The lubrication conditions of friction pairs in water or aqueous solutions are crucial to the performance and lifespan of key mechanical components in engineering applications. In our previous research, a promising in situ self-sensing method was proposed on the basis of liquid‒solid triboelectric signals generated from the rotation-induced streaming current. However, the understanding of the interfacial charging mechanism and the enhancement of the signal outputs from the viewpoint of the zeta potential are deficient. In addition, the influence of a convergent channel on the zeta potential needs further investigation, which fits most engineering conditions for seals or bearings because of the hydrostatic or hydrodynamic effect. Herein, electrode-coated silicon nitride (Si₃N₄) composites are prepared via laser machining and magnetron sputtering. The interfacial charging mechanism is proposed on the basis of a comprehensive investigation of the effects of the electrode area ratio, surface roughness, and liquid ion concentration on the zeta potential. The zeta potential originates from the combined effects of the dissolution of metallic electrodes and the hydration effect of Si₃N₄. The interfacial charging mechanism can be explained by the ion absorption of the ceramic substrate and the conduction behavior of the electrode layers. Moreover, samples with convergent profiles along the fluid flow exhibit a greater absolute value of the zeta potential than divergent samples do, and a negative relationship between the zeta potential and convergent slope is observed. Finally, design criteria for self-sensing friction pairs are proposed for enhancing the interfacial charging performance: an optimal electrode area ratio of 40%, a surface roughness of 0.1–0.2 μm, and an aqueous solution with a moderate number of hydrated ions. Working conditions with a large variation in the film gap are preferable in terms of discernibility and sensitivity. This work builds a bridge between the interface charging mechanism and the self-sensing application of liquid‒solid triboelectric behaviors on the basis of streaming current input.

Two types of commercial WC-Ni samples were irradiated with the High-intensity pulsed ion beam (HIPIB). Both the surface characteristics and tribo-characteristics of the non-irradiated and irradiated WC-Ni samples, sliding against graphite under water lubrication, were compared. Quite low steady friction coefficients (approximately of 0.02) of the irradiated WC-Ni were observed. The surface topographies and components were investigated. The quite low friction of the irradiated WC-Ni samples was ascribed to the higher fluid retention capability of the latter and the tribofilm formed during sliding.

The effects of surface roughness characteristics on the fluid load capacity of tilt pad thrust bearings with water lubrication were studied by the average flow model. The flow factors utilized in the average flow model were simulated with various surface roughness parameters including skewness, kurtosis and the roughness directional pattern. The results indicated that the fluid load capacity was not only affected by the RMS roughness but also by the surface roughness characteristics. The fluid load capacity was dramatically affected by the roughness directional pattern. The skewness had a lower effect than the roughness directional pattern. The kurtosis had no notable effect on the fluid load capacity. It was possible for the fluid load capacity of the tilt pad thrust bearings to be improved by the skewness and roughness direction pattern control.

The frictional performance of materials used in face seals is critical to the sealing performance. Silicon carbide is commonly used in hard rings because of its abrasion resistance, corrosion resistance, and thermal shock resistance. In this study, the frictional performance of silicon carbide, including graphite-added silicon carbide, under water and lubrication-absent conditions was studied by using a Falex-1506 tribotester and different working parameters. In addition, the morphology of the worn surfaces was observed using scanning electron microscopy and the damage was characterized to understand the tribological behavior of different silicon carbides. The results suggest that the friction coefficients decrease with increasing pressure under water lubrication conditions because of the water within the holes on the surface of the materials. The percentage of water lubrication increases, whereas the percentage of solid friction decreases when the pressure increases. Under dry contact conditions, the friction coefficients change negligibly with increasing pressure and graphite-added silicon carbide shows better frictional performance.