Effect of vacuum atomic oxygen irradiation on the tribological properties of fullerene-like carbon and MoS2 films

The development of highly reliable, low-friction, durable lubrication materials and technologies applicable to the space environment will be of great importance to improve the lubrication status and life of space equipment. Fullerene-like films exhibit excellent ultra-low friction and wear resistance under atmosphere and vacuum, and are considered to be one of the most promising materials for space lubrication. In this work, the effect of vacuum atomic oxygen on the mechanism of action and tribological properties of fullerene-like carbon and MoS2 films were investigated. After atomic oxygen irradiation, the content of odd-membered rings in the fullerene-like carbon films decreased, the sp2 carbon converted to sp3. Besides, the total proportion of carbon atoms in the form of oxides did not increase significantly (from 11.3% to 13.0% only), and the hydrogen content in the films did not change significantly due to the existence of the cage-like structure of the fullerene-like carbon films. After atomic oxygen irradiation, it was more difficult to form fullerene-like nanostructures at the interface of the friction surface during the friction process, resulting in the increase of friction coefficient. For the MoS2 film, the hardness was drastically decreased after atomic oxygen irradiation, causing it to wear out quickly under high contact stress.