TOF‐SIMS. The results showed that the friction coefficient and wear loss decreased gradually with the increase of the LiNTF2 content; when the LiNTF2 content reached a certain value (10%), the friction coefficient and wear loss did not change much. Tribofilm composed of titanium oxide, Al2O3, TiFO2, AlOF2, Ti2O4F and Al2O3F plays a major role in lubrication and anti‐friction effect.

Fabrication of DDP-functionalized carbon nitride nanosheets via thiol-ene “click” reaction as lubricant additives

Herein, the functionalized graphite carbon nitride (DDP@g-C3N4) nanosheets were successfully prepared via the surface self-assembly method combined with “click” reaction. Firstly, the 3-(trimethoxysilyl) propyl acrylate (TOPA) was self-assembled onto the g-C3N4 surface to obtain TOPA@g-C3N4, then the dialkyl dithiophosphate (DDP) was grafted onto TOPA@g-C3N4 via thiol-ene “click” reaction formation of DDP@g-C3N4. The load-carrying capacity of PAO10 is increased to 900 N from 200 N with 1.5 wt% DDP@g-C3N4 addition, and the average COF decreased from 0.17 to 0.10, accompanied by a 96.7 % decrease in wear volume. This improved lubricating performance is attributed to the formation of a continuous protective film including iron oxides, iron sulfide, and iron phosphate via tribochemical reactions, which prevent direct contact and seizure between friction pairs.

The Tribological Properties of Plasma Electrolytic Oxidation Layers Synthesized on Arc Spray Coatings on Aluminum Alloys in Contact with Various Friction Materials

Oxide layers on the surface of the aluminum alloys D16 and AMg6 and on arc coatings sprayed with electrode wires made of the alloys D16 and AMg6 were synthesized using plasma electrolytic oxidation (PEO). The microstructure, phase composition and micro-hardness of the PEO layers were studied. In addition to the two main phases (α-Al2O3 and γ-Al2O3), a small amount of a metastable crystalized Al2.427O3.64 phase was found in their structure. A comparison was made of the wear resistance and friction coefficients of the synthesized PEO layers during friction tests in pairs with other PEO layers, a galvanic chromium coating, cast iron, steels and bronze of the BrC30 type. The results of the friction tests for the various PEO layers on aluminum alloys in tribo-contact with high-hardness elements made of hardened or chrome-plated steel justify the possibility of their use in a friction pair. We experimentally showed the influence of glycerin additive in motor oil 15W30 on the change in the friction coefficient of the PEO layers synthesized on the aluminum alloys and on the arc-sprayed coatings on their surfaces in tribocouples with hardened steel.

Research on tribological performance of textured thrust bearing using gray relational degree and improved multi-objective water circulation algorithm

Abstract To enhance the loading capacity of the oil film, reduce the lubricating oil temperature, and minimize the deformation of the friction pairs, three types of concave textures were proposed. The tribological properties of the thrust bearing underwent multi-objective optimization analysis using the two different methods. By comparing the two methods, it was found that the improved algorithm (MOWCA) demonstrated better optimization performance. Under this algorithm, when the texture shape was triangular, the number of textures was 18n, the size was approximately 0.135 mm, and the spacing between textures was approximately 4.6 mm, the loading capacity of the oil film increased by approximately 26.11%, and the temperature decreased by approximately 0.46%.

Friction Reduction Achieved by Ultraviolet Illumination on TiO2 Surface.

Controlling friction by light field is a low-cost, low-energy, non-polluting method. By applying ultraviolet light on the surface of photosensitive materials, the properties of the friction pairs or lubricant can be influenced, thus achieving the purpose of reducing friction. In this study, TiO2, an inorganic photosensitive material, was selected to investigate the modulating effect of light fields on friction lubrication when using polyalphaolefin (PAO) base oil as a lubricant, and the modulation law of light fields on the friction lubrication behavior was investigated under different loads (1-8 N), different speeds (20-380 mm/s), and different viscosities (10.1-108.6 mPa·s) of PAO base oil. The experimental results showed that light treatment could reduce the friction coefficient of PAO4 base oil lubrication from 0.034 to 0.016, with a reduction of 52.9% under conditions of 3 N-load and 56.5 mm/s-speed, and the best regulation effect could be achieved under the mixed lubrication condition. After TiO2 was treated with ultraviolet light, due to its photocatalytic property, PAO molecules were oxidized and adsorbed on the TiO2 surface to form an adsorption layer, which avoided the direct contact of rough peaks and thus reduced the friction coefficient. This study combines photosensitivity, photocatalysis, and friction, presenting a method to reduce the friction coefficient by applying a light field without changing the friction pairs or lubricants, which provides a new direction for friction modulation and gives new ideas for practical applications.

Study of the Dependence of the Friction Force and Coefficient of the Abrasive in the Metal Contact Zone on Various Factors

In the article, the interaction of the coefficient of friction for friction pairs operating under conditions of abrasive wear is considered, depending on a number of factors. Thus, the friction coefficient is one of the main indicators characterizing the performance of friction nodes. Analytical expressions obtained based on the calculation of the results of the conducted tests using mathematical statistical and mathematical methods allow to determine the coefficient of friction and allow the designer to effectively choose the material and oils before designing.

Study on the tribological characteristics of surface triangular textured TC4 alloy prepared by SLM technology

Surface Triangular Textured TC4 Alloy specimens were prepared by 3D printing technology (SLM technology: selective laser fusion). Effects of wedge-shaped triangular textures with different texture area occupancy on hardness, friction and wear of the 3D printed TC4 alloy specimens were studied, in comparison with non- textured specimens. SFT -2 M pin-disc friction and wear testing machine was used to perform friction and wear experiments under 46 # mechanical oil lubrication conditions, and MH-500 Vickers hardness tester was used to measure hardness of the specimens. Scanning electron microscope (SEM), energy spectrometer (EDS), and electronic balance instrument were used to characterize the wear scar morphology, element content, wear amount, etc. of the specimens. Using the Fluent module in ANSYS Workbench software, we studied the mechanism for the reduction in the friction coefficient between friction pairs during the relative movement in lubricating oil. Results of the study show that the hardness of the 3D printing specimen is significantly greater than that of the non- textured one. In each group of experiments, the wedge triangular textured specimens showed better tribological properties, and the 3D printed specimen with an area occupancy of 22. 53 % exhibited the smallest average friction coefficient (0.17) and higher wear resistance than other specimens. The dynamic pressure effect due to the wedge triangle texture inside the lubricating oil film is the main reason for the reduced friction coefficient between the friction pairs.

Friction, Wear, and Corrosion Behavior of Nitrocarburized HT250 Gray Cast Iron

This study employed friction and wear experiments on nitrocarburized HT250 gray cast iron, utilizing GCr15 cemented carbide balls as the friction pair, to investigate the friction behavior and wear mechanism of the compound layer, diffusion layer, and matrix. The findings indicate that the diffusion layer exhibits the highest wear resistance, followed by the compound layer, while the matrix shows the lowest wear resistance. At lower loads, the wear form of the compound layer is characterized by minor flaking wear, the diffusion layer exhibits minor flaking and abrasive wear, and the matrix displays minor adhesive wear accompanied by abrasive wear. With increasing loads, the wear form of the compound layer transitions to flaking and abrasive wear, the diffusion layer shows fatigue flaking wear, and the matrix demonstrates severe adhesive wear, fatigue flaking wear, and abrasive wear. Electrochemical impedance spectroscopy and potentiodynamic polarization were employed to study the corrosion behavior of the compound layer, diffusion layer, and matrix in a 3.5wt% NaCl solution. The results indicate a 27.7% decrease in the corrosion current density of the compound layer compared to the matrix, with the diffusion layer exhibiting a corrosion current density two orders of magnitude lower than both the matrix and compound layer. In electrochemical impedance spectroscopy, the diffusion layer shows the highest impedance modulus, largest phase angle amplitude, and circular arc radius. It shows that the corrosion resistance of HT250 gray cast iron is improved after nitrocarburizing, especially the diffusion layer.

Study on friction and wear behavior of gray cast iron with different carbon content at different temperatures

In this paper, we study the friction and wear properties of gray cast iron with different carbon contents at various ambient temperatures. We also examine the failure forms of gray cast iron friction and wear. The research concludes that under low-temperature wear conditions, the graphite in the gray cast iron structure can enter into the interface between the friction pair, have a lubricating effect on the wear surface, and reduce the friction coefficient and wear loss of the gray cast iron material. As the graphite content in the gray cast iron structure increases, its lubrication and protection effects enhance. Consequently, the primary cause of wear failure in gray cast iron is fatigue peeling induced by plastic deformation. Under high-temperature wear conditions, an oxide layer gradually forms on the wear surface. As the experimental temperature increases, the thickness of the oxide layer on the wear surface also increases. When the oxide layer formed on the wear surface reaches a certain level of thickness, the internal expansion stress of the oxide layer increases considerably, causing the oxide layer to peel off and increase the roughness of the wear surface, friction coefficient, and wear loss. Additionally, an increase in the graphite content in the gray cast iron structure makes the surface more prone to oxidation. This leads to increased friction coefficient and wear loss, with the wear failure of gray cast iron primarily caused by the peeling of the oxidation layer.

Optimization and tribological performance of PEEK based composite coatings reinforced with PTFE for friction pairs of aviation hydraulic pumps

In this study, polyetheretherketone (PEEK) based composite coatings reinforced with polytetrafluoroethylene (PTFE) were applied to copper steel bimetallic plates. The impact of process parameters on the tribological properties of the coatings was thoroughly investigated. The results indicated that the optimized PTFE/PEEK2.2 coating exhibited commendable friction reduction and wear resistance performance when subjected to aviation kerosene lubrication. It was observed that the hot-pressing temperature has the most significant influence on the bearing capacity and wear rate of the coatings. In contrast, the hot-pressing pressure primarily affects the average friction coefficient. The primary wear mechanism observed in these coatings is adhesive wear. These findings suggest promising application prospects for the composite coatings in aviation hydraulic pumps, underscoring their potential to significantly improve overall performance.

Effect and performance analysis of different surface treatments on polymer-metal friction pairs

The reliability of machinery can be directly impacted by severe wear and failure of joint bearings, particularly under harsh operating conditions or after prolonged use. The study aimed to investigate the impact of various surface treatments on the properties of materials using a disc-disc contact friction machine to simulate working conditions similar to those experienced by joint bearings. The application of chrome plating resulted in a significant enhancement in performance, leading to a 20% reduction in the coefficient of friction and an 80% decrease in the wear rate to 0.071 and 1 × 10−5 mm3/(N·m), respectively, at 30 MPa and 42 mm/s. Additionally, it increased the bonding of the transfer film base by 20% compared to untreated specimens, as indicated by nano-scratch tests. On the one hand, the elevated hardness of the chrome-plated coating facilitates uniform load distribution, while on the other hand, the presence of microcracks on the surface aids in retaining a greater amount of abrasive debris and in the formation of a more effective transfer film. Consequently, this diminishes the wear of the polymer material. This discovery has the potential to influence the improvement of surface treatment procedures and the selection of materials for the advancement of engineering practices.

Effect of laser surface texturing on friction performance and surface damage of silicon nitride ceramic

ABSTRACT Laser surface texturing (LST) with different patterns was performed on silicon nitride (Si3N4) ceramic. Effect of patterns created by LST on coefficient of friction (COF) and surface damage under dry friction was investigated. Results indicated that fluctuation of COF decreased with the increasing loading force for both un-textured and textured samples. Under the same loading force, COF of Si3N4 ceramic with textured patterns was more stable than the samples with smoothly finished surface. The COF of textured samples was not always lower than that of un-textured samples. This may be caused by differences in the distribution of debris and the continuity of surface contact. The worn surface existed damages of plow and crack. However, peeling was observed on un-textured samples only. The surface damage of textured samples was slighter than un-textured samples. Especially under the high loading force, catastrophic damage appeared on the smooth surface. The worn surface of textured samples still maintained the similar state. This could be mainly due to the more complex friction process on the surface of textured sample. The wear rate of the frictional pair was also studied. The mechanisms of friction process for smooth and textured surface were analyzed.

Analysis of Dynamic Wear Characteristics of Joint Contact Friction Pair of Excavators Working Device

The working device of an excavator in construction machinery is prone to damage and wear under ordinary working conditions. Based on a model of an excavator under typical working conditions, the dynamic load-bearing situation of the three main joint friction subsets of the working device is simulated by using the virtual prototype technology; the location of the functional device with high stress is identified based on finite element analysis, and the correctness of the simulation results is verified by designing strain gauges. Based on this, the dynamic contact stress variation law of the contact surface of the end-face friction subsets was explored, and the end-face wear depth was calculated by combining Archard wear theory and finite element wear simulation technology; the specimens were worn on the end-face wear tester, and the surface wear was observed under the scanning electron microscope to summarize the wear mechanism and analyze the element content changes of the worn surface. The results show that the three main joints of the working device produce large dynamic fluctuations and are prone to wear, and the destructive degree is more prominent; the wear process is accompanied by higher temperatures, fatigue wear, and abrasive wear on the wear surface, and the wear depth value of the right end face is significantly larger than that of the left end face. This method has a significant reference value for reliability analysis and optimization improvement when using construction machinery’s main joint friction pairs.

Повышение износостойкости цилиндрических поверхностей трения комбинированной электромеханической обработкой

Processing technology and technological equipment for the formation of a wear-resistant surface layer by implanting materials based on tungsten carbide (WC), are viewed. The effect of implanted WC powder on the formation of gradient wear-resistant structures in the friction surface of carbon steel formed during the implementation of combined electromechanical processing (WRCEMP) technology, has been studied. Resulting from heat and pressure impact in the zone of plastic deformation, intensive austenization of steel occurs with dissolution of WC powder and subsequent formation of highly dispersed composite structures caused by the decomposition of undercooled tangstem-supersaturated austenite. Combined comparative friction and wear tests were carried out for structural steel 45 with a graded structure of a hardened surface and rather expensive and technologically- difficult to obtain modern wear-resistant coatings and materials. The issue of WRCEMP technology practical application used for the «axis of satellite – satellite» friction pair is viewed. An assessment of the durability increase of the «axis of satellite – satellite» interface during the implementation of the considered processing methods and innovative technology was taken. Recommendations for the use of combined electromechanical processing technology at machine-building enterprises as a highly effective way to ensure and improve the performance of machine parts at the stage of their manufacture are given.

Method of brake mechanisms thermal load control under the influence of automated braking system load modes

Introduction (problem statement and relevance). Most of the kinetic energy of a vehicle equipped with an anti-lock braking system (ABS) is damped due to friction work in the brakes. Besides the ABS function, the automated braking system implements a lot of functions of active safety and driver assistance systems by using regular service brake mechanisms as an actuator. Overheating of brakes, namely of their friction pairs, leads to the phenomenon of critical fading, which is accompanied by a sharp decrease in braking torque. Reducing the impact of this phenomenon is a very difficult task in terms of both taking into account the cost of the braking mechanism and its minimum complexity. The proposed procedure makes it possible to assess the influence of operation of various active safety and driver assistance systems on the thermal load of the brake mechanisms. The prospect of its expansion when creating new vehicle designs is also covered.The purpose of the study is to increase the reliability of brake mechanisms, braking characteristics stability by improvement of the procedure for calculation and reduction of the brake mechanism thermal load of the wheeled vehicles equipped with the automated brake system.Methodology and research methods. Theoretical and experimental studies were conducted in the paper. In the theoretical study, the main computational tool is the finite element method (FEM) with using of licensed software packages Abaqus CAE and SolidWorks Simulink.Scientific novelty and results. The thermal load estimation procedure for brake mechanisms of vehicles that are equipped with an automated brake system has been created. The calculation procedure developed takes into account the increase in the proportion of the vehicle kinetic energy that is extinguished in the brake mechanism of the vehicle equipped with different subsystem functions.Practical significance. Application of the developed complex calculation procedure with any thermal calculation complexes on the FEM basis will allow brake system developers to reduce the costs for intermediate tests for thermal load at the design stage, and upon that, the influence of functional subsystems of the automated brake system will be taken into account. Application of the suggested improvement of the monitoring and control systems for the automated brake system will reduce the probability of fading phenomenon occurrence.

Insight into the tribological performances of coconut shells as a potential natural water lubrication material

To better understand the tribological performance of coconut shell and to demonstrate its potential as a wear-resistant material for use in a water-lubricated environment, the microstructure of coconut shell was hereby characterized, and its hardness and water absorption properties were correspondingly measured. The tribological characteristics of coconut shells rubbing against a ZrO2 ceramic ball in dry and wet environments were studied, and the wear mechanism was revealed. The measurement characterization and experimental results indicate that the long axis of coconut shell ellipsoid cells grows along the direction of the long axis pointing towards the coconut shell ellipsoid, but this directionality has a relatively small impact on the tribological properties. The average sliding friction coefficient of coconut shell rubbing against ZrO2 ceramic balls is about 0.52 and 0.095, respectively under dry and wet friction conditions. Under dry friction conditions, the wear of coconut shells is mainly because of cell tearing, detachment and abrasive wear caused by alternating friction forces. Mainly considering the combined effects of the high hardness, high strength and good water absorption of coconut shells, as well as the water film at the friction interface, the friction force significantly reduces and makes it difficult to damage the cell structure, leading to a wear rate decrease by more than 100 times under wet friction conditions, much lower than that of lignum vitae. Overall, this study indicates the potential of coconut shell as a water lubricated friction pair material featuring excellent performance.