Double layer ZrSi₂-ZrC-SiC/SiC oxidation protective coating for carbon/carbon composites

A ZrSi₂-ZrC-SiC/SiC double layer coating was prepared on the surface of carbon/carbon (C/C) composites by pack cementation. The microstructure, oxidation and thermal shock resistance of the coating were studied. These results show that the outer coating is mainly composed of ZrSi₂, ZrC, SiC and Si respectively. Oxidation tests were conducted in air at 1173 K for 100 min and 1773 K for 67 h and a weight decrease of 0·37 and 0 ·12% were recorded. After 20 times thermal shocks between 1773 K and room temperature, the weight of the coated specimens increased by only 0·12%. The excellent thermal shock resistance is attributed to the aptness to oxidation of the minor phases distributing in the gaps among the SiC particles and the coarseness of the coating.