ABSTRACT
Development of solid lubricant materials that render reliable performance in ambient conditions, are amenable to industrial size and design complexities, and work on engineered surfaces is reported. These coatings are composed of Ti3C2Tx-Graphene Oxide blends, spray-coated onto bearing steel surfaces. The tribological assessment was carried out in ambient environmental conditions and high contact pressures in a ball-on-disc experimental set-up. The evaluation yielded that the use of Ti3C2Tx-Graphene-Oxide coatings led to substantial reduction in friction down to 0.065 (at 1 GPa contact pressure and 100 mm/s) in comparison to the uncoated of single-component-coated surfaces, surpassing the state-of-the-art. The coatings also provided excellent protection against wear loss of the substrate and counter-face. The results were explained based on the observations from Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and nanoindentation measurements. In operando formation of a dense, hard and stiff, dangling-bond-saturated tribolayer was observed to be the reason for the sustained lubricity even at high test loads and sliding speeds. This report presents the holistic exploration and correlation of structure-property-processing pertaining to the advancement of solid lubrication science.
Subject(s)
Graphite , Nanocomposites , Steel , Materials Testing , FrictionABSTRACT
High-contact stresses generated at the sliding interfaces during their relative movement provide a unique combination of local heating and shear- and load-induced compression conditions. These conditions, when involving the sliding of surfaces with certain material characteristics, may facilitate tribochemical reactions with the environment, leading to the formation of a protective, damage-suppressing tribofilm directly at the contact. Here, we employ the electrodeposition process to design a coating composed of a hard cobalt-phosphorous matrix with the inclusion of tribocatalytically-active nickel clusters. The coating is optimized in terms of its relative composition and mechanical characteristics. We demonstrate the excellent tribological performance of the coating in the presence of a hydrocarbon environment, both in the form of a liquid lubricant and as a hydrocarbon-saturated vapor. Characterization of the wear track indicates that the origin of such performance lies in the formation of a protective carbon-based tribofilm on the surface of the coating during sliding. These results contribute to the advancement of knowledge on material transformations in the contact, thus providing a robust and versatile approach to addressing tribological challenges in mechanical systems.
ABSTRACT
Toward the goal of achieving superlubricity, or near-zero friction, in industrially relevant material systems, solution-processed multilayer Ti3C2Tx-MoS2 blends are spray-coated onto rough 52100-grade steel surfaces as a solid lubricant. The tribological performance was assessed in a ball-on-disk configuration in a unidirectional sliding mode. The test results indicate that Ti3C2Tx-MoS2 nanocomposites led to superlubricious states, which has hitherto been unreported for both individual pristine materials, MoS2 and Ti3C2Tx, under macroscale sliding conditions, indicating a synergistic mechanism enabling the superlative performance. The processing, structure, and property correlation were studied to understand the underlying phenomena. Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy revealed the formation of an in situ robust tribolayer that was responsible for the performance at high contact pressures (>1.1 GPa) and sliding speeds (0.1 m/s). This report presents the lowest friction obtained by either MoS2 or MXene or any combination of the two so far.
