Reactive molecular dynamics simulations were conducted to investigate the tribological behavior between two amorphous iron oxide substrates with octene molecules confined between them. The results ...revealed that higher temperatures facilitated the degradation and oxidation of octene molecules, leading to an increased quantity of reaction products such as water and oxidation products like alcohols. Due to the obstructive action of water molecules, the octene and its oxidation products were able to adsorb onto the substrate surfaces, resulting in the formation of a stably adsorbed carbon-based tribofilm at elevated temperatures. In addition, the water layer also significantly reduces friction by preventing direct contact between the carbon-based tribofilm, even though only a small amount of octene molecules are present at the interface.
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Inherent strength-plasticity tradeoff and unfavorable anti-wear capacity of FCC-structured high-entropy alloys (HEAs) bottlenecks their applications in advanced industries. This work controllably ...deployed an enhanced heterostructure and graded grain distribution in the single FCC-phase HEA model according to the concept of selective solid solution, which contributed to the ultrahigh compressive strength at appreciable plasticity levels for allowing worn surface to accommodate tribological loading. Simultaneously, the multiscale FCC-coupled architecture with compositional fluctuation effectively inhibits high temperature softening and activates the in-situ tribochemistry protection of the duplex glaze-layer and recrystallized subsurface, reaching low wear between room-temperature and 800 °C. Our alloying strategy offers a novel avenue for further governing mechanical-tribological combined properties in applicable metallic systems.
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Prior studies suggest mechanical interlocking, preferential adhesion of polar polymers, and PTFE tribochemistry all contribute to the wear reduction in polar polymer-filled PTFE composites; whereas ...their relations remain poorly understood. This study aims to decouple the relevant mechanisms by investigating wear and tribofilm environmental sensitivities of a 5 wt% polyamide-imide (PAI) filled PTFE composite. The results highlight (1) strong correlation between a carboxylate-salt-rich transfer film and ultralow wear, and (2) a tribochemical interface gradient that discourages transfer film removal. We proposed that PTFE tribochemistry induces ultralow wear by significantly increasing (1) transfer film adhesion through a virtuous cycle of tribochemical accumulation and wear reduction and (2) transfer film cohesion by promoting a surface energy interface gradient beneficial to low wear.
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•Studying wear and tribofilm environmental sensitivities of a PAI-PTFE composite.•a virtuous cycle of tribochemistry and low wear increases transfer film adhesion.•a tribochemical surface energy interface gradient increases transfer film cohesion.•Increased transfer film adhesion and cohesion induce PAI-PTFE ultralow wear.•PTFE tribochemistry dominates wear reduction in the model material.
Nanocrystalline metal alloys have shown great promise as electrical contact materials, given their mechanical and tribological properties. In particular, platinum-gold (Pt–Au) nanocrystalline alloys ...have demonstrated coefficients of friction as low as 0.01 and specific wear rates on the order of 10−9 mm3 N−1 m−1, largely due to the formation of carbon-based tribofilms at the sliding interfaces. In this study, we advance our understanding of the Pt–Au tribofilm structure-property relations and growth mechanisms via high-throughput and high-resolution measurements as a function of Pt–Au composition. As the solute content increased from 0 at. % to 10 at. % Au, cross-sectional and plan-view transmission electron microscopy demonstrated a decrease in average grain size d and an accompanied increase in grain boundary (GB) segregation. The decrease in d and increase in GB solute segregation translated to a decrease in modulus Er and an increase in hardness H as determined via nanoindentation; the Er trend was mainly described using a rule-of-mixtures approximation, whereas the H trend was ascribed to solid solution strengthening and GB stabilization. The steady state-friction μ and wear rate decreased with the addition of Au; low Au-content films showed substrate wear, while high Au-content films showed stable tribofilm growth in both macroscale and nanoscale friction tests. The carbon bonding configuration of the tribofilms was investigated by near-edge X-ray absorption fine structure spectroscopic analyses and found to be similar to that of hydrogenated amorphous carbon films. Altogether, the study provided insight into the mechanistic origins of the tribofilms, thus opening the door to tunable properties ranging from mitigation for electrical contacts to the creation of self-healing films for solid lubricants.
•Pt–Au nanocrystalline alloys exhibit low friction and wear via tribofilm growth.•Tribofilm structure-property relations revealed for different Pt–Au compositions.•Grain size decreased and grain boundary solute segregation increased as Au increased.•Friction and wear decreased and tribofilm stability increased as Au increased.•Molecular bonding in tribofilms similar to hydrogenated amorphous carbon films.
Recent demonstration of two dimensional (2D) solid lubricant materials to minimize friction to unmeasurable levels (superlubricity) and reduce wear at macroscale propelled further research ...investigations in the direction of exploring their potential in industrially relevant material combinations such as steel and diamond-like-carbon (DLC) in sliding contact. In this study, we have used a combination of 2D materials i.e. Graphene and MoS2 as a solid lubricant to reduce friction and wear in steel-hydrogenated DLC contacts even at high contact pressures and sliding speed. Sliding friction tests conducted under dry nitrogen conditions shows a reduction of friction and wear by 16 and 29 times, respectively as compared to Steel vs H-DLC (baseline) experiments and friction and wear by a factor of 43 and 434, respectively, compared to self-mated steel vs steel experiments. Optical and Raman investigations of the material pairs and the wear debris analysis in TEM indicated the formation of amorphous carbon mixed graphene layers at the sliding interface leading to such dramatic reductions in friction and wear.
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Two triazine derivatives, 6-(diethanolamino)−2,4-bi-(sodium sulfanilate-yl)−1,3,5-triazine (STB) and 6-(ethyl xanthate)−2,4-bi-(sodium sulfanilate-yl)−1,3,5-triazine (STC) were synthesized and used ...as additives in water-glycol base fluid (mass ratio 1:1). Water solubility tests indicated that STB and STC met the solubility prerequisite for a water-soluble additive. The tribological tests by using a four-ball tribometer showed that, STB and STC both improved greatly the PB value, antiwear and friction-reducing capacities of the base fluid. Based on friction test results and wear scars’ analysis, it was concluded that the differences in tribological performances of STB and STC samples were mainly due to the differences of the sulfur content and the sulfur activity in additives. XPS found that STB-tribofilm mainly contained sulfate, but STC-tribofilm additionally contained sulfide.
•Preparing two sulfur-containing triazine derivatives as lubricant additives in water-glycol.•The as-prepared additives have good water solubility.•The effects of sulfur atoms on the solubility, corrosivity and tribological properties of the additives were studied.•The additives display excellent antiwear and friction-reducing performances.•Tribochemistry mechanisms of the additives were investigated by using XPS.
Water-solubility alcohols are reported to exhibit excellent lubricity at both low and high normal loads during sliding, and the lubrication mechanisms for water-solubility alcohols are well known ...until now. However, the lubricity of water-insolubility alcohols is rarely reported and its lubrication mechanisms were still not well understood so far. Here, we first investigate the lubricity of cyclohexanol between self-mated YG8 balls. The experimental and computational results reveal that cyclohexene and its derivative, and tungsten oxide is initially indeed formed during sliding, then, the polymerization is induced by friction-induced effect between cyclohexene and its derivative, revealing that the formation of polymers can effectively stabilize friction coefficient, and the formation of tungsten oxide plays an important role in enhancing wear resistance. Besides, for 196 N, the formation of carbon quantum dots makes friction coefficient reduce with increasing sliding time compared to that of 98 N. The new find will be potentially applied in machinery and equipment.
Mixed lubrication is a contact condition when the total load is carried by both the fluid lubricant and the solid contacting asperities. The aim of this study is to couple tribochemistry with ...lubrication. A recent semi-deterministic tribochemical model of tribofilm growth is integrated in a deterministic mixed lubrication model. The model considers the variable hardness of the tribofilm and enables the study of lubrication and tribochemistry and their mutual interaction. Results from the current model are compared against the previously published results. The model can be easily adapted to actual experimental conditions and geometries. The model can be used beyond pure boundary lubrication conditions to monitor tribofilm growth under mixed lubrication conditions.
•A new mixed lubrication model including tribochemistry and wear is established.•Tribochemical effects across the whole lubrication regime spectrum can be analysed.•Greater triboactivation and thicker tribofilms predicted as lambda ratio is reduced.•Tribofilm growth is patchy, with patches growing in the sliding direction.•The interaction between tribofilm growth and wear is complex.
Optimizing the MoS2-based coating to overcome its humidity sensitivity is still a challenge. In this work, MoS2/Pb composite coatings with various Pb contents were synthesized by unbalanced magnetron ...sputtering system. The microstructures of the coatings change from loose columnar structure for pure MoS2 to a compact featureless structure for Pb doped MoS2. The hardness and elastic modulus of the MoS2/Pb composite coatings gradually increase with the Pb content increase and exhibit a maximum value at Pb content of 8.9at%. Further increase in the Pb content results in a decrease in the hardness and elastic modulus of the coatings. The tribological performance of the coatings was systematically evaluated under different humidity conditions, and the underlying mechanisms were investigated. The results show that the mechanical property of the coating determines the wear properties under dry air; whereas the antioxidant property of the coating becomes prominent with regard to the wear-resistant in humid environmental. This benefits us to tailor or select the MoS2-based composite coatings for different operating conditions.
•The MoS2/Pb composite coatings with dense morphology were prepared.•Suitable doping of Pb improved the mechanic properties of the coatings.•Under dry air, the tribo-performance of the coatings was determined by H/E value.•Under humid air, the tribo-performance was controlled by antioxidant property.•The coating of suitable doping of Pb showed high environmental adaptability.
Cr-doped diamond-like carbon (Cr-DLC) coatings were deposited and investigated for their tribological properties. A hybridized deposition technique consisted of a bipolar plasma-based ion ...implantation and deposition (PBII&D) and magnetron sputtering was used for the deposition. Raman spectra revealed an increase of ID/IG upon the Cr introduction, indicating the embedded CrCx act as catalysts to produce sp2 sites. The coefficients of friction (COF) were effectively reduced once MoDTC was added to the base oil. X-ray photoelectron spectroscopy (XPS) confirmed the presence of MoO3, MoS2, and MoS2−xOx in the MoDTC-derived tribofilm. The contribution of MoS2−xOx decreased with the Cr content, suggesting that the wear particles of CrCx intervenes in the process of MoDTC decomposition by preventing the oxidation of MoS2 sheets.
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