This study investigates the formulation-dependent tribochemical regulation of TiO₂ nanoparticles in molybdenum dithiocarbamate (MoDTC), zinc dialkyldithiophosphate (ZDDP), and their blended lubricant systems. Reciprocating ball-on-disk tribological tests were conducted under a normal load of 20 N, corresponding to Hertzian contact pressure of 1.33 GPa. TiO₂ nanoparticles promoted MoS₂-rich tribofilm formation in the lubricant with single MoDTC, which led to reduction of both the coefficient of friction and wear of counterparts. Conversely, in the MoDTC-ZDDP blended system, TiO₂ drove interfacial reactions toward high-valence Mo oxides and sulfate species, leading to increased wear. Atomic force microscope measurements confirmed that protruded MoS₂-rich tribofilm formed by lubricant containing MoDTC and TiO₂ exhibited low shear strength, whereas the protruded oxide/sulfate-rich tribofilm formed by lubricant containing MoDTC-ZDDP and TiO₂ generated higher local friction. These findings reveal that TiO₂ nanoparticles function as selective tribochemical regulators whose effects are governed by interfacial reaction competition and additive compatibility, rather than universally enhancing lubrication performance. This work provides critical mechanistic insights for rational design of nanoparticle-modified lubricant formulations.

Ultra-high temperature ceramics (UHTCs) exhibit ultra-high melting points and relatively high mechanical performance, making them ideal coating materials for extreme environment applications like hypersonic vehicles. Recently, novel design strategies of UHTCs coatings have been proposed, mainly including the composition and structural design. In this article, state-of-the-art approaches including multilayer and gradient UHTC coatings for enhanced mechanical and ablation resistance, surface engineering for the improvement of coating adhesion, materials and microstructural design for thermal insulation, laser ablation protection, and drag reduction were reviewed. Furthermore, advanced designing and fabrication techniques for UHTC coatings are also prospected, which can provide insights for the development of next-generation multi-functional UHTC coatings for harsh conditions.

Polytetrafluoroethylene (PTFE) has been widely used as a lubrication additive for reducing friction and wear; however, the hydrophobic nature of PTFE restricts its application in eco-friendly water-based lubrication systems. In this study, for the first time, we designed novel PTFE@silica Janus nanoparticles (JNs) to meet the requirement for additives in water-based lubricants, which have excellent dispersion stability in water attributed to the unique amphiphilic structure. By introducing the lubrication of the aqueous dispersion of the JNs with a concentration of 0.5 wt%, the coefficient of friction (COF) and wear volume were reduced by 63.8% and 94.2%, respectively, comparing to those with the lubrication of pure water. Meanwhile, the JNs suspension also exhibits better lubrication and wear-resistance performances comparing to commercial silica and PTFE suspensions. The excellent tribological behaviors of PTFE@silica JNs as nano-additives could be attributed to the synergetic effect of the two components, where the PTFE provided lubrication through the formed tribofilms on the friction pairs, and the rigid silica further enhanced the wear-resistance performance. Most importantly, the unique structure of JNs makes it possible to use PTFE as an additive in water-lubrication systems. Our study shed light on the design and application of novel JNs nanomaterials as additives to meet the requirements of future industrial applications.

Superlubricity has drawn substantial attention worldwide while the energy crisis is challenging human beings. Hence, numerous endeavors are bestowed to design materials for superlubricity achievement at multiple scales. Developments in graphene-family materials, such as graphene, graphene oxide, and graphene quantum dots, initiated an epoch for atomically thin solid lubricants. Nevertheless, superlubricity achieved with graphene-family materials still needs fundamental understanding for being applied in engineering in the future. In this review, the fundamental mechanisms for superlubricity that are achieved with graphene-family materials are outlined in detail, and the problems concerning graphene superlubricity and future progress in superlubricity are proposed. This review concludes the fundamental mechanisms for graphene superlubricity and offers guidance for utilizing graphene-family materials in superlubricity systems.