Fabrication and tribological properties of B2O3 as friction reducing coatings for carbon-carbon composites

B2O3 lubricating coatings for the SiC coated C/C composites were prepared by a slurry brushing method. The morphologies, components, and structure of the as-prepared coatings were characterized by SEM and XRD. The friction coefficient of the coatings was also tested. The lubricating mechanism of the coating is discussed. Results show that the friction coefficient of the coatings is 0.06–0.08, which is less than that of the carbon/carbon composites (0.15–0.18). The decrease of the friction coefficient of C/C composites after adding a SiC/B2O3 coating is attributed to the formation of a lubricious layer of boric acid from the boron oxide after exposure to the moisture in air.