Structure original of temperature depended superlow friction behavior of diamond like carbon

As one kind of traditional and widely used solid lubricant, diamond like carbon films have been approved to have temperature dependent ultra-low friction behaviors. However, the mechanism of this observation is not fully clarified. By using high resolution transmission electron microscopy, Raman spectrum and tribometer, we monitored the nanostructure transformation of wear debris and friction coefficient evolution from 25 °C to 200 °C. High temperature promotes graphitization and enhances the formation of graphene nanoscrolls (GNSs), which results in decrease of friction coefficient. For example, at 150 °C, more spherical shape graphene nanoscrolls appear in debris and a balance between graphitization and nanoscrolls crimping is established, which leads to the lowest friction coefficient at 0.012. However, when the temperature is too high (200 °C), such a balance is destroyed and the nanoscrolls tend to be disordered with sharp edges, which causes the failing of superlow friction state. The results demonstrated that temperature could change the fine structure of graphene nanoscrolls, which ultimately determines the tribological behavior of DLC film. Moreover, the structure evolution of graphene nanoscrolls should be the compulsory result of competition between the thermodynamic formation of graphene layers and the dynamics of nanoscrolls crimping. [Display omitted] •Friction induced graphene nanoscrolls are the key structural factor of superlow friction of DLC.•Temperature affects the fine structure of graphene nanoscrolls, resulting in interface contact state transformation.•The competition between graphitization and crimping process is the reason for graphene nanoscroll evolution.