Stable high-temperature superlubricity enabled by thermomechanical-induced interfacial graphitization and...

Area of Science:

• Materials Science
• Tribology
• Surface Engineering

Background:

• Achieving stable superlubricity in diamond-like carbon (DLC) films at high temperatures in air is challenging due to hydrogen loss and oxidation.
• Thermal degradation and oxidation compromise the structural integrity and lubricating properties of DLC films.

Purpose of the Study:

• To investigate silicon-doped hydrogenated amorphous carbon (a-C:H:Si) films for high-temperature superlubricity in air.
• To elucidate the mechanisms behind the enhanced tribological performance of these films.

Main Methods:

• In situ Raman spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy to analyze film evolution during sliding.
• Transmission Electron Microscopy (TEM) and Electron Energy Loss Spectroscopy (EELS) to characterize the tribofilm structure.
• Tribological testing at 300 °C in atmospheric air.

Main Results:

• Silicon-doped a-C:H:Si films demonstrated robust superlubricity (friction coefficient μ ≈ 0.002) at 300 °C in air.
• Oxygen accelerated graphitization, while silicon formed a stabilizing SiO_x layer.
• A transferable tribofilm composed of graphite-like layers and carbon onions was observed.

Conclusions:

• The study identified a synergistic mechanism involving oxygen-driven graphitization and SiO_x-mediated structural stabilization.
• This approach enables high-temperature superlubricity in solid lubrication coatings for extreme environments.
• Silicon doping offers a promising strategy for designing advanced DLC-based solid lubricants.