Stable lubrication in air and vacuum of GO-Al3+ coating via strong chemical bonding and reactive sites passivation by aluminum ions

Graphene oxide (GO), as a layered two-dimensional nanomaterial, is usually considered as potential candidate of solid lubricant because of its unique physical, chemical, and mechanical properties. However, its tribological behaviors strongly relate to the lubrication environment and the interlayer bonding strength. In this work, a bio-inspired GO-Al3+ coating with nacre-like layer-by-layer compact structure is constructed by using aluminum ions (Al3+) as the cross-linkers. As a comparison, a GO-spin coating with the same thickness is also fabricated by means of spin coating technique. The results show that the lubrication performance of the GO-spin coating is strongly dependent on the environment conditions; namely, it has good lubrication property in air while fails in vacuum due to the lack of passivating species. For the GO-Al3+ coating, the introduction of Al3+ passivates the reaction sites on GO sheets, preventing lubrication failure of GO coating in vacuum. Besides, the introduction of Al3+ dramatically enhances the interlayer bonding strength of coating, which results in high efficiency of load transfer and improved mechanical properties, therefore reducing wear loss with a thinner transfer film both in air and vacuum environments.