Significant Reduction Of Friction Coefficient Research Articles

Improving frictional and insulation performance with silica-coated titanium dioxide additives in grease

PurposeThe purpose of this study was to synthesize composite nanoparticles (TiO2@SiO2) via the chemical deposition method and investigate their efficacy as additives in polytetrafluoroethylene (PTFE) lubricating grease. The focus was on examining the frictional and conductive properties of the TiO2@SiO2 grease using a friction tester.Design/methodology/approachComposite nanoparticles (TiO2@SiO2) were synthesized using the chemical deposition method and incorporated into PTFE grease. Frictional and conductive properties were evaluated using a friction tester. Surface morphology and chemical composition of wear tracks were analyzed using scanning electron microscope and X-ray photoelectron spectroscopy, respectively.FindingsIncorporating TiO2@SiO2 at a mass fraction of 1 Wt.% led to a significant reduction in friction coefficient and wear width. The wear depth exhibited a remarkable decrease of 260%, while the contact resistance reached its peak value. This improvement in tribological properties could be attributed to the presence of TiO2@SiO2, where TiO2 served as the core and SiO2 as the shell during the friction process. The high hardness of the SiO2 shell contributed to enhanced load-bearing capacity. In addition, the exceptional insulation properties of SiO2 demonstrated excellent electron-capturing capabilities, resulting in improved friction and insulation performance of the TiO2@SiO2 lubricating grease.Originality/valueThis study demonstrates the potential of TiO2@SiO2 composite nanoparticles as additives in lubricating greases, offering improved friction and insulation performance. The findings provide insights into the design of advanced lubricating materials with enhanced tribological properties and insulation capacity, contributing to the development of more efficient and durable lubrication systems.

Tribological performance of a surfactant derived from its structure of molecular aggregates in water

Surfactants are promising additives for water-based lubricant surfaces due to their ability to adsorb on metal surfaces and reduce friction under boundary lubrication. In this study, the aggregation behavior of surfactants in aqueous solutions and their effects on friction and anti-wear properties were investigated using sodium 2-hexyldecanoate (2HDNa) as an example. The results revealed that 2HDNa forms vesicles at low concentrations and transits to micelles at higher concentrations. The presence of vesicles led to a significant reduction in friction coefficient and improved anti-wear properties by forming an absorbed film, which was confirmed by neutron reflectometry (NR). The findings of this study emphasize the lubrication and anti-wear performance of vesicles and the importance of surfactant concentration control in water-based lubrication.

A comparative study of limit diagram of ultrasonic-assisted and conventional hot incremental forming of Ti-6AL-4V alloy

Electric hot incremental forming (EHIF) technique is a novel sheet metal forming method for low-formability materials like Mg and Ti-6Al-4V alloys. There are some defects in EHIF including low surface quality, unexpected sheet tear, and oxidation of the fabricated workpieces. These defects limit its widespread use. In this article, longitudinal ultrasonic vibrations of forming tools are used for Ti-6Al-4V sheets in the EHIF process. This technique led to a significant reduction of friction coefficient and improvement of workpieces’ surface quality. Also, a combination of mechanical vibrations and heat reduced the phase transformation temperature of α phase (HCP structure) to the more formable β phase (BBC structure) at 600 °C. It improved Ti-6Al-4V sheets’ formability. In this study, various tensile and compressive strains were created by manufacturing different geometries such as cone, frustum, torispherical, and five-lobe. These strains are used to compare the forming limit diagram of the ultrasonic-assisted and conventional hot incremental forming. The design of the experiment and analysis of variance were employed to identify the optimum condition for creating the largest strains. Also, effective parameters were optimized by response surface methodology. Then major and minor strains for both techniques were compared. Achieved strains in all types of geometries for ultrasonic-assisted technique were higher than those achieved by a conventional process.

Ultra-dispersive sulfonated graphene as water-based lubricant additives for enhancing tribological performance

The weak dispersion stability of graphene in water restricts its practical application as water-based lubricant additives. Herein, sulfonated graphene (SGO) with ultra-dispersive and superior lubrication performance was synthesized by means of sulfonating graphene oxide (GO). It was found that SGO was well dispersed in water. Besides, viscosity of water was enhanced by 25.8 % after adding 0.2 wt. % of SGO, which might be favorable to enhance film thickness between tribo-pairs. Furthermore, SGO lubrication contributed to significant reduction in friction coefficient (CoF) and wear scar diameter (WSD) by 74 % and 15.7 %, respectively. SGO exhibited the better lubricity in comparison to GO, which could be ascribed to that adsorption ability of -SO3H groups was stronger than that of -OH and -COOH groups.

THE EFFECT OF HEAT TREATMENT AND SURFACE ANODIZATION ON FRICTION AND WEAR COEFFICIENT OF ALUMINIUM 2024 USING PIN ON DISK METHOD

The use of aluminum alloys as a material for engineering components that rub against each other is increasing, so it is important to know the friction characteristics of these aluminum alloys. In this study, Aluminum 2024 was given heat treatment with variation in aging time and anodization. Then, the wear and friction coefficient tests were carried out using a pin tool on the disc. The effect of aging time and surface anodization on wear tests are carried out to determine the amount of wear and the coefficient of friction test is carried out to determine the coefficient of friction of the material when it rubs against a pin made of AISI 52100 Steel. The coefficient of friction test is carried out by adding lubrication as a parameter. The test results showed that the aluminum material given heat treatment had better resistance than that which was not heat treated. This is because the heat treatment creates precipitates that can increase the aluminum's hardness and wear resistance. Whereas for anodized specimens, the alumina layer can act as an abrasive grain when given a high enough friction and load continuously, so the wear testing mode changes from dry sliding wear to three body abrasive wear and decreased wear resistance. From the friction coefficient test results, the aging time affects the hardness of the aluminum alloy, which leads to the value of the coefficient of friction. The harder the sample surface, the smaller the coefficient of friction obtained. Furthermore, applying lubricant to the sample will also decrease the value of the friction coefficient of the sample. Lubricating oil will provide a more significant reduction in friction coefficient than air. Finally, the anodizing surface on the sample will act as a lubricant reservoir when it occurs.

Performance improvement of foil air journal bearing employing micro-pocket and textures on top compliant surface

Investigations to reduce the friction and improve the dynamic performance of a self-acting air foil journal bearing have been performed and presented herein employing the texture, micro-groove and micro-pocket on the top foil. Significant improvements in the static and dynamic performances have been found in presence of micro-pocketed/grooved and textured top foils in comparison to conventional plain foil. The micro-pocketed top foil yields better performance as compared to textured and conventional cases. In the presence of micro-pocket on top compliant foil, the bearing yielded a significant reduction in friction coefficient varying in the range of 8%–11% as compared to conventional one. Moreover, better dynamic stability has also been found even at lightly loaded conditions in the presence of texture and micro-pocket.

XANES Study of Tribofilm Formation With Low Phosphorus Additive Mixtures of Phosphonium Ionic Liquid and Borate Ester

The development of low phosphorus engine oils is important to minimize phosphorus-induced exhaust catalyst poisoning and resulting in harmful emissions. In this study, low phosphorus oil formulations were prepared by using an ashless additive mixture of borate ester (SB) with ionic liquid composed of a phosphonium cation and phosphate anion (P_DEHP) at 350 and 700 ppm phosphorus. Tribological properties of this binary additive system were evaluated using a reciprocating cylinder on a flat test configuration. Favorable interaction between P_DEHP and SB resulted in a significant reduction in friction coefficient and wear volume, in particular for P_DEHP(700P) + SB oil blend. Time-scale analysis of tribofilm formation was determined by running the tribological experiments for 5, 15, and 60 min duration. Electrical contact resistance (ECR) results revealed that the addition of P_DEHP at 350 ppm of phosphorus to SB at 500 ppm of boron can reduce the incubation time from 300 to 100 s for stable tribofilm formation. X-ray absorption near-edge spectroscopy (XANES) analysis of tribofilms indicates that the tribofilm mechanism for additive mixtures of P_DEHP and SB initially involves the formation of boron oxide-based films, which later interact with phosphorus to form boron phosphates in addition to iron phosphates. Incorporation of the high amount of boron phosphates in addition to boron oxide/acid and iron phosphates in the tribofilms contributed to the improved tribological performance of P_DEHP(700P) + SB oil. XANES results reveal that tribofilms formed due to the interaction of SB and P_DEHP evolve to a cross-linked structure, wherein the chain length of polyphosphates is increased with the increase in rubbing time.

An experimental approach to study thermal and tribology behavior of LPG refrigerant and MO lubricant appended with ZnO nanoparticles in domestic refrigeration cycle

The present article experimentally examines the application of ZnO nanoparticles in refrigeration cycle. Nanoparticles overcome the energy consumption issue by improving the compressor lubrication characteristics. In this study, the ZnO nanolubricant is proposed as a promising lubricant to improve the lubrication characteristics of domestic refrigerator compressors. Effect on compressor suction-discharge characteristics as well as energy consumption of refrigeration cycle has been observed using ZnO nanoparticles with pure refrigerant (Liquid Petroleum Gas). The physics involved behind the communication of nanoparticles with base refrigerant has been more clarified by performing tribological tests (i.e., measurement of viscosity and friction coefficient) of compressor lubricant for dissimilar fractions of nanoparticles. Thermal conductivity test on lubricant with distinct fractions of nanoparticles has also been conducted. The results showed that ZnO nanoparticles additive in mineral oil increases the viscosity which leads to a significant reduction in friction coefficient inside the compressor piston cylinder assembly which leads to a significant improvement in compressor energy consumption. The friction coefficient of nanolubricant with fraction of 0.7 g/L are about 11.1–25% lower than that of base lubricant. The compressor energy consumption was saved about 0.44–10% for employing ZnO nanolubricant with a mass fraction about 0.1 g/L to 0.7 g/L. Thermal conductivity was significantly enhanced (about 41%) using ZnO nanoparticles in mineral oil. The results of the present study assure better, effective and suitable performance of LPG as alternative refrigerant in refrigeration cycles.

Mechanical and Tribological Characteristics of Cladded AISI 1045 Carbon Steel.

This study introduces a newly developed cladding device, through printing AISI 1045 carbon steel as single and double layers onto American Society for Testing and Materials (ASTM) H13 tool steel plate. In this study, the mechanical and tribological characteristics of single and double layers were experimentally investigated. Both layers were polished first and then subjected to ultrasonic nanocrystal surface modification (UNSM) treatment to improve the mechanical and tribological characteristics. Surface roughness, surface hardness and depth profile measurements, and X-ray diffraction (XRD) analysis of the polished and UNSM-treated layers were carried out. After tribological tests, the wear tracks of both layers were characterized by scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDX). The surface roughness (Ra and Rz) of the single and double UNSM-treated layers was reduced 74.6% and 85.9% compared to those of both the as-received layers, respectively. In addition, the surface hardness of the single and double layers was dramatically increased, by approximately 23.6% and 23.4% after UNSM treatment, respectively. There was no significant reduction in friction coefficient of both the UNSM-treated layers, but the wear resistance of the single and double UNSM-treated layers was enhanced by approximately 9.4% and 19.3% compared to the single and double polished layers, respectively. It can be concluded that UNSM treatment was capable of improving the mechanical and tribological characteristics of both layers. The newly developed cladding device can be used as an alternative additive manufacturing (AM) method, but efforts and upgrades need to progress in order to increase the productivity of the device and also improve the quality of the layers.

Applications of microwave heat treatment process to enhance the surface properties of bronze and steel materials used in journal bearing

Journal bearings are important conformal sliding contact machine elements widely used in industrial applications to support cylindrical shafts subjected to radial loads. Wear in journal bearings propagate due to increase in fatigue load cycles, lubricant degradation, misalignment, etc. Hence, it is important to minimize the occurrence of wear in journal bearings by improving their mechanical properties. Microwave heat treatment process is one of the recent developments emerged to improve the surface properties of materials in which energy is directly delivered to the material surface through molecular interaction with the electromagnetic field. In the present work, microwave heat treatment process was used to improve the performance of journal and bearing materials. Further, the microwave-treated journal and bearing specimens were used to conduct performance evaluation experiments under hydrodynamic lubrication regime operating condition. Results highlighted the importance of microwave treatment to reduce wear in both journal and bearing components. A significant reduction in friction coefficient and specific wear rate values were obtained, which resulted in a considerable improvement in the operating performance of the journal bearing system with respect to the increase in fatigue load cycles.

Tribological Behavior of Surface Textured Gray Cast Iron at Different Texture Density by Ultrafast Laser

Abstract Laser surface texturing process involves the creation of microfeatures, e.g., tiny dimples, that are usually distributed in a certain pattern, covering only a fraction of the surface of the material that is being treated. This process offers several advantages for tribological applications, including improved load capacity, wear resistance, lubrication lifetime, and reduced friction coefficient. In the present study, surface modification of gray cast iron using femtosecond laser irradiation is adopted in order to establish an optimal geometric pattern with dimple features and dimensions, to improve wear and friction behavior. The surface texturing of gray cast iron was done with the help of an ultrafast laser with a pulse duration of 100 fs and wavelength of 800 nm. The effect of a range of process parameters, such as pulse energy, scan velocity, and textured density, on the performance characteristics of laser-textured samples was investigated. The laser surface textures were examined using an opto-digital 3-D microscope. The friction and wear tests under starved lubrication condition were performed using a ball-on-disk tribometer. The textured surfaces cause a significant reduction in friction coefficient (by 72 %) and wear (by 19 %) over the untextured surfaces. Furthermore, an analysis of wear tracks using a scanning electron microscope and energy-dispersive x-ray spectroscopy show a significant improvement in wear resistance. The wear track of the textured surface exhibited a significant reduction of wear debris and was found to be smoother than the untextured surface. Among various patterns tried, the pattern with 55 % texture density gave the best results.

Theoretical and numerical modeling of tool–chip friction in ultrasonic-assisted turning

Decrease of friction in tool–chip contact zone is a key subject in metal cutting operation. Therefore, effect of ultrasonic vibration in this area is analyzed by using experimental and simulation methods. In this study, a theoretical model is firstly developed based on the shear friction model, and then sticking–sliding contact zones plus their contact lengths are defined in order to simulate conventional and ultrasonic-assisted turning. Accordingly, shear angle, sticky length, and cutting forces were measured in experiments as input parameters for the calculation of friction coefficients. As a result, intermittent contact of vibrated tool decreases the time of thermal conduction in tool–chip interface, resulting in a significant reduction in friction coefficient and contact length, particularly, in sticky region.

Enhanced tribo-chemical properties of oxygen functionalized mechanically exfoliated hexagonal boron nitride nanolubricant additives

Two dimensional (2D) materials with layered lattice structure as nanofluid additives are useful to improve the tribological properties of metallic sliding interfaces. To enhance the tribological efficiency, the bulk crystalline hexagonal boron nitride (h-BN) powder sample was mechanically exfoliated by ball milling, and further processed through ultrasonication for de-aggregation. High resolution X-ray diffraction (HR XRD) and high resolution transmission electron microscopy (HR TEM) results clearly indicate the exfoliation of bulk h-BN into thinner two-dimensional (2D) crystalline sheets without creating noticeable structural defects. The topography of exfoliated nanosheets is well confirmed by atomic force microscopy (AFM). Oxygen functionalization into the h-BN nanosheets after the mechanical exfoliation was investigated by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Oxygen functionalization of h-BN improved the cohesive compatibility between h-BN and commercial 10W30 lubricant oil for stable dispersion. Friction coefficient and wear of sliding metallic interfaces were reduced significantly in the presence of few layered exfoliated h-BN nanofluid as compared to neat lubricated oil. Micro- XPS and energy-disperse X-ray spectroscopy (EDX) analysis demonstrated the presence of adsorbed h-BN tribofilm in the metallic wear track. Thin 2D sheets of h-BN nanofluid was effective as an additive for low shear resistance under the tribo stressed condition which is the main reason for significant reduction in friction coefficient. Moreover, the enhanced wear resistance of exfoliated h-BN additives was explained by low shear resistance and high compressive/tensile strength of planer sheets which restricted the mechanical damage and protected the metallic interfaces against deformation and wear.

Effect of debris size on the reciprocating sliding wear of aluminium

The literature is controversial in relation to the influence of wear debris on tribological behaviour. Some works have shown that the presence of debris is fundamental to the formation of a protective tribolayer, thus reducing friction, whereas others showed that the presence of wear debris could contribute to increase friction coefficient due to the energy spent dragging them into the contact. This work aims to study the influence of the presence of wear debris, simulated by Al2O3 particles, on the tribological behaviour of an aluminium-steel pair under reciprocating sliding contact. Special emphasis is given to the particle size (0.05 µm, 0.1 µm, 1 µm and 10 µm). The particles were dispersed in distilled water (2 wt.%) as the source of debris. Reference tests were carried out solely in the presence of distilled water. The addition of alumina particles contributed to a significant reduction in friction coefficient, in particular for the largest particles (diameter ϕ=10 µm). When the larger particles were added, it was possible to observe the formation of a tribolayer on the sample surface leading to a gain of mass. In opposition, the wear rate of the counter body increased when large particles were added and the wear tracks showed strong evidence of abrasive wear. This suggests that hard and large wear debris, incorporated in the tribolayer formed on the samples, can act as hard protuberances, leading to abrasive wear of the counterbodies. When small particles were added, friction was still reduced when compared with the reference test, but the reduction of the friction coefficient was less significant. Small particles reduced the steel counter body wear rate and did not affect significantly the wear rate of the aluminium samples. It is proposed that small debris can get entrapped in the surface irregularities of the specimens and therefore participate less in the formation of the tribolayers.

Study of hydrodynamic behaviour of large bearings depending on the viscosity of the lubricant

The research refers to study of hydrodynamic behavior of large bearings equipped with automatic lubrication system, where the liquid used may have a viscosity with variable values depending on the temperature or depending on the additive used. The introduction of additives with nanoparticles causes modification of viscosity and a significant reduction of friction coefficient. This study establishes a direct link between the friction, viscosity and tensions that occur in the contact area. Experimental studies confirm improving tribological properties of the contact area between the bearing rollers and raceways, through attracting nanoparticles on surfaces in contact and reducing friction coefficient. Accomplished finite element analysis showed decrease of the contact stresses, therefore decrease of the wear and increase the life of the bearing. Research has concluded that influencing viscosity and friction coefficient of lubricant can result in reducing wear of the bearing components, as well as increase the lifetime of bearing.

Effect of Polypropylene Modification by Impregnation with Oil on Its Wear and Friction Coefficient at Variable Load and Various Friction Rates

Laboratorial two-body wear testing was carried out in order to assess effects of polypropylene modification by impregnating it with oils on friction coefficient and wear in comparison to those parameters of unmodified polypropylene, Teflon, and polyamide during operation under conditions of sliding friction without lubrication. Wear behaviour of the tested specimens was investigated using ASTM G77-98 standard wear test equipment. Recording program made it possible to visualise and record the following parameters: rotational speed and load, linear wear, friction coefficient, temperature of the specimen, and ambient temperature. In addition, wear mechanisms of the analysed materials were determined with use of scanning electron microscopy. In the case of the remaining tested polymers, the most important mechanism of wear was adhesion (PP, PTFE, PA 6.6, and PA MoS2), microcutting (PTFE, PA 6.6, and PA MoS2), fatigue wear (PTFE), forming “roll-shaped particles” combined with plastic deformation (PA 6.6 and PA MoS2), and thermal wear (PP). Impregnation of polypropylene with engine oil, gear oil, or RME results in significant reduction of friction coefficient and thus of friction torque, in relation to not only unmodified polypropylene but also the examined polyamide and Teflon.

Characterization of duplex coating system (HVOF + PVD) on light alloy substrates

Light metals such as aluminium or magnesium alloys play an important role in many different industrial applications. However, aluminium and especially magnesium alloys show relatively poor resistance to sliding wear, low hardness and load bearing capacity, so that surface performance improvement is recommended, often by PVD processes.This study evaluates the tribological improvement achieved by applying a duplex coating on AW-7022 aluminium alloy or AZ91 magnesium alloy substrates, consisting of a thick coating interlayer, deposited by High Velocity Oxygen Fuel (HVOF), followed by a PVD (TiN, TiAlN) or PE-CVD (DLC) hard top layers.The deposition of thermal sprayed HVOF coatings, as primary layer, leads to improvement of the load bearing capacity of the substrates and allows reducing the tendency of hard thin top layer to cracking and delamination when it is directly deposited on a softer substrate. The number of laps to failure, in the pin-on-disc wear tests, of TiN and TiAlN PVD coatings deposited on the harder interlayer HVOF coating were significantly higher (3000 and 1400 laps, respectively) than the values measured for these coatings deposited directly on the aluminium substrate (140 and 120 laps, respectively).The best combination of properties was obtained with the DLC top layer deposited on the thermally sprayed coatings, with a significant reduction of friction coefficient (<0.10), which remains almost unchanged even after 40,000 laps in the pin-on-disc wear tests.

Structure, mechanical and tribological characterisations of pulsed DC magnetron sputtered TiN-WSx composite coating

Pulsed DC magnetron sputtered TiN-WSx composite coatings were investigated in terms of their structural, mechanical and tribological properties. The coatings were synthesized in Ar and N2 mixed environment from separate Ti and WS2 targets. Compositional variation was performed by systematically varying the Ti cathode current while keeping the same for WS2 cathode at a fixed value. EDS analysis of the films revealed that the cumulative (W + S) content varied from 8.9 to 42.0 wt%. The films were, however, sulphur deficient, S/W at.% ratio being in the range of 0.6–0.78. GIXRD spectra indicated coexistence of (002) oriented WS2 phase along with polycrystalline TiN phase, as confirmed by HRTEM revealing presence of WS2 in nanocluster form within TiN columnar structure. FESEM micrographs showed decrease in agglomerated grain size and densification of columnar structure with increase in (W + S) content. The adhesion also scaled with (W + S) content up to 27.8 wt%. The nanohardness of the composite coatings, however, progressively decreased from 27.3 GPa to 17.3 GPa with increasing content of (W + S). Significant reduction in friction coefficient and wear rate could also be recorded for the composite coatings, as compared to TiN, the best being obtained for the one containing 15.0 wt% of (W + S).

Enhanced Lubricity of SnO2 Nanoparticles Dispersed Polyolester Nanofluid

Nanofluid lubrication is a novel approach for enhancing energy efficiency of the sliding interfaces which is useful for reducing friction and wear of the machine elements. The SnO2 nanoparticles (NPs) of 25 nm size and concentration 0.03 mg mL–1 dispersed in polyolester (POE) oil is found to exhibit significant reduction in friction coefficient and wear up to 38 and 42%, respectively, in comparison to neat POE oil. It is also found that the lubrication efficiency depends on size of the NPs, dispersion stability, and concentration. Fourier transform infrared red spectroscopy confirmed that the chemical stability of the POE was preserved after the tribology test and there was no product due to oxidation reaction. Formation of low shear strength tribofilm containing organic compounds and SnO2 nanoparticles was key factor in reduction of the friction and protection against wear and deformation.

A functional effect of the superficial mechanical properties of articular cartilage as a load bearing system in a sliding condition

Abstract The structure and composition of articular cartilage show depth-wise inhomogeneity and anisotropy. In particular, the dense collagen network covers and reinforces the superficial tangential zone of the tissue. It is thought that this peculiar structure offers the excellent tribological property of articular cartilage. The purpose of this study was to investigate the functionality of the superficial tangential zone (STZ) of articular cartilage as a load bearing system. The 2-dimensional finite element (FE) model was accepted for sliding configuration with sufficient extent of sliding distance. The standard model as a control was carried from our previous study, which included depth-dependent Young׳s modulus of the solid phase, fiber reinforcement with strain-dependency and permeability with compaction effect. The mechanical property of the superficial layer was modified for a parametric study of its functionality. According to research results in the past, the tangential stiffness of the fiber reinforcement of the STZ model was enhanced, and the following anisotropic permeability was also modified. The stationary contact condition and the migrating contact condition were examined to compare the effect of the superficial tangential layer. The result showed that the significant reduction of friction coefficient was found in migrating contact condition of the STZ model. In the observation of field output of FE analysis, the contacting surface formed a thin low permeability layer, which would enable the high fluid pressure and the low fluid flow at the same time. It seemed that the stiffening of the fiber reinforcement of the superficial layer promoted the formation of the low permeability layer. Beyond the effectivity of the fiber reinforcement of biphasic matrix on the interstitial fluid pressurization, the findings of this study indicated that the compaction effect on the permeability would involve a quite complex phenomenon in long term migrating contact sliding.