Macroscale superlubricity enabled by the synergy effect of oil and S–C co-infiltration coating on 20CrMnTi steel surface

To explore macroscopic superlubricity in industrial fields, S–C co-infiltration treatment refers to the sulfurization of carburized gear steel to achieve a synergistic lubrication effect. The carburized layer at the bottom provides high-strength support. The surface sulfurized layer with pores immersed in oil shows good solid‒liquid synergistic lubrication to realize stable superlubricity under loads of 0–800 N. Although stable superlubricity is lost after the load is increased to 1,200 N, the tribological coefficient and wear depth are reduced by 72.9% and 19.4%, respectively, compared with those of the original surface. This paper proposes a novel oil‒solid synergistic superlubricity system, which has significant potential for practical applications.