The rapid development of aerospace industry has made more and more machinery parts of equipment working at high temperature. Due to the lubrication failure of lubricating oil and grease at high temperature, solid lubricant coatings are almost the only effective method to achieve super low friction at high temperature. In recent years, the tribological properties of diamond-like carbon (DLC) films have been extensively studied at high temperature. The present study reviews the microstructure of DLC films and the influence of doping different elements on the structure of DLC films. Second, the mechanical properties and thermal stability of pure DLC films and DLC doped with different elements are also described. DLC films have different microstructures and tribological properties by different preparation methods. Finally, the high-temperature lubrication failure mechanism of DLC films and the tribological properties of DLC films when doped with different elements are discussed from the macro and micro perspectives.

In the present work, first, we show that sliding Nitinol 60 alloy against steel under castor oil lubrication exhibits a new case of superlubricity (coefficient of friction CoF ≪ 0.01). So far, CoF below 0.01 have never been achieved under boundary lubrication at high contact pressure and in presence of vegetable oil as a green lubricant. Next, it is demonstrated that superlubricity is controlled by tribochemical reactions, involving chemical degradation of castor oil and the formation of metal oxy-hydroxides. Finally, to explain these findings, we propose a novel superlubricity mechanism consisting of hexanoic acid molecules intercalated between nickel and iron oxy-hydroxide lamellar layers, a structure very similar to the one found in Fe-Ni batteries. We propose that superlubricity is achieved due to repulsive electrostatic forces acting between the intercalated metal oxy-hydroxide lamellar compounds. This system would be suitable for practical engineering applications in many fields including biotechnologies.

Superlubricity is defined as a sliding regime in which friction or resistance to sliding almost vanishes. While there are a number of superlubricity, providing a high temperature superlubricity remains a challenge. Here we present a high temperature superlubricity achieved from the diamond like carbon (DLC) films friction system. Superlubricity is found about 0.008 for more than 100 000 seconds at the steady state at the temperature of 600 °C due to the formation of the self-generated lubricious composite oxides of γ-Fe₂O₃ and SiO₂ at the contact surfaces through tribochemistry reaction during the running-in process. We propose a superlubricity system based on the repulsive electrostatic forces between the self-generated composite oxides due to high temperature oxidation reaction and the shielding action of hydrogen at the contact surface, which is seem to be a reasonable explanation for super low friction at the elevated temperature.