Special mechanical and tribological protecting effects of the in-situ grown carbon coating on natural rubber

Carbon coatings were deposited on natural rubber (NR) following continuous carbon plasma treatment over varying durations. The microstructures, mechanical properties, and tribological behaviors were analyzed using scanning electron microscopy, infrared spectroscopy, Raman spectroscopy, and a tribometer, among other techniques. The analysis revealed that the carbon coatings are amorphous, featuring a dense and finely structured cauliflower morphology at the nanoscale. A transitional layer between the NR substrate and the carbon coating, evolving due to gradual physicochemical changes at the interface, was identified. The experimental results prove the in-situ growth mechanism of amorphous carbon film, that is, transition of organic carbon structure in the polymer was transformed into an inorganic amorphous carbon structure, and then the epitaxial growth of amorphous carbon films was realized. Observations indicated that, while the hard carbon coating exhibited cracking under lower-pressure scratch tests, it remained well-adhered to the soft NR substrate without any delamination, even under increased pressure. Additionally, the coatings provided effective tribological protection for the NR substrate, reducing both friction and wear. The distinctive mechanical and protective tribological properties of the carbon coating, in-situ grown on the NR substrate, are attributed to the robust adhesion facilitated by the transitional layer.