Semi in-situ analysis of isolated tribo-film islands at the contact interface in the super-low friction of CNx coatings under extreme environment

No. 51405308

Water and oxygen content in nitrogen gas environment is a key point for the formation of tribo-film at the contact interface in the super-low friction of CNx coatings. To clarify the role of tribo-film in the super-low frictional behavior of CNx coatings, this application tends to carry out studies in three aspects: formation mechanism, evolution, and artificial control of isolated tribo-film islands at the contact interface in the super-low friction of CNx coatings under nitrogen gas environment with extreme water and oxygen content (ppm level). Super-low friction tests of CNx coatings are conducted by using an Extreme environment-Ball-on-disk tribometer-Raman-AFM system. The composition, the structure, the topography, and the mechanical behavior of isolated tribo-film islands are semi in-situ analyzed by Raman spectroscopy and atomic force microscopy (AFM), respectively, and then the evolution of geometric shape and local structure of isolated tribo-film islands is analyzed by using nano-scale contact mechanical method. By characterizing the tribo-film under the steady state, the local structural phase transition mechanism of isolated tribo-film islands induced by shearing force at the contact interface is revealed. By analyzing the tribo-film during the running-in process, the variation of critical rubbing distance with the maximum contact stresses on the surface of isolated tribo-film islands is elucidated. By controlling the initial running-in process, stable super-low friction of CNx coatings under nitrogen gas environment with water and oxygen content in the levels from ppm to percentage is obtained. The achievement of this project will provide research basis for friction reduction theory of tribo-film at the contact interface in the carbon-based coatings and design of energy-saving tribo-systems.