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.

Achieving Greener, Super-Robust Performance Water-Based Lubrication: Obtained by a Multifunctional Ionic Liquid Aqueous System and Formation of Unique Interfacial Interactions

“…For samples NLSA-P 2222 , NLSA-TEOA, and NLSA-CHOH, their extreme pressure can reach over 750 N; in particular, the load-bearing pressure of NLSA-CHOH can be up to 850 N. Structurally, the extreme pressure elements N, P, and S in the IL structure will be favorable to the exceptional load-bearing capacity, whose more detailed analysis is the coordination bonds formed between IL and the empty orbits of metals. 42 Among them, the N element is adsorbed to the surface through its lone pair electrons forming a coordination bond with the empty orbitals of the metal in the friction process. Also, the N element in the anion may be adsorbed to the positively charged metal surface by the electrostatic effect, while the weaker C−S bonds in the molecule will tend to form a reactive film that played the antiwear role.…”

“…The extreme load test (Figure f) found that the COFs of the IL water-based lubricating system were maintained at a stable and low level (less than 0.15). For samples NLSA-P 2222 , NLSA-TEOA, and NLSA-CHOH, their extreme pressure can reach over 750 N; in particular, the load-bearing pressure of NLSA-CHOH can be up to 850 N. Structurally, the extreme pressure elements N, P, and S in the IL structure will be favorable to the exceptional load-bearing capacity, whose more detailed analysis is the coordination bonds formed between IL and the empty orbits of metals . Among them, the N element is adsorbed to the surface through its lone pair electrons forming a coordination bond with the empty orbitals of the metal in the friction process.…”