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•Periodically multilayered and superlubricious MoS2-Ag film is designed based on ion beam assisted deposition (IBAD).•MoS2-Ag film demonstrates a superior lubricating durability with ...a superlow friction coefficient of 0.0065 triggered by DLC film.•Superlubricity highly depends on the synergistic effect from both physicochemical properties of shear-induced tribofilm and transformation of the MoS2-Ag surface.
Robust superlubricity of the disulphide-based film or diamond-like carbon (DLC) coating has been systematically investigated in relation to interfacial nanostructures and environmental atmospheres. Nevertheless, the frictional performances of the tribo-couple between them, especially the underlying mechanisms governing superlubricity are scarcely touched. In this study, we designed the periodically multilayered MoS2-Ag film based on ion beam assisted deposition (IBAD) and found a superior lubricating durability of the film with a superlow friction coefficient of 0.0065 triggered by DLC film under a load of 10 N in N2. The in-depth structural analysis on the contact areas of tribopairs were performed through Raman and high-resolution transmission electron microscopy (HRTEM). The results demonstrate that sliding-affected regions of the film generally undergo a deep amorphization transformation and the materials are transferred to counterfacing ball to form a multiphase tribofilm. The prevailing mechanisms emphasize that the superlubricious status highly depends on the synergistic effect from both the physicochemical properties of shear-induced tribofilm and the structural transformation of the MoS2-Ag surface by different contact mechanics and reconfiguration pathways. The findings shed light on the nature of tribochemical mechanisms of MoS2-Ag film and provide a new strategy to achieve macroscale superlubricity of the disulphide-related lubricants.
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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Nanofluids containing nanocomposite materials have broad application prospect in lubrication. In the present study, MoS2-Al2O3 nanocomposite was synthesized by solvothermal method. Then water-based ...nanofluid containing MoS2-Al2O3 nanoparticles was prepared and it exhibited optimal stability and wettability. The tribological properties of MoS2-Al2O3 nanofluid under steel/steel contact were investigated. Through chemical analysis of worn surface, tribochemical reactions occurred and tribofilm generated at friction interface were studied to reveal the lubrication mechanism. The results showed that MoS2-Al2O3 nanofluid exhibited outstanding effect on reducing the friction force and wear rate of friction pairs. The superior lubrication performance was partly attributed to the entry and movement of nanoparticles at friction interface. More importantly, due to interfacial tribochemistry, a tribofilm with double layer structure composed of adsorption film and reaction layer was formed on the metal surface, preventing the direct contact of steel surfaces. The adsorption film with a thickness of about 16 nm was predominated by amorphous substrates and crystal phases (ultrafine Al2O3 and MoS2 debris) embedded in the top. And the reaction layer beneath adsorption film contained high mechanical properties iron oxides (mainly Fe3O4 and Fe2O3) and self-lubricating Fe2(SO4)3, which further alleviated friction and enhanced the wear-resistance of materials.
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•MoS2-Al2O3 nanocomposite was synthesized and applied as lubricating additive.•MoS2-Al2O3 nanofluid showed excellent performance under steel/steel contact.•A double-layered tribofilm due to interfacial tribochemistry was formed on surface.•Iron oxides and Fe2(SO4)3 in reaction layer further alleviated friction and wear.
A novel nanomaterial reduced graphene oxide-Al2O3 nanocomposite (rGO-Al2O3) was synthesized through the hydrothermal method. The nanofluid containing rGO-Al2O3 nanocomposite was prepared as lubricant ...and exhibited superior dispersion stability. To clarify the lubrication mechanism of rGO-Al2O3 nanofluid, tribological tests and cold rolling lubrication experiments were conducted using the four-ball tribometer and two-high rolling mill. The results indicated that excellent anti-wear and friction-reducing properties as well as desired strip surface topography could be obtained under the lubrication of 0.20 wt% rGO-Al2O3 nanofluid. Induced by the interfacial tribochemical reaction, a bilayer lubrication film composed of adsorption film and reaction layer was formed at the friction interface. Through theoretical calculation and experimental characterizations, the thickness of lubrication film was about 25 nm. The adsorption film, dominated by nano-Al2O3 and graphene oxide fragments, played a vital role in synergistic lubrication. Meanwhile the reaction layer contained iron oxides (primarily Fe2O3 and FeO) with high mechanical properties. This bilayer structure ensured the denseness and continuity of the lubrication film, thus achieving significant lubrication performance.
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This review summarizes recent advances in the area of tribology based on the outcome of a Lorentz Center workshop surveying various physical, chemical and mechanical phenomena across scales. Among ...the main themes discussed were those of rough surface representations, the breakdown of continuum theories at the nano- and microscales, as well as multiscale and multiphysics aspects for analytical and computational models relevant to applications spanning a variety of sectors, from automotive to biotribology and nanotechnology. Significant effort is still required to account for complementary nonlinear effects of plasticity, adhesion, friction, wear, lubrication and surface chemistry in tribological models. For each topic, we propose some research directions.
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Over the decades, the application of mechanical force to influence chemical reactions has been called by various names: mechanochemistry, tribochemistry, mechanical alloying, to name but a few. The ...evolution of these terms has largely mirrored the understanding of the field. But what is meant by these terms, why have they evolved, and does it really matter how a process is called? Which parameters should be defined to describe unambiguously the experimental conditions such that others can reproduce the results, or to allow a meaningful comparison between processes explored under different conditions? Can the information on the process be encoded in a clear, concise, and self-explanatory way? We address these questions in this Opinion contribution, which we hope will spark timely and constructive discussion across the international mechanochemical community.
This work investigates the structure, mechanical, and tribological properties of Ta-xN coatings deposited using reactive High Target Utilization Sputtering (HiTUS) with a focus on the role of ...tribological layers formed in the sliding contacts. The scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy observations revealed that the gradual increase of nitrogen flow results in the transition from textured fcc Ta structure (without nitrogen) toward mixed sub-stoichiometric Ta-Ny/Ta2N/amorphous structures up to near-stoichiometric fcc TaN coatings. The highest hardness HIT ∼37 GPa and indentation modulus EIT ∼375 GPa as well as the lowest coefficients of friction (COF) in the range 0.16–0.36 and wear rates around 3 × 10−7 mm2/N·m were obtained in the layer with Ta2N structure. The unique combination of low COF and high wear resistance combined with high hardness and stiffness were attributed to the shear sliding between Ta2O5-based transfer film in the wear track and pure alumina ball.
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