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.
Hydrophobic surface modification is expected to reduce ice friction in high-speed winter sports such as bobsleigh and skeleton. Although hydrophobic coatings have notably reduced ice friction at the laboratory scale, their practical implementation is impeded by long processing times and difficulty of scaling to large or complex geometries. To overcome these limitations, this study introduces a UV-curable surface treatment method with rapid curing at room temperature for ice friction reduction, which is directly applicable to full-scale runners. UV-curable polydimethylsiloxane/polytetrafluoroethylene (PTFE) formulations with systematically varied PTFE concentrations were prepared and evaluated using a custom-built ice tribotester. The formulations were subsequently applied to full-scale runners and tested by professional athletes at a national training facility equipped with an artificial ice start track. In both unmanned and athlete-driven sled trials, the coatings reduced the sliding times and increased the peak velocities compared with bare runners, indicating a consistently enhanced glide efficiency. The UV-curable coatings therefore provide a practical and scalable alternative for ice friction reduction on steel-ice interfaces. Unlike conventional hydrophobic coating methods, the UV approach achieves rapid curing at room temperature and is directly applicable to full-scale runners, thereby bridging the gap between laboratory performance and real-world implementation.
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.
Poor heat dissipation and severe friction wear are prominent defects of cemented carbide in spray cooling friction environments, which restrict its service life. This work constructed HTDC surfaces integrated with bionic micro-textures, DLC films and hydrophilic coatings on cemented carbide substrates. The morphological characteristics of all multifunctional composite surfaces were characterized, which regulated their surface wettability. HTDC surfaces achieved the minimum contact angle of 3°. Enhanced wettability further improved heat dissipation characteristics, and HTDC delivered the maximum heat flux q with the shortest droplet evaporation time. Under dry friction, the average steady-state friction temperature Tfa, average coefficient of friction µa, maximum height of scratches Hmax, wear rate Wr and counterparts’ wear rate Wrc of HTDC were nearly equivalent to TDC (bionic micro-textures and DLC films). Under spray cooling, HTDC exhibited the lowest Tfa, µa, Hmax, Wr and Wrc among all samples, and its Wr was 87.6% lower than CC in the initial friction cycle. Mechanism analysis revealed that microgrooves captured wear debris to restrain three-body abrasive wear, and DLC films possessed self-lubricating property. Bionic micro-textures and DLC films jointly protected the hydrophilic coatings, thereby maintaining stable surface wettability, which enhanced q and reduced Tfa. This delayed the spalling of DLC films and ultimately improved friction performance. This work provides a novel surface modification scheme for cemented carbide under spray cooling environments, and offers reference for subsequent surface structure optimization.
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.
