Gewen Yi

Two-dimensional nanomaterials as grease additives have demonstrated significant research progress in the surface modification of mechanical friction pairs. However, single-component systems often struggle to meet composite lubrication demands under extreme conditions due to the antagonistic effect between antiwear and friction-reduction properties, limiting their engineering application. In this study, five greases were prepared using a multivariate compounding method. Among them, the ternary additive grease (GG2M2B), formulated with a mass ratio of 1:2:2 (1 wt % graphite, 2 wt % MoS₂, 2 wt % h-BN), exhibited superior stability and temperature resistance, showing a 6.5% increase in maximum operating temperature. The GG2M2B additive proved effective across wide load ranges (50–100 N) and at temperatures up to 200 °C. Analysis revealed that the additive reduced friction by leveraging its friction-induced physical properties. Specifically, it formed a stable tribo-film on the friction surfaces through a combination of friction-induced physical/chemical adsorption and tribochemical reactions. This resulted in a 49.8–52.7% reduction in the coefficient of friction and a 75–81.3% reduction in wear volume compared to the base grease. Further investigation indicated that the composite additive (G/MoS₂/h-BN) responded synergistically to high temperature, shear stress, and frictional heat. It underwent tribochemical reactions with iron (Fe) and oxygen (O) from the subsurface material, generating a series of compounds. These reactions significantly enhanced the friction performance and antiwear effectiveness. This study provides a novel component design strategy and theoretical foundation for developing adaptive composite grease additives.

The friction and wear performances of Haynes 25 alloy sliding against Si3N4 in a ball-on-disk configuration are investigated from room temperature (RT) to 800 °C. The friction-induced changes of morphology and chemical composition in the surface and subsurface regions of the wear tracks were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The results show that the friction coefficient (COF) decreases considerably via temperature, while the wear-rate increases and then decreases with temperature. During dry-sliding contact, the spontaneous formation of multiple metal oxides on the rubbing surface varies as a function of the test temperature, being responsible for either wear loss and/or a change of friction coefficient. The results of this study indicate that the presence of the glazed surface of Haynes 25 helps to lower friction. At 800 °C, a glaze layer with a multilayer structure appears on the rubbing surfaces, leading to the lowest friction coefficient and wear-rate.

Ni–Co–P/Si₃N₄ composite coatings were fabricated over an aluminum–silicon (Al–Si) substrate using a pulse-current electroplating process, in which the rapid deposition of an intermediate nickel–cobalt layer was used to improve coating adhesion. The microstructure, mechanical, and tribological behaviors of the electroplated Ni–Co–P/Si₃N₄ composite coating were characterized and evaluated. The results revealed that the electroplated Ni–Co–P/Si₃N₄ composite coating primarily consisted of highly crystalline Ni–Co sosoloid and P, and a volumetric concentration of 7.65% Si₃N₄. The electroplated Ni–Co–P/Si₃N₄ composite coating exhibited hardness values almost two times higher than the uncoated Al–Si substrate, which was comparable to hard chrome coatings. Under lubricated and dry sliding conditions, the electroplated Ni–Co–P/Si₃N₄ composite coating showed excellent anti-wear performance. Whether dry or lubricated with PAO and engine oil, the composite coating showed minimum abrasive wear compared to the severe adhesive wear and abrasive wear observed in the Al–Si substrate.

A comparative evaluation of the friction and wear behaviors of 40CrNiMoA steel and Inconel 718 alloy sliding against Si₃N₄ counterparts was conducted over a large temperature range from room temperature (RT) to 800 °C. The temperature-dependent tribological properties associated with the resulting chemical mitigation and structural adaptation of the solid sliding surface were clarified by surface/interface characterizations. The results revealed desirable performance in reducing friction and wear at elevated temperatures, which was associated with the resulting oxide composite film’s adaptive lubricating capability, whereas severe abrasive wear occurred at room/ambient temperatures. The oxidative-abrasive differentials for the two alloys were further discussed by considering the combined effect of temperature and stressed-shearing conditions.

A Cr-free Ni-based self-lubricating composites with MoS₂ and Ag as lubricants were fabricated by the powder metallurgy method. The microstructures were examined. The mechanical properties and tribological behaviors of the composites were evaluated from room temperature to 800 °C. The fractography was observed and the fracture mechanisms were analyzed. The morphologies and the phase compositions of worn surfaces were determined and the wear mechanisms were elaborated. The results indicate that MoS₂ did not completely decompose after sintering, and the NiMoAl-MoS₂-Ag composite has the best tribological properties (0.22, 1.68 × 10⁻⁵) at 800 °C. The main wear mechanisms are micro-ploughing and plastic deformation. The improvement of tribological properties was attributed to the formation of the lubricating film consisting of NiO, Mo oxides, various molybdates, and Ag particles. The reactions resulting in these compositions are proposed. The mechanical properties degrade with the rise of temperature and the addition of lubricants. Both NiMoAl and NiMoAlAg alloys exhibit micro-void accumulation fracture while the composites with MoS₂ reveal intergranular fracture.

Cross-sectional view FESEM images of (a) TiO₂ NRs, (b) PbS(4)/TiO₂ NRs (the insets show the top-view of the corresponding cross-sectional view FESEM images). 3D schematic diagrams of (c) TiO₂ NRs, (d) PbS(4)/TiO₂ NRs.

We firstly fabricated a peculiar 3D structure of Bi₂S₃ salix leaf-like nanosheet/TiO₂ nanorod branched heterostructure arrays by a convenient hydrothermal method and discussed their mechanism of improving photoelectrochemical cell (PEC) properties. The salix leaf-like Bi₂S₃ nanosheets (NSs) were grown on TiO₂ nanorod arrays through controlling the molar ratio of EDTA-Na₂/Bi³⁺ and the reaction time. The morphology, crystal structure, microstructure and optical performance of the 3D Bi₂S₃ NS/TiO₂ NRs at different reaction times were investigated. The results show that the branched heterostructure of 3D Bi₂S₃ NS/TiO₂ NR arrays exhibits enhanced photocurrent density and optical absorption, which were attributed to the larger Bi₂S₃ surface area, as well as a direct electron path within the salix leaf-like Bi₂S₃ NS and TiO₂ NR heterojunctions, resulting from more excitation sites of incident light. The photocurrent density of the 3D Bi₂S₃ NS/TiO₂ NR arrays was almost 9 times greater than that of pristine TiO₂ without a branching structure. The results of the present work demonstrate that fabrication of the branched Bi₂S₃ NS/TiO₂ NR heterogeneous structure is a significant fabrication technology with great promise in PECs.

TiO₂/CuInS₂/Bi₂S₃ core/shell/shell (CSS) nanorods (NRs) electrodes were synthesized by the successive ionic layer adsorption and reaction (SILAR) method and applied as the photoelectrodes for high performance in a photoelectrochemical (PEC) cell, wherein the narrow bandgap non-toxic materials, CuInS₂ and Bi₂S₃, were selected to expand the light absorption range to the near-infrared region. The uniform Bi₂S₃ layer was directly covered on the previously coated CuInS₂ layer on TiO₂ NRs to prevent the polysulfide electrolytes' corrosion of CuInS₂. The morphology, crystal structure, optical properties and PEC performance of plain TiO₂, single TiO₂/CuInS₂ core/shell (CS) and TiO₂/CuInS₂/Bi₂S₃ CSS NRs were investigated in detail. The deposition cycles of CuInS₂ and Bi₂S₃ on TiO₂ NRs were optimized to enhance the PEC performance of TiO₂/CuInS₂/Bi₂S₃ CSS composites electrodes. The results show that TiO₂/CuInS₂/Bi₂S₃ CSS obtained enhanced photoconversion efficiency (6 times higher than that of plain TiO₂ and 1.5 times than TiO₂/CuInS₂ CS). Therefore, the construction of CSS nanostructured composites electrodes through coupling single core/shell nanostructures with another narrow gap semiconductor shell suggests a promising design for improving the absorption efficiency and PEC performance of photoelectrodes.

Surface roughness plays an important role in affecting the adhesive force and friction force in microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS). One effective approach of reducing adhesion and friction of contacting interfaces is to create textured surface, which is especially beneficial for MEMS'/NEMS' production yield and product reliability. In this article, we present a convenient method to fabricate the nano‐textured surfaces by self‐assembling Au nanoparticles (NPs) on the silicon (100) surfaces. The nanoparticle‐textured surfaces (NPTS) with different packing density and texture height were prepared by controlling the assembling time and the size of Au NPs. The morphologies and chemical states of NPTS were characterized by atomic force microscope (AFM), field emission scanning electron microscope, and XPS. The adhesion and friction on the NPTS were studied by AFM with colloidal tip. The results show that the nano‐textured surfaces have effectively reduced adhesive force and friction force compared with the 3‐aminopropyl trimethoxysilane self‐assembled monolayer surfaces. The lowered adhesion and friction were attributed to the reduced real area of contact between NPTS and colloidal tip. The adhesion and friction of the NPTS are varying with the texture packing density and dependent on both the texture height and asperities spacing, which are related to the size and coverage ratio of NPs on surfaces. Copyright © 2011 John Wiley & Sons, Ltd.