In-Situ Self-Assembly of MoS ₂ Quantum Dots Inducing Ultra-Low Friction at Metal Interfaces

Friction at the steel–steel interface is primarily attributed to strong metallic bonds, which induce adhesive forces and localized plastic deformation. In this work, we applied MoS 2 quantum dots (MQDs) as a solid lubricant coating on the steel surface using a facile solution-based method, effectively mitigating these adverse effects and enabling ultralow friction on steel–steel contact. Under a dry atmosphere and elevated contact pressure (∼0.5 GPa), reciprocating wear tests show that the coefficient of friction decreases from ∼0.65 for bare steel contact to ∼0.013 (∼98% reduction), indicating a sustained ultralow friction regime. Interfacial characterization reveals that during sliding, the MQDs self-assemble in situ into layered MoS 2 nanosheets, which reorganize to form a dense, load-bearing tribofilm aligned with the sliding direction. The self-assembled tribofilm significantly diminishes interfacial shear strength and adhesion, thereby enabling the pronounced friction reduction observed under high pressure. This work provides insights into the friction-induced structural evolution of MoS 2 quantum dots at dry steel–steel interfaces and may offer guidance for future tribological studies at metal interfaces under relatively severe loading conditions.