SiC/C multi-layered coating contributing to the antioxidation of C/C composites and the suppression of through-thickness cracks in the layer

Silicon carbide/carbon multi-layered coatings have been formed on the surfaces of C/C composites. The multi-layered coatings were deposited by the CVD method at 1200 degreesC using SiCl4 C3H8 and H-2 gases. The principal idea of the present multi-layered coatings is to suppress the through-the-thickness coating cracks by making the thickness of each SiC and carbon layer lower than the corresponding critical thicknesses, h(c)s. The values of h(c)s for the SiC and carbon coatings were 0.2 mum and above 15 mum, respectively. The role of the SiC layers is oxidation protection and that of the carbon layers is to mechanically isolate each SIC layer. Based on theoretical and experimental discussions, the SiC/C multi-layered coating was shown to successfully suppress the through-thickness coating cracks. (C) 2001 Elsevier Science Ltd. All rights reserved.