Macroscale Superlubricity Induced by MXene/MoS₂ Nanocomposites on Rough Steel Surfaces under High Contact Stresses

Toward the goal of achieving superlubricity, or near-zero friction, in industrially relevant material systems, solution-processed multilayer Ti₃C₂T_<i>x</i>-MoS₂ blends are spray-coated onto rough 52100-grade steel surfaces as a solid lubricant. The tribological performance was assessed in a ball-on-disk configuration in a unidirectional sliding mode. The test results indicate that Ti₃C₂T_<i>x</i>-MoS₂ nanocomposites led to superlubricious states, which has hitherto been unreported for both individual pristine materials, MoS₂ and Ti₃C₂T_<i>x</i>, under macroscale sliding conditions, indicating a synergistic mechanism enabling the superlative performance. The processing, structure, and property correlation were studied to understand the underlying phenomena. Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy revealed the formation of an <i>in situ</i> robust tribolayer that was responsible for the performance at high contact pressures (>1.1 GPa) and sliding speeds (0.1 m/s). This report presents the lowest friction obtained by either MoS₂ or MXene or any combination of the two so far.