As high-end mechanical equipment put forward increasingly demanding requirements on the high performance characteristics — such as bearing-load capacity, working environment and service life — of self-lubricating moving parts, traditional lubrication materials are facing applied limitations under harsh and multi-environmental service conditions. Therefore, the development of functional lubrication materials with low friction, long life and multi-environmental adaptability has become a leading trend in recent years.
Recently, two teams of the Functional Lubrication Materials Research Group and the Engineering Special Lubrication Materials Research Group of the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, carried out joint research on the design and functional assembly of core-shell functional composites by virtue of interface interactions between different components.
A series of studies, in particular, were performed on the structural design, control strategies, regulation strategies, lubrication mechanisms and wear-resistance mechanisms of core-shell composites. The results provide an experimental basis and theoretical guidance for the design of strong and flexible functional lubrication materials with multi-environmental adaptability.
First, core-shell polytetrafluoroethylene@phenolic resin (PTFE@PR) composites were prepared using a combination of in-situ polymerization and hot-pressing techniques. These composites demonstrated excellent self-lubrication and wear-resistance properties under different temperatures, loads, speeds and degrees of roughness of the upper counterpart. Improved tribological performances were derived from the enhancement and formation of long-life composite transfer films with long-range, ordered, bi-phase polymer chains via friction induction.
In addition, a novel lubricating additive was designed and synthesized via the self-assembly of wrapped PTFE nanoparticles by exfoliated MXene (Ti3C2Tx) sheets. Then, pMXene@PTFE core-shell hybrids were introduced into the epoxy coating. The research results show that pMXene@PTFE not only alleviates the oxidation of MXene sheets but also synergistically optimizes lubrication and wear-resistance capabilities. Therefore, such epoxy-based composite coatings presented excellent friction-reduction and wear-resistance properties in dry air, humid air (RH=80%) and vacuum (3×10-5 mbar) environments, making stable, multi-environmental binary composite coatings a reality (Fig. b). The improvement of their performance primarily depends on the following points: (a) the lubricating, synergistic effect of MXene sheets and PTFE hybrid additives with a core-shell structure, (b) the good dispersibility and adhesion of the composite additives in the epoxy matrix and (c) the formation of a protective film on the counterpart.
In summary, core-shell structured lubrication materials have broad prospects for application in the design of synergistic composites at the micro level with different functional components, as well as for the development of multi-environmental, adaptive functional lubrication materials.
Related research results have been published in Tribology International (2020, 144, 106092 and 2021, 154, 106718) and Carbon (2021, 184, 12-23). Yawen Yang, PhD candidate, is the first author, and professors WANG Jinqing and WANG Honggang are co-corresponding authors.
These studies were funded by the National Natural Science Foundation of China.
Figure: The preparation and friction transfer mechanism of PTFE-based core-shell composite lubrication materials with environmental adaptability for multiple working conditions.
WANG Jinqing & WANG Honggang
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Lanzhou Institute of Chemical Physics