Mitigating severe wear in water-lubricated bearings through hydrophilic modification of Si3N4/PU composites

The severe wear of friction pairs in water-lubricated bearings, resulting from lubricating film instability under boundary lubrication, has hindered their development and application. Enhancing surface wettability to improve interfacial adsorption capacity for water molecules and promote stable water film formation under harsh operating conditions represents an effective approach for ameliorating lubrication performance in water-lubricated bearings. Hydrophilic-modified Si 3 N 4 /polyurethane (PU) composite materials were fabricated utilizing Si 3 N 4 ceramic/PU composite material fabrication technology combined with PMPC and β-cyclodextrin surface grafting techniques. Surface characteristics, mechanical properties, and tribological performance were systematically evaluated, specifically elucidating the influence mechanisms of hydrophilic groups on wettability and lubrication behavior. Results demonstrate that distinct hydrophilic groups differentially affect composite material performance, with β-cyclodextrin exhibiting more pronounced effects. Compared to the control group, the contact angles of PMPC and β-cyclodextrin-modified composite materials were decreased by 5.69% and 10.53%, respectively. Surface-bound hydrophilic groups lowered water-lubricated friction coefficients and effectively suppressed friction-induced vibration. Superior enhancement of tribological properties was provided by β-cyclodextrin modification relative to PMPC, with optimal performance achieved at solution –OH concentrations of 0.6 mol/L. This work presents a viable strategy for mitigating tribological challenges in water-lubricated bearing materials operating under boundary lubrication state. Graphical abstract