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.
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.
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.
In this work, the lubrication mechanisms of Nb-contained oxides were revealed by using the density functional theory (DFT) computation. Concretely, a series of Nb-contained oxides, e.g. Nb2O5, AgNbO3 ...and NiNb2O6 were generated through tribochemistry during the friction process of the fabricated NiAl/Nb/Ag coatings as the temperature was increased, and the friction coefficients decreased from 0.51 to 0.54 at low temperatures to 0.24 – 0.27 at elevated temperature. Computational results showed that the binding energy of the Nb – O bond (−15.3 eV) in Nb2O5 was much higher than those of the Ag – O (−0.59 eV) and Ni – O (−0.90 eV) bonds in AgNbO3 and NiNb2O6, indicating that the latter Ag – O and Ni – O bonds were much easier to be fractured or broken under the friction force. AgNbO3 and NiNb2O6 registered better lubrication performances than Nb2O5, which could account for the excellent tribological performance of the coatings at elevated temperatures. This investigation contributes to revealing the high-temperature lubrication mechanisms of Nb-contained oxides.
•Lubrication mechanisms of the Nb-contained oxides were revealed by the density functional theory (DFT) computation.•Nb-contained oxides, e.g. Nb2O5, AgNbO3 and NiNb2O6 were generated through tribochemistry with the temperature increasing.•The binding energy of Nb – O bond in Nb2O5 was much higher than those of Ag – O and Ni – O bonds in AgNbO3 and NiNb2O6.•AgNbO3 and NiNb2O6 registered better lubrication properties than Nb2O5.
In order to tackle the new challenges towards the reduction of carbon emissions in transport industry, the present work aims to understand the effect of the friction modifier (FM) molybdenum ...dithiocarbamate (MoDTC) on the performance of an automobile engine. A petrol engine has undergone motored test trials, measuring the friction torque reduction when the FM additive is blended into a fully formulated SAE 5W30 oil. Moreover, the engine has been dismantled after the test, investigating the tribochemistry of MoDTC at different key engine components undergoing boundary lubrication, using Raman microscopy. This work demonstrates that materials and contact pressure play a crucial role in MoDTC tribochemistry to form a low friction tribofilm, contributing to global engine friction reduction.
•The addition of 1% MoDTC additive to a fully formulated engine oil delivered a maximum friction torque reduction of 2.5%.•MoS2 was found in engine areas where boundary lubrication regime was met.•No MoS2 was found in non-ferrous surfaces.•Piston rings underwent measurable wear during motored tests, leading to coating removal.
Instant Lubricants
In article number 2302076, Philipp G. Grützmacher, Manel Rodríguez Ripoll, Carsten Gachot, Ali Erdemir, Maria Clelia Righi, and co‐workers demonstrate that when Se nanoparticles ...are sprinkled onto Mo or W metallic surfaces, friction comes down dramatically through the formation of transition metal dichalcogenides (TMDs) during sliding. Ab initio molecular dynamics simulations uncover the atomistic mechanisms responsible for the formation of these TMDs. Image credit: Hendrik Ehrich contributed substantially to the image design.
The functionality of graphene as lubricant material is affected by extrinsic factors, such as the film thickness and the environmental conditions. Graphite lubricating capability depends as well on ...air humidity. To accurately describe the tribochemistry mechanisms underlying these behaviours we adopt a Quantum Mechanics/Molecular Mechanics approach. We show that reactive edges are able to cause a huge friction increase, which is quantified for graphene flakes between sliding diamond surfaces. Moreover, folds spontaneously formed in single layer graphene under tribological conditions are shown to be highly reactive due to carbon re-hybridization. This observation offers a new hint for interpreting the dependence of graphene friction on the number of layers. Both water and oxygen molecules are found to be effective in quenching the reactivity of defects by dissociative chemisorption. However, peculiar mechanisms of water molecules makes humidity more effective than oxygen for enabling the lubricity of graphitic media. They include collective processes as Grotthus-like proton diffusion enhanced by confinement, and the strong change in hydrophilic character of the passivated media. This comprehensive study sheds a new light on debated issues of graphene and graphite tribology, and highlights the potentiality of these materials for metal-free catalysis, e.g., for H production by water splitting.
Onion-like carbon (OLC), spherical nanoparticles consisting of carbon shells, is capable of providing exceptional lubrication effects. Nevertheless, the underlying mechanism, especially the ...tribo-induced evolution of interfacial nanostructures and their correlation with the friction states, is not clear. In this work, OLC films with a thickness of ∼1 μm were synthesized by electrophoretic deposition on the mirror-polished stainless steel. The lubricity was evaluated by tailoring the sliding aspects including applied normal load, contact time, and counterface materials. It is found that the friction reduction level is highly dependent on the material transfer and transformation of the OLC surface and the physicochemical nature of the as-formed tribolayer in the contact areas. The subsurface of the OLC film always undergoes a deep amorphization transformation upon sliding. It is interesting to note that the tribolayer formed on the bare steel ball is mainly composed of highly ordered graphene-like nanoflakes derived from the sliding-induced degradation of OLC nanospheres. In comparison, the nanospherical carbon structure can be retained in the topmost subsurface of the tribolayer formed on the ceramic Si3N4 ball. Such a nanosphere-/amorphization-coupled interface is capable of providing a robust lubrication state under high contact stresses. The findings identify a new lubrication mechanism for the spherical carbon nanostructure, rendering them effective solid lubricants.
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