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.
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.
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.
Abstract
A practical high-specific-energy Li metal battery requires thin (≤20 μm) and free-standing Li metal anodes, but the low melting point and strong diffusion creep of lithium metal impede their ...scalable processing towards thin-thickness and free-standing architecture. In this paper, thin (5 to 50 μm) and free-standing lithium strips were achieved by mechanical rolling, which is determined by the in situ tribochemical reaction between lithium and zinc dialkyldithiophosphate (ZDDP). A friction-induced organic/inorganic hybrid interface (~450 nm) was formed on Li with an ultra-high hardness (0.84 GPa) and Young’s modulus (25.90 GPa), which not only enables the scalable process mechanics of thin lithium strips but also facilitates dendrite-free lithium metal anodes by inhibiting dendrite growth. The rolled lithium anode exhibits a prolonged cycle lifespan and high-rate cycle stability (in excess of more than 1700 cycles even at 18.0 mA cm
−2
and 1.5 mA cm
−2
at 25 °C). Meanwhile, the LiFePO
4
(with single-sided load 10 mg/cm
2
) ||Li@ZDDP full cell can last over 350 cycles with a high-capacity retention of 82% after the formation cycles at 5 C (1 C = 170 mA/g) and 25 °C. This work provides a scalable approach concerning tribology design for producing practical thin free-standing lithium metal anodes.
Tribofilm formation and growth play a vital role in friction reduction and antiwear enhancement. However, our understanding at the atomic level, particularly from a tribochemical viewpoint, is ...limited. Here, we elucidate α-lipoic acid ester tribofilm formation on ferrous interfaces using reactive molecular dynamics simulations. Our findings uncover a sequence where chemisorbed films initially develop through Fe-S bonding, followed by decomposition (C-O, C-S bonds) and polymerization reactions (S-S, S-O bonds). Thermal and mechanical forces collaboratively facilitate this process. The kinetic analysis demonstrates elevated activation volume exhibited a negative correlation with the reaction frequency difference. Normal stress boosts reactivity by encouraging the polymerization and reducing activation energy. This work offers a comprehensive understanding of α-lipoic acid ester tribofilm formation on ferrous interfaces.
•Reactions of α-lipoic acid ester on the ferrous surface were modeled.•Four basis reaction paths were found and the reaction network was built.•Activation volume exhibited a negative correlation with the total reaction frequency difference.•The normal stress promote the polymerization reaction and lowering the activation energy.
The mechanocatalytic formation of carbonaceous films at the interface between sliding metallic contacts is simultaneously advantageous for reducing friction and adhesion in several tribological ...applications and detrimental for electrical contacts as they can induce device failure by increasing the contact resistance. Yet, remarkably little is still known about the chemistry, structural and mechanical properties, and tunability of these interfacial layers. In this study, we performed contact pressure-dependent tribological experiments in dry nitrogen containing trace organics on four, nanocrystalline Pt–Au alloys (Au from 0 at.% to 10 at.%) – a promising class of alloys for ultralow wear and electrical contact applications. The ex-situ, multi-technique characterization results did not only provide insights into the chemical nature and mechanical behavior of the mechanocatalytic, carbon-rich films formed on Pt–Au surfaces, but also revealed the interplay between catalytic and mechanochemical tribofilm formation controlled by the composition-dependent electronic structure of the Pt–Au substrate and the applied contact pressure. The results of this work provide guidelines for tailoring nanocrystalline alloys to control their mechanocatalytic activity on the basis of variations of the alloy mechanical properties and element's electronic structure with the alloy stoichiometry.
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High-entropy alloys (HEAs) with a single-phase face-centered cubic (FCC) structure generally have excellent plasticity. However, its limited room temperature strength and hardness result in lower ...wear resistance, which hinders tribological and engineering applications. In this paper, the pack-boronizing method was used to improve the tribological properties of Al0·1CoCrFeNi HEAs with a single-phase FCC structure. The boronizing treatment was carried out at 900 °C for 2, 4, 6, and 8 h, respectively. The structure and phase formation of boronized alloys were studied. Moreover, the reciprocating sliding wear behavior of boronized alloys against Si3N4 balls in dry and deionized water was investigated. A boronized layer with a double-layer structure was formed on the HEA surface, with a total thickness of about 17.3–58.5 μm. The wear mechanism of boronized alloy was transformed from the abrasive and delamination wear to the polishing effect with increasing the boronizing time in air. In contrast, the wear mechanism of boronized alloys in the deionized water gradually changed from the two-body to three-body wear with increasing the boronizing time. Meanwhile, the wear mechanism of the Si3N4 counterface was also transformed to three-body wear gradually.
•The maximum hardness of boronized HEAs is higher 7 times than that of annealed HEAs.•The wear rate of boronized HEAs was much lower than that of as-cast HEAs.•The wear mechanism of boronized HEAs in air was abrasive wear and polishing effect.•Wear mechanism of HEAs in deionized water was two-body and three-body abrasive wear.•The lubrication of deionized water led to lower friction coefficient and wear rate.
Dry sliding wear tests were performed for Ti–6Al–4V alloy on a pin-on-disc wear tester. The wear behavior of Ti–6Al–4V alloy at sliding velocities of 0.5–4m/s was studied and the tribo-oxides and ...their function were explored. Ti–6Al–4V alloy presented a marked variation of wear rate as a function of velocity. With the rise and fall of wear rate, Ti–6Al–4V alloy underwent the transitions of wear mechanisms from the combination of delamination wear and oxidative wear at lower speeds to delamination wear at 2.68m/s, and then to oxidative wear at 4m/s. These phenomena were attributed to the appearance and disappearance of tribo-oxides. In spite of trace or a small amount, tribo-oxides would change the wear behavior, and even wear mechanism.
•The velocity caused a marked variation of wear rate in Ti–6Al–4V alloy.•Ti–6Al–4V alloy presented the transitions of wear mechanisms with velocity.•Velocity-induced tribo-oxides changed the wear behavior and mechanism.
Diamond-like carbon films (DLC) with different silicon contents combined with W interlayer are deposited by plasma-assisted reactive magnetron sputtering. The structures and high-temperature ...tribological properties of the films are investigated. The results reveal that the pure DLC film is worn out at 400 °C because of graphitization, while the Si-DLC film with Si content of 4.56 at.% keeps low friction coefficient (0.2–0.05) at high temperature up to 500 °C. The 14.56 at.% Si-DLC film failed at 500 °C induced by the formation of SiO2. The improved high-temperature tribological performance of the 4.56 at.% Si-DLC film is attributed to the tribochemistry of W interlayer at 500 °C which formed a film composed of tungsten oxides and carbide.
•DLC films (pure DLC, 4.56 at.% and 14.56 at.% Si-DLC) with W interlayers are deposited by reactive magnetron sputtering..•The structure and in situ high-temperature tribological properties of the films are investigated.•4.56 at.% Si-DLC film with W interlayer forms a new layer at 500 ℃ to lower the COF and its formation mechanism is discussed.
The tribochemistry and transfer film formation at the metal/polymer interface plays an essential role in surface protection, wear reduction, and lubrication. Although the topic has been studied for ...decades, challenges persist in clarifying the nanoscale mechanism and dynamic evolution of tribochemical reactions. To investigate the tribochemistry between iron and polytetrafluoroethylene (PTFE) in ambient and cryogenic environments, we have trained and expanded a ReaxFF reactive force field to describe iron–oxygen–water–PTFE systems (C/H/O/F/Fe). Using ReaxFF molecular dynamics simulations, we find that mechanical shearing of single asperity induced the degradation of PTFE molecules and radicals, showing subsequent oxidation and hydroxylation reactions of the radicals initiated by C–C bond cleavage, in agreement with previous experimental observations. Furthermore, we studied mechanisms of interfacial tribochemical reactions and formation of transfer films. We found that tribochemical wear and Fe–C and Fe–F bonding networks are important mechanisms for anchoring molecular chains to form a transfer film on the iron countersurface. Hydroxyl groups can dehydrogenate to form short and strong chelation bonds with the Fe2O3 countersurface. A friction-induced oriented molecular layer plays a key role in reducing friction, which is responsible for the excellent lubrication property. By varying temperatures in the range of 10–300 K, we found a nonmonotonic change in friction with a maxima at 100 K. At cryogenic temperatures, the molecular mobility was obviously suppressed, while the chain rigidity was enhanced, resulting in the less oriented interface and brittle-like shear interface, which is responsible for nonmonotonic friction. This work elucidates mechanisms of tribochemical reactions and transfer film formation between iron and PTFE at the atomistic level, facilitating design and development of self-lubricating materials, especially under harsh conditions.
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