Tribological properties of molybdenum disulfide films doped with amorphous carbon in vacuum and high-temperature environments

Molybdenum disulfide (MoS₂) is a multifunctional material primarily used in lubrication, electronics, and catalysis. MoS₂ films are widely utilized in the aerospace industry due to their excellent lubrication properties. These films are applied in aircraft landing gear, engine components, and moving parts of spacecraft to ensure efficient operation and minimize frictional wear. However, under high-temperature conditions, MoS₂ films are susceptible to oxidation into molybdenum trioxide, significantly degrading their lubricating performance and restricting their applicability in high-temperature environments.

Herein, MoS₂ films were enhanced by doping them with amorphous carbon to improve their mechanical properties and high-temperature tribological performance. Using direct-current magnetron sputtering, medium-frequency magnetron sputtering, and high-power pulsed composite sputtering techniques, MoS₂-C composite films were fabricated. The effects of doping amorphous carbon and its concentration on the microstructure, mechanical properties, and tribological performance of MoS₂ films were thoroughly investigated.

The results revealed that the MoS₂-C composite films exhibited a preferential orientation of the (002) crystal plane. Amorphous carbon incorporation into the MoS₂ matrix resulted in a dense and uniform structure while reducing surface roughness. This structural modification enhanced the mechanical and tribological properties of the films. Doping MoS₂-C composite films with an optimal amount of amorphous carbon significantly improved their mechanical properties. Their nanohardness and elastic modulus reached 5.50 and 82.53 GPa, respectively, while substrate adhesion strength increased to 8.30 N, approximately 3.6 times higher than that of pure MoS₂ films. These improvements suggest that amorphous carbon addition enhances the mechanical strength and durability of the films. At room temperature, both MoS₂ and MoS₂-C composite films exhibited poor tribological performance, primarily due to the infiltration of moisture molecules from air into the MoS₂ interlayers. This results in MoS₂ oxidation, compromising the lubrication properties of the films. Meanwhile, the tribological performance of MoS₂-C composite films substantially improved in a vacuum environment, attributed to the isolation from oxygen, preventing oxidation and allowing the films to maintain their lubricating properties. Under high-temperature conditions (100 ℃-300 ℃), MoS₂-C films outperformed pure MoS₂ films by maintaining a lower friction coefficient. MoS₂-C films with 37.41% atomic percentage of carbon exhibited the lowest wear rate of 9.75×10^-8 mm/(N·m) while showing a friction coefficient of 0.008 at 200 ℃, which is the lowest value among all samples. Notably, at 300 ℃, pure MoS₂ films quickly failed due to oxidation, whereas MoS₂-C composite films retained a lower friction coefficient and longer wear life. This improvement is primarily attributed to the incorporation of carbon, which effectively inhibits MoS₂ oxidation in high-temperature environments.

MoS₂-C composite films exhibit enhanced wear resistance and load-bearing capacity at elevated temperatures. These findings suggest that doping amorphous carbon into MoS₂ films significantly improves their tribological and mechanical properties, especially under high-temperature conditions. MoS₂-C composite films demonstrate excellent wear resistance and prolonged service life, making them promising for high-temperature lubrication applications. By optimizing the carbon content, it is possible to further enhance the high-temperature lubrication performance of MoS₂ films while maintaining their excellent mechanical properties. This provides new possibilities for developing advanced tribological coatings that effectively perform under harsh operating conditions.