Multi-environmental adaptive lubricating coatings achieved by the formation of aluminum phosphate amorphous passivation film and P–C bond

Abstract

In the complex and harsh operating environments of critical moving components in aerospace, it is still a challenge for current lubricating coatings that survive in various environment. Herein, we prepared phosphate bonded lubricating coatings containing MoS₂/Cr₂O₃ composite nanoparticles, graphene and mullite whiskers, which performed well in various conditions (friction coefficient below 0.3), including wide temperature range (−120–500 °C), nitrogen, water vapor (30–90% RH), and salt spray (3.5 wt.% NaCl) environments. The lubricating phase and various fillers were filled into the reticulated crosslinked structure of the phosphate binder, which improved the bonding strength and hardness of the coating. Stable low friction was achieved by the aluminum phosphate amorphous passivation film formed on the friction interface and the synergetic layered lubrication of graphene and MoS₂. H⁺ and OH⁻ groups dissociated from water molecules reacted with the high-activity hanging bonds at graphene edges in humidity environment, maintaining its lubricating characteristic. At elevated temperature, the P–C bond formed by the reaction of P in phosphate binder with high-energy hanging covalent bonds at the graphene boundaries reduced intergranular adhesion and oxidation. The results provide an effective strategy for improving the environmental adaptability of solid lubricating coatings and expanding the application scope.