Macroscale superlubricity with a high load-carrying capacity enabled by nitrogen-doped graphene quantum dots in lubricated silicon-doped amorphous carbon films

Nadeem, Irfan (author), Finšgar, Matjaž (author), Dražić, Goran (author), Ambrožič, Bojan (author), Malok, Matjaž (author), Cavaleiro, Albano (author), Kalin, Mitjan (author)

Achieving macroscale superlubricity with engineering materials is highly desirable for energy conservation, environmental benefits, and longevity of mechanical components. However, attaining superlubricity in aqueous-lubricated systems with enhanced load-bearing capacity remains challenging in metallic materials. Herein, nitrogen-doped graphene quantum dots (NGQDs) as a nano-additive in aqueous glycerol facilitate macroscale superlubricity between friction pairs of steel and silicon-doped hydrogenated amorphous carbon (a-C:H:Si). Superlubricity is observed in boundary-lubrication regime with a friction coefficient of 0.0055–0.0097 under various sliding conditions. Notably, the wear of the steel counterface (k = 8.51 × 10−9 mm3/Nm) decreased by 47.8%, resulting in a final contact pressure of 206.7 MPa, which exceeds values reported for aqueous-lubricated systems during superlubricity. The lubrication mechanism reveals that NGQDs' adsorption on the steel-worn surface, coupled with the tribocatalytic generation of FeNxCy moieties on a-C:H:Si surface, is crucial for reducing friction. These FeNxCy moieties, with a multitude of active sites, facilitate the subsequent anionic adsorption of pyrrolic-rich NGQDs. Simultaneously, the formation of amorphous graphitic film, driven by continuous shearing and exfoliation of graphene sheets within the adsorbed NGQDs, contributes to the stability of superlubricity. These findings provide insights into the functional characteristics of NGQDs for achieving superlubricity in aqueous-lubricated systems, paving the way for future energy-saving applications.

• Language: English
• Keywords: macroscale superlubricity, metallic materials, streel
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FS - Faculty of Mechanical Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2025
• Number of pages: 21 str.
• Numbering: Vol. 6, iss. 7, art. 2400671
• PID: 20.500.12556/RUL-175988
• UDC: 620.1/.2
• ISSN on article: 2688-4062
• DOI: 10.1002/sstr.202400671
• COBISS.SI-ID: 236432131
• Publication date in RUL: 17.11.2025

Record is a part of a journal

• Title: Small structures
• ISSN: 2688-4062
• COBISS.SI-ID: 176172547

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: supemazljivost, kovinski materiali, jeklo