In an article recently published in the journal Applied Surface Science, researchers discussed the synergistic lubrication processes of molybdenum disulfide films under graphene-oil lubricated circumstances.
Study: Synergistic lubrication mechanisms of molybdenum disulfide film under graphene-oil lubricated conditions. Image Credit: Artbox/Shutterstock.com
Friction and wear cause energy consumption which can be solved with lubrication. Solid lubricants offer a high bearing capacity, a wide temperature range, and excellent space adaptation, but they also have some drawbacks such as heat conduction difficulty and debris production. When functioning alone, solid-liquid synergistic lubrication can compensate for limitations.
Two-dimensional (2D) layered nano-materials utilized as solid lubricants, such as molybdenum disulfide (MoS2), graphene, and tungsten disulfide (WS2), have shown to be potential candidates. 2D materials are frequently employed as lubricant additives in lubricants to achieve various contact-area functionalities.
Graphene is a 2D substance that is commonly utilized as a lubricant additive. Graphene may easily enter friction surfaces and lessen contact between them when the friction surfaces move relative to each other due to its nano-layered structure. Graphene, on the other hand, is easily agglomerated. Graphene oxide is a derivative of graphene that may be functionalized chemically and is compatible with liquid lubricants. On the synergistic effect of solid lubricating film and lubricating oil additives on friction response, there are few relevant studies.
About the Study
In this study, the authors discussed the development of solid-liquid composite coating using a MoS2 layer under graphene hybrid gear oil lubrication conditions. A graphene-like transfer film was generated at the frictional contact surfaces.
The team investigated the effects of Isopropyl triisostearyl titanate modified graphene oxide (T-GO) as a lubricating oil addition on tribological performances for synergistic lubrication along with the friction/wear behaviors and lubrication mechanisms of various lubrication methods. An atomic force microscope was used to examine the film's surface morphology and roughness (AFM).
The researchers used the Raman spectrometer with 532 nm laser excitation to get Raman spectra of GO, MoS2, and T-GO. The tribological features of lubrication combinations such as MoS2 film lubrication, gear oil, synergistic lubrication of MoS2 film, and the solid-liquid composite lubricating coating consisting of graphene oil and MoS2 film were investigated using a ball-on-plate tribometer.
The wear scar lubricated by T-GO hybrid gear oil-lubricated MoS2 film revealed two distinct peaks at about 1350 cm-1 and 1580 cm-1, which corresponded to the graphene D and G bands. The solid-liquid composite lubricating coating was generated by the synergistic effect of the gear oil-lubricated MoS2 film, which lowered the friction coefficient and wear volume by 46.7% and 97.1%, respectively, after the addition of T-GO to the gear oil. In the range of 668.4-964.0 MPa, the friction coefficient of MoS2 lubrication reduced as the contact pressure increased. T-GO had an ID/IG value of 0.9673, while GO had an ID/IG value of 0.9152.
The anti-friction and anti-wear properties of the prepared solid-liquid composite coating were reduced by 13.0% and 37.4%, respectively, when compared to gear oil-lubricated MoS2 film, and 46.7% and 97.1%, respectively, when compared to simply MoS2 film. As a result, the excellent lubrication function of MoS2-based solid-liquid lubricating coatings was attributed not only to the structural advantages of MoS2 and graphene but also to the solid-liquid synergism and transfer film, which improved the interfacial load-bearing capacity and anti-friction/wear behaviors.
When compared to onefold lubrication, the solid-liquid composite lubricating coating lowered friction coefficient by 46.7% and wear volume by 97.1%. T-GO was constantly transported to the friction contact surface, which formed a graphene-like transfer coating that improved the interfacial load-bearing capacity as well as anti-friction/wear capabilities.
In conclusion, this study investigated the tribological properties of a MoS2-based solid-liquid lubricating layer, with a focus on the use of graphene hybrid gear oil. Three types of lubrication systems were developed: MoS2 film and gear oil synergistic lubrication, MoS2 film lubrication, and the MoS2 film-T-Go hybrid oil composite lubricating coating. Experimentally, the effects of T-GO as a lubricating oil additive on tribological performance for synergistic lubrication were explored. Their tribological characteristics were also thoroughly examined.
To obtain uniformly distributed graphene gear oil, isopropyl triisostearoyl titanate was used to modify graphene oxide. T-GO provides a good lubricating effect when used together.
The authors mentioned that in general, a solid-liquid composite lubricating coating with strong tribological properties could significantly reduce energy loss while also contributing to carbon neutralization and carbon peak. They believe that it could be the start of a new lubricant generation. They also emphasized that to increase the performance characteristics of the solid-liquid composite lubrication of MoS2 films at high temperatures, further study is needed.
Yang, Y., Fan, X., Yue, Z., et al. Synergistic lubrication mechanisms of molybdenum disulfide film under graphene-oil lubricated conditions. Applied Surface Science 153845 (2022). https://www.sciencedirect.com/science/article/abs/pii/S0169433222013897