Research Progress of Hexagonal Boron Nitride in Lubrication

Hexagonal boron nitride (h-BN) is a lubricant additive with considerable application potential. Its layered structure provides low interlayer shear strength, while its favorable thermal stability, chemical inertness, and electrical insulation make it attractive for demanding lubrication environments. However, the tribological performance of h-BN depends not only on interlayer sliding but also on the combined effects of material structure, lubricant medium, and operating conditions. Its practical application is further constrained by insufficient compatibility with certain media, inefficient delivery into the contact zone, and limited retention at the sliding interface, thereby compromising sustained friction reduction and wear protection. This review focuses on the structure-interface-performance relationships of h-BN-based lubricant additives and summarizes advances in size and morphology control, surface functionalization, and composite design, with particular emphasis on how these strategies affect the dispersion of h-BN in lubricant media, its delivery to the contact zone, and its participation in interfacial protective layers. The tribological behavior of h-BN-based additives under different lubricant media and service conditions is further compared to clarify their effective performance windows and practical application boundaries. Finally, the key challenges that remain in controlled synthesis and structural regulation, dynamic interfacial evolution, and service-oriented performance validation are summarized, providing a framework for material structural design, mechanistic analysis, and application-specific assessment.