Effect of temperature and layer thickness on these strengths of carbon bonding for carbon/carbon composites

In order to apply carbon/carbon composites (C/Cs) to various hot structures, secondary bonding techniques effective at elevated temperatures are frequently required. In the present study, carbon bonding between lamination type C/Cs was formed by the carbonation of polymer adhesive, and the strength of the bonding was evaluated at temperatures up to 2273 K in a vacuum using the double-notched shear method. The results revealed that bonding strength increased with increasing temperature and became higher than the inter-laminar shear strength of the substrate C/C when the bonding layer was thin. The enhancement of carbon bonding strength with increasing temperature was shown to be caused mainly by the evaporation of absorbed gases, probably water, up to temperatures of 1800 K with a slight additional contribution of thermal residual stress. It was also shown that heat treatment at higher temperatures made the bonding stronger.