Search

For the purpose of extensive application of superlubritic solid films material, the steel substrate as the most widely used engineering material should be taken into consideration instead of lab-used Si substrates. In present work, the bilayer a-C:H/MoS 2 film was grown on a 9Cr18Mo steel substrate with a Ti/TiN/TiCN transition layer to assure strong interfacial adhesion. A steady state of superlubricity (friction coefficient ~ 0.008) was obtained under high normal loads (beyond 15 N) in open atmosphere not only on Si substrate but also on 9Cr18Mo steel substrate, though the roughness of which is 10 times higher than that of the Si substrates. Compared to the naked 9Cr18Mo steel, the introduction of the a-C:H/MoS 2 film can reduce the friction coefficient and wear rate to nearly 1/50 and 1/6, respectively. Detailed experimental studies reveal that realization of ultralow friction is attributed to low contacting stress (5 N and 11 N) induced structure of oriented molybdenum disulfide in wear debris. Further, amorphous molybdenum disulfide accelerates the formation of oriented graphene ribbon under high contacting stress (15 N and 20 N) at the contact interfaces helping to achieve superlubricity. Thus, our work here provides a strategy for design an industrial scale superlubricity friction system. [Display omitted] • Superlubricity (friction coefficient ~ 0.008) was obtained on 9Cr18Mo steel. • Superlubricity can be ascribed to MoS 2 structure promote the formation of oriented graphene ribbont. • Our work here provides a strategy for design an industrial scale superlubricity friction system. [ABSTRACT FROM AUTHOR]

Although MoS 2 film plays an important role in reducing friction, however, it will collapse down at higher loads. To prevent the failure of MoS 2 under higher load, in present work, structure bilayer a-C:H/MoS 2 films were prepared via PVD/PECVD hybrid method. The component, bonding structure, morphology as well as trichology and mechanical properties of the films were investigated, respectively. The results show that MoS 2 film stack uniformly on a-C:H film's surface. Due to the special design of the structure, the bilayer a-C:H/MoS 2 film show a sufficient decrease of friction coefficient compared with that of a-C:H film. In addition, the superlubricity state was achieved at very high loads, which can be ascribed to the low shear force and incommensurability contact between adjacent MoS 2 layers. And a-C:H film here plays as foundation stone of supporting MoS 2 film and enforcing its adhesion on silicon substrates, which inhibits slipping away of MoS 2 film under shear force. Our work can open a new mind to help design the high loads capability of MoS 2 based films, which can break the deadlock of the bad loading ability and achieve superlubricity at even higher loads for MoS 2 based films. Unlabelled Image • The bilayer a-C:H/MoS 2 films were prepared via PVD/PECVD hybrid method. • The superlubricity could be ascribed to the low shear force and incommensurability contact between adjacent MoS 2 layers. • The a-C:H film plays as foundation stone of support MoS 2 film and enforce its adhesion on the substrates. [ABSTRACT FROM AUTHOR]

Carbon quantum dots (CQDs) and ionic liquid (IL) nanoparticles were fabricated by simple modification. The structures and properties of these particles were measured with HRTEM, FTIR, Raman Spectrometer and friction test. More importantly, IL-modified CQDs as lubricant material demonstrated excellent tribological performance and obtained a super-low friction coefficient about 0.006 and wear rate about 0.7 × 10 −14 m 3 /Nm with the CQDs content of 3.6%. The results revealed that IL-modified CQDs might provide a new idea to investigate various lubricant materials to achieve super-low friction and could be intensively studied for other practical applications. [ABSTRACT FROM AUTHOR]

Though amorphous carbon films are kinds of most distinguished lubricant materials, the friction coefficients of commercial amorphous carbon films are in the range of 0.05–0.40. To reduce the friction coefficients of those amorphous carbon films from the order of 0.01 to 0.001 range is still a big challenge. In order to solve the problem, in present work, a new strategy, called catalytic superlubricity, is proposed and carried out to achieve superlubricity by in-situ formation of graphene via introducing gold onto hydrogenated amorphous carbon (Au@a-C:H) film during friction. The results show that mulilayer graphene along with oriented polyolefin-like structures are formed due to the catalysis of Au nanoparticles, which is embedded in amorphous carbon matrix. Furthermore, the density functional theory calculations indicates that interlayer binding energy between graphene and the hydrogenated amorphous carbon (a-C:H) films' surface is comparable to that between graphene layers, resulting in low interfacial interactions between sliding interfaces for low friction. Then, the low interfacial interactions lead to superlubricity with a friction coefficient of 0.003. This study opens up a new routing for facile and scale up fabrication of superlubricant a-C:H films in industrial applications. [Display omitted] • Catalytic superlubriciy strategy was firstly proposed by introduced Au onto a-C:H film. • A low friction coefficient of about 0.003 is realized of Au@a-C:H film. • The weak interaction between graphene and saturated carbon matrix benefit for easy sliding. [ABSTRACT FROM AUTHOR]

Abstract Fullerene-like hydrogenated carbon (FL-C:H) films hold superlubricity properties at room condition, which important for saving energy, for engine use, however, high temperature serving (below 500 °C) are needed considering. In this paper, FL-C:H films were annealed with protecting of nitrogen. The tribological test show that all films have superlubricity properties, of which friction coefficient are 0.008 (200 °C), 0.005 (250 °C), 0.004 (300 °C), 0.005 (400 °C), 0.004 (500 °C), respectively. In addition, the hardness is incremental when the annealed temperature increased from 200 to 300 °C, and decremental from 300 °C to 500 °C. Interestingly, the changes of hydrogen content can be neglect in present work. Combined HRTEM, Raman spectra and XPS results, one can speculate that the degree of order for FL-C:H films increase along with the argument of annealed temperature, but competition of growth and ordering of short-chain hydrocarbon and graphene stacks that determine the hardness and H3/E2 ratio, which further influences the wear volumes. However, the friction coefficient only depends on curved grahene which can formation scroll graphene between contact surface to low friction force. Highlights • Though the highest hardness turn out under annealing at 300 °C, the elastic recovery of films is the highest at 500 °C. • The C-C sp2 content raises and the C-C sp3 content reduces with increase of annealing temperature. • All samples, show superlubricity (0.004∼0.005) properties, which is correlated with fullerene-like structure. [ABSTRACT FROM AUTHOR]

Onion-like carbon films were prepared by constant current high-frequency dual-pulsed plasma enhanced chemical vapor deposition technique. Owing to the unique carbon onions both in bulk and debris of nanostructured carbon matrix, the films not only showed a super-high elastic recovery up to 92%, but also obtained a super-low friction coefficient below 0.01 and wear rate about 6.41 × 10 −18  m 3 /Nm in ambient atmosphere. The carbon onions achieved an incommensurate contact and played as “molecular bearing” in the friction process, resulting in both super-low friction and wear rate. [ABSTRACT FROM AUTHOR]

High load-bearing and ambient robust superlubricity of graphene/MoS 2 heterojunctions enabled by contact stress dispersion. [Display omitted] • A novel principle for achieving high load-bearing structural superlubricity based on contact stress dispersion is demonstrated. • The contact stress dispersion maintains 2D material integrity and promotes heterointerfacial contact acquirement. • Macroscale structural superlubricity is investigated for the first time at 15N engineering load under ambient air. • A ball-on-disk sliding shearing technique is developed to produce almost less edge- and plane-defect graphene paper. Superlubricity from two dimensional (2D) materials has aroused increasing interest in recent years; however, it can only be achieved below millinewton loads under ambient condition. How to obtain high load-bearing and ambient robust superlubricity remains a challenge but is highly desirable. Here, we use the deformation of highly elastic fullerene-like hydrogenated carbon (FL-C:H) substrate on a large area, to disperse high contact pressure applied on graphene/MoS 2 heterojunctions and avoid structure destruction caused by stress concentration. The contact pressure diffusion ensures the structural integrity of 2D materials and promotes their heterointerfacial contact, resulting in high load-bearing superlubricity. Moreover, the maintenance of structural integrity, combined with the preparation of graphene with few defects by using a vacuum ball-shearing exfoliated graphene (BSEG) technique, remarkably weakens environmental chemical interaction to reach ambient robust superlubricity. The BSEG/MoS 2 /FL-C:H system achieves macroscale superlubricity under vacuum (0.009) and ambient conditions (0.007 at 20% RH, 0.009 at 40% RH) and at engineering load of 15 N. The applied load is far higher than 35 mN that is the known largest values. Atomistic simulations reveal the overall link between contact stress dispersion and experimental observations. This work reveals a novel principle of achieving high load-bearing and ambient robust superlubricity based on contact stress dispersion, and helps to bridge structural superlubricity to practical applications, potentially dramatically reducing energy dissipation. [ABSTRACT FROM AUTHOR]

Both nitrogen and silicon-doped carbon (a-CN x :H and a-CSi:H) films show superlubrcity properties in distinguished sliding conditions, but most running machines are required to serve in humidity air atmosphere. Therefore, we aim to explore N and Si doping effects on tribology of a-C:H films and reveal the basic factors of superlubricity in open atmosphere with a humidity of 41%. In present work, three kinds of films (a-C:H, a-CN x :H and the a-CSi:H films) were prepared on n-Si(100) substrates by plasma-enhanced chemical vapor deposition (PECVD). The thickness, element distribution, bonding topolograph and nanostructure of all films before and after friction test, including wear debris, tracks and debris, were detected by means of XPS, Raman, HRTEM and SEM, etc.. Compared with hydrogenated carbon film (a-C:H), the highest COF (0.089) and wear rate (3.61 × 10−7 mm3/Nm) of a-CN x :H film are attributed to forming Fe 3 C, Fe 2 O 3 and Cr 2 O 3 on the slide surface due to the chemical reaction with moisture atmosphere, which caused by the emission of N element via the broken C N structure that induced more activity dangling bonds. However, the silicon-doped carbon film (a-CSi:H) exhibited extremely low COF (0.007) and extremely low wear rate (4.76 × 10−8 mm3/Nm), which can be ascribed to the Si which is more reactive with moisture atmosphere, prohibiting the oxidization of carbon matrix and helping to forming more curved graphene structures to low the friction force. Unlabelled Image • Introduction of N increases hardness and elastic recovery because of graphitization. • Introduction of Si increases the hardness only owing to decreased fraction of sp2 boding structure. • a-CN x :H film shows highest wear rate and COF, due to the oxidization and carbonization occurred in the friction interface. • a-CSi:H film shows lowest wear rate and COF, due to the passivation of –OH and the existence of curved structures. [ABSTRACT FROM AUTHOR]