Wear Reduction Research Articles

Lubricity effectiveness of bio-lubricant modified with multi-wall carbon nanotube and organic polymer

The development of effective bio lubricants with anti-friction and wear properties is gaining recognition due to their ecofriendly nature and good lubrications in mitigating challenges associated with friction and wear on tribo-components during lubrication. In this research, rapeseed oil served as the base lubricant, and the high frequency reciprocating rig was utilized to examine the responsiveness of the multiwall carbon nanotubes (MWCNTs) and Eichhornia crassipes carboxylmethyl cellulose (EC-CMC) polymer additives. To determine the constituents and strength of the formulations, the samples were characterized using scanning electron microscope, Energy-dispersive X-ray, Fourier transform infrared spectroscopy, Raman, and X-ray photoelectron spectroscopy. The tribological test was conducted in terms of synergistic tendency, load carrying capacity, friction and wear reduction as well as tribo-film nature. The investigation came to the following conclusions: Depending on the operating conditions, all nanoparticle suspensions showed decreases in friction and wear relative to the base oil; MWCNTs yielded better wear reduction performance while EC-CMC demonstrated outstanding friction reduction operations compared to based lubricant; the suspensions with 0.8% MWCNTs +0.5% EC-CMC had the best tribological behavior, exhibiting high percentage reduction on friction (67.8%) and wear (37.9%) with low levels on the surface roughness. Using XPS analysis, the detection of additive elements and tribo-films on the wear surfaces was validated, and their nature was analyzed in the context of the related tribo-chemistry findings. The study concluded that effective friction reduction during testing is a result of the additive's rapid penetration into the interface region and its nanosized structure.

DDP-functionalized UiO-67 nanoparticles as lubricating oil additives for friction and wear reduction

Engineering the surface and interface of nanomaterials by precise molecular modification is essential for improving interfacial compatibility and dispersion stability in liquid. We report three different molecular structures of dialkyldithiophosphate (DDP) functionalized metal organic frameworks (MOFs) nanoparticles as oil additives can realize friction and wear reduction. UiO-67 nanoparticles were modified respectively by DDP molecules with different alkyl chains of various lengths and branches. Molecular dynamic simulation demonstrated DDP molecules were on the surface and in the pores of UiO-67 nanoparticles. The UiO-67@DDP additives in oil strongly reduced the coefficient of friction and wear volume by more than 50%. Additionally, the protective tribo-film formed by the deposition of UiO-67@DDP nanoparticles and tribo-chemical reaction contributes to the mitigation of friction and wear.

Influence of Bogie Maintenance and Retrofitting on Wheel Wear: Analysis Using Integer Programming and Multibody Simulation

Brazilian railroads are continuously looking to increase their asset performance. In this sense, wheel/rail interface studies have been conducted, which allowed benefits that were not previously considered. Improved wheel/rail contact can significantly reduce maintenance costs, increase energy efficiency, and increase operational safety. For rolling stock, wheel consumption usually has the highest maintenance cost and is among the highest total costs of a railroad. Therefore, the understanding of wheel wear behavior, which is carried out in an integrated manner with permanent track and operating conditions, must be investigated in depth. This study aims to analyze the influence of bogies on wheel wear. Two aspects were considered: maintenance conditions and bogie design. The maintenance conditions were evaluated through wayside and field measurements. The collected data were later statistically evaluated and modeled in integer programming to optimize and review the maintenance strategy, which could avoid premature wheel scrapping after 5 years, allowing for a regular wheel life of 9 years. This analysis has allowed for the development of a new bogie maintenance parameter, which is not defined in manual and rule standards. The bogie design modernization was analyzed using the VAMPIRE multibody simulation software. The retrofitted bogie was modeled to improve the dynamic behavior and analyzed using wheel/rail contact theory. The polymer suspension elements’ modelings were thoroughly detailed for each property to illustrate the retrofit’s design features. Therefore, to calculate the gains of the retrofitted bogie, a methodology was built to compare the results of wheel wear in a real railroad track section. This methodology can be used to show that the retrofit can provide a reduction in wheel wear of 40% for ride control for a broad gauge (1600 mm).

Wheel wear reduction of a mechatronic two-axle vehicle controlled with feedforward wheelset steering approaches

The mechatronic vehicle developed within the Shift2Rail projects Run2Rail, Pivot, NEXTGEAR, and Pivot2 is evaluated with respect to wheel wear. The KTH wear model is used to determine the coefficients of Archard’s wear map to reproduce measured worn wheel profiles of the present vehicle running on Metro Madrid line 10. The same wear model is then used to evaluate the performance of the mechatronic vehicle controlled with two variants of a feedforward controller. The first one uses on-board measurements, while the second one is optimised using firefly optimisation algorithms assuming knowledge of the travelled track. The control strategy based on on-board measurements shows improvements above 60% in terms of lost wheel volume due to wear, compared to the standard bogie vehicle. The optimised controller reaches improvements above 70%. Good coherence is found between improvements predicted with the wear number and the ones achieved in terms of lost wheel volume.

A snowboard-inspired lubricating nanosystem with responsive drug release for osteoarthritis therapy

Most of present works of osteoarthritis (OA) therapy are focusing on reducing friction and improving drug loading capacity, while little attention is paid to realizing long-time lubrication and on-demand drug release. In this study, inspired by snowboards with good solid–liquid interface lubrication, a fluorinated graphene based nanosystem with dual functions of long-time lubrication and thermal-responsive drug release was constructed for OA synergetic therapy. An aminated polyethylene glycol bridging strategy was developed to enable covalent grafting of hyaluronic acid on fluorinated graphene. This design not only greatly increased the nanosystem’s biocompatibility, but also reduced the coefficient of friction (COF) by 83.3 % compared to H2O. The nanosystem showed long-time and steady aqueous lubrication behavior even after more than 24,000 times of friction tests, and a low COF of 0.13 was obtained with over 90% wear volume reduction. Diclofenac sodium was controllably loaded and sustained drug release was tuned by near-infrared light. Moreover, anti-inflammation results showed that the nanosystem had good protective effect on inhibiting OA deterioration, which could up-regulate cartilage anabolic genes of Col2α and aggrecan while down-regulating catabolic proteases genes of TAC1 and MMP1. This work constructs a novel dual-functional nanosystem that realizes friction and wear reduction with long lubrication life, and shows thermal-responsive on-demand drug release with good synergistic therapeutic effect of OA.

Fabrication of ionic liquid-functionalized covalent organic frameworks for friction and wear reduction

Herein, the ionic liquid functionalized covalent organic frameworks (COFs) nanosheets were successfully prepared via solvothermal reaction and then surface modification. Firstly, the COF with –OH groups (COF-OH) can bond with isocyanate (TDI) via the reactions between –OH group of COF-OH and para-NCO group of TDI, then the NH2-ionic liquid ([NH2C2MIm][Br]) can graft onto COF-OH surface (Br-IL@COF-OH) via nucleophilic addition reactions between –NH2 and ortho-NCO group. The as-prepared Br-IL@COF-OH exhibited outstanding lubrication performance as oil-based lubrication additives, with a trace amount addition of 2.0 wt%, the friction coefficient decreases from 0.144 to 0.102, and the wear volume decreases from 1.38 × 104 μm3 to 2.58 × 103 μm3, nearly 81.4%. The remarkable tribological properties are derived from the formation of stable protective film, which is composed of a physical adsorption layer via grafting ionic liquid and the friction film via tribochemical reaction.

Tribological Properties of Attapulgite Nanofiber as Lubricant Additive for Electric-Brush Plated Ni Coating

In order to expand the application field of attapulgite in tribology, the tribological properties of attapulgite as a lubricant additive on electric-brush plated Ni coating were investigated using the ball-disc contact mode of a SRV-IV friction and wear tester. The worn surfaces were characterized and analyzed via scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Results indicated that the friction-reducing and antiwear properties of 150 SN lubricating oil on the Ni coating were remarkably improved by an appropriate amount of attapulgite. Tribofilm mainly composed of Ni, NiO, SiO2, Al2O3, graphite, and organic compounds was formed on the worn surface under the action of attapulgite, which was responsible for the reduction of friction and wear.

A comprehensive study on the particulate matter characteristics of a friction material containing blast furnace slags

Recent studies have indicated the positive aspects of adding blast furnace (BF) slags on the friction and wear properties of different composite materials. However, the corresponding studies on the extremely important particulate matter (PM) emissions characteristics are seldom explored. This one-of-a-kind study examined the PM characteristics of two types of BF slags in detail. The slags were added in an in-house formulated friction material formulation with limited constituents to highlight the role of the added slags. Pin on disc tests were conducted at a mild wear testing condition with added attachments to the equipment to count and collect emitted particles at different particle size range. A significant reduction in pin wear and collected emitted particles were seen with the slag presence. The friction coefficient of the slag specimens was slightly lower than the reference sample. Through SEM and TEM analysis, it was seen that the slags actively contributed to and supported the formation of smooth, compacted, and extended secondary contact plateaus. From this study, the utilization of slags for specific applications is further evaluated, paving the path for subsequent inclusion/ replacement of conventional constituents in friction material compositions.

Triboactive coatings for wear and friction reduction in chain drives

Using hard triboactive (Cr,Al,X)N coatings (X = Mo, Cu) on chain pins is promising to increase the energy efficiency and sustainability of chain drives. (Cr,Al,X)N coatings, when interacting with lubricants, can build a tribofilm in the contact zone which has wear- and friction-reducing properties. These tribofilms can also be transferred to the surface of the chain bush, protecting it from wear. In this study, these coatings were tribologically investigated via pin-on-disc tribometer and a chain-joint tribometer under grease lubrication. The results showed that the (Cr,Al,Mo)N coating achieved the lowest total wear volume and lowest friction coefficient. The tribofilms showed a comparable composition on chain pins and bushes after the tests indicating a transfer of the tribofilm.

Three-dimensional temperature distribution of aircraft tyre tread at touchdown

PurposeThe aircraft’s tyres are forced to spin up at touchdown. A considerable amount of frictional energy will be converted into heat, raising the tread temperature and leading to thermal wear. This study aims to develop a model to analyse the tread heat and discuss the effectiveness of two wear reduction methods.Design/methodology/approachThe tread temperature is calculated using Laplace’s Equation. The efficiency of pre-rotation and soft landing in reducing tyre heat is studied using a developed three-dimensional heatmap method.FindingsThe result indicates that pre-rotation can significantly lower landing gear’s heat generation at touchdown. The soft landing, instead, has an insignificant or counterproductive effect.Research limitations/implicationsThe pre-rotation can significantly increase the tyre’s lifespan and cut the replacement cost. The emission of tyre particles into the environment can be reduced to protect the planet and human health.Originality/valueFew studies have used a theoretical model to estimate the tread temperature. The existing studies have only dealt with the maximum tread temperature or the tread centreline temperature, which is insufficient to discuss the heat across the entire tread. However, the heatmap method in this paper can do the job.

Experimental Study on the Reduction Effect of Pit Texture on Disassembly Damage for Interference Fit

After remanufacturing disassembly, several kinds of friction damages can be found on the mating surface of interference fit. These damages should be repaired and the cost is closely related to the severity of damages. Inspired by the excellent performance of surface texture in wear reduction, 5 shapes of pit array textures are added to the specimens’ surface to study their reduction effect of disassembly damage for interference fit. The results of disassembly experiments show that the order of influence of texture parameters on disassembly damage is as follows: equivalent circle diameter of single texture, texture shape and texture surface density. The influence of equivalent circle diameter of single texture and texture shape are obviously more significant than that of texture surface density. The circular texture with a surface density of 30% and a diameter of 100 μm shows an excellent disassembly damage reduction effect because of its perfect ability of abrasive particle collection. And the probability of disassembly damage formation and evolution is also relatively small on this kind of textured surface. Besides, the load-carrying capacity of interference fit with the excellent texture is confirmed by load-carrying capacity experiments. The results show that the load-carrying capacity of the excellent texture surface is increased about 40% compared with that of without texture. This research provides a potential approach to reduce disassembly damage for interference fit.

Superlubricity of Titanium Alloy Enabled by MoS2 Flakes and a-C:H Film

Titanium alloys are often used in engineering fields including aerospace, cryogenic technologies, and weaponry due to their remarkable qualities. However, several issues including a high coefficient of friction, weak wear resistance, and low hardness hinder their widespread usage. Despite several efforts to enhance their tribology, achieving ultra-low friction on titanium alloy surfaces remains a challenging problem in materials science. Here, we report on the superlubricity of a MoS2 + a-C:H (Mo-a films) composite film, prepared by magnetron sputtering and spraying to lubricate titanium alloy surfaces. Robust superlubricity was achieved by the Mo-a composite films with a coefficient of friction (COF) below 0.007 in a helium environment. Compared to the reference titanium alloy substrates, the introduction of Mo-a composite film reduced the friction coefficient to roughly 1%, and the a-C:H film reduced wear by three orders of magnitude. High-resolution characterizations indicate that this enhanced tribology can be attributed to the formation of transfer film, which is enriched with nanostructured graphene sheets and MoS2 nanoscrolls, and is formed due to shear stress-induced structural transformation of a-C:H films and MoS2 nanosheets. This transfer film transitioned the initial high-resistance steel-to-a-C:H contact to super low-resistance steel-to-transfer film contact, thus achieving superlubricity and a remarkable wear reduction. This work outlines a pathway to solving the poor wear resistance and high friction coefficient problem of titanium alloy surfaces, which can be an important guideline for applications of titanium alloys in mechanical engineering.

Green hydrophobic deep eutectic solvents as low-viscosity and efficient lubricants

Development of novel green lubricants that meet low viscosity and effective anti-wear requirements is a tireless pursuit to improve fuel economy and reduce exhaust emissions, as well as enhance reliability. Herein a series of hydrophobic deep eutectic solvents (HDESs) with ultra-low viscosity were successfully synthesized by combining eco-friendly economical DL-menthol (DL) with fatty acids of various alkyl chain lengths. According to quantum chemistry method, weak hydrogen bond interaction between DL and fatty acid was calculated. The as-prepared DL-based HDESs lubricants present prominent physicochemical properties and lubrication functions. Thereinto, DL+Dodecanoic acid HDES with a low viscosity of 8.73 mm2/s (40 °C) achieves a 23.05 % reduction in friction and a 44.22 % reduction in wear compared to the PEG 200 base oil at 491N. According to experimental characterizations and first-principles calculations to reveal their anti-wear mechanism, the excellent wetting and ultra-low viscosity of the HDESs fluid facilitates rapid physisorption and chemisorption. Meanwhile, the absorbed film contributes to the formation of the long alkyl chains flow layer and the tribo-chemical film composed of hydrocarbon (CxHy), oxy hydrocarbon (CxHyOz) fragments and iron oxide/hydroxide-rich layer, which endows HDESs with excellent lubrication properties. This founding furnishes a new strategy to design green low-viscosity and high-performance anti-wear HDESs lubricants in sustainable lubrication applications.

Wear reduction by toughness enhancement of disc tool in Nomex honeycomb composites machining

In the machining of traditional metallic materials, high hardness is primary property that tool designers are committed to pursuing to improve wear resistance. In this study on machining of Nomex honeycomb composites (NHCs), it was revealed that high toughness is the dominant factor for wear resistance of disc tool. A comparative study was designed, including normal characteristics, hardness enhancement, and toughness enhancement. The material properties of the three pre-treatment methods were compared. The importance of toughness and hardness was evaluated from tool wear and surface quality. The results indicated that toughness-enhanced tools could be machined to produce the sharper cutting edges. Simultaneously, the toughness-enhanced tool was better suited to the high periodic cyclic impact loads in ultrasonic vibration machining.

Numerical investigation and optimization of the geometric profiles of dimple bottom structure in frictional interaction pairs

Dimple texture forming in the interaction pairs is a wear reduction technique like lubrication. Dimple-texturing is an efficient and sustainable way of altering the surface topography to improve the tribological characteristics of interacting surfaces. In this work, sliding interaction pairs with circular dimples, three different dimple bottom structures, namely flat, V-shaped and U-shaped, are selected for numerical investigation using the Reynolds equation to enhance the hydrodynamic characteristics. The numerical design and investigation on the dimple area density (ρ), aspect ratio (λ), and flow velocity (V) is done using unblocked central-composite design (UCD) under response surface methodology (RSM) along with multi-objective gray relation analysis method for individual dimple bottom structures to minimize the coefficient of friction and increase the load bearing capacity in the interaction pairs. The flat bottom structure exhibits excellent load-bearing capacity and minimum coefficient of friction when compared to V-shaped and U-shaped bottom structures. Compared to flat bottom structure, the V-shaped and U-shaped bottom structures has 40.37% and 7.81% lesser load-bearing capacity, respectively, and 54.08% and 7.81% higher coefficient of friction, respectively. In a flat bottom structure, the flow velocity is identified as an effective variable factor to improve the outcome characteristics, followed by dimple area density and aspect ratio. The optimal dimple area density and aspect ratio values are observed in the range of 30–40% and 0.025 – 0.030, respectively. In addition, the optimal value of flow velocity is observed to be 2.5 m/s.

Wear Reduction via CNT Coatings in Electrical Contacts Subjected to Fretting

Carbon nanotubes (CNT) are of great interest to the research community due to their outstanding mechanical, transport, and optical properties. These nanoparticles have also shown exceptional lubricating capabilities, which coupled with their electrical conductivity show promising results as solid lubricants in electrical contacts. In this study, three different CNT coatings were deposited over copper platelets via electrophoretic deposition and subsequently tribo-electrically characterized including electrical contact resistance evolution during fretting wear, wear protection, chemical analysis of fretting marks, as well as influence of CNT coating thickness, duration and normal load applied during fretting, and atmospheric humidity. Thicker CNT coatings show improved wear protection while retaining similar electrical behavior as uncoated copper, or even improving its electrical contact resistance. Moreover, the compaction of the porous CNT coating is crucial for optimal electrical performance at low humidity. For longer fretting tests (150,000 and 500,000 cycles), the coatings are displaced thus affecting the wear protection offered. However, the coatings stabilize and reduce ECR compared to uncoated samples. Furthermore, thicker CNT coatings can bear higher loads during fretting due to the increased lubricant reservoir, with carbonaceous tribofilm remaining at the contacting interface after 5,000 fretting cycles regardless of normal load.Graphical

Study of steel matrix composite samples with 12%Wt TiB2 produced by spark plasma sintering

Composites consisting of a steel matrix reinforced with diluted ceramics have been investigated as a way to reduce weight and increase wear resistance. This paper describes a composite made with TiB2 ceramic powder and a microalloyed steel turned into powder by the top-down technique. The dispersion method of 12% weight percentage of TiB2 particles in the steel powder was performed by cryomilling techniques. With this powder, bulk TiB2 steel/ceramic samples were produced using the Spark Plasma Sintering (SPS) process. The produced steel matrix composite samples with 12%wt TiB2 were characterized and showed a low level of porosity. The multiphysics fields associated with the SPS process activated the recovery mechanisms that formed a nanostructure in the ferritic matrix. The dispersion of TiB2 particles in microalloyed caused a reduction in abrasive wear of 36.8% as compared with low alloy steel used. This reduction was accompanied by a 5% reduction in density.

Lithium Citrate Triggered Macroscopic Superlubricity with Near-Zero Wear on an Amorphous Carbon Film

An amorphous carbon (a-C) film shows substantial potential for friction and wear reduction. In this work, the robust superlubricity state with a coefficient of friction of 0.002 at the maximal pressure of 1.15 GPa was realized when lithium citrate (LC) was applied as the lubricating additive in ethylene glycol (EG) to lubricate the Si3N4/a-C friction pair based on the ball-on-plate friction test. The wear rate of the a-C film was 4.5 × 10-10 mm3/N·m, which was reduced by 98.3% compared to that of the film lubricated with EG. Friction promoted the chemisorption of the LC molecules via the tribochemical reaction between the carboxylate radicals and the a-C film. The exposed lithium ions could adsorb water molecules to form a hydration layer, providing extremely low shear strength. Furthermore, the colloidal silica layer formed on the Si3N4 ball via the tribochemical reaction could reduce friction. It was difficult to destroy the formed tribochemical films under high contact pressure because they were robust, preventing the direct contact of the friction pair and resulting in the near-zero wear of the a-C film.

Influence of the alloying elements on the tribological performance of DLC coatings in different sliding conditions

Reduction of friction and wear at the sliding surfaces are the main concern in several applications. From an extensive list of low friction hard coatings, DLC type is one of the most studied and develop for achieving low wear and friction. The addition of an alloying element is extensively used, since it can change significantly the coatings performance. Therefore, in this research the tribological behaviour of DLC coatings alloyed with different elements was evaluated, since no works comparing the tribological properties of DLC films with approximately the same alloying elements concentration are reported in the literature. The coatings were deposited by physical vapor deposition and alloyed with: tungsten (W), silver (Ag), silicon (Si), silicon and oxygen (SiO), with concentrations of metallic elements between 10 and 15 at. % and a pure DLC coating was also deposited for comparison purposes. The coatings hardness varied between 23 GPa for the pure DLC and 11 GPa for the alloyed with Si and O. The tribological behaviour of the coatings was evaluated by pin-on-disk against 10 mm 100Cr6 steel balls, at room temperature (RT) and 100 °C. The best wear resistance was achieved with the pure DLC and DLC-W for RT tests. At RT the lowest friction was obtained with the DLCSi and DLCSiO coatings. Despite of the low COF values, those coatings displayed the highest specific wear rate values among all the films. This is attributed to the presence of hard SiC particles stick at the ball counterpart which promotes severe abrasion of the coatings surface. The increase of the temperature to 100 °C increases significantly the friction coefficient for the DLC and DLC-W coatings, whilst, for DLC-Ag, DLC-Si and DLC-SiO coatings a slight decrease is noticed. At this temperature DLCAg coating is the more performing due to the formation of a tick tribolayer rich in Ag adhered at the counterpart surface. With this work it was concluded that friction and wear are not directly related, and the third bodies formed on the sliding surfaces have major influence on the tribological performance of the system.

Surface Modification of β-MnO2 Nanorods as Nanolubricant

Introduction: Nanolubricants are substances that use nanoparticles as lubricant additives. The proposal for wear reduction has piqued interest in nanolubricants. Particle agglomeration is the main drawback of using nanomaterials as lubricating oil additives, and creating novel nanolubricants is one of the most difficult challenges. Objective: Evaluation of the nano β-MnO2 nanorods as nanoadditives for enhancing lubricating oil characteristics. Methods: After producing β-MnO2 nanorods by a modified hydrothermal process, oleic acid was used to modify their surfaces. Next, the physical and tribological characteristics of lubricating oil before and after the addition of nanoadditives were assessed. Results: The physical parameters of lubricating oil, including flash point, pour point, thermal stability, antiwear ability, and viscosity, were all improved by varying concentrations of surface-modified MnO2 nanorods by rates 8.19%, 50%, 63.04%, 10.9%, 8.96% at 40ºC and 4.18% at 100ºC, respectively. The findings demonstrate that the shear strain is reduced and an anti-wear boundary coating is created as a result of the deposition of nanoparticles produced by tribochemical reaction products during the friction process. Conclusion: The development of a protective film using nanoadditives improves lubricant requirements, ushering in a revolution in the lubricant industry.