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Porous materials have recently attracted significant attention in the aerospace and biomedical fields for addressing issues related to friction and wear. Porous materials are beneficial in applications where continuous lubrication is not feasible or for components that operate under extreme conditions, such as high speeds, elevated temperatures, and heavy loads. The pores can serve as reservoirs for liquid lubricants, which are gradually released during the operation of the components. The tribological properties of these materials depend on their porosity, the lubricants used, and any additional additives incorporated into the porous materials. This review article provides insight into common fabrication techniques for porous materials and examines their tribological performance for all three classes of materials—polymers, metals, and ceramics. Additionally, it discusses design criteria for porous self-lubricating materials by highlighting the critical properties of both the substrate and lubricants. [ABSTRACT FROM AUTHOR]

The present work reports the utilization of laser treatment for the structuring of a B2O3 coating on ceramic substrates. The two ceramic substrates, pure Al2O3, and Al2O3-20wt% B2O3, were prepared in-house using cold pressing and sintering route. The coatings were prepared by applying the ethanol-B2O3 slurry on the ceramic substrate using a dip coater followed by drying at 100 °C. The dried coatings were subjected to the continuous laser at 22, 29, and 36 W of laser power to achieve the final coating. Coating characterization by X-ray diffraction (XRD) revealed the importance of laser power on controlling the phases of B2O3, which are H3BO3, HBO2, and amorphous B2O3. The crystallinity index (CI) of the coatings calculated using XRD spectrum decreased with an increase in laser power. The coating processed at 36 W showed the lowest CI that reveals higher amorphous B2O3 content. Sliding tests conducted in a controlled humid environment at three sliding velocities suggested a direct relationship between tribological performance and CI value—coating with lower CI value provided consistent lower COF. Additionally, a strong influence of the substrate on tribological performance was also observed—the coatings on the Al2O3-20wt%B2O3 substrate performed superior compared to the coating on the pure Al2O3. The effect of substrates is discussed in terms of thermal conductivity to achieve higher amorphous B2O3 content and the initial surface roughness of the substrates. [ABSTRACT FROM AUTHOR]

Abstract Both surface texture and multiphase lubricants (additives in base oil) influence the friction and wear performance during sliding. However, the synergy of their interaction is still unknown. In the present investigation, an effort is made to understand the influence of environmental friendly multiphase lubricants on the friction and transfer layer formation during sliding against various surface textures. In this study, unidirectional surface textures were created and sliding tests were conducted against various grinding angles of the unidirectional texture. The sliding tests were conducted in multiphase lubricants consisting of canola oil (biolubricant) and nano-additives (graphene) at various concentrations. The results showed that the coefficient of friction (COF) and transfer layer formation was influenced by the grinding angle. However, it was found that this influence can be minimized by using an optimum concentration of graphene in canola oil. A minimum COF of 0.05 ± 0.01 could be achieved for various grinding angles by utilizing a specific concentration of graphene. It was found that a high concentration of Gr (3 wt%) was required when sliding at 0° and a low concentration of Gr (1 wt%) was required when sliding at 45° to achieve the minimum COF. This was attributed to the variations in asperity and Gr additive interaction when sliding at different grinding angles. The present study details the observed friction and transfer layer formation results and analyzes the mechanism of multiphase lubrication during sliding at various grinding angles. An asperity interaction model for sliding against various grinding angles and in a multiphase lubricant with varying additive concentrations has also been presented. Highlights • Multiphase lubricants (MPLs) can minimize the effect of surface texture on friction. • Minimum friction can be obtained using optimum concentration of Gr in MPLs. • Required optimal concentration of Gr varied as a function of the grinding angle. • Mechanism of asperity and Gr additive interaction was the key for low friction. • Bio-based MPLs have potential as green alternatives for petroleum-based lubricants. [ABSTRACT FROM AUTHOR]