A Si-SiC oxidation protective coating for carbon/carbon composites prepared by a two-step pack cementation

To prevent carbon/carbon (C/C) composites from oxidation, a Si-SiC coating has been prepared by a two-step pack cementation technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis show that the coating obtained by the first step pack cementation is a porous β-SiC structure, and a dense structure consisting α-SiC, β-SiC and Si is obtained after heat-treatment by the second step pack cementation. By energy dispersive spectroscopy (EDS) analysis, a gradient C-SiC transition layer can be formed at the C/C-coating interface. The as-received coating has excellent oxidation protection ability and can protect C/C composites from oxidation for 166 h at 1773 K in air. The weigh loss of the coated C/C is due to the formation of bubble holes on the coating surface and through-coating cracks in the coating.