Combined effect of WS2 and Ti3C2Tx MXene favors oil-based ultra-low friction on rough steel-steel interface at elevated temperatures

Abstract

The lubrication performance of liquids is severely restricted and is degraded in high-temperature environments. Stable and reliable lubrication in high temperature environments has been a long-standing goal in various industrial fields. In this study, WS₂ and Ti₃C₂T_x MXene nanoflakes were used as oil-based lubricant additives to generate ultra-low friction and even superlubricity (friction coefficient of ∼0.007) at elevated temperatures (400°C), which has hitherto not been achieved by both individual pristine materials, WS₂ and Ti₃C₂T_x MXene. Viscosity and thermogravimetric characterization revealed improvements in the high-temperature rheological properties and thermal stability of the lubricating base oil, indicating improved load-bearing and continuous lubrication capabilities at elevated temperatures. X-ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy demonstrated that the formation of an iron/titanium/tungsten-rich oxide lubricious thin film at the sliding interface reduced the interfacial shear stress, which was responsible for the observed friction and wear reductions at high contact pressures (> 1.1 GPa). Although the titanium/tungsten oxide film was gradually removed after prolonged sliding, a sufficiently thick iron oxide film maintained a low friction coefficient for at least 2 h. The improved surface quality facilitates the achievement of ultra-low friction and reduced wear. The proposed lubrication methodology has a broad utilization potential as a wear-reduction strategy across various industrial fields at elevated temperatures.