Achieving high temperature lubrication of MoS₂-Bi₂O₃ nanoparticles composite: Through the formation of nanocrystalline ternary oxide and glaze layer

Molybdenum disulfide (MoS₂) is an excellent lubricant used in aerospace. Its ability to lubricate and resist wear at temperatures above 400 °C remains a significant challenge, due to its high temperature oxidation. Herein, we demonstrate that excellent high-temperature lubrication can be achieved with coefficient of friction (COF) of 0.21–0.26 at 450–800 ℃ by compounding bismuth oxide (Bi₂O₃) nanoparticles with MoS₂. The improvement of tribological properties above 450 ℃ was due to the synergistic lubrication of MoS₂ and Bi₂O₃. When the temperature was higher than 600 ℃, the tribo-chemical reaction driven by continuous stress and temperature, induced the formation of new ternary oxides (Bi₂MoO₆ and Bi₂Mo₃O₁₂) with low shearing nano-grain structure, and a continuous dense lubricating glaze layer composed of Bi₂O₃, MoO₃, Bi₂MoO₆ and Bi₂Mo₃O₁₂ was formed at the friction interface. In Bi₂MoO₆ layered structure, the distortion of MoO₆ octahedral structure led to the increase of interlayer distance, which weakened the coupling effect between ions, thus contributing to low shear strength and good lubricity. Our research indicates that the formation of low shear strength Bi₂MoO₆ ternary oxide is helpful to the realization of high temperature lubrication, which provides a strategy to expand the high temperature lubrication range of MoS₂-based solid lubricant.