Roles of transfer layer and surface adhesion on superlubricity behaviors of diamond-like carbon film depending on rotating and reciprocating motion

[Display omitted] •Rotating motion enables a longer superlubricity state than reciprocating motion.•Graphitized tribofilm is stable in rotational motion but not in reciprocating motion.•Strong adhesion and bidirectional motion make the tribofilm easier to be removed.•Synergistic effect of graphitized interfaces contributes a longer superlubricity life. The superlubrictiy behavior and mechanism of diamond-like carbon (DLC) film in vacuum were researched under rotating and reciprocating motion. Compared with the reciprocating motion, DLC film can reveal a more stable superlubricity state and lower wear under rotating motion. TEM, AFM, Raman and the first-principles calculation results show that the transfer layer would be quickly removed under reciprocating motion, but could be maintained stably under rotational motion, which may be one of the key factors for the stable superlubricity state of DLC films under rotating motion. The removal of tribofilm under reciprocating motion may be attributed not only to the stronger impact and instability in friction interface, but also to the strong adhesion effect of the friction interface.