Although superlubricity in silicon-doped hydrogenated diamond-like carbon coatings can enhance mechanical energy efficiency, but it is heavily dependent on special conditions, high contact loads and inert atmospheres. In this work, we proposed a strategy that combines pre-graphitization with tailored counterpart material to construct a weak chemically bonded interface for superlubricity. The fabricated Si-DLC:H coating exhibits high adhesion and mechanical properties (H=17.5 GPa, E = 130 GPa), enabling stable superlubricity (COF=0.009 ± 0.5‰) under N2. Friction-induced graphitization occurs concurrently with the formation of powdery wear debris, SiOx nanoparticles dispersed in a sp2-rich loose layer on the wear track. This debris forms a distinctive friction interface characterized by weak chemical bonding and low shear strength, ultimately leads to superlubricity. Supported by RMD simulations, this study provides a comprehensive understanding of the dynamic evolution of friction interface. It breaks through the conventional graphitization mechanism, and clarifies the macroscopic superlubricity mechanism from the perspective of weak chemical bond breaking and graphitization.
Hydraulic systems are widely used in marine engineering, but seawater ingress may degrade lubricants and exacerbate tribocorrosion. Here, two surface-active ionic liquids—triethanolammonium N-lauroyl-L-alaninate (ALA-IL) and triethanolammonium N-lauroyl-L-glutamate (GLA-IL)—bearing monocarboxylic and dicarboxylic polar headgroups, respectively, were synthesized and evaluated as dual-function lubricating and tribocorrosion-inhibiting additives for AISI 1045 steel in saline medium. ALA-IL exhibits a lower friction coefficient because its low steric hindrance promotes more compact packing of hydrophobic chains. In contrast, GLA-IL exhibits lower wear volumes and maintains tribocorrosion inhibition efficiencies exceeding 80% even at 10 N and 200 rpm. Increasing load and rotational speed progressively disrupt the tribofilms, highlighting pressure–shear-induced film degradation. Surface analyses reveal differences in IL adsorption, film formation, and tribochemical behavior. ReaxFF-MD simulations reveal pressure–shear-dependent Fe–O bond exchange and mechanically adaptive interfacial coordination, while first-principles calculations identify carboxyl/carboxylate groups as primary adsorption sites and reveal deprotonation-assisted multidentate adsorption of GLA-IL. Overall, monocarboxylic ALA-IL promotes compact interfacial packing and lower friction, whereas dicarboxylic GLA-IL strengthens Fe–O coordination and tribofilm stability, thereby enhancing wear and tribocorrosion resistance.
To investigate the engineering effects of raceway waviness on the lubrication state of angular contact bearings, a dynamic model of angular contact ball bearings is coupled with a mixed thermal elastohydrodynamic lubrication (TEHL) model. Circumferential sinusoidal waviness is used to represent the machined surface topography of the inner and outer raceways. The Newton–Euler method is employed to formulate the dynamic differential equations of the rolling elements, cage, and inner ring, while the multigrid method is used to solve the governing equations of point-contact mixed TEHL incorporating raceway waviness. The effects of waviness amplitude on film pressure, film thickness, and temperature are systematically examined under three conditions: waviness only on the inner raceway, waviness only on the outer raceway, and simultaneous waviness on both raceways. The results show that increasing waviness amplitude markedly intensifies film pressure fluctuations and local pressure concentration, thereby reducing the minimum film thickness and increasing film temperature. Under identical operating parameters, outer raceway waviness causes more severe deterioration of lubrication performance than inner raceway waviness because centrifugal force amplifies the contact load. In-phase superposition of inner and outer raceway waviness produces coincident wave crests and the strongest squeezing effect, resulting in the greatest deterioration of lubrication performance. By contrast, an anti-phase arrangement allows partial compensation between wave crests and troughs and therefore alleviates lubrication deterioration to some extent.
Composite bearing pads comprising a polymer lining, metal backing, and a flexible support pad are being considered for wind turbine main shaft bearings. Multilayer heat transfer in the solids and the coupled deformation of the assembly are key challenges in their performance analysis. A mixed thermo-elastohydrodynamic model is developed for these bearings, explicitly accounting for heat transfer through the oil film, PEEK layer, and metal backing, as well as the combined deformation of the PEEK-metal-support assembly. The predicted temperatures agree well with measurements. Results under representative wind loads show that the interfacial temperature is governed by instantaneous frictional heating and thermal history, while heat transfer in the solids exhibits pronounced spatial gradients and thermal lag. The flexible support pad alleviates edge loading through overall pad settlement and tilting, thereby reducing contact pressure and local temperature rise. The results provide a theoretical basis for the design of composite bearings for wind turbine main shaft.
Wear-related surface degradation limits the application of EH40 steel under ambient- and low-temperature conditions. To mitigate this problem, four Ni-rich multi-principal-element alloy coatings with nominal V contents of 0, 2, 4, and 6 at% were fabricated on EH40 steel by extreme high-speed laser cladding. The coatings were designated V0, V2, V4, and V6, respectively, and their microstructure, hardness, and reciprocating dry-sliding behavior at 25 and −40 ℃ were systematically investigated. All coatings exhibited a γ-FCC-dominated matrix. A local Laves-type precipitate was identified in V0, whereas partially interconnected σ-type precipitates occurred at cellular boundaries in V6. Increasing the V content progressively increased the coating hardness, whereas the wear resistance varied non-monotonically. V4 exhibited the best wear resistance at both temperatures, while V6 showed increased cracking, delamination, and debris removal despite its higher hardness and lower friction coefficient. Lowering the temperature to −40 ℃ increased the friction coefficients but reduced the wear rates of all coatings. Multicomponent tribo-oxidation occurred at both temperatures, with composition-dependent changes in the tribochemical surface layers. At −40 ℃, reduced oxide-assisted shear accommodation was associated with higher friction, whereas low-temperature hardening restricted indentation and ploughing, thereby reducing wear. These findings clarify the distinct chemical and mechanical factors governing temperature-dependent tribological behavior and provide guidance for the compositional design of wear-resistant coatings for EH40 steel.
