Morphology‐Dictated Interfacial Stacking of TiO 2 Nanosheets Delivers Robust Tribofilms under Extreme Pressure

Under extreme pressure (EP), lubricating base oils with low viscosity frequently suffer from film rupture, leading to severe adhesive wear and lubrication failure. Although nano‐additives can reinforce the sliding interface, how their morphology dictates stacking behavior and tribofilm formation remains poorly understood. In this study, we investigate anatase TiO 2 nanosheets (ANS) and nanoparticles (ANP) to reveal how additive morphology governs tribological performance. We found that ANS reduced the friction coefficient (COF) by 56% and wear by 88% compared to base oil, while boosting EP load capacity by 6.8 times. Under applied normal load, the ANS physically reorient and stack into a dense, continuous tribofilm that effectively shields surface asperities. Conversely, ANP form an island‐like, loosely packed tribofilm with poor load capacity. Beyond physical shielding, ANS exert a mechanical polishing effect that drives iron wear debris to react with oil hydrocarbons. This tribochemical process builds a Fe‐rich reinforced structure, drastically improving the hardness and stability of the tribofilm. Ultimately, this work provides a morphology‐driven engineering pathway for designing robust lubricants operating under extreme conditions.