Genesis of Superlow Friction in Strengthening Si-DLC/PLC Nanostructured Multilayer Films for Robust Superlubricity at Ultrahigh Contact Stress

Abstract

Diamond-like carbon (DLC) films have significant potential to provide solutions for the friction reduction and the lubricity problem of mechanical moving friction pairs. However, the realization of excellent lubrication or even superlubricity and long lifetime under heavy loading conditions is still a great challenge, which is crucial for the applications of DLC in harsh environments. Here, we construct a group of property-strengthening Si-DLC/PLC multilayer films that could withstand ultrahigh contact stresses and achieve robust superlubricity. Under a peak Hertz contact stress of up to 2.37 GPa, the setup of a bilayer thickness of 324 nm enables the multilayered film (an overall film thickness of 1.53 μm) to achieve a superlow coefficient of friction toward 0.001 and an ultralow wear rate of 3.13 × 10^–9 mm³/Nm. An alternating load reciprocating friction test emphasizes that this strengthening nanostructured Si-DLC/PLC multilayer possesses a kind of load self-adaptation because of its in situ nanoclustering transformation and local ordering of sp²-C phases at the sliding interface. The genesis of self-adaptation to the applied load is evaluated comprehensively to reveal its strengthening and toughening structural characteristics and robustness of the near-zero friction and wear features. The findings provide a significant design criterion for carbon-based solid lubricants applicable to harsh loading environments.