Heating induced nanostructure and superlubricity evolution of fullerene-like hydrogenated carbon films.

Abstract Fullerene-like hydrogenated carbon (FL-C:H) films hold superlubricity properties at room condition, which important for saving energy, for engine use, however, high temperature serving (below 500 °C) are needed considering. In this paper, FL-C:H films were annealed with protecting of nitrogen. The tribological test show that all films have superlubricity properties, of which friction coefficient are 0.008 (200 °C), 0.005 (250 °C), 0.004 (300 °C), 0.005 (400 °C), 0.004 (500 °C), respectively. In addition, the hardness is incremental when the annealed temperature increased from 200 to 300 °C, and decremental from 300 °C to 500 °C. Interestingly, the changes of hydrogen content can be neglect in present work. Combined HRTEM, Raman spectra and XPS results, one can speculate that the degree of order for FL-C:H films increase along with the argument of annealed temperature, but competition of growth and ordering of short-chain hydrocarbon and graphene stacks that determine the hardness and H3/E2 ratio, which further influences the wear volumes. However, the friction coefficient only depends on curved grahene which can formation scroll graphene between contact surface to low friction force. Highlights • Though the highest hardness turn out under annealing at 300 °C, the elastic recovery of films is the highest at 500 °C. • The C-C sp2 content raises and the C-C sp3 content reduces with increase of annealing temperature. • All samples, show superlubricity (0.004∼0.005) properties, which is correlated with fullerene-like structure. [ABSTRACT FROM AUTHOR]