Effect of Irradiation Dose on the Structure and Tribological Performance of Ti:WS₂/PFPE Composite Lubricating System in Atomic Oxygen Environment

Perfluoropolyether (PFPE) oil possessing higher oxidation stability than hydrocarbon lubricant is combined with Ti:WS2 film to construct a solid-liquid composite lubricating system. The results indicate that atomic oxygen (AO) irradiation generates some important effects for the Ti:WS2/PFPE composite lubricating system. With an increase of irradiation dose, the molecular structure of PFPE oil experiences carbon chain breakage and appears to be an obvious molecule for cross-linking and polymerization. Meanwhile, Ti:WS2 film also is oxidized to a different extent to form WO3. The changes in the solid-liquid system resulted in greatly different tribological properties of the Ti:WS2/PFPE system. The friction coefficient of the system significantly increases with low-dose irradiation, while inversely, the value sharply decreases with high-dose AO, which is related to the presence of WO3 and formation of a transfer film. Finally, the failure mechanism of Ti:WS2/PFPE system under AO irradiation has been revealed.