Thermal stability of diamond-like carbon–MoS2 thin films in different environments

• Thermal stability of diamond-like carbon (DLC) and DLC–MoS2 films were evaluated.
• DLC–MoS2 films can be synthesized by biased target ion beam deposition technique.
• Comparing with DLC films, the DLC–MoS2 thin films showed higher thermal stability.
• DLC–MoS2 film is thermally stable up to 400 °C in air and 500 °C in low pressure.
• Formation of MoS2 − xOx is responsible for higher thermal stability of DLC–MoS2 film.

Diamond-like carbon (DLC) based coatings are ideal for low friction and wear resistant applications. For those tribological applications, the coatings may expose to high temperature environments. Therefore, the thermal stability of the coating is very important for its long-term performance. In this work, DLC–MoS2 composite thin films were synthesized using biased target ion beam deposition technique in which MoS2 was produced by sputtering a MoS2 target using Ar ion beams while DLC was deposited by an ion source with CH4 gas as carbon source. DLC films without MoS2 deposited under similar conditions were used as reference samples. After the deposition, DLC and DLC–MoS2 thin films were heat-treated in ambient air and low pressure environments at different temperatures ranging from 100 to 600 °C for 2 h. The effect of annealing on the structure, mechanical and tribological properties of the resulting films were studied by means of Raman spectroscopy, X-ray absorption near edge structure, scanning electron microscopy, nanoindentation, and ball-on-disk testing. The results showed that the structure, hardness, Young's modulus, friction coefficient and wear coefficient of the DLC films were stable up to 200 °C annealing in air and 300 °C in low pressure. At higher temperature, the annealing led to the transformation of sp3 to sp2, which degraded the mechanical and tribological properties of the thin films. Comparing with the DLC films, the DLC–MoS2 thin films showed a slower rate of graphitization and higher structure stability throughout the range of annealing temperatures, indicating a relatively higher thermal stability.